CN116122296A - Construction and design method of newly-built foundation pit support structure adjacent to existing foundation pit - Google Patents

Construction and design method of newly-built foundation pit support structure adjacent to existing foundation pit Download PDF

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CN116122296A
CN116122296A CN202211577002.8A CN202211577002A CN116122296A CN 116122296 A CN116122296 A CN 116122296A CN 202211577002 A CN202211577002 A CN 202211577002A CN 116122296 A CN116122296 A CN 116122296A
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foundation pit
guard
newly
support
piles
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葛佳佳
何寨兵
李科
姚嘉楠
周强
李强
徐长节
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Zhejiang Hanghai Intercity Railway Co ltd
Zhejiang University ZJU
East China Jiaotong University
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Zhejiang Hanghai Intercity Railway Co ltd
Zhejiang University ZJU
East China Jiaotong University
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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D17/00—Excavations; Bordering of excavations; Making embankments
    • E02D17/02—Foundation pits
    • E02D17/04—Bordering surfacing or stiffening the sides of foundation pits
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22—Piles
    • E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22—Piles
    • E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
    • E02D5/46—Concrete or concrete-like piles cast in position ; Apparatus for making same making in situ by forcing bonding agents into gravel fillings or the soil
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/13—Architectural design, e.g. computer-aided architectural design [CAAD] related to design of buildings, bridges, landscapes, production plants or roads
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/20—Hydro energy

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Abstract

The construction and design method of a new foundation pit support structure adjacent to an existing foundation pit, wherein the new foundation pit support structure uses a guard pile adjacent to an excavated foundation pit as a part of the guard pile of the new foundation pit; the guard piles are used as the guard structures of the excavated foundation pit (1) and also used as the guard structures of the newly-built foundation pit (4); the guard piles are connected with the guard structure of the newly-built foundation pit through inner supports; and the guard piles are connected with structural columns of the excavated foundation pit through supporting oblique beams. The invention provides a design calculation method for the axial force of a shared fender post inclined support. The construction method of the invention uses the guard piles close to the excavated foundation pit as the guard piles of the newly-built foundation pit, wherein the shared guard piles (2) are connected with a newly-built foundation pit guard system through horizontal supports (3), and are connected with structural columns of the excavated foundation pit through supporting diagonal beams. The invention has the characteristics of saving cost, being convenient for construction and being beneficial to safety and stability of the foundation pit.

Description

Construction and design method of newly-built foundation pit support structure adjacent to existing foundation pit
Technical Field
The invention relates to a foundation pit support structure and construction, in particular to a construction and design method of a newly-built foundation pit support structure adjacent to an existing foundation pit, and belongs to the technical field of building engineering.
Background
With rapid development of underground space excavation, the surrounding environment of a foundation pit is increasingly complex, and the situation that a plurality of adjacent foundation pits are excavated simultaneously is more and more common. Meanwhile, the excavation area of the foundation pit is continuously increased, and the construction of dividing a large foundation pit into small foundation pits in the construction is also a current common method.
The foundation pits are influenced by factors such as excavation unloading and the like, and the foundation pits have obvious influence on each other in construction. In the prior design construction, the 'isolation' measures are often adopted for the adjacent foundation pit, so that disturbance to the adjacent foundation pit is avoided as much as possible, and the foundation pit group is not only uneconomical but also unreasonable in stress sometimes.
Therefore, it is important to provide a new foundation pit support structure adjacent to the existing foundation pit for the design and construction of the adjacent foundation pit and a construction method thereof.
Disclosure of Invention
The invention aims to solve the technical problem that the adjacent foundation pits are affected by each other, and provides a construction and design method of a new foundation pit support structure adjacent to the existing foundation pit.
The technical scheme of the invention is that a newly-built foundation pit support structure adjacent to an existing foundation pit is formed, and a guard pile adjacent to an excavated foundation pit is used as a part of the guard pile of the newly-built foundation pit; the guard piles are used as the common guard piles of the guard structures of the excavated foundation pit and the guard structures of the newly-built foundation pit; the novel foundation pit support structure adopts a scheme of combining row piles with reinforced concrete support, and the novel foundation pit is arranged by adopting a gusset and diagonal bracing; the shared guard piles are connected with the guard structures of the newly-built foundation pit through inner supports; the shared guard piles are connected with structural columns of the excavated foundation pit through inclined supports, one ends of the inclined supports are connected with top beams of the shared guard piles, and the other ends of the inclined supports are connected with the structural columns.
The excavated foundation pit and the newly-built foundation pit are both inner support type enclosure structures; the elevation of the capping beam of the guard pile of the excavated foundation pit is consistent with the elevation of the capping beam or the supporting elevation of the newly-built foundation pit, and the excavated foundation pit is not constructed by a main structure of +/-0.0 m or more.
The row piles are combined with the reinforced concrete supporting scheme, the row piles adopt bored piles, and a row of triaxial cement stirring piles are arranged outside the row piles to stop water and soil; and the southeast corner and southwest corner areas of the foundation pit are supported by adopting all-convolution occluding piles combined with three reinforced concrete supports, and a row of high-pressure jet grouting piles are arranged outside the occluding piles for water stopping.
The newly built foundation pit support structure is characterized in that an inclined support is arranged at a proper position of a foundation pit floor slab, the upper end of the inclined support is propped under a crown beam, and the force of the shared support pile is transmitted to the floor slab; in order to prevent stress concentration at the connection position of the floor, brackets are arranged at the contact nodes of the inclined support and the floor, so that the safety strength of the structure is enhanced.
In order to ensure safe operation of the foundation pit support structure, the invention provides a shaft force design calculation method aiming at the shared support pile inclined support.
According to the invention, a multi-support equivalent beam method is adopted to carry out stress analysis calculation, the axial force on the horizontal support transmitted by the non-shared fender post is calculated first, and then the shared fender post is subjected to stress analysis and solved. The calculation principle of the multi-channel support equivalent beam method is the same as that of a single channel, and in order to calculate the solid end bending moment and the counter force of each pivot conveniently, software can be utilized to solve the solid end bending moment and the counter force of each pivot.
Before calculation, each soil layer is weighted and averaged to obtain the weighted average weight gamma, the weighted average internal friction angle phi and the weighted average cohesive force c of the soil layer.
The method comprises the following steps of calculating the internal force of three horizontal supports of a non-shared fender post:
(1) And calculating the soil pressure coefficient Ka and Kp.
(2) And calculating the soil pressure intensity acting on the pile body, and drawing a soil pressure distribution map.
(3) And calculating the distance y between the zero point (approximate zero moment point) of the soil pressure and the bottom of the foundation pit, wherein the passive soil pressure in front of the pile body is equal to the active soil pressure behind the pile body at the position y.
(4) The bending moment of each fixed end of the continuous beam and the counter force of each fulcrum are calculated according to the multi-span continuous beam, and at the moment, the bending moment and the counter force can be solved by means of a structural mechanics method or by using software such as a structural mechanics solver and midas, mathcad.
And calculating the inclined support of the shared fender post:
(1) After the three horizontal supporting shaft forces are obtained, the three horizontal supporting shaft forces can be applied to the common fender post, and a calculation diagram of the common fender post is drawn.
(2) According to the method of the equivalent continuous beam, the bending moment of each fixed end of the continuous beam and the reaction force diagram of each supporting point can be obtained by means of a structural mechanics method or a structural mechanics solver, midas, mathcad and other software solving.
Thus, the horizontal component of the diagonal bracing shaft force can be obtained; if the included angle between the diagonal brace and the common guard pile is alpha, the axial force of the diagonal brace can be further calculated. In addition, in order to better consider the asymmetry of the foundation pit, when the supporting rigidity is used, the supporting fixed point adjusting coefficient can be introduced to adjust the foundation pit, so that the calculation result is more accurate and reliable.
The invention discloses a construction method of a newly built foundation pit support structure adjacent to an existing foundation pit, which comprises the following steps:
step1, leveling the site, constructing a foundation pit fender post to be opened, pouring and curing the fender post by adopting C30 concrete until the design strength is reached.
Step2, constructing an inclined support of the common guard pile of the excavated foundation pit, wherein one end of the inclined support is anchored into a capping beam of the common guard pile, and the other end of the inclined support is anchored into a structural column.
Step3, constructing a first horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post.
Step4, constructing a first enclosing purlin, and connecting the end part of the horizontal support with the enclosing pile by concrete pouring and curing until the design strength is reached.
Step5, excavating earthwork, and excavating the area of the newly built foundation pit to the height of the second horizontal support.
Step6, constructing a second horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post.
Step7, constructing a second purlin, and connecting the end part of the horizontal support with the fender post by concrete pouring and curing until the design strength is reached.
Step8, excavating earthwork, namely excavating the area of the newly built foundation pit to the height of the third horizontal support.
Step9, constructing a third horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post.
Step10, constructing a third purlin, and connecting the end part of the horizontal support with the fender post by concrete pouring and curing until the design strength is reached.
Step11, excavating earthwork, and excavating a region of the newly built foundation pit to the bottom of the foundation pit.
And Step12, after the new construction is completed, pouring a bottom plate for the pouring area and curing until the design strength is reached.
According to the construction method of the newly-built foundation pit enclosure structure adjacent to the existing foundation pit, the horizontal support of the newly-built foundation pit is used as the inner support to be connected with the enclosure pile of the excavated foundation pit, the enclosure pile of the excavated foundation pit is made to be a common enclosure pile, the inclined support is arranged at the structural column of the excavated foundation pit, the junction of the excavated foundation pit and the newly-built foundation pit is extended to the support-changing enclosure purlin by adopting the structural beams, the structural beams are connected by adopting the channel steel connecting structural plates to be firmly supported by the support-changing enclosure purlin, the two ends of the channel steel are firmly supported by adopting the steel plate gaskets, the support-changing structure of the excavated foundation pit is reinforced, and therefore the water and soil pressure after the enclosure wall of the newly-built foundation pit is resisted and transferred integrally, and the influence of horizontal displacement on support can be further reduced, so that the safety of foundation pit engineering is better ensured.
The invention has the beneficial effects that the stress of the surrounding structure of the newly built foundation pit can be reduced by using the surrounding piles close to the foundation pit to carry out stress, the pile spacing can be increased, and the supporting sectional area is reduced, so that the manufacturing cost is reduced. The foundation pit support structure is safe and stable, and the stress system can be more reasonable and the foundation pit is more stable by considering the general condition of two or more foundation pits through using the foundation pit support piles close to the foundation pit to bear the stress.
Drawings
FIG. 1 is a schematic plan view of the present invention utilizing immediately adjacent foundation pit fender piles to create newly built foundation pit fender piles;
FIG. 2 is a schematic cross-sectional view of the present invention utilizing immediately adjacent foundation pit fender piles to create a newly constructed foundation pit fender pile;
FIG. 3 is a schematic plan view of an excavated foundation pit support change;
FIG. 4 is a schematic plan view of an excavated foundation pit diagonal bracing;
FIG. 5 is a pile body soil pressure distribution diagram of an embodiment;
FIG. 6 is a bending moment and fulcrum reaction force diagram of each fixed end of the continuous beam of an embodiment;
FIG. 7 is a computational schematic of an embodiment fender post;
FIG. 8 is a diagram of the reaction force at each fixed end of a continuous beam of an embodiment;
in the figure, 1 is an excavated foundation pit; 2 is a shared guard pile; 3 is a horizontal support; 4 is a newly built foundation pit; 5 is an inclined support; 6 is an original pressure top beam; 7 is a capping beam; 8 is a structural floor slab; 9 is a support-changing enclosing purlin; 10 is channel steel; an 11-bit structural beam; 12 is a change support beam; and 13 is a structural column.
Detailed Description
The technical scheme of the invention is further described below by the specific embodiments with reference to the accompanying drawings.
Fig. 1 is a schematic plan view of a new foundation pit enclosure using a foundation pit enclosure pile in close proximity to an existing foundation pit, and as can be seen from the figure, the new foundation pit enclosure structure in close proximity to the existing foundation pit comprises an excavated foundation pit 1, a shared enclosure pile 2, a support 3 of the new foundation pit and a new foundation pit 4.
As shown in fig. 2, in this embodiment, the right side of the shared pile 2 is connected with a newly built foundation pit enclosure system through a horizontal support 3, and the left side of the shared pile 2 is connected with the main structure of the excavated foundation pit 4 through an inclined support 5; one end of the inclined support 5 is connected with the top beam 7, and the other end is fixed on the structural floor slab 8; the roof beam 7 is mounted on the original roof beam 6.
As shown in fig. 3, which is a schematic plan view of the support replacement of the excavated foundation pit, in this embodiment, the newly-built foundation pit support structure needs to be converted by the excavated foundation pit guard piles, so that the support replacement of the excavated foundation pit needs to be reinforced.
The specific reinforcement measures are as follows: the junction of the excavated foundation pit and the newly-built foundation pit adopts a method that the structural beams 11 extend to the support-changing enclosing purlin 9, and the structural beams 11 are connected with the structural plates 8 and the support-changing enclosing purlin 9 through channel steel.
As shown in fig. 4, one end of the diagonal brace 5 of this embodiment is connected to the capping beam of the common fender post 2, and the other end of the diagonal brace 5 is connected to the structural post 13.
The non-public guard post part is connected with the main structure of the excavated foundation pit and the guard posts through the exchange support beams 12, one exchange support beam 12 is arranged for every three guard posts, and the middle of the two guard posts is arranged. One end of the support beam 12 is firmly supported by the enclosure pile, and the other end of the support beam is anchored into the outer wall of the basement by a main reinforcement.
The support changing structure is arranged at the elevation of the two floors and the first floor.
The length of the inclined support main reinforcement anchored into the structural column and the capping beam should meet the related specification requirements. The width of the diagonal braces 5 should be the same as the width of the corresponding structural posts 13. The width of the inclined support 5 is adjusted to the same width at the position with smaller local column width, and the height is unchanged.
This embodiment is further described by taking an engineering 44-story building as an example.
And the excavation depth of the basement of a 44-layer building of a certain engineering is 16.45m, and the basement is in an irregular hexagon.
The adjacent building is a 26-layer building, 3 layers of underground, the excavation depth of the basement is 16.45m, and the basement is regular quadrilateral.
The plan view of the foundation pit is shown in fig. 1, and the three supporting systems are arranged in the embodiment, wherein the first supporting system is arranged on the upper part of the basement, the second supporting system is arranged in the middle of the basement, the third supporting system is arranged on the lower part of the basement, and the three supporting systems are all reinforced concrete supporting systems.
The design scheme comprises the following steps:
(1) 4, designing a newly-built foundation pit 4 enclosure structure: the width of the enclosure structure is 1000mm, the depth is 32m, and the concrete adopted by the enclosure pile is C30.
(2) Newly-built foundation pit 4 supports design: as shown in fig. 1, the EF side and BD side are gussets, the GF side and CD side are gussets, and the CG side and CD side are gussets. The support is made of C30 concrete, and the thickness of the protective layer of the support main reinforcement is 25mm. The supporting cushion layer is made of 10cm thick C15 plain concrete, and a layer of asphalt felt is additionally paved, the width of each cushion layer is 20cm larger than the supporting width, and the supporting bottom cushion layer is cleaned to prevent people from being injured by falling when the supporting bottom cushion layer is excavated under the supporting bottom.
(3) The foundation pit inclined support 5 design is finished after excavation: as shown in fig. 2, one end of the diagonal brace 5 is anchored into the common fender post capping beam 7, as shown in fig. 4, the other end of the diagonal brace 5 is anchored into the structural post 13, the width of the diagonal brace cross section is 800×800mm, the width of the partial post is 700mm, and the width of the diagonal brace 5 cross section is adjusted to 700×800mm.
(4) Foundation pit support replacement design is finished after excavation: as shown in fig. 1 and 3, the boundary between BD and DC adopts a method that a structural beam 11 extends to a support-changing purlin 9, structural beams are connected by adopting 20b channel steel to connect a structural plate 8 and the support-changing purlin 9, and two ends of the channel steel are firmly supported by adopting steel plate gaskets with the thickness of 10mm and the thickness of 300 multiplied by 130 mm. The support changing structure is arranged at the elevation of the two floors and the first floor.
(5) Support column design: the vertical upright post of the cast-in-situ reinforced concrete supporting system is a bored pile, the upper part of the upright post is a cross truss, the cross truss is deep into the vertical upright post pile for 2m, the strength grade of the concrete of the newly driven upright post pile is C25, and the construction requirement of the engineering pile is met by using the engineering pile as the upright post. The superfilling height of the newly driven upright post pile is 1200mm.
An example is provided below as a method for calculating the axial force of the diagonal braces of the shared fender post, in this embodiment, a multi-support equivalent beam method is adopted to perform the force analysis calculation, the axial force on the horizontal support transmitted by the non-shared fender post is calculated first, and then the force analysis and the solution are performed on the shared fender post.
The calculation principle of the multi-channel support equivalent beam method is the same as that of a single channel, and in order to calculate the solid end bending moment and the counter force of each pivot conveniently, software can be utilized to solve the solid end bending moment and the counter force of each pivot.
The calculation assumes: the wall body is a rigid body, the back of the wall body is vertical, the back of the wall body is smooth, no friction force exists between the back of the wall body and the filled soil, and the surface of the filled soil behind the wall body is horizontal
The calculation conditions are as follows: the first horizontal support is positioned at 0m underground, the second horizontal support is positioned at 5.75m underground, the third horizontal support is positioned at 10.25m underground, the foundation pit bottom is positioned at 16.45m underground, the upper load q=20kn/m, one layer of basement floor is positioned at 5.35m underground, and two layers of basement floor are positioned at 9.85m underground
And before calculation, carrying out weighted average on each soil layer to obtain weighted average weight gamma, weighted average internal friction angle phi and weighted average cohesive force c of the soil layer.
Table 1 shows the basic physical and mechanical parameters of soil layers.
From the table, γ=18.92 kN ∙ m calculated -3 ，c=11.77kPa，φ=22.35°。
Table 1 basic physical and mechanical parameters table for soil layer
Figure DEST_PATH_IMAGE001
The method comprises the following steps of calculating the internal force of three horizontal supports of a non-shared fender post:
1. calculating the soil pressure coefficient Ka, kp
Figure 114392DEST_PATH_IMAGE002
Figure DEST_PATH_IMAGE003
Calculated, ka=0.449, kp=2.227.
2. The soil pressure intensity acting on the pile body is calculated and the soil pressure distribution map is drawn, as shown in fig. 5.
3. And calculating the distance y between the zero point (approximate zero moment point) of the soil pressure and the bottom of the foundation pit, wherein the passive soil pressure in front of the pile body is equal to the active soil pressure behind the pile body at the position y.
Figure 156166DEST_PATH_IMAGE004
Thus, the earth pressure zero point position y=4.35 m is calculated.
4. Calculating bending moment of each fixed end of the continuous beam and counter force of each supporting point according to the multi-span continuous beam, and solving the bending moment and the supporting point counter force by means of a structural mechanics method or using software such as a structural mechanics solver and midas, mathcad; the inverse diagram is shown in fig. 6.
Calculated N 1 =148.57kN，N 2 =229.84kN，N 3 =913.17kN。
Calculating the inclined struts of the shared fender piles:
1. after the three horizontal supporting shaft forces are obtained, the three horizontal supporting shaft forces can be applied to the common fender post, and a calculation sketch of the common fender post is drawn, and the calculation sketch is shown in fig. 7.
2. According to the method of the equivalent continuous beam, the bending moment of each fixed end of the continuous beam and the counterforce diagram of each fulcrum can be obtained by means of a structural mechanics method or a structural mechanics solver, midas, mathcad and other software, and the counterforce diagram of each fulcrum is shown in fig. 8.
Calculated, F 1 = 151.09kN. If the included angle between the diagonal brace and the common guard pile is taken as alpha, the axial force of the diagonal brace can be calculated to be N=F 1 /sinα。
In addition, in order to better consider the asymmetry of the foundation pit, when the supporting rigidity is used, the supporting fixed point adjusting coefficient can be introduced to adjust the foundation pit, so that the calculation result is more accurate and reliable.

Claims (7)

1. The novel foundation pit support structure is characterized in that the novel foundation pit support structure uses a guard pile adjacent to an excavated foundation pit as a part of the guard pile of the novel foundation pit; the guard piles are used as the common guard piles of the guard structures of the excavated foundation pit and the guard structures of the newly-built foundation pit; the novel foundation pit support structure adopts a scheme of combining row piles with reinforced concrete support, and the novel foundation pit is arranged by adopting a gusset and diagonal bracing; the shared guard piles are connected with the guard structures of the newly-built foundation pit through inner supports; the shared guard piles are connected with structural columns of the excavated foundation pit through inclined supports, one ends of the inclined supports are connected with top beams of the shared guard piles, and the other ends of the inclined supports are connected with the structural columns.
2. The newly constructed pit enclosure immediately adjacent to an existing pit of claim 1, wherein both the excavated pit and the newly constructed pit are internal bracing enclosures; the elevation of the capping beam of the guard pile of the excavated foundation pit is consistent with the elevation of the capping beam or the supporting elevation of the newly-built foundation pit, and the excavated foundation pit is not constructed by a main structure of +/-0.0 m or more.
3. The newly-built foundation pit support structure adjacent to the existing foundation pit according to claim 1, wherein the row piles are combined with a reinforced concrete supporting scheme, the row piles adopt bored piles, and a row of triaxial cement stirring piles are arranged outside the row piles to stop water and soil; and the southeast corner and southwest corner areas of the foundation pit are supported by adopting all-convolution occluding piles combined with three reinforced concrete supports, and a row of high-pressure jet grouting piles are arranged outside the occluding piles for water stopping.
4. The newly-built foundation pit enclosure immediately adjacent to an existing foundation pit according to claim 1, wherein the newly-built foundation pit enclosure transmits the force of the common enclosure pile to the floor by arranging a diagonal brace at a proper position of the floor of the foundation pit and pushing the upper end of the diagonal brace under the crown beam; in order to prevent stress concentration at the connection position of the floor, brackets are arranged at the contact nodes of the inclined support and the floor, so that the safety strength of the structure is enhanced.
5. The newly-built foundation pit enclosure immediately adjacent to an existing foundation pit according to claim 1, wherein the axial force calculation method of the diagonal bracing is as follows:
firstly, carrying out weighted average on each soil layer to obtain weighted average weight gamma, weighted average internal friction angle phi and weighted average cohesive force c of the soil layer;
the three horizontal supporting internal forces of the non-shared guard piles are calculated as follows:
(1) Calculating a soil pressure coefficient Ka and Kp;
(2) Calculating the soil pressure intensity acting on the pile body, and drawing a soil pressure distribution map;
(3) Calculating the distance y between the zero point of the soil pressure and the bottom of the foundation pit, wherein at the y position, the passive soil pressure in front of the pile body is equal to the active soil pressure behind the pile body;
(4) Calculating bending moment of each fixed end of the continuous beam and counter force of each fulcrum according to the multi-span continuous beam, and solving the bending moment and the counter force by means of a structural mechanics method or using a structural mechanics solver and midas, mathcad software;
the calculation steps of the shared guard pile inclined support are as follows:
(1) After three horizontal supporting shaft forces are obtained, the three horizontal supporting shaft forces can be applied to the common fender post, and a calculation sketch of the common fender post is drawn;
(2) According to the method of the equivalent continuous beam, solving by means of a structural mechanics method or a structural mechanics solver and midas, mathcad software, so as to obtain bending moment of each fixed end of the continuous beam and a counterforce diagram of each fulcrum;
thus, the horizontal component of the diagonal bracing shaft force can be obtained; if the included angle between the diagonal brace and the common guard pile is alpha, the axial force of the diagonal brace can be further calculated.
6. A construction method for implementing the new foundation pit enclosure adjacent to the new foundation pit enclosure of any one of claims 1-5, the construction method comprising the steps of:
step1, leveling a site, constructing a foundation pit fender post to be opened, pouring and curing the fender post by adopting C30 concrete until the design strength is reached;
step2, constructing an inclined support of the common guard pile of the excavated foundation pit, wherein one end of the inclined support is anchored into a capping beam of the common guard pile, and the other end of the inclined support is anchored into a structural column;
step3, constructing a first horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post;
step4, constructing a first enclosing purlin, and casting and connecting the end part of the horizontal support and the enclosing pile by concrete and curing until the design strength is reached;
step5, excavating earthwork, namely excavating a region of the newly built foundation pit to the height of the second horizontal support;
step6, constructing a second horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post;
step7, constructing a second purlin, and casting and connecting the end part of the horizontal support and the fender post by concrete and curing until the design strength is reached;
step8, excavating earthwork, namely excavating a region of the newly built foundation pit to the height of a third horizontal support;
step9, constructing a third horizontal support, and enabling the end part of the horizontal support to be adjacent to the newly-built foundation pit fender post and the shared fender post;
step10, constructing a third purlin, and casting and connecting the end part of the horizontal support and the fender post by concrete and curing until the design strength is reached;
step11, excavating earthwork, namely excavating a region of the newly built foundation pit to the bottom of the foundation pit;
and Step12, after the new construction is completed, pouring a bottom plate for the pouring area and curing until the design strength is reached.
7. The method for constructing a new foundation pit enclosure structure adjacent to an existing foundation pit according to claim 6, wherein the method is characterized in that the horizontal support of the new foundation pit is used as an inner support to be connected with the enclosure pile of the excavated foundation pit, the enclosure pile of the excavated foundation pit is made into a common enclosure pile, inclined supports are arranged at the structural columns of the excavated foundation pit, the junction of the excavated foundation pit and the new foundation pit is extended to a support-changing enclosure purlin by adopting structural beams, structural plates are connected between the structural beams and the support-changing enclosure purlin by adopting steel plate gaskets at two ends of the channel steel, the support-changing structure of the excavated foundation pit is reinforced, and therefore, the whole structure is formed to resist and transfer the water and soil pressure after the enclosure wall of the new foundation pit.
CN202211577002.8A 2022-12-09 2022-12-09 Construction and design method of newly-built foundation pit support structure adjacent to existing foundation pit Pending CN116122296A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116815790A (en) * 2023-08-28 2023-09-29 上海建工一建集团有限公司 Foundation pit supporting servo system with two sides adjacent to protection objects and construction method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116815790A (en) * 2023-08-28 2023-09-29 上海建工一建集团有限公司 Foundation pit supporting servo system with two sides adjacent to protection objects and construction method thereof
CN116815790B (en) * 2023-08-28 2023-11-17 上海建工一建集团有限公司 Construction method of foundation pit supporting servo system with two sides adjacent to protection object

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