A method for constructing a "pit-in-pit-in-pit" foundation

Abstract

The application provides a "pit-in-pit-in-pit" foundation construction method, solves the problem that the commercial and residential projects near the rail transit facilities are difficult to be constructed under the condition of protecting the rail transit engineering in the deep foundation pit implementation stage of the construction, and utilizes the bored pile support, two steel sheet piles and the inner support form to combine, divides the single deep foundation pit into three sections in the form of "pit-in-pit-in-pit", improves the safety factor in the process of reducing the construction difficulty, and carries out the flow construction according to the core tube three sections, the main building raft and the podium raft, removes the corresponding support after the construction of one section of structure, is high in construction safety factor, is low in construction limitation, is small in site requirement, is few in types of mechanical equipment used in construction, effectively protects the subway in the foundation construction process, and reduces the influence on the subway and the urban rail transit engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building construction, in particular to a foundation construction method of "pit in pit in pit". BACKGROUND

[0002] Since entering the 21st century, the urbanization level in China has been continuously improving, and rail transit has been continuously developing at a high speed. More and more commercial and residential projects rely on rail transit for construction and implementation. Such TOD projects take public transportation hubs as starting points, and the traffic system is connected in all directions, providing great convenience for residents. However, due to the proximity of such projects to rail transit facilities and the small construction site, how to protect the implemented rail transit project becomes the first difficulty in the deep foundation pit implementation stage of construction. SUMMARY

[0003] In order to solve the problem of the commercial and residential project near the rail transit facility in the background art, which is difficult to protect the rail transit project under the condition of small construction site in the deep foundation pit implementation stage of construction, the present application provides a foundation construction method of "pit in pit in pit".

[0004] The technical scheme of the present application is: a foundation construction method of "pit in pit in pit", comprising the following steps: S1~cleaning the construction site, drilling and pouring pile construction and crown beam construction are carried out at the corresponding place of the construction site according to the construction drawing, and drilling and pouring pile and crown beam are obtained;

[0005] S2~large earthwork excavation is carried out on the inner side of the crown beam, and when the excavation is stopped when the underground raft foundation cushion plane is reached, a large foundation pit is formed, temporary slope protection construction is carried out on the circumferential side of the large foundation pit, and a ground beam is constructed at the bottom of the large foundation pit;

[0006] S3~main building raft steel sheet pile and core tube steel sheet pile construction are carried out in the large foundation pit according to the construction drawing, the main building raft steel sheet pile is located on the outer side of the core tube steel sheet pile, and there is a gap between the main building raft steel sheet pile and the core tube steel sheet pile;

[0007] S4~ground beam construction is carried out on the top of the drilling and pouring pile on the inner side of the core tube steel sheet pile;

[0008] S5~a core tube construction foundation pit is excavated in the core tube steel sheet pile, and the method of excavating while supporting the core tube steel sheet pile is used for construction when the core tube construction foundation pit is excavated;

[0009] S6~the drilling and pouring pile in the core tube construction foundation pit is broken;

[0010] S7~core tube cushion pouring, brick mold membrane and waterproof construction are carried out, and the surface of the core tube cushion is higher than the top of the drilling and pouring pile after breaking.

[0011] S8~The core tube is poured in layers, and a steel plate for stopping water is reserved between the concrete layers of each layer, and the support of the core tube steel sheet pile is removed in layers while pouring, until the core tube structure pouring construction is completed;

[0012] S9~The core tube steel sheet pile is pulled out, and the pile hole left after the core tube steel sheet pile is pulled out is backfilled;

[0013] S10~Referring to the construction method of the core tube structure of S4~S8, a main building raft plate construction pit is excavated downward between the main building raft plate steel sheet pile and the core tube structure, and the main building raft plate is constructed in the main building raft plate construction pit;

[0014] S11~The main building raft plate steel sheet pile is pulled out, and the pile hole left after the main building raft plate steel sheet pile is pulled out is backfilled;

[0015] S12~The podium raft plate is constructed.

[0016] Preferably, when the bored pile construction in step S1 is performed, the central axis of the casing is aligned with the center of the pile position determined by the bored pile, and the deviation is not more than 20mm, and the verticality of the casing is maintained;

[0017] After the casing is fixed, the bottom of the casing is backfilled and tamped with clay in layers;

[0018] If the hole bottom soil layer of the casing is not sticky and solid, and leakage and collapse occur at the hole bottom, the hole bottom should be excavated and replaced with soil, and after backfilling and tamping 300mm~500mm thick cohesive soil at the bottom of the pit, the casing is placed;

[0019] After the casing is installed in the hole, the upper opening of the casing is symmetrically hoisted tightly with steel wire rope to prevent the casing from moving downward in the hole.

[0020] Preferably, when the foundation pit excavation of the core tube construction pit and the main building raft plate construction pit is performed, the main structure is not covered and backfilled, or the main structure does not reach the anti-floating requirement, and the anti-floating measures such as continuous dewatering and drainage in the foundation pit must be used;

[0021] When the foundation pit is excavated, the layered excavation method is used, and the excavation depth of each layer is not more than 2m;

[0022] When the foundation pit is excavated to 300mm from the bottom of the pit, manual excavation must be used to avoid over-excavation and under-excavation of the foundation pit.

[0023] Preferably, the main building raft plate steel sheet pile and the core tube steel sheet pile in step S3 are both constructed by using Larsen steel sheet piles, and the construction steps of the Larsen steel sheet pile are as follows,

[0024] S3.1~Check the center line of the steel sheet pile, and check each steel sheet pile of the Larsen steel sheet pile, and remove the steel sheet pile with serious corrosion and deformation of the connecting lock;

[0025] S3.2~Before piling, grease is applied to the lock of the Larsen steel sheet pile;

[0026] S3.3~When piling, the Larsen steel sheet pile is installed by a crawler excavator with a vibration hammer, and a screen type piling method is used for construction, and the lower end of the Larsen steel sheet pile is inserted into the soil with a depth of not less than 2m of the required excavation depth of the foundation pit;

[0027] S3.4~The adjacent Larsen steel sheet piles are tightly connected in sequence to make the Larsen steel sheet piles connected end to end and closed into a circle;

[0028] S3.5~The Larsen steel sheet pile is checked for water tightness, and the leakage is welded and repaired, and the pile body needs to be checked every day during the construction of the foundation pit excavation.

[0029] Preferably, in step S3.3, the screen type piling method is used for construction, 10-20 steel sheet piles are inserted into the guide frame in a row to form a screen, and then the steel sheet piles are installed;

[0030] Usually, 1-2 steel sheet piles at both ends of the screen wall are installed to the design elevation, and the 1-2 steel sheet piles at both ends are fixed on the surrounding purlin by welding, and then the steel sheet piles are installed in sequence by 1 / 3 or 1 / 2 of the height of the steel sheet pile;

[0031] The construction sequence of the screen type piling method includes forward sequence, reverse sequence, reciprocating sequence, middle sequence, and composite sequence;

[0032] The selection principle of the construction sequence of the screen type piling method is that when the steel sheet piles installed at both ends are inclined in reverse, the forward sequence should be used for installation; otherwise, the reverse sequence is used for installation; when the steel sheet piles installed at both ends remain vertical, the reciprocating sequence can be used for installation; when the length of the sheet pile wall is very long, the composite sequence can be used for installation.

[0033] Preferably, when the core tube steel sheet pile is pulled out in step S9, the specific steps of pulling out the steel sheet pile are as follows,

[0034] S9.1~When pulling out the steel sheet pile, first vibrate the lock of the steel sheet pile with a vibration hammer to reduce the adhesion of the soil, then vibrate and pull out the steel sheet pile, and for the steel sheet pile that is difficult to pull out, first vibrate the steel sheet pile down 100-300mm with a vibration hammer, and then alternately vibrate and hit the steel sheet pile with the vibration hammer;

[0035] S9.2~During the pulling process, for the steel sheet pile with large pulling resistance, intermittent vibration method is used, each vibration is 15min, and the continuous vibration time of the vibration hammer is not more than 1.5h;

[0036] S9.3~After the pile is pulled out, the pile hole left after the pile is pulled out is backfilled, the backfilling method is filling method, and the material used in the filling method is water-washed sand.

[0037] Preferably, when the steel sheet pile is pulled to be slightly higher than the foundation cushion, the pulling is paused, and the surrounding soil layer is vibrated by the vibration hammer for 3~8 minutes to make the surrounding soil layer collapse and partially fill the soil hole.

[0038] Preferably, in step S5, the support of the core tube steel sheet pile is supported by two layers of first steel cross braces and second steel cross braces arranged in an upper and lower interval, and the first steel cross brace is located above the second steel cross brace.

[0039] Preferably, when step S8 is performed, the core tube is poured in three layers in sequence, and the specific construction steps are as follows,

[0040] S8.1~Before the first pouring, the vertical and horizontal reinforcement of the first layer of steel mesh is bound in the core tube construction foundation pit, the top of the second layer of steel mesh is lower than the second steel cross brace, and the construction formwork of the water collecting well and the elevator shaft is installed;

[0041] S8.2~The first pouring is performed, the first pouring is performed to 300mm below the second steel cross brace, the first pouring concrete body is formed, the first water stop steel plate is pre-embedded at the surface construction joint of the first pouring concrete body, the water collecting well and the elevator shaft are left in the first pouring concrete body, and the top of the vertical reinforcement of the first layer of steel mesh is exposed from the top of the first pouring concrete body;

[0042] S8.3~The second steel cross brace is removed, the construction formwork of the water collecting well and the elevator shaft is raised for the second time, the vertical and horizontal reinforcement of the second layer of steel mesh is bound, the vertical reinforcement of the second layer of steel mesh is fixedly connected with the upper end of the vertical reinforcement of the first layer of steel mesh, and the top of the second layer of steel mesh is lower than the first steel cross brace;

[0043] S8.4~The second pouring is performed to 1200mm below the first steel cross brace, and the second pouring is performed to avoid directly above the water collecting well and the elevator shaft, the second pouring concrete body is formed, the second water stop steel plate is pre-embedded at the surface of the second pouring concrete body 9, and the top of the vertical reinforcement of the second layer of steel mesh is exposed from the top of the second pouring concrete body;

[0044] S8.5~The first steel cross brace is removed, the surface of the ground beam is chiseled, and the construction formwork of the water collecting well and the elevator shaft is raised for the third time;

[0045] S8.7~The third pouring is performed, the third pouring is performed to the design height of the core tube structure, the third pouring concrete body is formed, and the ground beam is poured into the third pouring concrete body;

[0046] S8.9~The third water stop steel plate is pre-embedded at the connecting surface of the third pouring concrete body and the main building foundation.

[0047] Preferably, the second steel cross brace comprises a rod-shaped steel cross brace body, and an end plate is fixedly arranged at an end of the steel cross brace body, wherein the diameter of the end plate is greater than the diameter of the steel cross brace body,

[0048] A plurality of reinforcing plates are fixedly arranged at the outer periphery of the end of the steel cross brace body in a circumferential and spaced manner, the reinforcing plate is in a right-angle plate structure, one right-angle side of the reinforcing plate is fixedly connected with the steel cross brace body, and the other right-angle side of the reinforcing plate is fixedly connected with the end plate;

[0049] A plurality of rib plates are fixedly arranged on the web plate of the I-shaped steel in a spaced manner along the extending direction of the I-shaped steel, and the rib plates are fixedly connected with the two side plates of the I-shaped steel at the same time;

[0050] The end plate is fixedly connected with the side plate of the I-shaped steel away from the core tube steel sheet pile;

[0051] The steel bracket in a right-angled triangular structure is fixedly arranged on the core tube steel sheet pile, and the steel bracket is supported at the bottom of the end plate;

[0052] The first steel support has the same structure as the second steel cross brace, and the connection structure of the first steel support and the core tube steel sheet pile is the same as the connection structure of the second steel cross brace and the core tube steel sheet pile.

[0053] The advantages of the present application are as follows: the present application utilizes the bored pile support and the two steel sheet piles and the inner support form to combine, divides the single deep foundation pit into three sections in the form of "pit-in-pit-in-pit", improves the safety factor in the process of reducing the construction difficulty, and cooperates with the effective construction deployment to carry out the flow construction according to the core tube three sections, the main building raft and the podium raft, removes the corresponding support after the construction of one section of structure, has high construction safety factor, low construction limitation, small requirement for the site, few types of mechanical equipment used in the construction, effectively protects the subway in the process of foundation construction, and reduces the influence on the subway and urban rail transit engineering.

[0054] The steel sheet piles and the steel cross braces of the pit support can be repeatedly used, and can be allocated to other projects for adjustment after the completion of the project, and are green and environmentally friendly. DETAILED DESCRIPTION

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0056] Figure 1Fig. 1 is a top view of the structure after the core tube excavation of Example 1 is completed;

[0057] Figure 2 Fig. 2 is a front view of the structure of the core tube interior of Example 1;

[0058] Figure 3 Fig. 3 is a structure diagram of the core tube structure of Example 1 after the first pouring construction;

[0059] Figure 4 Fig. 4 is a structure diagram of the core tube structure of Example 1 after the second pouring construction;

[0060] Figure 5 Fig. 5 is a structure diagram of the core tube structure of Example 1 after the third pouring construction;

[0061] Figure 6 Fig. 6 is a structure diagram of the connection between the steel cross brace and the core tube steel sheet pile of Example 1;

[0062] In the figure, 1 is the underground raft foundation cushion layer plane, 2 is the main building raft steel sheet pile, 3 is the core tube steel sheet pile, 4 is the first steel cross brace, 5 is the second steel cross brace, 501 is the steel cross brace main body, 502 is the end plate, 503 is the reinforcing plate, 504 is the I-beam, 505 is the rib plate, 6 is the core tube structure cushion layer bottom plane, 7 is the bored pile, 8 is the first pouring concrete body, 9 is the first water stop steel plate, 10 is the water collecting well groove, 11 is the elevator shaft groove, 12 is the second pouring concrete body, 13 is the second water stop steel plate, 14 is the ground beam, 15 is the third pouring concrete body, 16 is the water collecting well cover plate, 17 is the third water stop steel plate, 18 is the shear wall, 19 is the steel bracket, and 20 is the main building raft. DETAILED DESCRIPTION

[0063] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0064] Example 1: A “pit-in-pit-in-pit” foundation construction method, comprising the following steps:

[0065] S1~cleaning the construction site, drilling and pouring pile construction and corbel construction are performed at the corresponding positions of the construction site according to the construction drawings, to obtain the bored pile 7 and the corbel;

[0066] When the bored pile construction is performed, the center axis of the pile casing is aligned with the pile position center determined by the bored pile 7, the deviation is not greater than 20 mm, and the verticality of the pile casing is maintained;

[0067] After the casing is fixed, the bottom of the casing is backfilled and tamped with clay;

[0068] If the soil at the bottom of the casing is not sticky and the bottom of the hole collapses due to leakage, the bottom of the hole should be excavated and replaced with soil, and after the bottom of the pit is backfilled with 300-500mm thick cohesive soil, the casing is placed;

[0069] After the casing is installed in the hole, the upper opening of the casing is symmetrically hoisted with steel wire rope to prevent the casing from moving downward in the hole.

[0070] S2~Large earth excavation is carried out inside the corbel, and when it is excavated to the underground raft foundation cushion layer plane 1 as shown, Figure 2 the large excavation is stopped, a large foundation pit is formed, temporary slope protection construction is carried out on the side of the large foundation pit, and ground beam construction is carried out at the bottom of the large foundation pit;

[0071] Then use a small excavator to dig the main building pile cap, and a large excavator to turn the soil behind the small excavator, and the earthmoving vehicles follow up in time;

[0072] When excavating to the main building raft foundation position, first use a large excavator to clean the surface soil, leaving 20cm, and then use a small excavator to excavate the details.

[0073] S3~According to the construction drawings, the main building raft steel sheet pile 2 and the core tube steel sheet pile 3 are constructed in the large foundation pit, the main building raft steel sheet pile 2 is located outside the core tube steel sheet pile 3, and there is a gap between the main building raft steel sheet pile 2 and the core tube steel sheet pile 3, as shown in Figure 1 and Figure 3 ;

[0074] The main building raft steel sheet pile 2 and the core tube steel sheet pile 3 are both constructed using Larsen steel sheet piles, and the construction steps of the Larsen steel sheet pile are as follows,

[0075] S3.1~Release the steel sheet pile centerline, check each Larsen steel sheet pile, and remove the steel sheet piles with severe corrosion and deformation of the connecting lock;

[0076] S3.2~Before piling, grease is applied to the lock of the Larsen steel sheet pile;

[0077] S3.3~When piling, the Larsen steel sheet pile is constructed using a crawler excavator with a vibration hammer, and a screen type piling method is used, and the lower end of the Larsen steel sheet pile is inserted into the soil with a depth of not less than 2m of the required excavation depth of the foundation pit;

[0078] When the screen type piling method is used for construction, 10-20 steel sheet piles are inserted into the guide frame in a row, making it a screen, and then it is constructed;

[0079] Generally, 1-2 steel sheet piles at both ends of the screen wall are driven to the design elevation, and the 1-2 steel sheet piles at both ends are fixed on the surrounding purlin by welding, and then the steel sheet piles are driven into the middle according to the order of 1 / 3 or 1 / 2 sheet pile height;

[0080] The construction sequence of the screen type driving method includes forward sequence, reverse sequence, reciprocating sequence, middle sequence, middle and sequence, and composite sequence.

[0081] The construction sequence selection principle of the screen type driving method is that when the steel sheet piles at both ends are inclined in reverse, the forward sequence should be used for driving; otherwise, the reverse sequence should be used for driving; when the steel sheet piles at both ends remain vertical, the reciprocating sequence can be used for driving; when the length of the sheet pile wall is very long, the composite sequence can be used for driving.

[0082] S3.4~The adjacent Larsen steel sheet piles are sequentially tightly connected to make the Larsen steel sheet piles connected end to end and closed into a ring;

[0083] S3.5~The Larsen steel sheet piles are checked for water tightness, and the welding repair is performed on the leakage. The pile body inspection needs to be performed every day during the construction period of the foundation pit excavation.

[0084] S4~The construction of the ground beam 14 is performed at the top of the bored pile 7 inside the core tube steel sheet pile 3.

[0085] S5~The core tube construction foundation pit is excavated inside the core tube steel sheet pile 3, and the method of supporting the core tube steel sheet pile 3 while excavating is used for construction during the excavation of the core tube construction foundation pit.

[0086] Specifically, as shown in Figure 2 The support of the core tube steel sheet pile 3 is supported by the two layers of first steel cross braces 4 and second steel cross braces 5 arranged at an interval, and the first steel cross brace 4 is located above the second steel cross brace 5. In this embodiment, the structure of the first steel cross brace 4 is the same as that of the second steel cross brace 5, and the connection structure of the first steel cross brace 4 and the core tube steel sheet pile 3 is the same as that of the second steel cross brace 5 and the core tube steel sheet pile 3.

[0087] As shown in Figure 6 In this embodiment, the structure of the second steel cross brace 5 and the connection structure of the second steel cross brace 5 and the core tube steel sheet pile 3 are taken as examples to describe the specific connection structure between the steel support and the steel sheet pile in detail, and the specific description is as follows.

[0088] The second steel cross brace 5 includes a rod-shaped steel cross brace body 501, and an end plate 502 is fixedly arranged at the end of the steel cross brace body 501, and the diameter of the end plate 502 is greater than the diameter of the steel cross brace body 501.

[0089] The end outer periphery side of the steel cross brace body 501 is fixedly provided with a plurality of reinforcing plates 503 arranged in a ring shape at intervals, the reinforcing plate 503 is a right angle plate structure, one right angle side of the reinforcing plate 503 is fixedly connected with the steel cross brace body 501, and the other right angle side of the reinforcing plate 503 is fixedly connected with the end plate 502;

[0090] The inner side of the core tube steel sheet pile 3 is fixedly provided with a ring of I-shaped steel 504 connected in a head-to-tail manner, a plurality of rib plates 505 are arranged at intervals on the web plate of the I-shaped steel 504 along the extension direction of the I-shaped steel 504, and the rib plate 505 is fixedly connected with the two side flanges of the I-shaped steel 504;

[0091] The end plate 502 is fixedly connected with the side flange of the I-shaped steel 504 away from the core tube steel sheet pile 3;

[0092] The core tube steel sheet pile 3 is fixedly provided with a steel bracket 19 of a right triangle structure, and the steel bracket 19 is supported at the bottom of the end plate 502.

[0093] Since the required excavation depth in the core tube is large, and the steel cross brace is provided with two rows, a long arm excavator is required for earth excavation, and the long arm excavator cannot excavate to the position between the steel sheet pile and the cast-in-place pile, so manual excavation is required to ensure that the core tube steel sheet pile 3 is clean, and to avoid the falling of miscellaneous soil during construction due to incomplete cleaning, causing personnel injury.

[0094] After the core tube steel sheet pile 3 is excavated, the core tube is dredged, and the silt on the side wall is cleaned.

[0095] S6~Breaking the pile of the cast-in-place pile 7 in the core tube construction foundation pit.

[0096] S7~Performing core tube cushion pouring, brick membrane and waterproof construction, the surface of the core tube cushion is higher than the top of the cast-in-place pile 7 after pile breaking.

[0097] S8~Performing layered pouring on the core tube, and reserving water stop steel plates between the concrete layers of each layer, and simultaneously performing layered removal construction of the support of the core tube steel sheet pile 3 during pouring, until the core tube structure pouring construction is completed;

[0098] In the present embodiment, as shown in Figures 3-5 The core tube is poured three times in sequence, and the specific construction steps are as follows,

[0099] S8.1~Before the first pouring, the vertical and horizontal reinforcement bars of the first layer of reinforcement mesh are bound in the core tube construction foundation pit, the top of the second layer of reinforcement mesh is lower than the second steel cross brace 5, the construction formwork of the water collecting well groove 10 and the elevator well groove 11 is installed;

[0100] S8.2~First pouring is conducted to 300mm below the second steel cross brace 5 (to facilitate the lap length of waterproofing membrane and the reserved water stop steel plate), forming the first poured concrete body 8, and embedding the first water stop steel plate 9 at the surface construction joint of the first poured concrete body 8, leaving the water collecting well groove 10 and the elevator shaft groove 11 in the first poured concrete body 8, and exposing the vertical reinforcement of the first layer of steel reinforcement net on the top of the first poured concrete body 8;

[0101] S8.3~The second steel cross brace 5 is removed, the construction formwork of the water collecting well groove 10 and the elevator shaft groove 11 is raised for the second time, the vertical reinforcement and the horizontal reinforcement of the second layer of steel reinforcement net are bound, the lower end of the vertical reinforcement of the second layer of steel reinforcement net is fixedly connected with the upper end of the vertical reinforcement of the first layer of steel reinforcement net, and the top of the second layer of steel reinforcement net is lower than the first steel cross brace 4;

[0102] S8.4~The second pouring is conducted to 1200mm below the first steel cross brace 4, and avoids the direct upper part of the water collecting well groove 10 and the elevator shaft groove 11, forming the second poured concrete body 12, embedding the second water stop steel plate 13 on the surface of the second poured concrete body 9, and exposing the vertical reinforcement of the second layer of steel reinforcement net on the top of the second poured concrete body 12;

[0103] S8.5~The first steel cross brace 4 is removed, the surface of the ground beam 14 is roughened, and the construction formwork of the water collecting well groove 10 and the elevator shaft groove 11 is raised for the third time;

[0104] S8.7~The third pouring is conducted to the designed height of the core tube structure, forming the third poured concrete body 15, and making the ground beam 14 be poured in the third poured concrete body 15;

[0105] S8.9~The third water stop steel plate 17 is embedded at the connecting surface of the third poured concrete body 15 and the main building foundation.

[0106] S9~The core tube steel sheet pile 3 is pulled out, and the pile hole left after the core tube steel sheet pile 3 is pulled out is backfilled;

[0107] When the core tube steel sheet pile 3 is pulled out, the specific steps are as follows,

[0108] S9.1~When the pile is pulled out, the lock of the steel sheet pile is first vibrated by the vibration hammer to reduce the adhesion of the soil, and then the pile is pulled out while being vibrated. For the steel sheet pile that is difficult to pull out, the steel sheet pile can be vibrated down by 100~300mm by the vibration hammer first, and then the vibration hammer is alternately vibrated and hit to pull out the steel sheet pile;

[0109] S9.2~When the steel sheet pile is pulled out to be slightly higher than the foundation cushion, the pulling is paused, and the surrounding soil layer is vibrated by the vibration hammer for 3~8 minutes to make the surrounding soil layer fall and partially fill the soil hole.

[0110] S9.3~In the process of pulling out the pile, for the steel sheet pile with large pulling resistance, the intermittent vibration method is used, each vibration lasts for 15 minutes, and the continuous vibration time of the vibration hammer is not more than 1.5 hours;

[0111] S9.4~After the pile pulling is completed, the pile hole left after the pile pulling is backfilled, and the backfilling method is the filling method, and the material used in the filling method is water-washed sand.

[0112] S10~Referring to the construction method of the core tube structure of S4~S8, the same is to carry out construction in the order of ground beam pouring-ground excavation-steel cross support-supporting-ground excavation-steel cross support-supporting-ground excavation-ground beam roughening-brick mold membrane and waterproof coiled material construction-layered pouring and installation of water stop steel plate, excavate a main building raft construction pit downward between the main building raft steel sheet pile 2 and the core tube structure, and carry out construction of the main building raft 20 in the main building raft construction pit.

[0113] S11~Referring to the pulling out construction mode of the core tube steel sheet pile 3 in step S9, the main building raft steel sheet pile 2 is pulled out, and the pile hole left after the main building raft steel sheet pile 2 is pulled out is backfilled.

[0114] S12~Construction of the podium raft.

[0115] The process principle of the application: the foundation construction method of the TOD project "pit in pit in pit" utilizes the combination of bored pile support and two steel sheet piles and internal support form, divides a single deep foundation pit into three sections in the form of "pit in pit in pit" for excavation, improves the safety factor in the process of reducing the construction difficulty, and cooperates with effective construction deployment to carry out the construction of the main building foundation structure in four sections of core tube three sections, main building raft and podium raft. In the construction process, measures such as water stop and impermeable and finished product protection are added, the corresponding support is removed after the construction of one section of structure is completed, the construction safety factor is high, the subway is effectively protected in the foundation construction process, and the influence on the subway and urban rail transit project is reduced.

[0116] The method features of the application: (1) the foundation pit construction stage of the TOD project is narrow and close to the subway vehicle depot, the combination of bored pile support and two steel sheet piles and internal support form is used, the support and foundation construction process has low construction restriction, the site requirement is small, and the type of mechanical equipment used in construction is small.

[0117] (2) the foundation is divided into three sections of core tube, main building raft and podium raft for segmented and sequential construction according to the support form, the corresponding support is removed after the construction of one section of structure is completed in the process of sequential construction of the foundation, the construction safety factor is high, the subway is effectively protected in the foundation construction process, the construction difficulty is reduced, and the influence on the subway and urban rail transit project is reduced.

[0118] (3) Green environmental protection, wherein the steel sheet piles and steel cross braces of the pit support in the foundation pit can be repeatedly used, and can be allocated to other projects for adjustment after the project is completed.

[0119] The social benefits of the present application: the foundation construction method of the TOD project "pit-in-pit-in-pit" has completed the key task of protecting the existing metro vehicle depot during the construction process of the TOD Bai-di super high-rise residential project, and solved the construction difficulty of the small site during the foundation pit construction stage, and provided a reference for other TOD projects and super high-rise buildings near urban rail transit projects during the foundation construction stage.

[0120] The use of the present technology can greatly improve the safety of the foundation construction process of the TOD project, successfully complete the protection of the existing metro structure, solve the construction difficulty of the small site during the foundation pit construction stage of the TOD Bai-di super high-rise residential project, and can reasonably arrange the construction, successfully complete the foundation pit excavation and basement construction task, speed up the construction progress, and achieve the expected goal.

[0121] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims, not by the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for constructing a "pit within a pit" foundation, characterized in that, The process includes the following steps: S1~ Clean the construction site, and according to the construction drawings, carry out the construction of bored piles and capping beams at the corresponding locations on the construction site to obtain bored piles (7) and capping beams; S2~ Large earthwork excavation is carried out inside the crown beam. When the excavation reaches the plane of the underground raft foundation cushion layer (1), the large earthwork excavation is stopped to form a large foundation pit. Temporary slope protection construction is carried out on the periphery of the large foundation pit, and ground beam construction is carried out at the bottom of the large foundation pit. S3~According to the construction drawings, the main building raft sheet piles (2) and the core tube sheet piles (3) are constructed in the large foundation pit. The main building raft sheet piles (2) are located outside the core tube sheet piles (3). There is a gap between the main building raft sheet piles (2) and the core tube sheet piles (3). S4~ Construction of the ground beam (14) is carried out on the top of the bored pile (7) inside the core tube steel sheet pile (3); S5~ The core tube construction pit is excavated inside the core tube steel sheet pile (3). When the core tube construction pit is excavated, the core tube steel sheet pile (3) is supported at the same time. S6~ Break the bored piles (7) in the core tube construction pit; S7~ Carry out the core tube cushion layer pouring, brick formwork and waterproofing construction, the surface of the core tube cushion layer is higher than the top of the drilled pile (7) after the pile is broken; S8~ The core tube is poured in layers, and a water-stop steel plate is reserved between each concrete layer. At the same time, the support of the core tube steel sheet pile (3) is removed in layers while pouring, until the core tube structure is poured. S9~ Pull out the core tube sheet pile (3) and backfill the pile hole left after the core tube sheet pile (3) is pulled out; S10~Referring to the construction method of the core tube structure of S4~S8, the main building raft foundation pit is excavated downward between the main building raft steel sheet pile (2) and the core tube structure, and the main building raft (20) is constructed in the main building raft foundation pit. S11~ Pull out the steel sheet piles (2) of the main building raft foundation and backfill the pile holes left after pulling out the steel sheet piles (2) of the main building raft foundation; S12 ~ Podium raft foundation construction; In step S8, the core tube is poured in three layers. The specific construction steps are as follows. S8.1 Before the first pour, tie the vertical and horizontal bars of the first layer of steel mesh in the core tube construction pit. The top of the second layer of steel mesh is lower than the second steel cross brace (5). Install the construction templates for the water collection well trench (10) and elevator well trench (11). S8.2~ The first pouring is carried out, and the first pouring is 300mm below the second steel cross brace (5) to form the first pouring concrete body (8). The first water-stop steel plate (9) is pre-embedded at the construction joint on the surface of the first pouring concrete body (8). A water collection well groove (10) and an elevator well groove (11) are left in the first pouring concrete body (8). The top of the vertical bar of the first layer of steel mesh is exposed at the top of the first pouring concrete body (8). S8.3 Remove the second steel cross brace (5), raise the construction template of the water collection well trench (10) and elevator well trench (11) for the second time, tie the vertical and horizontal bars of the second layer of steel mesh, so that the lower end of the vertical bar of the second layer of steel mesh is fixedly connected to the upper end of the vertical bar of the first layer of steel mesh, and the top of the second layer of steel mesh is lower than the first steel cross brace (4). S8.4~ The second pouring is made to 1200mm below the first steel cross brace (4), avoiding the top of the water collection well (10) and the elevator well (11), forming the second poured concrete body (12). The second water-stop steel plate (13) is pre-embedded on the surface of the second poured concrete body (12), and the top of the vertical bar of the second layer of steel mesh is exposed above the top of the second poured concrete body (12). S8.5 Remove the first steel cross brace (4), roughen the surface of the ground beam (14), and raise the construction templates of the water collection well (10) and elevator well (11) for the third time; S8.6~ The third pouring is carried out to the design height of the core tube structure, forming the third pouring concrete body (15), so that the ground beam (14) is poured into the third pouring concrete body (15); S8.7~ A third waterstop steel plate (17) is pre-embedded at the connection surface between the third poured concrete body (15) and the main building foundation.

2. The "pit within a pit within a pit" foundation construction method as described in claim 1, characterized in that: When carrying out the construction of the bored pile in step S1, the central axis of the casing is aligned with the center of the pile position measured by the bored pile (7), and the deviation is not greater than 20mm, and the casing is kept vertical. After the casing is fixed, use clay to backfill and compact the bottom of the casing in layers. If the soil layer at the bottom of the casing hole is not compacted and leakage and collapse occur at the bottom of the hole, the bottom of the hole should be dug deeper and the soil replaced. After backfilling and compacting a 300mm~500mm thick layer of cohesive soil at the bottom of the pit, the casing should be installed. After the casing is installed in the hole, it should be symmetrically tightened with steel wire rope at the top to prevent it from sliding down inside the hole.

3. The "pit within a pit within a pit" foundation construction method as described in claim 1, characterized in that: When excavating the foundation pit for the core tube construction and the raft foundation pit for the main building, if the main structure has not been backfilled with soil or has not met the main structure's anti-buoyancy requirements, continuous dewatering and drainage measures must be adopted in the foundation pit to eliminate buoyancy. When excavating the foundation pit, a layered excavation method is adopted, and the excavation depth of each layer is no more than 2m; When the foundation pit is excavated to 300mm from the bottom, manual excavation must be used to avoid over-excavation or under-excavation.

4. The "pit within a pit within a pit" foundation construction method as described in claim 1, characterized in that: In step S3, Larssen sheet piles were used for the construction of the main building raft foundation sheet piles (2) and the core tube sheet piles (3). The construction steps for the Larssen sheet piles are as follows: S3.1~ Mark out the centerline of the sheet piles, inspect each Larssen sheet pile, and remove sheet piles with rusted or severely deformed interlocking joints; S3.2 Before driving the piles, apply grease to the interlocks of the Larssen sheet piles; S3.3~When driving the Larssen sheet piles, a tracked excavator with a vibratory hammer shall be used for driving, and a screen-type driving method shall be adopted. The lower end of the Larssen sheet pile shall be driven into the soil to a depth of not less than 2m of the depth of the foundation pit to be excavated. S3.4 ~ Adjacent Larssen sheet piles are connected in a tight, sequential manner, so that the Larssen sheet piles are connected end to end and form a circle; S3.5~ Conduct a water tightness test on the Larssen sheet piles, weld and repair any leaks, and conduct daily pile inspections during the excavation of the foundation pit.

5. The "pit within a pit within a pit" foundation construction method as described in claim 4, characterized in that: When using the screen-type driving method in step S3.3, insert 10-20 steel sheet piles in a row into the guide frame to form a screen shape before driving them. Typically, one or two sheet piles at each end of the screen wall are driven to the design elevation and fixed to the waler by welding. Then, sheet piles are driven into the middle in sequence at 1 / 3 or 1 / 2 of the sheet pile height. The construction sequence of the screen-style driving method includes forward sequence, reverse sequence, reciprocating sequence, split sequence, neutralization sequence, and composite sequence; The principle for selecting the construction sequence of the screen-type sheet pile driving method is as follows: when the sheet piles at both ends are inclined in the opposite direction, the forward sequence should be used; otherwise, the reverse sequence should be used. When the sheet piles at both ends are kept vertical, the reciprocating sequence can be used. When the sheet pile wall is very long, a composite sequence can be used.

6. The "pit within a pit within a pit" foundation construction method as described in claim 1, characterized in that: When extracting the core tube sheet pile (3) in step S9, the specific steps for pile extraction are as follows. S9.1 When extracting a sheet pile, first use a vibratory hammer to loosen the interlocks of the sheet pile to reduce soil adhesion, and then extract while vibrating. For sheet piles that are difficult to extract, you can first use a vibratory hammer to vibrate the sheet pile down 100-300mm, and then use a vibratory hammer to alternately vibrate and extract. S9.2~ During the pile extraction process, for sheet piles with high extraction resistance, intermittent vibration method is adopted, with each vibration lasting 15 minutes and the continuous vibration time of the vibratory hammer not exceeding 1.5 hours; S9.3 After the pile extraction is completed, the pile hole left after the pile extraction is backfilled. The backfilling method is the filling method, and the material used for the filling method is water-flushed sand.

7. The "pit within a pit within a pit" foundation construction method as described in claim 6, characterized in that: When the sheet pile is pulled up to a height slightly higher than the foundation pit cushion, the pulling is paused, and the pile is vibrated for 3 to 8 minutes to allow the surrounding soil to collapse and partially fill the hole.

8. The "pit within a pit within a pit" foundation construction method as described in claim 1, characterized in that: In step S5, the core tube steel sheet pile (3) is supported by two layers of first steel cross bracing (4) and second steel cross bracing (5) arranged at intervals. The first steel cross bracing (4) is located above the second steel cross bracing (5).

9. A foundation construction method for a "pit within a pit" as described in claim 1, characterized in that: The second steel cross brace (5) includes a rod-shaped steel cross brace body (501), and an end plate (502) is fixedly provided at the end of the steel cross brace body (501). The diameter of the end plate (502) is larger than the diameter of the steel cross brace body (501). Multiple reinforcing plates (503) are fixedly provided on the outer periphery of the end of the steel cross brace body (501). The reinforcing plates (503) are right-angled plate structures. One right-angled side of the reinforcing plate (503) is fixedly connected to the steel cross brace body (501), and the other right-angled side of the reinforcing plate (503) is fixedly connected to the end plate (502). The inner side of the core tube sheet pile (3) is fixed with a ring of I-beams (504) connected end to end. Multiple ribs (505) are provided at intervals along the extension direction on the web of the I-beam (504). The ribs (505) are also fixedly connected to the two side flanges of the I-beam (504). The end plate (502) is fixedly connected to the wing plate on the side of the I-beam (504) away from the core tube sheet pile (3); A steel bracket (19) with a right-angled triangular structure is fixed on the core tube sheet pile (3), and the steel bracket (19) is supported on the bottom of the end plate (502); The structure of the first steel cross brace (4) is the same as that of the second steel cross brace (5), and the connection structure between the first steel cross brace (4) and the core tube sheet pile (3) is the same as that between the second steel cross brace (5) and the core tube sheet pile (3).

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