CN104102767A

CN104102767A - Numerical simulation analysis method for influence of adjacent underpinning pile foundation by shield construction

Info

Publication number: CN104102767A
Application number: CN201410290394.9A
Authority: CN
Inventors: 袁鸿; 刘熙; 杨雄飞; 韩军
Original assignee: Jinan University
Current assignee: Jinan University
Priority date: 2014-06-25
Filing date: 2014-06-25
Publication date: 2014-10-15
Anticipated expiration: 2034-06-25
Also published as: CN104102767B

Abstract

The invention discloses a numerical simulation analysis method for the influence of adjacent underpinning pile foundation by shield construction. The method comprises the following steps: (1) according to a specific underpinning engineering proposal, a finite element model of a pile foundation underpinning single pile is established; (2) a shield excavation process is simulated, comparative analysis is carried out for underpinning pile foundation deformation and hypogenic change condition before tunnel excavation, during tunnel excavation and after tunnel excavation; (3) through changing parameters of each engineering factor in the specific underpinning engineering proposal, finite element models under multiple groups of different working conditions are established, comparative analysis is carried out for underpinning pile foundation deformation and hypogenic change condition under different working conditions, and an influence effect rule of each engineering factor to the underpinning pile foundation after tunnel excavation is obtained; (4) according to the specific underpinning engineering proposal, finite element model of multiple pile foundation underpinning piles are established, and the feasibility of the underpinning engineering proposal is verified by utilizing the underpinning pile foundation deformation and hypogenic change condition. The method has the innovative significance, and the engineering application prospects are wide.

Description

Shield-tunneling construction is to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation

Technical field

The present invention relates to a kind of Numerical Analysis methods, especially a kind of shield-tunneling construction, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, belongs to shield-tunneling construction to the contiguous analysis field that underpins Influence of Pile Foundation.

Background technology

Along with society and economic flourish, subway has become the important vehicles, and subway tunnel adopts shield method excavation conventionally, in the time of construction, influencing each other between shield machine, stratal configuration and Adjacent Buildings is a very complicated process, wherein relate to numerous controlled and uncontrollable factors that affect construction effect, be difficult to think prediction.Therefore, inevitably exist some shortcomings with not enough in current research discussion, the main problem existing has:

1) experimental formula method is the analysis and summary to empirical data, but data are subject to the restriction of concrete engineering singularity, tends to exist instable problem, is difficult to accomplish perfect matching with certain formula curve.The calculated amount of analytical method is large, and does not have to form the unified approach that is applicable to various engineering situation, and in practice, limitation is larger, seldom adopts.The organize models that needs of model test method tests, and engineering is simulated.But all need to, for the test of concrete engineering specific design, have nonrepeatability, the financial resource and material resource of cost are more, can cause larger waste.While utilizing numerical analysis method to simulate engineering, exist equally certain difficulty.

2) numerous to the research of Tunnel Engineering in, be mostly to carry out further investigated for ground settlement and stratum deformation problem, the theoretical comparative maturity, the method that obtain are relatively reliable.But for constructing tunnel and the research of Mutual Influence Law between contiguous construction of structures around, but just just progressively carrying out in the last few years, also do not form perfect analysis system, the factor that affects engineering effort is also not yet clear and definite, and the technical research achievement phoenix feathers and unicorn horns especially of outstanding pile foundation underpinning problem, therefore the research of this respect also has very large development space.

Summary of the invention

The object of the invention is the defect in order to solve above-mentioned prior art, provide a kind of and can verify that the shield-tunneling construction that specifically underpins engineering proposal feasibility is to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation.

Object of the present invention can be by taking following technical scheme to reach:

Shield-tunneling construction, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, comprises the following steps:

1) according to specifically underpining engineering proposal, choose suitable soil body piece size, determine tunnel-liner, grouting layer and underpin material and the parameter thereof of pile foundation, and lateral stiffness reduction coefficient to tunnel-liner and the processing of grouting layer be optimized, set up the finite element model of pile foundation underpinning single pile;

2) according to step 1) finite element model set up, adopt life and death unit controls method to shield tunneling process simulation, to before tunnel excavation, in tunnel excavation and the situation of change of the pile lateral displacement of tunnel excavation after finishing, pile body vertical displacement, pile body friction force, pile body axle power compare analysis, obtain underpining the Changing Pattern of pile foundation deformation and internal force, for Engineering Quality Control provides numeric reference foundation;

3) specifically underpin by changing the parameter that underpins distance, stake end and horizontal median axis position, tunnel, upper load active position and these engineering factors of grouting pressure between pile foundation in engineering proposal, adopt step 1) and step 2) method set up the finite element models of organizing under different operating modes more, situation of change to pile lateral displacement, pile body vertical displacement, pile body friction force, pile body axle power and moment of flexure under each operating mode compares analysis, obtain each engineering factor after tunnel excavation to underpining the influence rule of pile foundation;

4) according to specifically underpining engineering proposal, set up the finite element model of many of pile foundation underpinnings, utilize the situation of change that underpins pile foundation deformation and internal force, checking underpins the feasibility of engineering proposal.

As a kind of embodiment, step 2) described employing life and death unit controls method is to shield tunneling process simulation, specific as follows:

A) set up soil model according to the soil layer situation that specifically underpins engineering proposal, reserved underpinned pile base location, applies the constraint in horizontal shift direction to the soil body at reserved location place, guarantees that the soil body can not clamp-on; Weight application, obtains the stressed and deformation of the soil body under deadweight, preserves as initially stress file derivation;

B) set up the soil body and underpin the coefficient model of pile foundation, and reading in initially stress file, to underpining pile foundation weight application, applying pile top load in former stake position;

C) kill tunneling part soil body unit, simulation tunnel Stress relieving of surrounding rocks 25%, tunneling surrounding soil is oppositely applied to 75% primary stress, apply 0.15Mpa grouting at the tail of the shield machine pressure simultaneously;

D) simulated ground stress has discharged 75%, tunneling surrounding soil is oppositely applied to 25% primary stress, applies grouting at the tail of the shield machine pressure simultaneously;

E) simulated ground stress is complete, only tunneling surrounding soil is applied to grouting at the tail of the shield machine pressure;

F) cancel grouting pressure, activate liner structure and grouting layer unit;

Wherein, step a)～b) be the simulation before tunnel excavation; Step c)～e) be the simulation in tunnel excavation; Step is f) simulation after tunnel excavation finishes.

As a kind of embodiment, steps d) in the method that adopts of the simulation of terrestrial stress be: adopt step excavation pattern, the soil body unit of tunnel internal after excavation is set as to " dummy cell ", calculate the borderline nodal force in tunnel, by these force reactions in boundary node, with simulation primary stress, carry out simulated ground stress release by the size and the direction that change acting force.

As a kind of embodiment, the pile top load that step b) applies is 250～300t; Steps d) and e) the grouting at the tail of the shield machine pressure that applies be 0.1～0.2Mpa.

As a kind of embodiment, step a) described soil model is D-P constitutive model.

As a kind of embodiment, step 1) described soil body piece is of a size of 46m × 48m, on Width, gets 8D, and in short transverse, corresponding earth's surface is got in shield structure top, and soil body edge, below to shield shell outside is not less than 30m.

As a kind of embodiment, step 1) material that adopts of described tunnel-liner is that C30 concrete is built, and thickness is 0.3m, and Poisson ratio is 0.2, and severe is 26KN/m ³; The material that described grouting layer adopts is soil cement, and thickness is 0.2m, and Poisson ratio is 0.2, and severe is 21KN/m ³; The described pile foundation that underpins is for two stake beam type underpinning structures, and the material that wherein needle beam adopts is that C40 concrete is built, length × height=12.55m × 2m, and Poisson ratio is 0.2, severe is 27.5KN/m ³; Underpinned pile is the boring concrete-pile of diameter 1.2m, length 27m, and pile body adopts C30 concrete to build, and Poisson ratio is 0.2, and severe is 26KN/m ³.

As a kind of embodiment, step 1) the lateral stiffness reduction coefficient of described tunnel-liner is 0.85

As a kind of embodiment, step 1) processing of described grouting layer, be specially: in shield method tunnel construction process, after shield tail shell is pushed ahead, supporting role before the shield structure soil body around loses, internal stress discharges, shield machine is to afterbody space position spray injecting paste material simultaneously, under the effect of grouting at the tail of the shield machine pressure and inside soil body stress, the complicated annular mixolimnion of the soil body, injecting paste material and an air multiphase coexistence will be formed at shield tail, adopt and wait this layer material of generation layer simulation, these in generation the parameter of layer choose as follows:

Elastic modulus is 1e ⁹; Poisson ratio is 0.2; Thickness adopts formula choose, wherein for the theoretical value in shield tail space, go 1/2 of difference between shield structure external diameter and lining cutting external diameter; η is for adjusting coefficient, and span is 0.7～2.0. soil property is harder, and value is less.

As a kind of embodiment, the unit that described finite element model is chosen comprises PLAN42 unit, CONTA172 unit and TARGE169 unit, wherein: adopt the PLAN42 unit simulation soil body, underpin pile foundation and tunnel structure; Adopt the CONTA172 unit simulation soil body, underpin the connection function between pile foundation and tunnel structure; Adopt TARGE169 unit to simulate specifically underpining engineering proposal as object element.

The present invention has following beneficial effect with respect to prior art:

The inventive method adopts the D-P constitutive model of the soil body, utilize large software ANSYS to set up finite element model contiguous internal force and the deformation that underpins pile foundation in shield-tunneling construction process carried out to the analysis of system, to applying of shield tail radial grouting pressure in tunnel excavation, the sclerosis of grout layer, the details such as the progressively release of terrestrial stress have been carried out detailed simulation, also the rubbing contact between pile foundation and the soil body has been carried out to rational setting, can set up the model under the different operating modes of many groups simultaneously, further analyze the pile spacing underpining between pile foundation, stake end position, stake footpath, the engineering factors such as grouting pressure are in constructing tunnel, on the impact of pile foundation internal force and distortion, and then checking specifically underpins the feasibility of engineering proposal, there is innovative significance, have future in engineering applications widely.

Brief description of the drawings

Fig. 1 is the Numerical Analysis methods process flow diagram of the embodiment of the present invention 1.

Fig. 2 is the finite element model schematic diagram that the embodiment of the present invention 1 is set up.

Fig. 3 a is the stress cloud atlas in Y-direction before the embodiment of the present invention 1 simulation tunnel excavation; Fig. 3 b is the stress cloud atlas in soil body Y-direction before the embodiment of the present invention 1 simulation tunnel excavation; Fig. 3 c is the stress cloud atlas in underpinning structure Y-direction before the embodiment of the present invention 1 simulation tunnel excavation.

Fig. 4 a is the figure that affects that the embodiment of the present invention 1 simulation tunnel is constructed on pile lateral displacement; Fig. 4 b is the figure that affects that the embodiment of the present invention 1 simulation tunnel is constructed on pile body vertical displacement; Fig. 4 c is that the embodiment of the present invention 1 simulation tunnel is constructed on facing the figure that affects of tunnel side-friction force; Fig. 4 d is the affect figure of the embodiment of the present invention 1 simulation tunnel construction on back of the body tunnel side-friction force; Fig. 4 e is the figure that affects that the embodiment of the present invention 1 simulation tunnel is constructed on axial force of pile.

Fig. 5 a is that the embodiment of the present invention 1 is simulated the affect figure of piles with different interval S on pile lateral displacement; Fig. 5 b is that the embodiment of the present invention 1 is simulated the affect figure of piles with different interval S on pile body vertical displacement; Fig. 5 c is that the embodiment of the present invention 1 is simulated piles with different interval S to facing the figure that affects of tunnel side-friction force; Fig. 5 d is that the embodiment of the present invention 1 is simulated the affect figure of piles with different interval S on back of the body tunnel side-friction force; Fig. 5 e is that the embodiment of the present invention 1 is simulated the affect figure of piles with different interval S on pile body axle power.

Fig. 6 a is that the embodiment of the present invention 1 is simulated the affect figure of piles with different end position on pile lateral displacement; Fig. 6 b is that the embodiment of the present invention 1 is simulated the affect figure of piles with different end position on pile body vertical displacement; Fig. 6 c is that the embodiment of the present invention 1 is simulated piles with different end position to facing the figure that affects of tunnel side-friction force; Fig. 6 d is that the embodiment of the present invention 1 is simulated the affect figure of piles with different end position on back of the body tunnel side-friction force; Fig. 6 e is that the embodiment of the present invention 1 is simulated the affect figure of piles with different end position on pile body axle power.

Fig. 7 a is that the embodiment of the present invention 1 is simulated the affect figure of different load positions on pile lateral displacement; Fig. 7 b is that the embodiment of the present invention 1 is simulated the affect figure of different load positions on pile body vertical displacement; Fig. 7 c is that the embodiment of the present invention 1 is simulated different load positions to facing the figure that affects of tunnel side-friction force; Fig. 7 d is that the embodiment of the present invention 1 is simulated the affect figure of different load positions on back of the body tunnel side-friction force; Fig. 7 e is that the embodiment of the present invention 1 is simulated the affect figure of different load positions on pile body axle power.

Fig. 8 a is that the embodiment of the present invention 1 is simulated the affect figure of different grouting pressures on pile lateral displacement; Fig. 8 b is that the embodiment of the present invention 1 is simulated the affect figure of different grouting pressures on pile body vertical displacement; Fig. 8 c is that the embodiment of the present invention 1 is simulated different grouting pressures on the figure that affects that faces tunnel side-friction force; Fig. 8 d is that the embodiment of the present invention 1 is simulated the affect figure of different grouting pressures on pile body axle power.

Fig. 9 a is that the embodiment of the present invention 1 simulation underpins the pile body horizontal distortion curve map in many situations; Fig. 9 b is that the embodiment of the present invention 1 simulation underpins the pile body Vertical Settlement deformation curve figure in many situations; Fig. 9 c is that the embodiment of the present invention 1 simulation underpins and faces tunnel side-friction force curve map in many situations; Fig. 9 d is that the embodiment of the present invention 1 simulation underpins the back of the body tunnel side-friction force curve map in many situations; Fig. 9 e is that the embodiment of the present invention 1 simulation underpins the pile body axle force curve figure in many situations.

Embodiment

Embodiment 1:

As shown in Figure 1, the present embodiment is worn one three engineering across 9 story frame structures as example under certain section of left tunnel line on No. six lines of Guangzhou Underground, this project scheme adopts Bored Pile Foundation, and be single-column single pile cap, now adopt Pile Underpinning Technology to underpin the affected pile foundation in structure bottom, to control the impact of shield tunneling on structure pile foundation.The shield-tunneling construction of the present embodiment, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, comprises the following steps:

1) according to the engineering proposal of the present embodiment, choose suitable soil body piece size, determine tunnel-liner, grouting layer and underpin material and the parameter thereof of pile foundation, and lateral stiffness reduction coefficient to tunnel-liner and the processing of grouting layer be optimized, utilize large-scale finite element method (fem) analysis software ANSYS to set up the finite element model of pile foundation underpinning single pile;

1.1) choose suitable soil body piece size

Generally, the soil body that the excavation in tunnel is only adjusted the distance in the scope of the 3-5 times of tunnel excavation width in center, tunnel (width) produces actual influence, in the STRESS VARIATION at 3 times of width places generally 10% once, at the stress range at 5 times of width places generally 3% once; But consider the marginal contribution that will eliminate in FEM (finite element) calculation, the soil body piece of analyzing should not be obtained too small, final decision soil body piece is of a size of: 46m × 48m, on Width, get 8D (8 times of diameter widths), in short transverse, corresponding earth's surface is got in shield structure top, and soil body edge, below to shield shell outside is not less than 30m.

1.2) determine tunnel-liner, grouting layer and underpin material and the parameter thereof of pile foundation

Edpth of tunnel is taken as 25m, described in underpin pile foundation for two stake beam type underpinning structures, material and parameter thereof that tunnel-liner, grouting layer, needle beam and underpinned pile adopt, as shown in table 1 below;

Structure	Material	Size	Poisson ratio v	Severe (KN/m3)
					Tunnel-liner	C30 concrete	Thickness: 0.3m	0.2	26
Grouting layer	Soil cement	Thickness: 0.2m	0.2	21
					Needle beam	C40 concrete	Length × height=12.55m × 2m	0.2	27.5
Underpinned pile	C30 concrete	Diameter D=1.2m; Length L=27m;	0.2	26

Table 1 tunnel-liner, grouting layer and underpinned pile sill parameter list

1.3) the lateral stiffness reduction coefficient to tunnel-liner and the processing of grouting layer are optimized

1.3.1) the lateral stiffness reduction coefficient of tunnel-liner is optimized

When Shield Tunneling is simulated, owing to there being certain difference between practice of construction situation and ideal situation, thus parameter to be optimized, to the operating mode of closing to reality more, after tunnel lining structure moulding, between each tunnel lining segment, need will link by cross bolts and longitudinal bolt, form a coefficient entirety, but just because of the existence of these bolts, make the rigidity of whole tunnel lining structure will have comparatively significantly variation, so time need to carry out an appropriate reduction to its rigidity in simulation, owing to adopting two dimensional model analysis, only consider the variation of lateral stiffness at this, in the time that shield tunnel pipe ring is carried out to analytical calculation, take into full account the singularity of pipe ring structure, the pipe ring of shield tail is made up of polylith pipe sheet assembling, between section of jurisdiction and section of jurisdiction, be connected by joint, in the time carrying out numerical simulation, select and revise usual computing method by pipe ring designs simplification, its basic thought is the annulus using pipe ring as a rigidity homogeneous, due to the existence of joint between section of jurisdiction, after simplification, the bendind rigidity of pipe ring changes, need to revise the rigidity of pipe ring with effective rigidity reduction coefficient η, according to multiple analysis of project example, get lateral stiffness reduction coefficient η _horizontal=0.85, relatively can approach actual condition.

1.3.2) the processing optimization of grouting layer

In shield method tunnel construction process, there is great impact in the space producing when shield tail comes to nothing on stratum deformation, simulate exactly coming to nothing and slip casting situation of shield portion, the FEM Analysis is had great significance, the actual conditions in shield tail space are very complicated, after shield tail shell is pushed ahead, supporting role before the shield structure soil body around loses, internal stress discharges, shield machine is to afterbody space position spray injecting paste material simultaneously, under the effect of grouting at the tail of the shield machine pressure and inside soil body stress, will form a soil body at shield tail, injecting paste material, the complicated annular mixolimnion of the multiphase coexistences such as air, but in the process of finite element analogy, we need to do rational simplification to the parameter of the material of this layer of COMPLEX MIXED layer, in the generations such as employing layer, are simulated this layer material, complicated Deng the material composition in layer, and the shared ratio row of each composition not only have pass with foundation soil body itself, also there is close contacting with the operating technique of shield tail.The parameter of equity generation layer is chosen specific as follows:

Elastic modulus: wait the materials such as the generation layer mixture by the soil body, injecting paste material, air and the soil body and injecting paste material to form.Therefore roughly should be between grout and soil Deng the elastic modulus of generation layer, and the ratio shared with various compositions be relevant, according to the engineering proposal actual conditions of the present embodiment, waits the elastic modulus of generation layer to be taken as: 1e ⁹;

Poisson ratio: choosing also of Poisson ratio shown pass with concrete material and the shared ratio of material, still because Poisson ratio span is little, limited on the impact of result of calculation, so generally can directly recently replace by the Poisson of soil cement, be taken as 0.2;

Thickness: generally, wait thickness and the shield tail space unequal of generation layer, its thickness depends primarily on character and the grouting at the tail of the shield machine pressure of the soil body; When the soil body is hard, grouting at the tail of the shield machine pressure is when large, when soil body autostability is better, after shield structure comes to nothing, surrounding soil only can have less distortion to shield tail space, waits the Thickness Ratio shield tail space theoretical value of generation layer little.But in the time that the shield structure soil body is around relatively soft, when shield tail comes to nothing, injecting paste material will be penetrated in the soil body, form the potpourri of the soil body and injecting paste material, wait the thickness in generation layer will be greater than theoretical value, concrete thickness is chosen can be with reference to following formula:

δ = η \overset{\cdot \cdot}{A}

Wherein, for the theoretical value in shield tail space, go 1/2 of difference between shield structure external diameter and lining cutting external diameter; η is for adjusting coefficient, span is 0.7～2.0,. soil property is harder, value is less, and in the engineering proposal of the present embodiment, the solum that shield structure passes through is the micro-zone of weathering of rock, soil property is harder, therefore get η=0.9, calculate δ=0.2 × 0.9=0.18m, the thickness as shield tail etc. in analyzing for layer;

1.4) utilize large-scale finite element method (fem) analysis software ANSYS to set up the finite element model of pile foundation underpinning single pile

Adopt the PLAN42 unit simulation soil body, underpin pile foundation and tunnel structure, PLANE42 unit be a kind of can be for the solid element of analysis of two-dimensional structure; PLANE42 unit both can set it as the flat unit of analyzing plane stress or plane stress, can be seen as again axisymmetric element, and can obtain good sunykatuib analysis effect;

Adopt the CONTA172 unit simulation soil body, underpin the connection function between pile foundation and tunnel structure, utilizing in the process of ANSYS analytical structure, the processing of surface of contact is a difficulties, the region of surface of contact often has incomprehensiveness, can change along with the change of numerous influence factors such as boundary condition, load, material properties.And, be complex at face with the situation that contacts of face, relate to numerous mechanics problems, there is the non-linear of height; CONTA172 unit is exactly a kind of three node osculating elements that can be used for analysis of two-dimensional plane-plane contact, and in there being the surface of 2d solid unit of middle node, the solid element covering with it has same geometrical property.CONTA172 unit can be used between two dimension target face (TARGE169 unit) and flexible face contact and slippage case study in, if cell surface permeates on intended target face, think the phenomenon coming in contact; The x axle of CONTA172 unit is along the definition of I-J direction, and the order of contact detection and cell node is closely related.This unit can use and analyze multiple two-dimensional state of stress, comprises the situation under plane strain state, plane stress state and rotational symmetry, and stress state can be surveyed pairing automatically according to the situation of the corresponding stress state of solid element that covered below.

Adopt TARGE169 unit to simulate specifically underpining engineering proposal as object element, TARGE169 unit is all kinds of two dimension targets unit with osculating element effect as description, generally, osculating element need to cover on the borderline solid element of deformable body, and will come in contact effect with target face.In ANSYS, target face is carried out discretely, becomes a series of TARGE169 object elements, object element can by and corresponding contact unit share real constant success and osculating element formation contact right.Object element can bear the effects such as power, moment, translation; Target face can be simulated with one group of object element, organizes different object elements more and combines and can obtain different target face.Rigid body or beformable body can be served as target face, different, just-soft contact mode in, always target face is chosen as to rigid body, and simulate soft-when soft contact, must adopt a contact cover lip-deep analog form of beformable body therein;

According to the unit of choosing above, the finite element model of foundation as shown in Figure 2.

2.1) to shield tunneling process simulation

2.1.1) determine the load of finite element model, according to the process of tunneling shield construction, be mainly concerned with following several load:

Deadweight: the soil body, pile body and tunnel structure are all in the effect that is subject to gravity in gravity field.Particularly, for soil body material, due to characteristics such as the compressibility of its material own are large, consolidation time is long, will there is larger distortion in the soil body under gravity stress.And pile body and tunnel structure are due to the distortion that excavation impact produces, after being conducted oneself with dignity settlement stability, the soil body occurs, therefore this soil body partial dislocation need to be deducted.In simulation, adopt and import the initially method of stress file, eliminate the Influence of Displacement that the soil body produces due to deadweight.

Pile top load: underpining in scheme, underpining pile foundation need to replace former pile foundation to bear top pillar transmitting the load getting off, but be that two stake beam types underpin due to what adopt in this model, top pillar transmits the load getting off and is not directly loaded into the top that underpins pile foundation, but be carried in former stake position, underpin the top of beam, load is: P=270t.

Grouting pressure: in the process of shield method tunnel construction, in the time that shield tail is thrown off the soil body, can adopt synchronous grouting mode at shield tail, injecting paste material is filled among the space between lining cutting and the soil body.In order to reach evenly full filling effect, need to apply grouting pressure at shield tail.In this model, its value is taken as 0.15Mpa.

Surrouding rock stress: ground is at a series of operation of nature such as the sedimentation of native state process, accumulation, weathering through accumulating over a long period formation, and inside has the existence of primary stress; Usually, before excavation construction, on border, tunnel, the soil body of every bit is all under the effect of primary stress, in a kind of stable equilibrium state; In the time of excavation, the rock mass of tunnel segment is hollowed out, and stress and the constraint condition on its border all changes, inner primary stress discharges, and great variation all occurs for stress field and displacement field, and stress redistribution, finally reaches new balance.

2.1.2) set up soil model according to the soil layer situation of the engineering proposal of the present embodiment, the soil layer situation of the engineering proposal of the present embodiment can be divided into the soil body following five layers: a, artificial earth fill; B, Muddy Bottoms silty clay soil; C, sand; D, the severely-weathered band of rock; E, the micro-zone of weathering of rock, this soil model is D-P (Drucker-prager) constitutive model, in model, reserved underpinned pile base location, applies the constraint in horizontal shift direction to the soil body at reserved location place, guarantees that the soil body can not clamp-on; Weight application, obtains the stressed and deformation of the soil body under deadweight, preserves as initially stress file derivation;

2.1.3) set up the coefficient model of the soil body, needle beam and underpinned pile, and read in initially stress file, to underpining pile foundation weight application, apply the pile top load of 270t in former stake position;

By step 2.1.2)～2.1.3) Y-direction that obtained stress cloud atlas as shown in Figure 3 a; For the ease of analyzing, respectively stake and native Y-direction stress situation are extracted, the stress cloud atlas obtaining is as shown in Fig. 3 b and Fig. 3 c;

From Fig. 3 b and Fig. 3 c, before excavation, under the effect of gravity stress, it is large that resistance to shear of soil roughly becomes along with the increase of soil depth, but at the position near pile body, because underpinned pile has with respect to the soil body trend moving down under load action under post, native land body provides friction force upwards to stake; On the contrary, stake just has downward rubbing action to the soil body.So for the soil body of the same degree of depth, by the stress being greater than away from the underpinned pile soil body, be presented as the situation of upwards swelling in the large stressor layers of stake side near a stress that the soil body in week is suffered on stress cloud atlas.Simultaneously in pile foundation underpinning structure, needle beam is different from the girder construction in superstructure, and needle beam is bearing on soil layer, and at the bottom of it is subject to upper post, load does the used time, fractional load can be passed to beam substratum, cause beam substratum stress to be greater than and underpin pile foundation soil layer stress in addition; For underpinning structure, on the top that underpins beam, owing to being subject to the effect of load under post, corresponding position has occurred that obvious stress increases.Underpining in scheme, underpinned pile stretches into needle beam certain length, and its distortion has been subject to the constraint of beam, therefore the connection of the two is considered as affixed in the time of model simplification.Therefore, in the time that load under post produces buckling effect to underpinning structure, underpining beam downward deflection occurs, there is the malformation of " evagination " shape in two underpinned piles.For underpinned pile pile body, due to the Overlay of the side-friction force of surrounding soil, the stress in the inner Y-direction of pile body reduces gradually along pile body buried depth; Analyze through above, known above analog result is reasonable, can meet basic principles of soil mechanics, can carry out next step excavation;

2.1.4) kill tunneling part soil body unit, simulation tunnel Stress relieving of surrounding rocks 25%, tunneling surrounding soil is oppositely applied to 75% primary stress, apply 0.15Mpa grouting at the tail of the shield machine pressure simultaneously;

2.1.5) simulated ground stress has discharged 75%, tunneling surrounding soil is oppositely applied to 25% primary stress, applies 0.15Mpa grouting at the tail of the shield machine pressure simultaneously; The method that the simulation that terrestrial stress discharges adopts is: adopt step excavation pattern, the soil body unit of tunnel internal after excavation is set as to " dummy cell ", calculate the borderline nodal force in tunnel, by these force reactions in boundary node, with simulation primary stress, carry out simulated ground stress release by the size and the direction that change acting force;

2.1.6) simulated ground stress is complete, only tunneling surrounding soil is applied to 0.15Mpa grouting at the tail of the shield machine pressure;

2.1.7) cancel grouting pressure, activate liner structure and grouting layer unit;

2.2) (being above-mentioned steps 2.1.4～2.1.6) and tunnel excavation in (being after above-mentioned steps 2.1.3 completes), tunnel excavation before tunnel excavation are finished after pile lateral displacement Ux, pile body vertical displacement Uy, pile body friction force, the situation of change of pile body axle power of (being after above-mentioned steps 2.1.7 completes) compare analysis

2.2.1) analysis of underpinned pile pile body deformation

What in this model, adopt is two stake beam type underpinning structures, but in the time analyzing, in order to react more simply the stressed and deformation of pile foundation, now underpining pile foundation mainly for left side discusses, due to model employing is symmetrical structure, load in model is also that symmetry applies, and the force and deformation situation that underpins pile foundation obtaining also has symmetry, is suitable for too right side and underpins pile foundation therefore the left side obtaining underpins the conclusion of pile foundation.

2.2.1.1) Analysis of Lateral Displacement

Due to when the modeling, be coordinate axis initial point taking center, tunnel, getting its right-hand and top is positive dirction, so from Fig. 4 a:

A, before tunneling shield method excavation, underpining pile foundation is not completely vertically to insert the soil body, but has had less inclination and deflection.In the affixed position of needle beam and pile foundation, there is the horizontal shift of trend centric load direction.And on the contrary, having there is again larger negative displacement on the top (buried depth is about in the scope of 2-9m) of pile body, maximum negative displacement is 2.62mm.Due to structural symmetry load symmetry, therefore from two deformation forms, pile body top mainly presents the variation tendency of " drum type evagination ", the distortion of pile body lower end is relatively little.This be due to, when applied upper load on needle beam after, there is downward deflection deformation in needle beam, because adopting consolidation style to connect between beam stake, therefore along with the warpage at needle beam two ends, pile foundation tip position also can produce inside corner and bending, cause connecting portion to centric load direction indent, in horizontal direction, show as the displacement in positive dirction, pile body deviates from centric load direction evagination, shows as to deviate from centric load direction and move in horizontal direction.This " drum type evagination " trend reduces gradually along pile body, until less negative displacement just appears in pile body bottom again, stake end horizontal shift Ux is-0.71m approximately to have reduced 73% compared with maximal value.This is because stake end soil layer is micro-weathered rock formation that elastic modulus is larger, and the distortion of pile body is had to very strong restriction ability.

B, in the time that tunnel excavates, the horizontal shift Ux that underpins pile body top changes little, the basic deformation that keeps " drum type evagination ", but when after tunnel excavation, the soil body at position, tunnel is hollowed out, for being bearing in the needle beam on soil body top, lower support power reduces, cause the downward deflection deformation of beam body to strengthen, and then cause that the pile body top affixed with it distortion that curves inwardly is more obvious, horizontal shift value Ux increases to some extent.There were significant differences with the horizontal distortion situation of excavating front pile body, and after tunnel excavation, the horizontal shift of the following part of pile body 19m has obvious increase before excavating.Special in stake end position, horizontal shift, from become-2.42mm of original-0.71mm, has approximately increased 243%.Because in the simulation of subordinate phase, think the progressively reduction of tunnel elastic modulus of soil body, inside soil body stress progressively discharges, and the horizontal distortion away from tunnel hole occurs tunnel surrounding soil, and this deformation tendency is to justify petal-shaped outwards progressively expansion in both sides, tunnel.Meanwhile, in subordinate phase, apply the radial grouting pressure of 0.15Mpa around along tunnel.Under the effect of grouting pressure, the additonal pressure of tunnel surrounding soil increases.Underpin pile body just under this soil deformation pressure and the two joint effect of grouting pressure, deviate from the displacement of tunnel direction.

C, in the time that tunnel excavation finishes, there is " bow " font variation along pile body in the drift displacement curve.The upper part condition of shifting one's love remains unchanged substantially, and just the maximum forward horizontal shift of pile body stage casing increases.At pile body 19m, with down to stake end position, horizontal shift changes obviously, and the maximum horizontal displacement of whole pile body appears at tunnel horizontal axis correspondence position, is approximately 3.8mm, than having increased 44.9% before excavation.After constructing tunnel finishes, grouting pressure is cancelled, tunnel lining structure moulding, and the stress of tunnel surrounding progressively discharges complete, and soil body internal stress tends towards stability after heavily distributing.Because the pile peripheral earth within the scope of the 9m-18m of stake middle part is sitting at tunnel upper, face tunnel side resistance to shear of soil release rate large, cause pile body left and right unblanced earth pressure, the movement of pile body generation forward.And near tunnel horizontal axis correspondence position, liner structure is under the effect of the deadweight of the top soil body and bottom soil body resilience, occurring " " formula distortion, produces extruding to tunnel soil at both sides to horizontal ovum, and then causes that pile foundation also in this position, the displacement in larger negative direction occurs.But still due to the restriction of hard soil layer at the bottom of stake, below axis, tunnel, the horizontal shift of pile body reduces gradually along depth direction, the horizontal shift of stake end is only 2.7mm.

2.2.1.2) vertical displacement analysis

A, as shown in Figure 4 b, before tunnel excavation, there is a difference step in local (0m-3m position, stake top) in vertical displacement curve, thereafter just from evenly reducing along depth direction below 3m.Under upper load effect, underpin beam fractional load is delivered in lower overburden layer, soil body compression deformation is larger, underpins the corresponding sinking of beam.Stake top place is connected with needle beam, and its vertical displacement is subject to the vertical deformation effect of needle beam larger, therefore vertical displacement maximal value appears at position, stake top, is about for 5.8mm.After under needle beam, sleeping soil layer has been shared fractional load, all the other loads are delivered to underpinned pile top, pile body under the acting in conjunction of deadweight and load, pile body pressurized, pile body deforms because material compresses.And along with the increase of the degree of depth, soil is obvious to underpining the rubbing action of pile body, and pile body vertical displacement reduces gradually, and a stake end vertical displacement is only 4.62mm, is about 79.7% of a top vertical displacement.

B, in the time of tunnel excavation, the vertical displacement situation on pile body top is roughly the same when not excavating, is just due to excavation effect, the resilience of the soil body of tunnel bottom, pile foundation is had to the upwards trend of pushing tow, and making stake end vertical displacement become current by the 4.62mm before excavating is 4.55mm.

C, after tunnel excavation finishes, its vertical deformation Uy reduces gradually along pile body buried depth.Simultaneously relatively, before tunnel excavation, the value of its corresponding each point also obviously reduces, but reduces more not identically than row, and the reducing of pile body bottom reached 8% than row, and stake top reduce ratio less than 4%.This be due to tunnel excavation stable after, resistance to shear of soil ends that heavily distribute, stake holds the springback capacity of the soil body to reach maximal value.The distortion of liner structure simultaneously strengthens, and pile body flexural deformation is more obvious, causes the vertical displacement in Uy direction to reduce.

2.2.2) analysis of pile body friction force

After pile foundation is born upper load, need to rely on himself the carrying effect of pile side friction and end resistance competence exertion, therefore analyze the change in friction force rule of pile foundation, stressing conditions to further understanding pile foundation inside has very great meaning, the suffered friction force of pile body is relevant with the character of pile peripheral earth and the relative shift between the two, but the situation that pile body faces Ce Hebei tunnel, tunnel side is but not identical, therefore separately discuss at this.

2.2.2.1) face tunnel side-friction force

As shown in Fig. 4 c, facing in the pile foundation of tunnel side, having has appearred in friction force just negative situation.And for the different phase of excavation, the Changing Pattern of friction force is also different:

A, before tunnel excavation, there is the larger force of negative friction at 4m-18m place in pile foundation.Approximately there is 10m place in Maximum Negative Frictional Force, is 33.08KN; Below 18m, the soil body to the friction force of pile foundation for just, and roughly increase with buried depth, friction force value constantly increases, reach after maximal value 71.486KN due to " soil arch " effect, the native relative displacement of stake reduces, the performance of a stake end friction resistance, stake side-friction force no longer increases, and stake bottom end side friction force is only 22.691KN.The factors such as the relative displacement of the suffered friction force of pile body and character, pile body buried depth and the stake soil of pile peripheral earth are relevant.Pile body is above the position of facing tunnel side and occur the force of negative friction is in pile body.Its side soil body bears the load action that top needle beam transmission comes, and compression deformation occurs, and pile body produces downward displacement relatively, and native land body applies the downward force of negative friction to stake.And in pile body bottom, pile body is subject to the effect of pile top load, there is downward relative displacement with respect to the stake side soil body, therefore friction force is for just.

B, in the time of tunnel excavation, the situation of the force of negative friction with for when excavation basically identical.But in positive friction region, particularly horizontal median axis above 6m in corresponding tunnel is to the pile body region at center, tunnel, and friction force obviously increases, and maximum amount of increase appears at 21.2m place, has reached 146.7%.And below tunnel horizontal median axis, friction force reduces before excavating, become 47.747KN from original 71.486KN.This phenomenon is mainly by when the tunnel excavation, applies that radial grouting pressure causes along tunnel around, for the above region of tunnel horizontal median axis, while applying grouting pressure, the soil body is produced to Additional stress component upwards, strengthened the relative displacement between pile body, friction force strengthens.In like manner, be the soil body below horizontal median axis, what be subject to is downward Additional stress component, has offset the relative displacement between part stake soil, and friction force reduces.But the pile body buried depth adopting in this programme is darker, pile body is longer, and the range of influence of grouting pressure is limited, therefore the change in friction force of pile body top is little.

C, when after tunnel excavation, the tunnel segment soil body hollows out, being changed significantly of friction force.The off-load of the tunnel upper soil body, cause the sleeping soil body under needle beam further to move down with respect to pile foundation, so producing the region of negative friction increases, the position of the neutral point between the positive force of negative friction drops to 19.5m by initial 18.3m, the value of maximum negative friction has increased 10.06%, becomes 36.408KN.Simultaneously, in pile body bottom, its side inside soil body stress is released on formed liner structure completely, liner structure is under the effect of the deadweight of the top soil body and bottom soil body resilience, there is the distortion of " horizontal ovum " formula, laterally extrusion soil, and then impact closes on and underpins the flexural deformation that pile foundation deviates from tunnel.The soil body is taking tunnel horizontal axis as boundary simultaneously, and the top soil body moves up, and the bottom soil body moves down, and cause the native relative displacement of stake more than horizontal median axis to increase, and relative displacement reduces below axis.Approximately there is the corresponding displacement of first horizontal median axis in maximal value, reaches 99.467KN.

2.2.2.2) back of the body tunnel side-friction force

As shown in Fig. 4 d, Shield Tunneling is less for the impact of the suffered friction force of back of the body tunnel side pile foundation.Before excavation, pile body is all subject to friction force upwards.And present on the whole along pile body buried depth the trend that friction force constantly increases.Underpin pile foundation has downward mobile trend with respect to the back of the body tunnel side soil body under pile top load effect, and maximal friction is 90.926KN.But after tunnel excavation finishes, because top, tunnel (17m-23.6m) resistance to shear of soil discharges completely, under the joint effect of the factors such as the soil body resilience of bottom, tunnel and tunnel lining structure transversely deforming, the both sides that underpin pile foundation are faced tunnel lateral earth pressure and are reduced, and tunnel surrounding soil release rate maximum, and radially reduce gradually.The back of the body tunnel side soil body is taking tunnel horizontal median axis as boundary, and the top soil body has downward change in displacement, and the motion of the bottom soil body is contrary, therefore in the scope of 17m-23.6m, friction force reduces, maximum has reduced 32%, is only 38.2KN; Owing to affected by excavation, near force of negative friction tunnel horizontal median axis correspondence position obviously increases, and friction force maximal value appears at the following 2.2m of tunnel horizontal median axis place, and its value is 101.43KN.

2.2.3) analysis of Internal forces

2.2.3.1) pile body axle power

Pile body, as foundation structure, is mainly born the load that superstructure transmits, and load is passed to lower sleeping hard soil layer.The mode of action of pile foundation and soil layer mainly contains two kinds, and a kind of is the rubbing action that relies on stake surrounding soil, and fractional load is delivered in ground; Another kind of mode is by stake end being directly bearing on soil layer, load being passed to the soil body.So, in the time that analysis underpins the axle power of pile foundation, must consider in conjunction with the variation tendency of friction force, just can obtain rationally result accurately.

As shown in Fig. 4 e, before tunnel excavation, the axle power of underpinned pile is gradually less trend along pile body generally.On stake top, the axle power of bearing is 965KN.This value is more much smaller than the theoretical value of load under 1/2 post, be only under post load 71.48%.In adopting two stake beam types to underpin, underground pile one underpins girder construction has very large difference with ground upper prop one girder construction.Underpin the position that beam is embedded in underground 3.2m.At the bottom of being subject to upper prop when load action, when underpining beam upper load is shared to pile foundation, also part upper load will inevitably be passed to the lower sleeping soil layer that underpins beam, the load that causes assigning to stake top far away from post at the bottom of load 1/2.More than pile body 6m, the change curve of axle power is mild, but still presents the trend reducing gradually along with the increase of the degree of depth, and in the time of degree of depth decline 6m, axle power only reduces 8%.In 6m-11m position, owing to being subject to facing the force of negative friction effect that tunnel side is larger, showing as generally pile body axle power and become large.Due to the increasing along with pile body buried depth, face the tunnel side force of negative friction and reduce gradually, finally become positive friction, reach after 11m when the pile body degree of depth therefore show as in pile body axle power, axle power significantly reduces, and pile body buried depth increases 16m, and pile body axle power reduces 88.53%.In the time of tunnel excavation and after tunnel excavation completes, the roughly variation tendency of axle power is generally with consistent before excavation.But after excavation, the neutral point that pile body faces the positive force of negative friction of tunnel side moves down, and the effect of the force of negative friction is more obvious.Although axle power still has reducing by a small margin in 0m-6m, the axle power growth region below 6m is elongated, becomes 6m-13m from the scope of original 6m-11m.And in this region, axle power has increased 79.835KN.Facing below tunnel side 19.5m, the positive friction causing due to excavation significantly increases, therefore tunnel axle power reduces rapidly below this position, pile body buried depth only increases 9m, and pile body axle power just reduces approximately 54%.

3) by above-mentioned numerical simulation analysis, can simulate rationally and effectively the digging process in adjacent stake tunnel, and know that tunnel excavation will produce the impact of can not ignore to the internal force and the deformation that underpin pile foundation, but want the size of this influence of labor, need in engineering proposal, underpin the distance S between pile foundation by changing specifically to underpin, stake end and horizontal median axis position, tunnel (i.e. stake end relative position), the parameter of stake footpath size and these engineering factors of grouting pressure, adopt step 1) and step 2) method set up the finite element models of organizing under different operating modes more, to pile lateral displacement Ux under each operating mode, pile body vertical displacement Uy, pile body friction force, the situation of change of pile body axle power N and moment M compares analysis, obtain each engineering factor after tunnel excavation to underpining the influence rule of pile foundation,

3.1) impact of underpinned pile pile spacing S

The pile spacing of underpinned pile refers to the distance between the axis of underpinned pile, is one of important duty parameter, for the operating mode under three groups of piles with different interval S, makes analysis with regard to pile foundation internal modification and stressing conditions:

As shown in Figure 5 a, no matter how pile spacing changes, all there is the situation of change of " bow " font at the horizontal shift Ux of pile body, twice negative displacement increases, a negative displacement reduces the form of (even displacement oppositely becomes positive displacement), and maximum displacement value all appears at horizontal median axis position, tunnel; In the time that pile spacing increases, pile body upper deformation amplitude increases, and the curve difference opposite sex obviously.Pile body lower deformation amplitude reduces, and Ux curve is close to and overlaps; In the time that pile spacing becomes 12m and 14m from 9.6m, position, stake top forward moves with pilespacing and increases, and has increased respectively 0.52mm and 0.74mm.Visible S increases, and underpins beam and lengthens, and has more upper load to be delivered in time sleeping soil layer, the deflection deformation aggravation of needle beam, and because position, stake top is connected with needle beam, the stake top distortion that underpins pile foundation therefore corresponding also strengthens.Simultaneously, when the increase of S, the maximum negative displacement value of pile body epimere increases, the maximum negative displacement value of pile body hypomere reduces, the maximum hogging moment of pile body epimere has increased respectively 37.2% and 46.7%, become 3.60mm and 3.85mm, and the maximum negative displacement of pile body hypomere reduces respectively 5.3% and 7.9%, become 3.62mm and 3.52mm.In the scope of the about 5m-14m in pile body stage casing, negative horizontal shift Ux significantly reduces, and pilespacing S is larger, and the decrease of negative displacement is less.In the time of S=9.6m and S=12m, the maximum decrease of negative displacement is respectively 3.91mm and 3.68mm, exceedes maximum negative displacement value, so there is positive displacement underpining pile foundation middle section position.And in the time of S=14m, the maximum decrease of negative displacement is only 3.43mm, there is not positive displacement in pile foundation stage casing, the increase principle of pile body epimere negative displacement is identical with the increase principle of stake top displacement, occurred larger recessed to due to the deflection of needle beam direction by pile body.And due to pile foundation from tunnel more away from, the impact of the excavation that is subject to is also just less, therefore when s increases, the horizontal shift Ux of a bottom reduces gradually.

As shown in Figure 5 b, for vertical displacement Uy, in same buried depth position, in the time that S is changed to 12m from 9.6m, underpinned pile pile spacing larger, vertical displacement value is larger.Maximum horizontal displacement Ux occurs in 6.69 of position, stake top, while being about S=9.6m obtained peaked 119.9%.And in the time that s is increased to 14m gradually, same buried depth position vertical displacement Uy slightly reduces, but variable quantity is little, and the situation of maximal value during only compared with S=12m reduced 4%; Pile spacing S is larger, and underpinned pile flexural deformation is larger, will cause vertical displacement to have the trend of increase.But S is larger, according to the described situation of the normal distribution curve in Peek formula, the distortion of the far-end soil body is less, and it is also less that pile body is subject to the impact of tunnel excavation, vertical displacement had to the trend reducing.So, comprehensive above-mentioned two kinds of impacts, vertical displacement is totally presenting the situation of change from the increase first increases and then decreases of S with pile spacing.

As shown in Figure 5 c, under the operating mode of different interval S, pile body has all occurred that friction force has and just has negative situation, and the maximal value of friction force all appears at tunnel horizontal median axis correspondence position.In the same buried depth of pile body position, when S=9.6m, friction force value is significantly greater than the situation of S=12m and S=14m, and now maximal friction is positive friction, is about 99.467KN, and the force of negative friction appears at the above position of 19m, pile body top, and maximal value is 36.4KN.And in the time of S=12m and S=14m, the friction force value of the two and variation tendency are comparatively approaching.Positive friction maximal value is 25.9KN and 22.2KN, and the maximal value during respectively compared with S=9.6m has reduced 73.9% and 77.6%.Meanwhile, on the neutral point position of the positive force of negative friction, move to 16m place, Maximum Negative Frictional Force is respectively 18.552KN and 20.615KN.The reducing of the force of negative friction reduces relevant with the relative displacement of facing the tunnel side soil body.In the time that S increases, under needle beam, bear the also corresponding increase of soil body volume of upper load, under identical upper load effect, the distortion of the soil body reduces, and the native relative displacement of stake reduces.

As shown in Fig. 5 d, can be clear that, when S=9.6m, the situation of change of friction force is obviously different from other two kinds of situations; When S=9.6m, back of the body tunnel side-friction force enlarges markedly near tunnel horizontal median axis correspondence position, and maximal value occurs in the following 2m of horizontal axis position, has reached 101.43KN.In the time that S is larger, the friction force of back of the body tunnel side obviously reduces.And in the time that S increases to a certain degree, the friction force of back of the body tunnel side is basic identical.The in the situation that of S=12m and S=14m, maximal value approximately occurs in pile body 11m-12m section, and maximal friction is respectively compared with having reduced 61.4% and 64.6% in the situation of S=9.6m.

As shown in Fig. 5 e, for the situation of change of pile body axle power, along with the increase of pile spacing S, underpining the load combination ratio that under beam, the soil body is shared increases, stake apical axis power reduces, differ larger therefore show as an apical axis power, but every axle power variation tendency that underpins pile foundation is roughly the same, is all roughly axle power and reduces along pile body.But the variation range of each is different, when S=9.6m, the minimum axle power of pile body is 38% of greatest axis power, and when S=12m and S=14m, the minimum axle power of pile body is only for being 35.5% and 26.1% of greatest axis power.The variation tendency of visible axle power, is to change on the basis of stake side-friction force, and the closer to tunneling, the amplitude of variation of axle power is larger, and it is obvious that axle power reduces situation; For underpining pile foundation, all effects due to the force of negative friction in 6m-13m position, top, axle power all has increase tendency in various degree in this position, and when S is less, the effect of the force of negative friction is more obvious, the amplification of axle power is larger, even, the in the situation that of S=9.6m, underpin the position of pile body middle part 11m-13m, pile body axle power has exceeded stake apical axis power, and for same pile body buried depth position, pile body axle power increases with S and progressively reduces.When S becomes 12m and 14m from 9.6m, the maximal value of pile body axle power, from 993.8KN, has become 806.1KN and 603.8KN, has reduced respectively 18.9% and 39.2%.

3.2) impact of stake end relative position

As shown in Figure 6 a, for different pile foundation length, the variation of horizontal shift is more obvious; In the time of L=20m, maximum horizontal displacement is negative displacement, appears at pile body 4m place, is 2.70mm.In the time that underpinned pile foundation pile end is positioned at tunnel horizontal median axis correspondence position, the impact that is subject to tunnel excavation is the most obvious, and the situation of change of its horizontal shift and another two kinds of situations exist marked difference.The horizontal shift on pile foundation top obviously reduces, and the horizontal negative displacement of bottom increases, and has reached 2.62mm, and has occurred the positive displacement of 2.49mm in stake end.In the time that stake end is positioned at below horizontal median axis, its maximum horizontal displacement appears at the corresponding displacement in axis, reaches 3.81mm, and the situation of maximum displacement during compared with L=20m and L=25m increased respectively 45.4% and 41.8%.

As shown in Figure 6 b, vertical displacement reduces along with the lengthening of pile body generally; In the time that pile body length is positioned at tunnel upper, vertical displacement is very large, while being about pile body L=25m situation 116.6% of maximum vertical displacement Uy, while being about axis below situation 138.7% of maximum vertical displacement Uy, pile body is shorter, and stake end bearing is in the larger soil layer of tunnel upper stress release rate, so the Influence of Displacement being subject to is large, and side, tunnel and below soil layer stress release rate are less, less on the impact of deformation of pile foundation.

As shown in Fig. 6 c, face tunnel side-friction force and all occur positive and negative situation about replacing, when L=20m, the position of neutral point is positioned at 12.2m place, is equivalent to 61% length place of pile body.Along with L increases as 25m and 28m, the position of neutral point declined respectively 4.4m and 7.1m, be positioned at 66% and 69% of pile body length separately mutually.Visible, along with the increase of pile foundation length, the neutral point position in pile foundation will move down along pile body.In the time that stake end is positioned at top, tunnel excavation cavern, maximal value appears at an end position, and Maximum Negative Frictional Force is 28.3KN, and maximum positive friction is 46.8KN.And being positioned at horizontal median axis position, tunnel and when following when stake end, Maximum Negative Frictional Force has increased respectively 17.4% and 28.7% during than L=20m.The maximal value of positive friction all appears at tunnel horizontal median axis correspondence position, and increases with pile foundation length, and positive friction maximal value increases, and is respectively 99.225KN and 99.467KN.

As shown in Fig. 6 d, for deviating from tunnel side, every pile base all presents the variation tendency that friction force increases along pile body.And it is basic identical to underpin the stressing conditions of pile foundation friction force at the above correspondence position of 20m under suffered friction force and other two kinds of operating modes when L=20m, only, at the long position of newly-increased stake separately, friction force further increases.The long variation of this explanation stake affects little on the Changing Pattern of the suffered friction force of pile foundation back of the body tunnel side.Just, when L=20m, maximal friction occurs in an end position, and its value is 55.5Kn, and along with the increase of L, maximum positive friction appears at tunnel horizontal median axis correspondence position, and the maximal value during compared with L=20m has increased respectively 8% and 82.6%.

As shown in Fig. 6 e, by finding out in three groups of pile foundation length situations, the top of pile foundation, value and the variation tendency of axle power are basic identical, but the bottom of pile foundation, in same buried depth position, a long pile foundation is larger in the pile body axle power of this position, and along with buried depth strengthens, the difference of axle power is larger, axle power difference on stake top is 92.11KN, and has arrived the stake end 20m degree of depth, and difference becomes 503.89KN.And stake is long, the suffered side-friction force of pile body is larger, to pile body axle power to reduce effect more obvious, when L=20m, axle power has reduced 587.5KN along stake, and in the time of L=25m and 28m, axle power has reduced 700.9KN and 616.7KN along stake.

3.3) impact of upper load active position

In the time utilizing underpinning structure to underpin upper load, tend to occur that a underpinning structure underpins the situation of several former pile foundations simultaneously.After the former stake of diverse location is underpined, upper load still acts on needle beam in situ.Different load positions, all can produce appreciable impact to the additional bending moment, the stake apical axis power etc. that underpin pile foundation generation, and then be embodied in the variation of deformation and internal stresses of pile foundation.Therefore, research upper load active position, on underpining the impact of pile foundation, has very great practical significance.

For concrete reflection underpins pile foundation suffered impact under the effect of diverse location upper load, get respectively that upper load acts on apart from needle beam left end 1/3L place, centre position and these three kinds of situations explain analysis apart from needle beam right-hand member 1/3 place.By more known to above three kinds of situations:

As shown in Figure 7a, in the time that upper load moves to right-hand member by left end gradually, the drift displacement curve of pile body becomes from nearly suberect bow font the bow font being tilted to the right, and pile body integral inclination degree strengthens.The variation maximum of stake top displacement, has increased 3.94mm to the right.Maximum displacement within the scope of pile body epimere 0m-10m reduces, and the 3.30mm while acting on apart from needle beam left end 1/3 position by F, is reduced to 0.99mm, has approximately reduced 69.8%.The maximum forward displacement at pile body middle part also along with F away from and reduce, be reduced to 0.85mm by 1.45mm.And underpining below pile foundation buried depth 20m, maximum horizontal negative displacement but along with F away from and increase, the maximum displacement value of pile body has increased 37.5%, has reached 4.51mm.This is because in the time that upper load F moves to right gradually, and eccentric throw increases, and additional bending moment increases, meanwhile, underpin beam, in load end pile foundation far away, larger buckling deformation has occurred, finally cause the final situation that has occurred that entirety is tilted to the right, top is out of shape aggravation to the right, and pile body bottom is away from former axial location.

As shown in Figure 7b, can be clear that, load is away from the displacement more of pile foundation, and the impact that pile foundation is subject to is less, and vertical displacement value is also less.In the time that top imposed load moves to right gradually, the 6.39mm of maximum vertical load during by high order end reduced respectively 12.7% and 24.6%, becomes 5.58mm and 4.82mm.

As shown in Fig. 7 c and Fig. 7 d, in the time that top imposed load moves to right gradually, can find out, the variation tendency of friction force of facing tunnel side in three kinds of situations is basic identical, and maximal friction all appears near tunnel horizontal median axis.But along with moving to right of load, pile body top is increased by the region of negative friction, and Maximum Negative Frictional Force increased by 99.4%, reaches 45.4KN.And the positive friction of pile body bottom is with the moving to right and reduce gradually of load, full the maximal friction of stake is reduced to 81.9KN by 112.5KN.This is because for different load positions, and both sides underpin pile foundation and distribute the pile top load of gained not identical.In the time that upper load moves to right gradually, the pile top load of left stake reduces gradually, and the move downward trend of pile body under load action reduces, and the relative displacement between stake soil increases, therefore the force of negative friction on top increases.And now after excavation finishes, the tunnel structures such as lining cutting are under the effect of the factors such as load at the bottom of the top soil body, post, and the distortion of generation is no longer symmetrical, and the distortion of loading position increases under nearly post, loading position distortion far away reduces, and causes the soil deformation on left tunnel right side not reciprocity.Therefore in the time that load moves to right, the distortion of the stake side soil body of left side pile foundation reduces, pile body maximal friction is reduced to 81.9KN by 112.5KN, approximately reduce 27.2%, and the pile body friction force of back of the body tunnel side is subject to the impact of load position less, its value remains unchanged substantially.

As shown in Fig. 7 e, for pile body axle power, can be clear that, along with moving to right of load position, for same buried depth position, pile body axle power reduces gradually.And in the time that F acts on left end, axle power has reduced 81.7% along pile body, axle power change curve tilts.And when load position gradually away from time, axle power along pile body change little, axle power change curve is tending towards vertically gradually, the difference of pile body axle power is less than 48.4%.

3.4) impact of grouting pressure

In the time of Shield Tunneling, when shield machine is pushed ahead, between excavation border and liner structure, need to rely on to apply grouting pressure, grout is injected among space.But meanwhile,, grouting pressure also can act on the tunnel soil body around, applies additonal pressure to the soil body, and then impact underpins the distortion of pile foundation.

As shown in Fig. 8 a and Fig. 8 b, analyze knownly, do not apply the situation of grouting pressure compared with applying the situation of 0.15Mpa grouting pressure, the variation tendency of horizontal distortion Ux more than pile foundation 15m is basic identical.But below 15m, the trend that pile body has negative direction to move, and along with the increasing of pile body buried depth, it is large that the horizontal shift difference of the two also becomes gradually.In the time of 15m, the horizontal level difference of the two is 0.29mm, and holds the difference of both horizontal shift Ux to reach 1.02mm in stake.In analysis before, when tunnel excavation, main range of influence is both sides, tunnel " circle petal " parts.Therefore even without applying grouting pressure, pile body still can be subject to the impact of soil deformation in tunnel excavation position, there is the position of negative direction, the horizontal shift of stake end is-0.74mm.And in the time applying grouting pressure, the soil body is subject to larger extra-stress, cause the negative horizontal level of pile foundation to increase, become 1.77mm in the horizontal shift of stake end, apply in the absence of grouting pressure, increase by 136.5%.And vertical displacement curve overlaps substantially, illustrate that grouting pressure is little to the influence of vertical displacement.

As shown in Figure 8 c, for the suffered friction force of pile body, grouting pressure is very little to the influence on pile body top, and friction force value does not have notable difference.But below pile foundation, particularly near tunneling, (in correlation curve figure, be mainly manifested in the scope of 16m-27m), grouting pressure is larger on the impact of friction force value.Show as facing tunnel side, in the scope of 20m-25m, the suffered positive friction of pile foundation increases.This has Additional stress component upwards just because of grouting pressure to the top soil body of tunnel horizontal median axis, and the relative displacement of pile body increases.In like manner, below axis, offset the relative displacement between part stake soil, positive friction reduces, and maximum positive friction is only 65.7% while not applying grouting pressure.The back of the body tunnel side soil body is not directly subject to the impact of grouting pressure, thus basic identical when carrying on the back the suffered friction force situation of tunnel side pile foundation and not applying grouting pressure, therefore do not carry out brief description of the drawings at this.

As shown in Fig. 8 d, for axial force of pile, below pile foundation 15m, for same pile body buried depth position, apply the internal force underpining in pile foundation after grouting pressure and be greater than the situation that does not apply grouting pressure, maximum reduction approximately occurs in 23.6m position, and axle power decrease is 109.11KN.

4) according to specifically underpining engineering proposal, set up the finite element model of many of pile foundation underpinnings, simulated in detail a underpinning structure and underpined the situation of many, utilize the situation of change that underpins pile foundation deformation and internal force, checking underpins the feasibility of engineering proposal;

4.1) pile foundation underpinning engineering design

Pile foundation underpinning step: measure unwrapping wire → foundation trench jet grouting pile construction → boring underpinned pile construct → construct foundation trench earth excavation and soil nailing bolt-spray support → underpinned pile cushion cap, underpin beam construction → pre-top, the backfill of envelope pile driving construction → pit earthwork, buildings and road recovery.

4.2) underpin the Deformation control of pile foundation

For the Deformation control of pile foundation, be mainly reflected in pile lateral displacement control and Vertical Settlement Deformation control.

4.2.1) control of horizontal displacement

For horizontal shift, according to " technical code for building pile foundation " requirement, when the horizontal bearing capacity of pile foundation is during with displacement control, the horizontal shift permissible value of stake can be taken as 10mm, and the horizontal shift permissible value of the works to horizontal shift sensitivity is taken as 6mm.When pile foundation level bearing capacity is during with strength control, can determine horizontal shift permissible value by following formula:

X_{0} = \frac{R_{ha} \times V_{x}}{α^{3} \times EI}

Wherein, R _harepresent horizontal bearing capacity of single pile eigenwert, V _xrepresent horizontal shift coefficient, α represents horizontal distortion coefficient; The circular of each parameter can, with reference to " technical code for building pile foundation ", in the engineering proposal of the present embodiment, be thought in the time that the horizontal loading of pile foundation is no more than 6m, thought that the horizontal distortion of pile foundation meets safety requirements.

Through rational numerical simulation, obtain underpining pile foundation and underpin after load action being subject to top, the variation of horizontal shift is as shown in Fig. 9 a, and left side underpins pile foundation and has occurred inclination to the right, and right side underpins pile foundation and has occurred inclination left.Left side maximum forward horizontal shift occurs in position, stake top, arrive 3.92mm, and owing to being subject to the impact of tunnel excavation, maximum negative sense horizontal shift, occurs in horizontal median axis 25m position, tunnel, and its value is 4.40mm.The horizontal distortion curve map of right side pile foundation has occurred that " bow " font changes, there is positive-displacement in pile body upper and lower, and pile body middle part has occurred that local negative sense displacement, maximum forward displacement occur in tunnel horizontal median axis correspondence position equally, maximum position value is 3.42mm.The maximum horizontal distortion of each is all less than 6mm, and think and adopt this to underpin scheme, under tunnel construction infection, the horizontal distortion engineering demands of pile foundation.

4.2.2) Vertical Settlement Deformation control

Usually, in engineering, Vertical Settlement distortion mainly need to meet four and control index, and they are respectively: settling amount: framed bent pile foundation 120mm, high-rise structures 150-350mm; Differential settlement: framework, limit organ timbering, other hyperstatic structures 0.0007-0.005L0; Tilt: crane rail level, multilayer high level, high-rise structures; Local dip: brick body bearing wall.In this programme, employing be to utilize two stake beam type underpinning structures to underpin top three across 9 story frame structures, so in the first three items that only needs to consider deformation of pile foundation, i.e. settling amount, differential settlement, and integral inclination situation.Wherein, for the deformation of pile foundation allowable value of buildings, can choose with reference to " technical code for building pile foundation " 5.3.4 bar, require as shown in table 2 below:

Table 2 deformation of pile foundation allowable value

According to Practical Project scheme, obtain underpining the sedimentation and deformation of pile foundation under Shield Tunneling impact as shown in Fig. 9 b, can find out that the settling amount that underpins pile foundation reduces gradually along pile body, and in same pile body buried depth position, the sedimentation and deformation that right side underpins pile foundation will obviously be greater than the distortion of left side pile foundation.The maximum settlement amount of left side pile foundation is 5.67mm, and right side maximum settlement amount is 6.80mm, all meets the requirement to neighboring piles maximum settlement amount in table 2.The maximum settlement of left and right pile foundation is poor is 1.125mm≤0.002L0, meets requirement poor to pile foundation settlement in construction project.And differential settlement is 0.0001≤0.003 with the ratio of pile spacing, therefore can there is not obvious integral inclination in top-out.

In sum, known by numerical simulation analysis, undertaken after pile foundation underpinning by this engineering proposal, underpin pile foundation under the impact of Shield Tunneling, suffered internal force is within bearing capacity of pile foundation scope, and malformation is in engineering allowed band, and underpinning structure is safe and reliable.Therefore, if adopt this programme in Practical Project, can ensure the normal use of top-out, can guarantee again carrying out smoothly of Shield Tunneling, scheme has engineering practical feasibility.

4.3) Internal force control of pile foundation

Specifically under beam TL1, underpin pile foundation suffered impact in the process of tunneling shield method excavation and do respective value sunykatuib analysis for underpining, owing to underpining beam TL1 after underpining, three load actions that post transmits such as top Z have been born simultaneously, no longer to apply symmetrical load in simulation process above, therefore left and right underpins the distortion of pile foundation and stressed different, should separately discuss, the Numerical results obtaining is as shown in Fig. 9 c and Fig. 9 d, after constructing tunnel finishes, due to the active position inequality of load, right side load is greater than left side load, pile foundation face tunnel side-friction force curve map in be presented as that left side pile foundation suffered maximal friction is 89.754KN, and though right side pile foundation is faced the maximal value of large side-friction force and has been reached 113.38KN, increase 26.3% compared with left side pile foundation.And in pile foundation back of the body tunnel side, within the scope of 16m-26m, for same pile body buried depth position, the friction force of left side pile foundation is significantly less than the friction force value of right side pile foundation, maximum difference has reached 16.9KN.And the force of negative friction of other positions value is basic identical.

As shown in Fig. 9 e, the pile body axle power that underpins pile foundation roughly presents the variation tendency reducing gradually along pile body, and the combined action of facing Ce Jibei tunnel, tunnel side-friction force due to pile body, on pile body axle force curve, all has a fragment position to occur the situation that axle power increases.For same pile body buried depth position, the axle power of right side pile foundation is obviously greater than left side pile foundation, and maximum difference has reached 862.7KN.And the position difference of pile foundation, pile body occurs that the position of greatest axis power is not identical yet.The axle power maximum position of left side pile foundation approximately appears at pile body buried depth 15m place, and its value is 945.12KN, and axle power maximal value 1647.4KN has just appearred in right side pile foundation at 10m pile body place.This underpins bearing capacity of pile foundation ultimate value is 4200KN, therefore the above-mentioned internal force value of pile foundation is all designing in allowed band, underpins pile foundation and can not destroy.

Therefore, in Analysis on Shield Tunnel Driven Process, the internal force of underpinning structure and distortion all meet the demands, upper building safety, and the engineering proposal of the present embodiment has very high feasibility.

The above; it is only patent preferred embodiment of the present invention; but the protection domain of patent of the present invention is not limited to this; underpin in engineering proposal as being applied to other; anyly be familiar with those skilled in the art in the disclosed scope of patent of the present invention; according to the present invention, the technical scheme of patent and inventive concept thereof are equal to replacement or are changed, and all belong to the protection domain of patent of the present invention.

Claims

1. shield-tunneling construction, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that comprising the following steps:

2. shield-tunneling construction according to claim 1, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that: step 2) described employing life and death unit controls method is to shield tunneling process simulation, specific as follows:

F) cancel grouting pressure, activate liner structure and grouting layer unit;

3. shield-tunneling construction according to claim 2 is to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, it is characterized in that: steps d) in the method that adopts of the simulation of terrestrial stress be: adopt step excavation pattern, the soil body unit of tunnel internal after excavation is set as to " dummy cell ", calculate the borderline nodal force in tunnel, by these force reactions in boundary node, with simulation primary stress, carry out simulated ground stress release by the size and the direction that change acting force.

4. shield-tunneling construction according to claim 2, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that: the pile top load that step b) applies is 250～300t; Steps d) and e) the grouting at the tail of the shield machine pressure that applies be 0.1～0.2Mpa.

5. shield-tunneling construction according to claim 2, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that: step a) described soil model is D-P constitutive model.

6. shield-tunneling construction according to claim 1 is to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, it is characterized in that: step 1) described soil body piece is of a size of 46m × 48m, on Width, get 8D, in short transverse, corresponding earth's surface is got in shield structure top, and soil body edge, below to shield shell outside is not less than 30m.

7. shield-tunneling construction according to claim 1, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that: step 1) material that adopts of described tunnel-liner is that C30 concrete is built, and thickness is 0.3m, and Poisson ratio is 0.2, and severe is 26KN/m ³; The material that described grouting layer adopts is soil cement, and thickness is 0.2m, and Poisson ratio is 0.2, and severe is 21KN/m ³; The described pile foundation that underpins is for two stake beam type underpinning structures, and the material that wherein needle beam adopts is that C40 concrete is built, length × height=12.55m × 2m, and Poisson ratio is 0.2, severe is 27.5KN/m ³; Underpinned pile is the boring concrete-pile of diameter 1.2m, length 27m, and pile body adopts C30 concrete to build, and Poisson ratio is 0.2, and severe is 26KN/m ³.

8. shield-tunneling construction according to claim 1, to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, is characterized in that: step 1) the lateral stiffness reduction coefficient of described tunnel-liner is 0.85.

9. shield-tunneling construction according to claim 1 is to the contiguous Numerical Analysis methods that underpins Influence of Pile Foundation, it is characterized in that: step 1) processing of described grouting layer, be specially: in shield method tunnel construction process, after shield tail shell is pushed ahead, supporting role before the shield structure soil body around loses, internal stress discharges, shield machine is to afterbody space position spray injecting paste material simultaneously, under the effect of grouting at the tail of the shield machine pressure and inside soil body stress, to form a soil body at shield tail, the complicated annular mixolimnion of injecting paste material and air multiphase coexistence, adopt and wait this layer material of generation layer simulation, in these,, parameter of layer chose as follows in generation:

10. according to the shield-tunneling construction described in claim 1-9 any one, vicinity is underpined the Numerical Analysis methods of Influence of Pile Foundation, it is characterized in that: the unit that described finite element model is chosen comprises PLAN42 unit, CONTA172 unit and TARGE169 unit, wherein: adopt the PLAN42 unit simulation soil body, underpin pile foundation and tunnel structure; Adopt the CONTA172 unit simulation soil body, underpin the connection function between pile foundation and tunnel structure; Adopt TARGE169 unit to simulate specifically underpining engineering proposal as object element.