LU502674B1

LU502674B1 - Safe bottom-up and top-down combined construction method for asynchronous excavation of ultra-deep foundation pit group

Info

Publication number: LU502674B1
Application number: LU502674A
Authority: LU
Inventors: Dong Liu; Hongqian Wang; Miaoxiang Lu; Tianci Xie; Xifei Deng; Jialin Wu; Shufang Hu; Zhihai Fang; Zihan Liu; Jie Wang; Qiutong Liu; Guanghui Zhang; Tao Chen; Nengwei Deng; Yang Wang; Shengtao Wang; Ping Jin; Ziyang Liu
Original assignee: China Tiesiju Civil Eng Group Co Ltd
Priority date: 2021-11-11
Filing date: 2022-08-16
Publication date: 2023-05-16
Also published as: CN114045870B; CN114045870A

Abstract

The present invention relates to the technical field of building engineering construction, and provides a safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group, including the following steps: adopting a high-rigidity enclosure structure during design of a construction scheme; arranging a connecting beam between adjacent foundation pits; arranging drawing strip and skirt foundation reinforcements inside a foundation pit and between the adjacent foundation pits; controlling a staggered height during excavation of the foundation pit; predicting a deformation trend of the foundation pit group by means of a data inversion system to guide key points of a next step of deformation control on the foundation pit; when the deformation amount of the foundation pit and buildings around the foundation pit exceeds a limit or the displacement rate exceeds an early warning value, taking corresponding deformation control measures; synchronously carrying out excavation of soil below a top-down construction plate and construction of an upper structure; and constructing the remaining main structures in a bottom-up manner. The present invention effectively solves the problem of deformation control during asynchronous construction of the ultra-deep foundation pit group in a soft soil stratum, and realizes the overall deformation control on the foundation pit group and the stable surrounding environment; and in addition, the construction method provided by the present invention has the advantages of high construction safety, fast construction progress, low construction cost and the like.

Description

SAFE BOTTOM-UP AND TOP-DOWN COMBINED CONSTRUCTION METHOD 502674

FOR ASYNCHRONOUS EXCAVATION OF ULTRA-DEEP FOUNDATION PIT GROUP

FIELD OF TECHNOLOGY

[0001] The present invention relates to the technical field of building engineering construction, and provides a safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group.

BACKGROUND

[0002] With the rapid development of urban metro construction, ultra-deep foundation pit projects for new metro stations in soft soil strata are not uncommon. The construction of ultra-deep foundation pit groups in soft soil strata frequently occurs, but there is no systematic deformation control method for asynchronous excavation of ultra-deep foundation pit groups in soft soil strata.

[0003] For the construction of ultra-deep foundation pit groups in soft soil strata, it is inevitable that adjacent foundation pits will have asynchronous excavation conditions due to the existence of problems such as construction site limitation, uneven mechanical configuration, and high difficulty in construction organization. If a conventional construction method is directly used for excavation, high construction difficulty and slow construction progress will be faced, and it is very easy to cause instability of foundation pits due to lack of standard risk early warning and deformation control methods for asynchronous excavation of foundation pit groups, thereby leading to major safety issues.

[0004] In view of that ensuring the safety and deformation control stability of asynchronous excavation of ultra-deep foundation pit groups in soft soil strata is a necessary condition for the implementation of projects for ultra-deep foundation pit groups in soft soil strata, a deformation control method suitable for asynchronous excavation of adjacent ultra-deep foundation pits in soft soil strata is proposed for a problem to be urgently solved at present.

SUMMARY

[0005] The technical problem to be solved by the present invention is to provide a safe bottom-up and top-down combined construction method suitable for asynchronous excavation of 1/26 an ultra-deep foundation pit group in a soft soil stratum, which can avoid the problems of high 50267 4 construction difficulty, slow construction progress, and easy instability of a foundation pit due to a conventional construction method, thereby ensuring smooth construction of the ultra-deep foundation pit group.

[0006] In order to solve the above technical problem, the present invention adopts the following technical solution:

[0007] A safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group, including the following steps:

[0008] S1: adopting a high-rigidity enclosure structure during design of a construction scheme;

[0009] S2: arranging a connecting beam between adjacent foundation pits;

[0010] S3: arranging drawing strip and skirt foundation reinforcements inside a foundation pit and between the adjacent foundation pits;

[0011] S4: controlling a staggered height during excavation of the foundation pit;

[0012] SS: predicting a deformation trend of the foundation pit group by means of a data inversion system to guide key points of a next step of deformation control on the foundation pit;

[0013] S6: when the deformation amount of the foundation pit and buildings around the foundation pit exceeds a limit or the displacement rate exceeds an early warning value, taking corresponding deformation control measures;

[0014] S7: synchronously carrying out excavation of soil below a top-down construction plate and construction of an upper structure; and

[0015] S8: constructing the remaining main structures in a bottom-up manner.

[0016] As one of preferred modes of the present invention, in the step S1, the high-rigidity enclosure structure comprises a diaphragm wall, and an underground wall (a lattice-shaped diaphragm wall) arranged inside the foundation pit; and a construction process includes: (1) constructing a guide wall; (2) forming a groove by a grooving machine; (3) placing a steel reinforcement cage (containing a joint), (4) performing underwater concreting; and (5) completing construction of the diaphragm wall.

[0017] Therefore, compared with other enclosure structures of bored piles or construction piles, the diaphragm wall in the present invention has higher rigidity and better anti-deformation ability; and the underground wall as a plain concrete wall for supporting an inner wall of the foundation pit has a better anti-deformation effect, and can be excavated and crushed in the construction of 2/26 foundation pit excavation, thereby effectively ensuring stable control on lateral displacement and 50267 4 deformation of the diaphragm wall.

[0018] As one of preferred modes of the present invention, in the step S2, the connecting beam is anchored in crown beams of the adjacent foundation pits, and the crown beams and first concrete supports of the adjacent foundation pits are connected as a whole; and meanwhile, the cross section size of the connecting beam at each corner 1s increased.

[0019] Therefore, the overall rigidity between the adjacent foundation pits is enhanced, and the top deformation of the foundation pit is reduced.

[0020] As one of preferred modes of the present invention, in the step S3, a circle of the skirt foundation reinforcements are arranged inside the foundation pit in a manner of being close to a diaphragm wall, inner sides of the skirt foundation reinforcements are provided with the drawing strip reinforcements, and a reinforcement depth is 3 m below the top-down construction plate and 4 m below a base, thereby reducing heave deformation of an excavation face; a circle of the skirt foundation reinforcements are arranged between the adjacent foundation pits in a manner of clinging to the diaphragm wall, inner sides of the skirt foundation reinforcements are provided with the drawing strip reinforcements, and a reinforcement depth is 4 m below the base from the top of a water barrier under the ground, thereby enhancing the stability of a middle soil stratum under the condition of asynchronous excavation of the adjacent foundation pits; and the foundation reinforcements adopt ¢850@600 high-pressure rotary jet piles, and a construction process includes: (1) measurement and positioning; (2) pre-stirring and sinking; (3) jet grout stirring and rising; (4) repeated stirring and sinking; (5) repeated stirring and rising; and (6) construction completion.

[0021] Therefore, the rigidity of soil around the diaphragm wall is enhanced to reduce the impact on the enclosure structure in foundation pit construction, thereby reducing the deformation of the foundation pit.

[0022] As one of preferred modes of the present invention, in the step S4, the staggered excavation height of the adjacent foundation pits is controlled to a maximum of no more than 8 m. Therefore, in order to avoid too great staggered height of excavation faces of two foundation pits, soil between the adjacent foundation pits produces an unbalanced moment, thereby causing too large deformation of the foundation pit.

[0023] As one of preferred modes of the present invention, in the step S5, an operation process 3/26 of the inversion system includes: (1) synchronizing on-site monitoring data; (2) uploading the 50267 4 monitoring data to a cloud server; (3) numerically simulating and inverting the monitoring data; (4) numerically simulating, forwardly analyzing and predicting deformation of the foundation pit; and (5) displaying a result. The deformation of the enclosure structure due to the excavation of the foundation pit and the deformation of the surrounding environment are visually displayed in the inversion system. According to a video and a safety factor, construction personnel decide the key points of the next step of deformation control on the foundation pit, and take the deformation control measures if necessary. The advantages are that more accurate numerical simulation can be carried out in combination with the on-site data to accurately predict the deformation of the foundation pit, and a dangerous area of the foundation pit can be discovered in advance, thereby guiding on-site construction to a certain extent.

[0024] As one of preferred modes of the present invention, in the step S6, the deformation amount exceeding the limit refers to that the enclosure structure of the foundation pit is laterally displaced by 40 mm or more, or that the enclosure structure of the foundation pit deforms by 0.4% h or more relative to the depth h of the foundation pit, or that the buildings around are displaced by 10 mm or more; and

[0025] the displacement rate exceeding the early warning value refers to that a horizontal displacement rate of the enclosure structure of the foundation pit is greater than or equal to 2 mm/d, or that the displacement rate of the buildings around is greater than or equal to 1 mm/d.

[0026] As one of preferred modes of the present invention, in the step S6, the corresponding deformation control measures include:

[0027] (1) adjustment of foundation pit excavation subareas:

[0028] when the horizontal displacement rate of the enclosure structure of the foundation pit reaches 2 mm/d or the displacement rate of the buildings around reaches 1 mm/d, a sectional skip excavation construction scheme for the foundation pit is adopted; and when displacement rates of an excavation section and structures around are greater than or equal to 2 mm/d, excavation of the section is suspended, and the excavation construction section is adjusted to an other stable area;

[0029] (2) backfilling and back-pressing in the pit:

[0030] when the horizontal displacement rate of the enclosure structure of the foundation pit or the displacement rate of the buildings around reaches 3 mm/d, unloading, and partial or complete 4/26 backfilling and back-pressing are performed to reach a previous support elevation; LU502674

[0031] (3) pressurization of an axial force servo system for a steel support:

[0032] when the enclosure structure of the foundation pit is laterally displaced by 40 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.4% h, or the buildings around are displaced by 10 mm, the maximum value of a preset axial force of the axial force servo system 1s adjusted to ensure the stable deformation trend of the excavation section; and

[0033] (4) arrangement of a temporary steel support:

[0034] when the enclosure structure of the foundation pit is laterally displaced by 50 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.5% h, or the buildings around are displaced by 40 mm, a row of steel supports are additionally erected on an erection work face outside an existing steel/concrete support.

[0035] As one of preferred modes of the present invention, in the step S7, upper and lower synchronous construction of the top-down construction plate includes: after the top-down construction plate is poured and has strength, construction of the upper main structure and excavation of the lower soil are simultaneously carried out, and only one layer of structure can be constructed on the top-down construction plate before construction of lower structures (a bottom plate, a side wall and a stand column) is completed; and a steel support is left in the construction of the upper structure of the top-down construction plate, and after the structure is completed and has design strength, the left support can be removed.

[0036] As one of preferred modes of the present invention, in the step S8, after the upper structure of the top-down construction plate is completed and has design strength, the remaining main structures are sequentially constructed in a bottom-up manner until the foundation pit is roofed.

[0037] As one of preferred modes of the present invention, the present invention is specifically suitable for construction of the ultra-deep foundation pit group in a soft soil stratum.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The type selection and arrangement of the enclosure structure of the foundation pit are optimized, and the stability of the enclosure structure of the foundation pit and the soil around is ensured.

[0040] (2) It is proposed that the staggered height of excavation faces of the adjacent 5/26 foundation pits is controlled to be 8 m, thereby ensuring the stability of deformation under the 0267 4 mutual influence of asynchronous excavation of the foundation pit group.

[0041] (3) Requirements for on-site monitoring and deformation control on the foundation pit are integrated, mechanical parameters of soil are inverted by means of displacement back analysis, mechanical parameters reflecting real situations of a research object are obtained, and the deformation trend of the foundation pit group and the safety factor are obtained to guide the key points of the next step of deformation control on the foundation pit during excavation.

[0042] (4) The early warning value for a deformation risk of the foundation pit and the deformation control method are adopted to jointly guarantee the problem of deformation control in asynchronous excavation of the foundation pit group.

[0043] (5) The excavation of the soil below the top-down construction plate and the construction of the upper structure are carried out synchronously, and the main structure of the foundation pit is fast sealed by the measures of leaving the steel support and the like, thereby ensuring the construction safety of the foundation pit group.

[0044] The present invention effectively solves the problem of deformation control during asynchronous construction of the ultra-deep foundation pit group in a soft soil stratum, and realizes the overall deformation control on the foundation pit group and the stable surrounding environment; and compared with a conventional construction method, the construction method provided by the present invention has the advantages of high construction safety, fast construction progress, low construction cost and the like, provides a complete practical and referable scheme for the construction of the ultra-deep foundation pit group in the soft soil stratum in the future, and has great application and promotion value in similar projects at home and abroad.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a construction sequence diagram of a high-rigidity enclosure structure in

Embodiment 1 (1, 2, 3, 4, and 5 in FIG. 1 correspond to construction steps performed in sequence);

[0046] FIG. 2 is an arrangement diagram of a connecting beam of adjacent foundation pits in

Embodiment 1;

[0047] FIG. 3 is a schematic diagram of drawing strip and skirt reinforcements of foundation 6/26 pits in Embodiment 1; LU502674

[0048] FIG. 4 is a construction sequence diagram of a foundation pit group in Embodiment 1 during staggered excavation (a, b, c, d, and f in FIG. 4 correspond to construction steps performed in sequence);

[0049] FIG. 5 is a schematic diagram of an inversion system in Embodiment 1 during operation;

[0050] FIG. 6 is a list display diagram of the inversion system in Embodiment 1; and

[0051] FIG. 7 is a schematic diagram of upper and lower synchronous construction of a top-down construction plate in Embodiment 1.

DESCRIPTION OF THE EMBODIMENTS

[0052] The embodiment of the present invention is described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed implementation modes and specific operation processes, but the scope of protection of the present invention is not limited to the embodiment described below.

[0053] Embodiment 1

[0054] A safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group provided by this embodiment is suitable for construction of the ultra-deep foundation pit group in a soft soil stratum, and includes the following steps:

[0055] One: a high-rigidity enclosure structure is adopted during design of a construction scheme.

[0056] The high-rigidity enclosure structure includes a diaphragm wall, and an underground wall (a lattice-shaped diaphragm wall) arranged inside a foundation pit. A construction sequence is as shown in FIG. 1, and includes: (1) a guide wall is constructed; (2) a groove is dug; (3) a steel reinforcement cage (containing a joint) is placed; (4) underwater concreting is performed; and (5) construction of the diaphragm wall is completed.

[0057] During the construction of the diaphragm wall of the foundation pit, the groove is formed by means of a hydraulic grab grooving machine, and the wall is protected with grout. The steel reinforcement cage is formed by once welding on a processing platform, and the diaphragm wall of each foundation pit is entirely lowered into the groove by a 450 t crane and a 150 t 7/26 crawler crane by means of a "lifting method". The underwater concreting is performed by means, 502674 of a double-tremie method, all concrete is commercial concrete, and a concrete truck directly performs concreting in place after arriving at the site. In addition, in order to ensure the clear width of a lining wall of a main structure, the diaphragm wall is considered to be placed outside by 50 mm according to the previous construction experience; the main enclosure structure is constructed according to a first phase; and an initial opening section is constructed first, and then a connecting section and a closing section are constructed. In order to reduce a cumulative error in the construction of the diaphragm wall, the maximum number of connecting sections should not exceed 5.

[0058] In this embodiment, according to the design of the high-rigidity enclosure structure, compared with other enclosure structures of bored piles or construction piles, the diaphragm wall in the present invention has higher rigidity and better anti-deformation ability; and the underground wall as a plain concrete wall for supporting an inner wall of the foundation pit has a better anti-deformation effect, and can be excavated and crushed in the construction of foundation pit excavation, thereby effectively ensuring stable control on lateral displacement and deformation of the diaphragm wall.

[0059] Two: a connecting beam is arranged between adjacent foundation pits.

[0060] As shown in FIG. 2, the connecting beam arranged between the adjacent foundation pits is anchored in corresponding crown beams, and the crown beams and first concrete supports of the adjacent foundation pits are connected as a whole. Meanwhile, the cross section size of the connecting beam at each corner is increased.

[0061] A size of the connecting beam is mainly 2,000 mm x 800 mm, but a size of the connecting beam at the corner is increased to 3,000 mm x 800 mm.

[0062] The concrete is C35 commercial concrete, and all concrete is poured in layers and vibrated by an immersion vibrator. When the concrete is vibrated, a vibrating rod should be inserted vertically into the concrete, and inserted into a lower layer that has not yet been initially set for 50-100 mm, so as to promote the combination of upper and lower layers. A distance between insertion points should not exceed 1.5 times of its radius of action. During use, it is necessary to get key points of "quick insertion and slow extraction" in vibration, vibration time of each insertion point should be 20-30 s, and a basis is that a concrete surface starts to bleed grout and does not bubble up. After the concrete is solidified, watering and coverage curing 8/26 should be carried out immediately, and curing time is not less than 14 days. The curing is carried 50267 4 out within 12-18 h after the concrete is poured. If it is poured in a hot and dry season, the curing time is advanced to within 8-14 h.

[0063] In this embodiment, according to the design of the connecting beam, the overall rigidity between the adjacent foundation pits is enhanced, and the top deformation of the foundation pit is reduced.

[0064] Three: drawing strip and skirt foundation reinforcements are arranged inside a foundation pit.

[0065] As shown in FIG. 3, a circle of the skirt foundation reinforcements are arranged inside the foundation pit in a manner of being close to a diaphragm wall, inner sides of the skirt foundation reinforcements are provided with the drawing strip reinforcements, and a reinforcement depth 1s 3 m below the top-down construction plate and 4 m below a base, thereby reducing heave deformation of an excavation face; and a circle of the skirt foundation reinforcements are arranged between adjacent foundation pits in a manner of clinging to the diaphragm wall, inner sides of the skirt foundation reinforcements are provided with the drawing strip reinforcements, and a reinforcement depth is 4 m below the base from the top of a water barrier under the ground, thereby enhancing the stability of a middle soil stratum under the condition of asynchronous excavation of the adjacent foundation pits. The foundation reinforcements adopt p850(@600 high-pressure rotary jet piles, and a construction process includes:

[0066] (1) Placement of a pile driver

[0067] A drilling rig is placed and kept horizontal, such that an axis of a drill pipe is vertically aligned with the center of a drilled hole. The drill pipe is kept vertical, and an inclination thereof should not be greater than 1.5%; and the distance between the drilling rig and a high-pressure grouting pump should not be too long, and the drill pipe of the drilling rig is positioned with a drill pipe guide frame.

[0068] (2) Penetration of a grouting pipe

[0069] The grouting pipe is inserted to a predetermined depth together with a drill bit of the rotary jet pile driver; and during this process, in order to prevent mud and sand from clogging a jet nozzle, water jetting and pipe insertion are carried out at the same time, where a water pressure should generally not exceed 1 MPa. If the pressure is too high, it is easy to collapse a 9/26 wall of the hole by jetting. LU502674

[0070] (3) Preparation of curing agent grout

[0071] 42.5 grade ordinary Portland cement 1s used as a curing agent for preparing the curing agent grout of a rotary jet pile. The cement content is determined according to the properties of reinforced soil and the requirement that the unconfined compressive strength of a single pile 1s not less than 1.0 MPa. À water-cement ratio of cement grout is determined by a test to be 1 : 1.5.

If cement storage time exceeds 3 months, a re-sampling test is carried out, and the cement is used according to its inspection result. The cement is reported to a supervision engineer for approval before use.

[0072] While the rotary jet pile penetrates into the grouting pipe, the curing agent grout (the cement grout) is stirred in a background, the grout is poured into a collecting hopper before press grouting, and the grout is prepared in strict accordance with design requirements.

[0073] (4) Jet grouting

[0074] The cement grout should be stirred within 1 h before jet grouting. When the jet nozzle reaches a design elevation, high-pressure water is first conveyed to clean the pipe, followed by the grout and compressed air, at the beginning of jet grouting. Rotary jet is performed at the bottom for 1 min, and rotation and lifting are carried out at the same time when a jet pressure and a jetted grout volume are reached. In order to prevent the grouting pipe from being twisted off, the rotation and lifting of the drill pipe must be continuous. When the grouting pipe cannot be lifted at one time and needs to be disassembled at multiple times, disassembly should be fast.

After the pipe is disassembled, a lap length of continuous jet should not be less than 10 cm, and the cement grout stirred for more than 4 h should not be used.

[0075] During the construction, the amount of grout spillover is controlled to be less than 20% of the grouting amount, and if it exceeds 20% or no grout spillover occurs at all, reasons are found out and corresponding measures are taken. A lifting speed may be 10-25 cm/min, a part that needs to be increased in reinforcement range or strength is re-jetted, and an actual pile top elevation should be 0.3-0.5 m higher than the design elevation.

[0076] (5) Pipe drawing and flushing

[0077] After the rotary jet construction is completed, the grouting pipe is quickly drawn out, equipment such as the grouting pipe is flushed with clean water, and no cement grout cannot be remained inside the pipe. In general, the grout is replaced with water to be jetted on the ground 10/26 to discharge all the grout in the grouting pump, the grouting pipe and a hose. LU502674

[0078] (6) Displacement of the pile driver

[0079] After the grouting pipe of the rotary jet pile driver is completely lifted out of the ground, a motor is turned off first, and then the pile driver is displaced to a new pile position.

[0080] In this embodiment, by the arrangement of the drawing strip and skirt foundation reinforcements, the rigidity of soil around the diaphragm wall and in the pit is enhanced to reduce the impact on the enclosure structure in foundation pit construction, thereby reducing the deformation of the foundation pit.

[0081] Four: a staggered height is controlled during excavation of the foundation pit.

[0082] A principle of staggered excavation of adjacent foundation pits includes "vertical layering, longitudinal sectioning, groove pulling in the middle, extension on two sides, soil remaining for wall protection, and completion of excavation and support within a limited time".

In the construction process, in order to complete the production of a bottom plate as soon as possible, the excavation adopts unprotected open cut excavation, and an open cut slope should be prevented from being too long and too high. When the foundation pit is excavated to a support erection work face, support erection is carried out immediately. After a concrete support reaches design strength, steel support erection is completed and an axial force is applied, a next unit of soil excavation can be performed. When adjacent foundation pit groups are not excavated synchronously, the staggered height of excavation faces should not be too large, generally 8 m, and excavation sections of the foundation pit group are ensured to be uniform, thereby preventing unbalanced loading.

[0083] As shown in FIG. 4, a construction process of staggered excavation is as follows:

[0084] (1) Referring to FIG. 4a, after the construction of the enclosure structure is completed, a foundation pit A is excavated first;

[0085] (2) Referring to FIG. 4b, the foundation pit A is excavated to a third layer, and a foundation pit B is excavated,

[0086] (3) Referring to FIG. 4c, a foundation pit AB group is excavated synchronously, and a top-down construction plate is first constructed for the foundation pit A;

[0087] (4) Referring to FIG. 4d, construction of an upper main structure of the top-down construction plate for the foundation pit A, and cover excavation of a lower foundation pit are carried out at the same time, and a top-down construction plate is constructed for the foundation 11/26 pit B; LU502674

[0088] (5) Referring to FIG. 4e, a bottom plate of the foundation pit A and the upper structure are constructed synchronously, and construction of an upper structure of the top-down construction plate for the foundation pit B and excavation of a lower foundation pit are carried out synchronously;

[0089] (6) Referring to FIG. 4f, the structure of the foundation pit A is roofed, and a bottom plate of the foundation pit B and the upper structure are constructed synchronously until the structure is roofed.

[0090] Five: a deformation trend of the foundation pit group is predicted by means of a data inversion system to guide key points of a next step of deformation control on the foundation pit.

[0091] An operation process of the inversion system includes: (1) on-site monitoring data is synchronized; (2) the monitoring data is uploaded to a cloud server; (3) the monitoring data is numerically simulated and inverted, (4) deformation of the foundation pit is numerically simulated, forwardly analyzed and predicted; and (5) a result is displayed. In this embodiment, the deformation of the enclosure structure due to the excavation of the foundation pit and the deformation of the surrounding environment are visually displayed in the inversion system.

According to a video and a safety factor, construction personnel decide the key points of the next step of deformation control on the foundation pit, and take the deformation control measures if necessary. The advantages are that more accurate numerical simulation can be carried out in combination with the on-site data to accurately predict the deformation of the foundation pit, and a dangerous area of the foundation pit can be discovered in advance, thereby guiding on-site construction to a certain extent.

[0092] Through inversion analysis and numerical simulation, the problem of deformation of the foundation pit and the problem of settlement deformation of the surrounding environment in the construction process are analyzed and predicted in time. A schematic diagram of an operation principle of an inversion system is as shown in FIG. 5.

[0093] First, construction personnel upload basic excavation information of a project to interact with data in a database, technical personnel export corresponding excavation information through the background database of a system, and monitoring personnel import real-time monitoring and measurement data matched with a construction progress; and then, the technical personnel carry out numerical simulation by means of large-scale geotechnical engineering 12/26 numerical simulation software GTS-NX on a local computer to obtain a numerical simulation 50267 4 result, and then upload it to a system interface in time for the construction personnel to use as a reference in the construction process.

[0094] Next, as shown in FIG. 6, in a list display part, the deformation of the enclosure structure due to the excavation of the foundation pit and the deformation of the surrounding environment are respectively displayed in a list. List display mainly includes a type of the project, a current excavation depth and an excavation condition thereof, a maximum deformation value, a safety factor and its corresponding more intuitive percentage progress bar under the current excavation depth, and a video of a deformation process of the enclosure structure caused between the excavation condition of the current excavation depth and a previous excavation condition displayed in a next column. According to the video and the safety factor, the construction personnel decide the key points of the next step of deformation control on the foundation pit, and take the deformation control measures if necessary.

[0095] Six: when the deformation amount exceeds a limit or the rate is too high, corresponding deformation control measures are taken.

[0096] The deformation amount exceeding the limit refers to that the enclosure structure of the foundation pit is laterally displaced by 40 mm or more, or that the enclosure structure of the foundation pit deforms by 0.4% h or more relative to the depth h of the foundation pit, or that the buildings around are displaced by 10 mm or more.

[0097] the displacement rate exceeding the early warning value refers to that a horizontal displacement rate of the enclosure structure of the foundation pit is greater than or equal to 2 mm/d, or that the displacement rate of the buildings around is greater than or equal to 1 mm/d.

[0098] There are corresponding deformation control measures as follows:

[0099] (1) Adjustment of foundation pit excavation subareas:

[0100] When the horizontal displacement rate of the enclosure structure of the foundation pit reaches 2 mm/d or the displacement rate of the buildings around reaches 1 mm/d, a sectional skip excavation construction scheme (a conventional and common mature scheme in the field) for the foundation pit is adopted, thereby reducing the "time and space effect" on the foundation pit during excavation, and reducing the adverse effect of wide-range unloading of soil during foundation pit excavation on adjacent buildings and the surrounding environment.

[0101] In addition, during actual construction, when displacement rates of an excavation 13/26 section and structures around are greater than or equal to 2 mm/d, excavation of the section 1950267 4 suspended, deformation remediation measures are taken, and the excavation construction section is adjusted to a relatively stable area for excavation.

[0102] (2) Loading (backfilling) and back-pressing in the pit:

[0103] When the horizontal displacement rate of the enclosure structure of the foundation pit or the displacement rate of the buildings around reaches 3 mm/d, the foundation pit tends to be instable, and unloading, and partial or complete backfilling and back-pressing are performed to reach a previous support elevation; and after deformation is stable and corresponding treatment measures are taken, excavation can be resumed.

[0104] (3) Pressurization of an axial force servo system for a steel support;

[0105] In general, the axial force servo system has the functions of real-time monitoring, alarming and automatic compensation of a support axial force, and the system can dynamically adjust the corresponding axial force according to preset axial force and upper and lower limits of each steel support. When the enclosure structure of the foundation pit is laterally displaced by 40 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.4% h, or the buildings around are displaced by 10 mm, the maximum value of the preset axial force of the axial force servo system needs to be adjusted, and the axial force 1s manually increased or reduced 1f necessary, thereby ensuring the stable deformation trend of the excavation section.

[0106] (4) Arrangement of a temporary steel support:

[0107] When the enclosure structure of the foundation pit is laterally displaced by 50 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.5% h, or the buildings around are displaced by 40 mm, a row of steel supports are additionally erected on an erection work face outside an existing steel/concrete support. The model and specification of the steel support and the preset axial force are determined by calculation, and the erection of the steel support should follow a principle of quality assurance and rapidity.

[0108] Seven: excavation of soil below a top-down construction plate and construction of an upper structure are carried out synchronously.

[0109] As shown in FIG. 7, in upper and lower synchronous construction of the top-down construction plate, after the top-down construction plate is poured and has strength, construction of the upper main structure and excavation of the lower soil are simultaneously carried out. In 14/26 lower cover excavation of the top-down construction plate, an excavator for excavating soil, 4502674 excavator for dumping the soil and a hydraulic grab for grabbing the soil are used in cooperation, and after excavation to the bottom of the pit, a concrete cushion, and a bottom plate of a main structure should be constructed in time, thereby shortening exposure time of the bottom of the pit.

The concrete cushion is made of fast-hardening concrete. After waterproof construction is completed, on-site construction organization is done well, and construction personnel are added to quickly bind steel bars of the bottom plate and pour concrete, thereby ensuring that the bottom of the foundation pit is sealed as soon as possible. Subsequently, a lower side wall and a stand column of the top-down construction plate are constructed. Before the construction of a side wall and a stand column of a bottom layer is completed, only a layer of structure (including a middle plate, a side wall and a stand column) on the top-down construction plate is constructed. In order to ensure the construction stability of the upper structure of the top-down construction plate, a steel support is left, and after the upper structure is completed and has design strength, the left support can be removed.

[0110] Eight: the remaining main structures are constructed in a bottom-up manner.

[0111] After a side wall, a stand column and a bottom plate of a lower layer of the top-down construction plate and a side wall, a stand column and a middle plate of an upper layer of the top-down construction plate are completed and have design strength, the remaining upper main structures (a side wall, a stand column, a middle plate and a top plate) are sequentially constructed in a bottom-up manner, and meanwhile, with the construction of the main structures, temporary lattice columns and left supports are removed until a main body is roofed.

[0112] According to the present invention, a deformation control scheme for foundation pit construction can be designed with reference to FIG. 1, FIG. 2 and FIG. 3 in the specific embodiment 1, an excavation scheme for construction is designed according to FIG. 4, the deformation control scheme is selected in the construction according to the principles as shown in FIG. 4, FIG. 5, FIG. 6 and FIG. 7, construction planning is carried out as shown in FIG. 4,

FIG. 5 and FIG. 6 introduce key schemes in detail, various measures are shared to ensure the stability of excavation of the foundation pit, and the deformation of asynchronous excavation of the adjacent ultra-deep foundation pits can be controlled by means of this scheme.

[0113] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements 15/26 made within the spirit and principle of the present invention shall be included in the scope Phi50067 4 protection of the present invention. 16/26

Claims

CLAIM LU502674

1. A safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group, comprising the following steps: S1: adopting a high-rigidity enclosure structure during design of a construction scheme; S2: arranging a connecting beam between adjacent foundation pits; S3: arranging drawing strip and skirt foundation reinforcements inside a foundation pit and between the adjacent foundation pits; S4: controlling a staggered height during excavation of the foundation pit; SS: predicting a deformation trend of the foundation pit group by means of a data inversion system to guide key points of a next step of deformation control on the foundation pit; S6: when the deformation amount of the foundation pit and buildings around the foundation pit exceeds a limit or the displacement rate exceeds an early warning value, taking corresponding deformation control measures; S7: synchronously carrying out excavation of soil below a top-down construction plate and construction of an upper structure; and S8: constructing the remaining main structures in a bottom-up manner.

2. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S1, the high-rigidity enclosure structure comprises a diaphragm wall, and an underground wall arranged inside the foundation pit; and a construction process comprises: (1) constructing a guide wall; (2) forming a groove by a grooving machine; (3) placing a steel reinforcement cage; (4) performing underwater concreting; and (5) completing construction of the diaphragm wall.

3. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S2, the connecting beam is anchored in crown beams of the adjacent foundation pits, and the crown beams and first concrete supports of the adjacent foundation pits are connected as a whole; and meanwhile, the cross section size of the connecting beam at each corner is increased.

4. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S3, a circle of the skirt foundation reinforcements are arranged inside the foundation pit in a manner of being close to a diaphragm wall, inner sides of the skirt foundation reinforcements are provided 17/26 with the drawing strip reinforcements, and a reinforcement depth is 3 m below the top-down, 0267 4 construction plate and 4 m below a base; a circle of the skirt foundation reinforcements are arranged between the adjacent foundation pits in a manner of clinging to the diaphragm wall, inner sides of the skirt foundation reinforcements are provided with the drawing strip reinforcements, and a reinforcement depth is 4 m below the base from the top of a water barrier under the ground; and the foundation reinforcements adopt 850@600 high-pressure rotary jet piles, and a construction process comprises: (1) measurement and positioning; (2) pre-stirring and sinking; (3) jet grout stirring and rising; (4) repeated stirring and sinking; (5) repeated stirring and rising; and (6) construction completion.

5. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S4, the staggered excavation height of the adjacent foundation pits is controlled to a maximum of no more than 8 m.

6. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S5, an operation process of the inversion system comprises: (1) synchronizing on-site monitoring data; (2) uploading the monitoring data to a cloud server; (3) numerically simulating and inverting the monitoring data; (4) numerically simulating, forwardly analyzing and predicting deformation of the foundation pit; and (5) displaying a result.

7. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S6, the deformation amount exceeding the limit refers to that the enclosure structure of the foundation pit is laterally displaced by 40 mm or more, or that the enclosure structure of the foundation pit deforms by 0.4% h or more relative to the depth h of the foundation pit, or that the buildings around are displaced by 10 mm or more; and the displacement rate exceeding the early warning value refers to that a horizontal displacement rate of the enclosure structure of the foundation pit is greater than or equal to 2 mm/d, or that the displacement rate of the buildings around is greater than or equal to 1 mm/d.

8. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S6, the corresponding deformation control measures comprise: 18/26

(1) adjustment of foundation pit excavation subareas: LU502674 when the horizontal displacement rate of the enclosure structure of the foundation pit reaches 2 mm/d or the displacement rate of the buildings around reaches 1 mm/d, a sectional skip excavation construction scheme for the foundation pit is adopted; and when displacement rates of an excavation section and structures around are greater than or equal to 2 mm/d, excavation of the section is suspended, and the excavation construction section is adjusted to an other stable area; (2) backfilling and back-pressing in the pit: when the horizontal displacement rate of the enclosure structure of the foundation pit or the displacement rate of the buildings around reaches 3 mm/d, unloading, and partial or complete backfilling and back-pressing are performed to reach a previous support elevation; (3) pressurization of an axial force servo system for a steel support: when the enclosure structure of the foundation pit is laterally displaced by 40 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.4% h, or the buildings around are displaced by 10 mm, the maximum value of a preset axial force of the axial force servo system is adjusted to ensure the stable deformation trend of the excavation section; and (4) arrangement of a temporary steel support: when the enclosure structure of the foundation pit is laterally displaced by 50 mm, the deformation of the enclosure structure relative to the depth h of the foundation pit reaches 0.5% h, or the buildings around are displaced by 40 mm, a row of steel supports are additionally erected on an erection work face outside an existing steel/concrete support.

9. The safe bottom-up and top-down combined construction method for asynchronous excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S7, upper and lower synchronous construction of the top-down construction plate comprises: after the top-down construction plate is poured and has strength, construction of the upper main structure and excavation of the lower soil are simultaneously carried out, and only one layer of structure can be constructed on the top-down construction plate before construction of a lower structure is completed; and a steel support is left in the construction of the upper structure of the top-down construction plate, and after the structure is completed and has design strength, the left support can be removed. 19/26

10. The safe bottom-up and top-down combined construction method for asynchronous 50267 4 excavation of an ultra-deep foundation pit group according to claim 1, wherein in the step S8, after the upper structure of the top-down construction plate is completed and has design strength, the remaining main structures are sequentially constructed in a bottom-up manner until the foundation pit is roofed. 20/26