Combined enclosure structure for foundation pit excavation and construction method

Abstract

The invention relates to the technical field of foundation pit excavation, and discloses a combined enclosure structure for foundation pit excavation and a construction method.The combined enclosure structure comprises a TRD retaining wall close to the inner wall of a foundation pit and a cast-in-situ bored pile row, the cast-in-situ bored pile row is located on the side, away from the foundation pit, of the TRD retaining wall, and the TRD retaining wall and the cast-in-situ bored pile row are arranged in parallel in the circumferential direction of the foundation pit; the cast-in-situ bored pile row comprises a plurality of cast-in-situ bored piles, and the top ends of the cast-in-situ bored piles are connected through a reinforced concrete top beam. According to the combined enclosure structure for foundation pit excavation and the construction method, the cast-in-situ bored pile row and the TRD retaining wall are combined for use, the structural strength and the water stopping performance can be effectively improved, the bearing capacity of the cast-in-situ bored piles is high, the shear resistance and the pulling resistance are good, the stability of a foundation pit and the safety and convenience of operation in the pit are guaranteed, and the construction period is shortened. And the displacement of the soil body at the pit bottom and outside the pit is controlled within a certain range, so that the normal use of adjacent buildings and municipal facilities is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit excavation, and in particular to a combined enclosure structure and a construction method for foundation pit excavation. Background Art

[0002] Foundation pit support refers to the temporary retaining structure built during foundation pit excavation to construct permanent tunnel structure facilities. Its function is to prevent the soil from collapsing into the foundation pit due to lateral pressure and to stop water.

[0003] Excavation of foundation pits, in which bored cast-in-place piles are a commonly used retaining structure, is prone to cause tilting of the retaining structure and deviation in the size of the main structure of the tunnel due to the constraints of surrounding buildings and underground pipelines, which places higher requirements on the safety of the supporting structure. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a combined retaining structure and a construction method for foundation pit excavation, which solve the problems mentioned in the above background.

[0005] The present invention provides the following technical solution: a combined retaining structure for foundation pit excavation, characterized in that it comprises: a TRD retaining wall close to the inner wall of the foundation pit and a bored cast-in-place pile row, the bored cast-in-place pile row is located on a side of the TRD retaining wall away from the foundation pit, and the two are arranged in parallel along the circumference of the foundation pit;

[0006] The bored pile row comprises a plurality of bored piles, and the top ends of the plurality of bored piles are connected by reinforced concrete cap beams.

[0007] Preferably, the thickness of the TRD retaining wall is 850 mm, the diameter of the bored piles is 800 mm, and the spacing is 1000 mm. The TRD retaining wall fits tightly with the bored pile row; the cap beam connects all the bored piles to enhance the overall stability and water-stopping performance.

[0008] A construction method of a combined retaining structure for foundation pit excavation, characterized in that it comprises the following steps:

[0009] Step S1, machinery entering the site: level the site and complete the machinery assembly and backstage layout, ensuring that the on-site construction site should have water, electricity, roads and site leveling, and meet the pile driver's load-bearing, transportation and construction requirements;

[0010] Step S2, surveying and setting out: laying out the control network according to the geographical conditions of the construction site, re-surveying and arranging the conductors, and planning the construction area;

[0011] Step S3, guide trench excavation: locate the center line of the TRD retaining wall according to the coordinates of the drawing, excavate the guide trench and hang the embedded box after verification;

[0012] Step S4, pile foundation positioning: set up a total station to adjust the position of the pile driver to ensure that the pile driver is stable and accurately positioned;

[0013] Step S5, cutting box installation: the cutting box is suspended in sections to the pre-buried hole, connected to the TRD host and driven into the designed depth;

[0014] Step S6, inclinometer installation: install a multi-section inclinometer in the cutting box to control the vertical accuracy of the wall to ≤1 / 200;

[0015] Step S7, trial wall construction: excavate the trial wall first, and record the parameters to adjust the subsequent construction;

[0016] Step S8, withdrawing excavation: the TRD host is connected to the cutting box, and excavation fluid is injected into the bottom of the cutting box to pre-cut the soil layer for a certain distance, and then withdrawing the excavation to the original position;

[0017] Step S9, solidification and stirring: inject solidification liquid and mud forcibly stir to form a cement soil continuous wall of equal thickness;

[0018] Step S10, pulling out the cutting box: after the construction is completed, the cutting box is pulled out in sections and moved to the next working surface;

[0019] Step S11, mechanical exit: withdraw the equipment after completing the TRD retaining wall construction;

[0020] Step S12, laying out the cast-in-place piles: cleaning the site and laying out the pile positions, nailing cross protection piles and checking the center of the casing;

[0021] Step S13, casing burying: burying the steel casing and monitoring its position, verticality and elevation in real time;

[0022] Step S14, mud treatment: preparing, circulating and storing mud in a circulation pool;

[0023] Step S15, drilling rig positioning: ensuring that the drilling rig guide rod, the rotary disk and the center line of the casing are in the same straight line;

[0024] Step S16, drilling: check the drill bit parameters and control the pile bottom elevation, and select the cutting teeth according to the soil layer;

[0025] Step S17, initial hole cleaning: removing drilling debris in the hole and adjusting mud concentration and sand content;

[0026] Step S18, hole inspection and confirmation: use the rope measuring method to check the hole depth, and clean the hole after confirmation by the supervisor;

[0027] Step S19, steel cage production: check the length and quantity of steel bars, and stagger the joint positions for cutting;

[0028] Step S20, installing the acoustic detection pipe: burying two acoustic detection pipes, the acoustic detection pipes are made of steel pipes with a diameter of 50 mm and a thickness of 3 mm;

[0029] Step S21, conduit installation: lowering the conduit, the conduit is made of a seamless steel pipe with a diameter of 250 mm and a thickness of 10 mm, and a quick threaded joint is used between two adjacent conduits;

[0030] Step S22, secondary hole cleaning: check the sediment thickness and mud index, and perform secondary hole cleaning if they are unqualified;

[0031] Step S23, concrete pouring: using a large aggregate hopper to seal the bottom and then using a small aggregate hopper to pour concrete;

[0032] Step S24, cap beam casting: casting the cap beam on the top of the bored pile to form an integral composite structure.

[0033] Preferably, in step S5, a designated crawler crane is used to lift the cutting box into the pre-buried hole section by section, the cutting box is fixed by a support table, the TRD host moves to the pre-buried hole position to connect the cutting box, and the TRD host returns to the predetermined construction position to perform the cutting box self-insertion excavation process.

[0034] Preferably, in step S8, after the TRD main engine returns to the predetermined position, the excavation fluid at the bottom of the cutting box is used to pre-cut the soil layer by 3-5m, and then withdraws to the origin for solidification and mixing.

[0035] Preferably, in step S10, after the construction of each working section of the trial wall and the TRD method cement soil mixing continuous wall is completed, the cutting box is pulled out in sections using a crane or a main machine, and the equipment is transferred to the next working surface to prepare for construction.

[0036] Preferably, in step S12, the construction site is reasonably arranged according to the on-site conditions, surface debris is cleaned and the site is leveled, surveying and layout personnel are organized, the required pile positions are laid out, cross protection piles are nailed, measurement verification is done, and records are kept for inspection. After the casing is lowered, the cross line is pulled up to verify whether the center point of the casing coincides with the center of the cross line to ensure the accuracy of the pile position.

[0037] Preferably, in step S16, the drill diameter protection device, drill diameter, and drill wear must be checked before drilling, and the drill wear exceeding the standard must be replaced in time during the construction process;

[0038] Correctly select the shape, specification and angle of the cutting teeth at the bottom of the drill bucket according to the soil conditions; calculate the pile bottom elevation based on the casing elevation, pile top design elevation and pile length so as to control it during drilling.

[0039] Preferably, the capacity of the large aggregate hopper meets the requirement that the first batch of concrete buried pipes has a depth of ≥1m, and a small aggregate hopper is replaced after the bottom is sealed to improve the demolition efficiency.

[0040] Preferably, in step S19, before cutting the steel bars, first check the lengths and quantities of various specifications of steel bars in the construction drawings, and then cut them after confirming that they are correct. According to the length of the original steel bars and the design length of the drawings and in combination with the requirements of the specifications, while meeting the design and specification requirements, reduce steel bar loss, reasonably match the steel bars, stagger the joint positions, and determine the cutting length of the steel bars.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention combines the bored cast-in-place pile row with the TRD retaining wall to effectively improve the structural strength and water-stopping performance. The bored cast-in-place pile has a strong bearing capacity and good shear and pull-out resistance, thereby ensuring the stability of the foundation pit and the safety and convenience of the operation in the pit. Moreover, the displacement of the soil at the bottom of the pit and outside the pit is controlled within a certain range, thereby ensuring the normal use of adjacent buildings and municipal facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the side view structure of the TRD retaining wall and bored pile row of the present invention;

[0044] Figure 2 It is a schematic diagram of the top view of the structure of the TRD retaining wall and bored pile row of the present invention;

[0045] Figure 3 It is a schematic diagram of the process of the present invention.

[0046] In the figure: 1. TRD retaining wall; 2. Bored and cast-in-place pile row. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] See also Figure 1-3 A combined retaining structure for foundation pit excavation, comprising: a TRD retaining wall 1 close to the inner wall of the foundation pit and a bored cast-in-place pile row 2, the bored cast-in-place pile row 2 is located on the side of the TRD retaining wall 1 away from the foundation pit, and the two are arranged in parallel along the circumference of the foundation pit, the bored cast-in-place pile row 2 comprises a plurality of bored cast-in-place piles, the tops of the plurality of bored cast-in-place piles are connected by reinforced concrete cap beams, the thickness of the TRD retaining wall 1 is 850 mm, the diameter of the bored cast-in-place piles is 800 mm, and the spacing is 1000 mm, the TRD retaining wall 1 is closely fitted to the bored cast-in-place pile row 2; the cap beam connects all the bored cast-in-place piles to enhance the overall stability and water-stopping performance.

[0049] A construction method of a combined retaining structure for foundation pit excavation, characterized in that it comprises the following steps:

[0050] Step S1, machinery entering the site: level the site and complete the machinery assembly and backstage layout, ensuring that the on-site construction site should have water, electricity, roads and site leveling, and meet the pile driver's load-bearing, transportation and construction requirements;

[0051] Step S2, surveying and setting out: laying out the control network according to the geographical conditions of the construction site, re-surveying and arranging the conductors, and planning the construction area;

[0052] Step S3, guide groove excavation: locate the center line of the TRD retaining wall 1 according to the coordinates of the drawing, excavate the guide groove and hang the embedded box after verification;

[0053] Step S4, pile foundation positioning: set up a total station to adjust the position of the pile driver to ensure that the pile driver is stable and accurately positioned;

[0054] Step S5, cutting box installation: the cutting box is hoisted in sections to the pre-buried hole, connected to the TRD host and driven into the designed depth, the crawler TRD host drives the chain saw type cutting box into the soil layer, and the excavation fluid is injected at the same time to achieve continuous cutting and mixing;

[0055] Step S6, inclinometer installation: a multi-section inclinometer is installed in the cutting box to control the vertical accuracy of the wall to ≤1 / 200. The inclinometer is a segmented sensor with each segment spaced 5m apart to monitor the verticality of the wall in real time;

[0056] Step S7, trial wall construction: excavate the trial wall first, record the parameters to adjust the subsequent construction, conduct a small-scale test wall before formal construction, record the excavation speed, mud ratio and other parameters, test whether the cutting box penetration depth, excavation fluid injection volume, etc. meet the design requirements, and optimize the subsequent construction process according to the trial wall effect;

[0057] Step S8, withdrawing excavation: the TRD host is connected to the cutting box, and excavation fluid is injected into the bottom of the cutting box to pre-cut the soil layer for a certain distance, and then withdrawing the excavation to the original position;

[0058] Step S9, solidification and stirring: inject solidification liquid and mud forcibly stir to form a cement soil continuous wall of equal thickness;

[0059] Step S10, pulling out the cutting box: after the construction is completed, the cutting box is pulled out in sections and moved to the next working surface;

[0060] Step S11, mechanical exit: withdraw the equipment after completing the construction of the TRD retaining wall 1;

[0061] Step S12, laying out the cast-in-place piles: cleaning the site and laying out the pile positions, nailing cross protection piles and checking the center of the casing;

[0062] Step S13, casing burying: burying the steel casing and monitoring its position, verticality and elevation in real time. When the drilling site is leveled, the steel casing is buried, and when the steel casing is sunk or buried, its plane position, verticality, elevation, etc. should be observed, controlled and adjusted in real time;

[0063] Step S14, mud treatment: preparing, circulating and storing mud in a circulation pool. During drilling, mud is prepared, circulated and stored in a mud circulation pool; during concrete pouring, mud is stored in a mud circulation pool and a mud storage pool;

[0064] Step S15, drilling rig positioning: ensure that the drilling rig guide rod, the rotary disk and the center line of the casing are in the same straight line. The drilling rig can be put into place only on the basis that the pile position is correct, the casing is buried in accordance with the requirements, and the casing elevation has been determined; the pile driver positioning must be accurate, horizontal, vertical and stable, and the center line of the drilling rig guide rod, the center line of the rotary disk and the center line of the casing should be kept in the same straight line;

[0065] Step S16, drilling: check the drill bit parameters and control the pile bottom elevation, and select the cutting teeth according to the soil layer;

[0066] Step S17, initial hole cleaning: the purpose of the initial hole cleaning is to remove the drilling debris in the hole and adjust the concentration of the mud in the hole and reduce the sand content in the hole;

[0067] Step S18, hole inspection and confirmation: the hole depth is checked by measuring rope method, and the hole is cleaned after confirmation by the supervisor. When the drilling depth reaches the design requirement, the hole depth is checked by measuring rope method and reported to the supervisor engineer for confirmation. The hole is cleaned after it meets the requirements;

[0068] Step S19, steel cage production: check the length and quantity of steel bars, and stagger the joint positions for cutting;

[0069] Step S20, installing the acoustic detection pipe: burying two acoustic detection pipes, the acoustic detection pipes are made of steel pipes with a diameter of 50 mm and a thickness of 3 mm;

[0070] Step S21, conduit installation: lowering the conduit, the conduit is made of a seamless steel pipe with a diameter of 250 mm and a thickness of 10 mm, and a quick threaded joint is used between two adjacent conduits;

[0071] Step S22, secondary hole cleaning: check the sediment thickness and mud index, if unqualified, perform secondary hole cleaning, calculate the sediment thickness at the bottom of the hole according to the final hole depth and check the mud index, if the sediment and mud index can meet the requirements, then there is no need for secondary hole cleaning and concrete is poured directly; if not, perform secondary hole cleaning immediately;

[0072] Step S23, concrete pouring: a large aggregate hopper is used to seal the bottom and then a small aggregate hopper is used to pour concrete. A large aggregate hopper is used for concrete bottom sealing, and the capacity must meet the calculated volume of the first batch of concrete pouring. After the bottom sealing is completed, a small aggregate hopper is used to facilitate construction and improve the progress of duct removal.

[0073] Step S24, crown beam casting: Cast the crown beam on the top of the bored pile to form an overall composite structure. After completing the previous steps, cast the crown beam to ensure the integrity of the composite structure.

[0074] The combination of bored cast-in-place pile row 2 and TRD retaining wall 1 can effectively improve the structural strength and water-stopping performance. The bored cast-in-place pile has strong bearing capacity, good shear and pull-out resistance, ensures the stability of the foundation pit and the safety and convenience of the operation in the pit, and controls the displacement of the soil at the bottom of the pit and outside the pit within a certain range, ensuring the normal use of adjacent buildings and municipal facilities. The TRD method, namely Trench Cutting Re-mixing Deep Wall Method, is composed of cement soil and steel, etc. It has a large construction depth, the maximum depth can reach 60m, adapts to a wide range of strata, has good excavation performance for hard strata, and has good wall quality. In the depth direction of the wall, it can ensure uniform cement soil quality, improve strength, small discreteness, and good water interception performance. The bored cast-in-place pile has strong bearing capacity, good shear and pull-out resistance.

[0075] Among them, in step S5, the cutting box is hoisted into the pre-buried hole section by section by a designated crawler crane, the cutting box is fixed by a support table, the TRD host moves to the pre-buried hole position to connect the cutting box, and the TRD host returns to the predetermined construction position to carry out the cutting box self-insertion excavation process.

[0076] Among them, in step S8, after the TRD main machine returns to the predetermined position, the excavation fluid at the bottom of the cutting box is used to pre-cut the soil layer by 3-5m, and then withdraws to the origin for solidification and mixing.

[0077] Among them, in step S10, after the construction of each working section of the trial wall and the TRD method cement soil mixing continuous wall is completed, the cutting box is pulled out in sections using a crane or a main machine, and the equipment is transferred to the next working surface to prepare for construction.

[0078] Among them, in step S12, the construction site is reasonably arranged according to the on-site conditions, the surface debris is cleaned and the site is leveled, and the surveying and layout personnel are organized to lay out the required pile positions, nail the cross protection piles, do a good job of measurement review, and keep records for reference. After the casing is lowered, the cross line is pulled up to check whether the center point of the casing coincides with the center of the cross line to ensure the accuracy of the pile position.

[0079] Among them, in step S16, the drill bit diameter protection device, drill bit diameter, and drill bit wear must be checked before drilling, and the drill bit that exceeds the wear standard during the construction process must be replaced in time;

[0080] Among them, the shape, specification and angle of the cutting teeth at the bottom of the drill bucket are correctly selected according to the soil conditions; the pile bottom elevation is calculated according to the casing elevation, the pile top design elevation and the pile length, so as to control it when drilling.

[0081] Among them, the capacity of the large aggregate hopper meets the requirement that the depth of the first batch of concrete buried pipes is ≥1m. After the bottom is sealed, a small aggregate hopper will be replaced to improve the demolition efficiency.

[0082] Among them, in step S19, before cutting the steel bars, first check the length and quantity of steel bars of various specifications in the construction drawing, and cut them after they are correct. According to the length of the original steel bar and the design length of the drawing and combined with the requirements of the specification, while meeting the design and specification requirements, reduce steel bar loss, reasonably match the steel bars, stagger the joint positions, and determine the cutting length of the steel bars.

[0083] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A combined retaining structure for foundation pit excavation, characterized in that: include: A TRD retaining wall (1) and a bored pile row (2) close to the inner wall of the foundation pit, wherein the bored pile row (2) is located on a side of the TRD retaining wall (1) away from the foundation pit, and the two are arranged in parallel along the circumference of the foundation pit; The bored cast-in-place pile row (2) comprises a plurality of bored cast-in-place piles, the top ends of which are connected by reinforced concrete cap beams.

2. A combined retaining structure for foundation pit excavation according to claim 1, characterized in that: The thickness of the TRD retaining wall (1) is 850 mm, the diameter of the bored piles is 800 mm, and the spacing is 1000 mm. The TRD retaining wall (1) fits tightly with the bored pile row (2); the cap beam connects all the bored piles to enhance the overall stability and water-stopping performance.

3. A construction method for a combined retaining structure for foundation pit excavation, characterized in that: The following steps are involved: Step S1, machinery entering the site: level the site and complete the machinery assembly and backstage layout, ensuring that the on-site construction site should have water, electricity, roads and site leveling, and meet the pile driver's load-bearing, transportation and construction requirements; Step S2, surveying and setting out: laying out the control network according to the geographical conditions of the construction site, re-surveying and arranging the conductors, and planning the construction area; Step S3, guide trench excavation: locate the center line of the TRD retaining wall (1) according to the coordinates of the drawing, excavate the guide trench and hang the embedded box after verification; Step S4, pile foundation positioning: set up a total station to adjust the position of the pile driver to ensure that the pile driver is stable and accurately positioned; Step S5, cutting box installation: the cutting box is suspended in sections to the pre-buried hole, connected to the TRD host and driven into the designed depth; Step S6, inclinometer installation: install a multi-section inclinometer in the cutting box to control the vertical accuracy of the wall to ≤1 / 200; Step S7, trial wall construction: excavate the trial wall first, and record the parameters to adjust the subsequent construction; Step S8, withdrawing excavation: the TRD host is connected to the cutting box, and excavation fluid is injected into the bottom of the cutting box to pre-cut the soil layer for a certain distance, and then withdrawing the excavation to the original position; Step S9, solidification and stirring: inject solidification liquid and mud forcibly stir to form a cement soil continuous wall of equal thickness; Step S10, pulling out the cutting box: after the construction is completed, the cutting box is pulled out in sections and moved to the next working surface; Step S11, machine exit: withdraw the equipment after completing the construction of the TRD retaining wall (1); Step S12, laying out the cast-in-place piles: cleaning the site and laying out the pile positions, nailing cross protection piles and checking the center of the casing; Step S13, casing burying: burying the steel casing and monitoring its position, verticality and elevation in real time; Step S14, mud treatment: preparing, circulating and storing mud in a circulation pool; Step S15, drilling rig positioning: ensuring that the drilling rig guide rod, the rotary disk and the center line of the casing are in the same straight line; Step S16, drilling: check the drill bit parameters and control the pile bottom elevation, and select the cutting teeth according to the soil layer; Step S17, initial hole cleaning: removing drilling debris in the hole and adjusting mud concentration and sand content; Step S18, hole inspection and confirmation: use the rope measuring method to check the hole depth, and clean the hole after confirmation by the supervisor; Step S19, steel cage production: check the length and quantity of steel bars, and stagger the joint positions for cutting; Step S20, installing the acoustic detection pipe: burying two acoustic detection pipes, the acoustic detection pipes are made of steel pipes with a diameter of 50 mm and a thickness of 3 mm; Step S21, conduit installation: lowering the conduit, the conduit is made of a seamless steel pipe with a diameter of 250 mm and a thickness of 10 mm, and a quick threaded joint is used between two adjacent conduits; Step S22, secondary hole cleaning: check the sediment thickness and mud index, and perform secondary hole cleaning if they are unqualified; Step S23, concrete pouring: using a large aggregate hopper to seal the bottom and then using a small aggregate hopper to pour concrete; Step S24, cap beam casting: casting the cap beam on the top of the bored pile to form an integral composite structure.

4. The construction method of a combined retaining structure for foundation pit excavation according to claim 3, characterized in that: In step S5, the cutting box is hoisted into the pre-buried hole section by section by a designated crawler crane, the cutting box is fixed by a support table, the TRD host moves to the pre-buried hole position to connect the cutting box, and the TRD host returns to the predetermined construction position to carry out the cutting box self-insertion excavation process.

5. The construction method of the combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: In step S8, after the TRD main engine returns to the predetermined position, the excavation fluid at the bottom of the cutting box pre-cuts the soil layer by 3-5m, and then withdraws to the origin for solidification and mixing.

6. The construction method of a combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: In step S10, after the construction of each working section of the trial wall and TRD method cement soil mixing continuous wall is completed, the cutting box is pulled out in sections by using a crane or a main machine, and the equipment is transferred to the next working surface to prepare for construction.

7. The construction method of a combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: In step S12, the construction site is reasonably arranged according to the on-site conditions, the surface debris is cleaned and the site is leveled, and surveying and setting out personnel are organized to lay out the required pile positions, nail the cross protection piles, do a good job of measurement and verification, and keep records for inspection. After the casing is lowered, the cross line is pulled up to verify whether the center point of the casing coincides with the center of the cross line to ensure the accuracy of the pile position.

8. The construction method of a combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: In step S16, the drill diameter protection device, drill diameter, and drill wear must be checked before drilling, and the drill wear exceeding the standard must be replaced in time during the construction process; Correctly select the shape, specification and angle of the cutting teeth at the bottom of the drill bucket according to the soil conditions; calculate the pile bottom elevation based on the casing elevation, pile top design elevation and pile length so as to control it during drilling.

9. The construction method of a combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: The capacity of the large aggregate hopper meets the requirement that the depth of the first batch of concrete buried pipes is ≥1m. After the bottom is sealed, a small aggregate hopper is replaced to improve the demolition efficiency.

10. The construction method of a combined enclosure structure for foundation pit excavation according to claim 3, characterized in that: In step S19, before cutting the steel bars, first check the length and quantity of steel bars of various specifications in the construction drawing, and then cut them after confirming that they are correct. According to the length of the original steel bar and the design length of the drawing and in combination with the specification requirements, while meeting the design and specification requirements, reduce steel bar loss, reasonably match the steel bars, stagger the joint positions, and determine the cutting length of the steel bars.

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