CN102561406A - Construction method for controlling back soil body deformation of open caisson - Google Patents

Abstract

The invention discloses a construction method for controlling soil deformation at the back of a caisson, which comprises step 1, lowering the groundwater level below the bottom surface of the caisson; step 2, increasing the overall rigidity of the caisson; and step 3, arranging multiple caissons alternately The jacking sequence of parallel pipe jacking; step 4, establish a simplified 3D finite element model of the caisson and its back soil and determine the jacking force pre-control parameters during jacking construction according to the maximum allowable deformation limit of the back soil ; Step five, use grouting process in the jacking construction to form a thixotropic mud sleeve with the effect of reducing friction and drag between the outer wall of the pipe jacking and the soil layer; Step six, according to the jacking sequence of parallel pipe jacking, pipe jacking Before construction, install testing instruments in the back soil to arrange measuring points, and adjust construction parameters according to the test information fed back from the measuring points during construction. The invention solves the deformation control problem of the soil at the back of the caisson due to the repeated action of the jacking force in the large-diameter parallel pipe jacking construction project, and has the beneficial effects of easy implementation and low cost.

Description

The Construction Method of Controlling the Deformation of the Soil at the Back of the Caisson

technical field

The invention relates to the technical field of underground construction engineering, in particular to a construction method for controlling soil deformation at the back of a caisson caused by large-diameter parallel pipe jacking construction.

Background technique

The pipe jacking technology is a non-excavation underground pipeline that uses hydraulic cylinders to push the pipe jacking machine and the pipe joints to be laid underground one by one from the pipe jacking working well to the pipe jacking receiving well without excavating the surface. laying construction process. Caissons are widely used as working wells in pipe jacking engineering.

During the pipeline jacking process, the reciprocating jacking force of the pipe jacking machine reacts to the back soil behind the back wall through the back wall. When the jacking force is too large and the soil at the back of the caisson is not stable enough, the soil at the back may be greatly deformed, so that part of the working return of the pipe jacking machine is consumed on the deformation of the soil at the back, reducing the The working efficiency of the pipe machine. Severe deformation of the back soil may also cause the back soil to be destroyed, making the jacking construction fail. On the other hand, the large deformation of the back soil will also cause damage to the roads or buildings around the caisson, thus triggering a series of environmental disasters. Therefore, it is very important to strictly control the soil deformation at the back of the caisson caused by pipe jacking construction to ensure the safety and smooth progress of the pipe jacking project.

After retrieving the existing technical literature, Yan Shaojun and Zhang Aihua published in "Coalfield Geology and Exploration" (February 2006, Vol. Three-dimensional analysis of deformation and deformation" (article number: 1001-1986 (2006) 01-0037-04) takes a pipe jacking project as the background, and uses Rankine's passive earth pressure theory to analyze the bearing capacity of the back soil. By changing the elastic modulus parameters of the back soil, taking different moduli and using the Drucker-Prager model to calculate, the corresponding maximum horizontal displacement value of the wall is obtained, and a conclusion is drawn: to improve the elastic modulus of the soil The amount can effectively reduce the horizontal displacement value of the back wall. However, this document only quantitatively calculates and analyzes the bearing capacity and displacement of the soil at the back of the caisson based on theory, and does not provide relevant technical measures to control the displacement of the soil at the back. At the same time, in the conclusion of this article, the author also pointed out the limitations of the method used, that is, the actual situation of repeated loading-unloading of pipe jacking was not considered.

Therefore, those skilled in the art are devoting themselves to developing a construction method for controlling the deformation of the soil behind the caisson, so as to solve the problem of controlling the deformation of the soil behind the caisson under complex loading, especially under the action of cyclic or changing repeated loads.

Contents of the invention

In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is to provide a control method for controlling the deformation of the caisson back soil under complex loading, especially under the action of cyclic or changing repeated loads. Deformed construction methods.

In order to achieve the above object, the present invention provides a construction method for controlling soil deformation at the back of the caisson, comprising the following steps: step 1, implement dewatering at the well point around the caisson, and lower the groundwater level to the bottom surface of the caisson Following; Step 2, strengthening the anchoring of the bottom of the caisson in the soil layer to improve the overall rigidity of the caisson; Step 3, alternately arranging the jacking sequence of a plurality of parallel pipe jacking; Step 4, establishing the caisson and the simplified three-dimensional finite element model of the back soil, and determine the jacking force pre-control parameters during the jacking construction according to the maximum allowable deformation limit of the back soil; step five, use grouting in the jacking construction The process makes the outer wall of the pipe jacking and the soil layer form a thixotropic mud sleeve with the effect of reducing friction and resistance; step 6, according to the jacking sequence of the parallel pipe jacking described in step 3, before the pipe jacking construction, after the pipe jacking Install testing instruments in the back soil to arrange measuring points, and adjust construction parameters according to the test information fed back from the measuring points during pipe jacking construction.

Further, in step 2, use a high-pressure water gun to clean the reserved groove on the inner side of the well wall above the blade foot, chisel all the concrete on the surface and expose the stones, and weld the reserved steel bars to the bottom plate steel bars.

Further, in step 2, a concrete bored cast-in-place pile is set at the bottom of the caisson to resist the reaction force caused by the top force; the poured pile is connected to the bottom of the caisson by an inverted trapezoidal pile cap; the pouring The pile top steel bars of the piles are anchored into the bottom plate of the caisson, and the cast-in-place piles are evenly distributed in each cell at the bottom of the caisson along the direction perpendicular to the jacking pipe jacking direction.

Further, in step three, the difference between the two jacking forces on the back wall of the caisson caused by simultaneous jacking of the two parallel jacking pipes does not exceed 20%.

Further, in Step 4, the stability analysis method is used to determine the jacking force pre-control parameters during jacking construction.

Further, in step 5, a plurality of grouting holes are evenly arranged in the circumferential direction of the tail of the machine head, and the grouting holes are all set on the three pipe joints behind the machine head, and then set on a pipe joint in every three joints. The grouting holes and the pipe joint grouting holes are arranged in an oblique 45° orthogonal circular crossing.

Further, in the fifth step, the friction reducer is lubricated with mud composed of bentonite, powdered chemical paste, soda ash and water.

Further, in step 6, according to the jacking sequence and the site conditions of the back soil, a lateral slope pipe and an earth pressure sensor are buried near the back wall at the back soil, and the surface test end adopts The way of surrounding brick wall is isolated from the surrounding.

Further, in step six, a test is performed after the back soil is consolidated to verify the availability of the measuring point; the same test step is performed before the parallel pipe jacking construction. When the back soil needs to be reinforced, vertical jet grouting piles are used for reinforcement within a certain range behind the back wall.

The beneficial effects of the present invention are:

The construction method for controlling the deformation of the soil at the back of the caisson of the present invention, through the above steps, solves the problem of controlling the deformation of the soil at the back of the caisson due to the repeated action of the jacking force in the large-diameter parallel pipe jacking construction project, making the caisson The deformation of the soil at the back of the caisson can be effectively controlled within the scope of the design requirements, ensuring the smooth progress of the pipe jacking project and minimizing the negative impact of the deformation of the soil at the back of the caisson on the surrounding environment. The construction method of the invention makes up for the deficiencies and defects of the existing construction technology, and has beneficial effects such as easy implementation and low cost.

The idea, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention.

Description of drawings

Fig. 1 is a schematic plan view of an embodiment of the present invention.

FIG. 2 is a schematic diagram of the cross-sectional state of FIG. 1 .

Fig. 3 is a structural schematic diagram of the concrete pouring pile at the bottom of the caisson.

Fig. 4 is a schematic diagram of a three-dimensional simplified model.

Fig. 5 is a schematic diagram of the plane positions of the monitoring points in the back soil.

Detailed ways

As shown in Fig. 1 and Fig. 2, a kind of construction method of controlling the deformation of caisson back soil of the present invention is applied to the following projects, the main culvert crosses the river course, and the length is 450 meters, adopting 4 jacking pipes 1 (each section of steel bar The specifications of concrete prefabricated pipe jacking are: inner diameter 3500 mm, length 2.5 meters, respectively 1#, 2#, 3#, 4#), each jacking pipe is composed of 180 prefabricated pipes, with large cross-section and long distance features.

The center distance between the jacking pipes 1 is 9.5 meters, and the elevations of the pipe bottom and pipe top are respectively -17.65 meters and -13.45 meters. The working well 21 on the south side and the receiving well 22 on the north side are both caisson structures, with a planar size of 37 meters x 22.5 meters, and the elevation of the blade foot is -21.0 meters. The pipe jacking 1 starts from the working well 21 on the south side and ends at the receiving well 22 on the north side. Arrow A shows the jacking direction.

Referring to Fig. 3, shown in Fig. 4, construction method of the present invention mainly comprises the following steps:

Step 1, implement well point dewatering around the caisson 4 (working well), and lower the groundwater level below the bottom surface of the caisson 4.

The method of precipitation is selected according to the hydrogeological conditions of the site, engineering design requirements and construction characteristics of caisson sinking. The depth of the precipitation well is:

H＝H ₁ +H ₂ +H ₃ +H ₄ +ir ₀

In the above formula: H is the depth of the precipitation well; H ₁ is the distance from the edge of the caisson to the surface; H ₂ is the required depth from the precipitation water level to the bottom of the caisson; H ₃ is the working length of the precipitation filter; H ₄ is the length of the sedimentation tube ; i is the hydraulic gradient; r ₀ is the equivalent calculation radius of caisson.

The distance between the precipitation well and the caisson wall is set between 4m and 8m according to the site conditions around the caisson.

In this embodiment, according to the detailed geological exploration data of the construction site, combined with the engineering design requirements and the construction characteristics of caisson sinking, a bridge-type water filter steel pipe well is used for dewatering. _H1 takes 25 meters; _H2 takes 1 meter; _H3 takes 2 meters; H ₄ is taken as 2 meters; i is taken as 1/5; r ₀ is taken as 17.5 meters, and the surplus amount is properly considered, and H is taken as 35 meters. The precipitation well is arranged on the periphery of the caisson, 7 meters away from the outer wall of the caisson.

The function of the first step is to increase the friction between the caisson wall and the bottom surface and the soil layer, and facilitate the implementation of the second step.

Step 2, strengthening the anchoring of the bottom of the caisson 4 in the soil layer 43 to improve the overall rigidity of the caisson 4 .

In step 2, the reserved groove 44 on the inner side of the caisson side wall 42 above the blade foot is rinsed clean with a high-pressure water gun, all the surface concrete is chiseled and the stones are exposed, and the reserved steel bar is welded to the steel bar of the caisson bottom plate 41, The length of the welded joint connection section is not less than 35d, where d is the larger diameter of the longitudinally stressed reinforcement.

Concrete bored piles 45 are set at the bottom of the caisson 4 to resist the reaction force caused by the jacking force. The cast-in-place pile 45 is connected with the caisson bottom plate 41 by an inverted trapezoidal pile cap. The pile top steel bars of the cast-in-place piles 45 are anchored into the caisson bottom plate 41, and the cast-in-place piles 45 are evenly distributed in each cell at the bottom of the caisson 4 along the direction perpendicular to the pipe jacking direction.

In this example, after the caisson 4 is sunk to the design elevation, after the grooves 44 reserved around are washed and the surface roughened, the reserved steel bars in the grooves 44 and the newly laid steel bars of the caisson bottom plate 41 are welded Connection, the welded joints are staggered from each other, d=28 mm, and the length of the welded joint connection section is taken as 1000 mm.

In addition, considering the site conditions at the bottom of the caisson, the cast-in-place pile 45 with a diameter of D=0.8 meters is selected, which is determined by Article 5.7.2 of the "Technical Specifications for Building Pile Foundations" (JGJ94-2008), and a total of 16 piles with a length of I=8 meters are required. Concrete cast-in-place piles are installed in each cell along the direction perpendicular to the jacking pipe jacking direction. The cast-in-place piles are connected to the bottom of the caisson by inverted trapezoidal pile caps, and the steel bars on the top of the piles are anchored into the bottom plate of the caisson.

The function of the second step is to improve the spatial deformation coordination of the caisson 4 under the action of the jacking force.

Step 3, alternately arrange the jacking sequence of the four parallel jacking pipes 1 . Select a reasonable jacking sequence according to mechanical equipment, site conditions and economical requirements to disperse the force of the back wall 5 and make full use of the overall stiffness of the caisson 4 at the same time.

In this example, there are four parallel jacking pipes 1 (respectively numbered 1#, 2#, 3#, 4#) that need to be jacked. Considering the limitation of equipment and economy, according to the principle of two jacking pipes in one group Jacking in stages. In order to reduce the mutual influence between the jacking pipes and prevent the force of the back wall 5 from being too concentrated, each group of jacking pipes is jacked up at the same time. When jacking, closely observe the readings of the oil cylinders on both sides, and control the difference between the jacking forces Vi and Vj on the back wall of the caisson caused by the jacking of the two pipes within 20%.

Step 4: Establish a simplified three-dimensional finite element model of the caisson 4 and its back soil 3 according to the engineering calculation accuracy requirements, and use the stability analysis method to determine the jacking construction according to the maximum allowable deformation limit of the back soil 3 The pre-control parameters of the jacking force.

According to the maximum allowable deformation limit of the back soil body 3 in step 6, the stability analysis method is used to take multiple sets of jacking force combination values to be applied to the model, and to carry out cyclic loading and unloading, and finally determine the most unfavorable jacking force of two parallel pipe jacking The combined value [Vi, Vj] is used as the jacking force pre-control parameter during jacking construction.

Vi=10290kN obtained in this embodiment, Vj=9650kN, the specific steps are:

1. The modeling range of the finite element model: in this project example, the width B=37 meters perpendicular to the pipe jacking direction, the side length of the pipe jacking reaction surface d=4.2 meters, the pipe jacking reaction surface and the sinking The distance s=12.2 meters between the tops of the wells. Therefore, the length L of the back soil body 3 of the caisson 4 is 35 meters, and the height h is 18 meters.

2. Boundary conditions of the model: Apply tangential uniform force at the bottom edge z=-1 meter of the back wall 5 and the two sides z=-1 meter, respectively simulate the friction force between the caisson bottom plate 41 and the soil, and the caisson Frictional force between the side wall 42 and the soil body; on the 4 pipe jacking reaction force acting surfaces at z=0 in the z direction, the reaction force is applied for each group of 2 pipe jackings according to the jacking sequence of step 3, and the remaining parts are not constrained. At the two sides x=-18.5 meters and x=+18.5 meters, except for the z=-1 meter part, the displacement in the x direction is restricted; at the bottom y=0, except for the z=-1 meter part, the displacement in the y direction is restricted ; The position at z=-20 meters on the back is to limit its displacement in the z direction; the position at y=+18 meters on the surface is a free surface.

3. Both the back soil body 3 and the back wall 5 are simulated by three-dimensional hexahedron solid elements, and the constitutive relationship of the soil body adopts the Mohr-Coulomb equal-area circle model considering elastic-plastic strain, and the back wall 5 is considered as an elastic body, without considering its plastic deformation. Between the back wall 5 and the back soil 3, the surface-to-surface contact characteristics of the rigid body-flexible body of the contact surface unit form are set, and the friction coefficient between the soil and the concrete is taken as 0.3.

Step 5: In the jacking construction, a high-efficiency grouting process is used to form a thixotropic mud sleeve with the effect of reducing friction and drag between the outer wall of the jacking pipe 1 and the soil layer, thereby reducing the impact of the jacking force on the back soil 3 Disturbance effect ensures the grouting effect of thixotropic mud.

A water-stop device with good waterproof effect is installed at the entrance and exit hole, and the sealing performance of the pipe joint is kept good to ensure that the slurry does not leak from the entrance and exit hole. Start grouting from the exit of the hole to prevent the jacking pipe from being gripped after entering the soil.

Specifically, make a circle of water-stop flange with a width of 25 cm at the entrance and exit of the hole, and make a circle of water-stop steel collar in the hole to connect with it. When the hole door is opened and the machine head enters the hole, grouting starts. A plurality of grouting holes (such as four) are evenly arranged in the circumferential direction of the tail of the machine head. The three pipe joints behind the machine head are all equipped with grouting holes, and then every three joints are provided with grouting holes. The grouting holes of the pipe joints are arranged in an oblique 45° orthogonal circular crossing arrangement. In the entire pipe jacking, a grouting section is set every 2 pipes, and each section has 4 grouting holes. The grouting holes at the tail of the machine head are used for synchronous grouting, and the grouting holes on the pipe joints are used for grouting. Slurry and slurry replenishment are carried out in sequence.

At the same time, a mud lubrication friction reducer composed of bentonite, powder chemical paste, soda ash and water can also be used. Specifically, the weight ratios of bentonite, CMC (powder chemical paste), soda ash and water are: 16%, 0.2%, 0.6%, 84%, and the mixed thixotropic mud is allowed to stand for 24 hours before pouring.

Step 6: According to the site conditions of the back soil body 3 and the jacking sequence of the parallel pipe jacking 1 in step 3, arrange and monitor the measuring points before the pipe jacking construction, and bury the back soil body 3 close to the back wall 5 The side slope pipe and the earth pressure sensor can adjust the construction parameters by feeding back the test information. The surface test end is isolated from the surrounding area by building a brick wall to avoid damage and interference from other construction processes.

Specifically, as shown in FIG. 5 , after the structural bottom sealing of the caisson 4 is completed, the test instrument is buried, and the inclinometer pipe and the earth pressure sensor are buried by backfilling the borehole. Set an earth pressure measuring point S1 and a displacement measuring point C1 between the 1# and 3# jacking reaction forces at a distance of 1 meter from the back wall 5. Set a soil pressure measuring point S2 and a displacement measuring point C-2 between the 2# and 4# jacking reaction forces 1 meter away from the back wall 5, and the buried depths of the measuring points S1, C1, S2, and C2 are equal. It is 10 meters away from the surface of the soil body 3 on the back. The test end exposed on the surface is surrounded by hollow bricks with a 0.5m x 0.5m enclosure to protect the measuring point.

After 7 days of soil consolidation at the point to be measured, the test was carried out. The readings of the points S1, C1, S2, and C2 were relatively stable, and the difference between the three consecutive values did not exceed 10% of the average value. About 40 days later, the pipe jacking construction began. Before that, the same steps were carried out to test the initial value, and the average value of the three data measured at this time was used as the initial value of the entire jacking process.

During normal jacking, the test frequency of each stage is twice a day. When the jacking force reading is too large or there is an abnormal situation on the ground surface, the test frequency should be appropriately increased as needed. The soil displacement values are all within the range of -30 mm to +30 mm, and the measured soil pressure values are normal, with the maximum value not exceeding 120kPa, and no additional soil reinforcement measures are required.

When the back soil body 3 needs to be reinforced, vertical jet grouting piles are used for reinforcement within the B/2 range behind the back wall 5 .

The present invention is closely combined with the construction process to take corresponding control measures, requires few additional procedures, can save construction time and reduce costs, and is a simple and practical method for reasonably controlling the deformation of the soil at the back of caissons in pipe jacking projects.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (10)

1. job practices of controlling open caisson back soil deformation may further comprise the steps:

Step 1 is implemented well-points dewatering at the open caisson periphery, groundwater table is reduced to below the bottom surface of said open caisson;

Step 2 is strengthened the integral rigidity of the said open caisson of the bottom anchoring in soil layer raising of said open caisson;

Step 3, the jacking order of alternately arranging a plurality of parallel push pipes;

Step 4 is set up the simplification three-dimensional finite element model of the said open caisson and the back soil body thereof, and the top power when allowing the distortion limit value to confirm jacking construction according to the maximum of the said back soil body is controlled parameter in advance;

Step 5 adopts grouting process to make in jacking construction and forms between outer wall and the soil layer of said push pipe to have the thixotropic slurry cover that the resistance effect falls in antifriction;

Step 6, according to the jacking of the said parallel push pipe of step 3 order, before the jacking construction in the said back soil body installation testing instrument carry out measuring point and arrange, in the jacking construction according to the detecting information adjustment construction parameter of said measuring point feedback.

2. job practices as claimed in claim 1 wherein, in the step 2, is rinsed the inboard reservation groove of the sword pin top borehole wall well with giant, and surperficial concrete is all cut a hole hair and exposed stone, and with reserved steel bar and the welding of base plate reinforcing bar.

3. job practices as claimed in claim 1 wherein, in the step 2, is provided with the reaction force that concrete drilling bored concrete pile causes with opposing top power in the bottom of said open caisson; Said castinplace pile adopts down trapezoidal pile cover to be connected with the bottom of said open caisson; The stake top reinforcing bar of said castinplace pile anchors into the base plate of said open caisson, and said castinplace pile is respectively distinguished in the bottom of said open caisson in the lattice along evenly distributing perpendicular to push pipe jacking direction.

4. job practices as claimed in claim 1, wherein, in the step 3, the difference of two top power behind two caused open caissons of said parallel push pipe jacking simultaneously on the parados is no more than 20%.

5. job practices as claimed in claim 1, wherein, in the step 4, the said top power when adopting the shakedown analysis method to confirm jacking construction is controlled parameter in advance.

6. job practices as claimed in claim 1; Wherein, In the step 5, evenly arrange a plurality of mud jacking hole, on the three-joint pipe joint of said head back the mud jacking hole is set all at head afterbody hoop; Have on the pipe joint joint in per backward again three joints the mud jacking hole is set, tube coupling mud jacking hole all is oblique 45 ° of orthogonal loops to arranged crosswise.

7. job practices as claimed in claim 1 wherein, in the step 5, adopts the mud lubrication anti-friction agent that is made up of swell soil, powder chemistry paste, soda ash and water.

8. job practices as claimed in claim 1; Wherein, in the step 6, according to the site condition of the jacking order and the said back soil body; Press close to parados place, said back at the said back soil body and bury skew back pipe and soil pressure sensor underground, test lead adopts the mode of brick work brick wall and isolates on every side on the face of land.

9. job practices as claimed in claim 8 wherein, in the step 6, is tested the availability with the checking measuring point behind said back soil solidifying; Before said parallel push pipe jacking construction, carry out same testing procedure.

10. job practices as claimed in claim 9 wherein, in the step 6, when the said back soil body needs reinforcement, is employed in and carries out vertical rotary churning pile in the certain limit behind the parados of said back and reinforce.

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