Construction method of pit-in-pit support row piles of deep foundation pit

Abstract

This invention provides a method for constructing retaining piles for a deep foundation pit within a pit, comprising the following steps: determining several sets of construction sequence groups by surveying the location of the retaining piles within the pit; for the preceding construction groups, excavating guide trenches and installing casings according to the construction sequence; constructing pile holes sequentially according to the construction sequence; each pile hole includes an empty drill section and an effective pile length section; connecting a simple hoist cage to a reinforcing cage at the bottom, lowering the simple hoist cage and reinforcing cage into the pile hole, with the top of the simple hoist cage connected to the pile hole opening; lowering a grouting pipe to pour underwater concrete to the top of the effective pile length section, and filling the empty drill section with fluidized solidified soil to the ground elevation; repeating steps 2-5 to construct the subsequent construction groups, forming the retaining piles within the pit; after the concrete has cured to the required standard, excavating the deep foundation pit and constructing the pit within the pit; and constructing a water-stop curtain on the outside of the retaining piles within the pit. This invention relates to the field of building construction technology and can solve the problems of high cost of backfilling empty drill sections with plain concrete and the easy cross-hole problems of backfilling empty drill sections with plain soil or yellow sand in the prior art.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a method for constructing retaining piles for deep foundation pits. Background Technology

[0002] Traditional deep foundation pit retaining wall pile reinforcement cages are installed using two long lifting bars. During the lowering process into the pile hole, the cage may rotate, causing the lifting bars to cross or even break, leading to the cage sinking to the bottom of the pile. This also makes it difficult to install the concrete pouring duct and ensures the correct pile top elevation.

[0003] Traditional deep foundation pit retaining wall piles use plain concrete to backfill the drilled sections, which increases costs. Plain concrete pile heads also affect earthwork excavation, further increasing construction costs. If plain soil or yellow sand is used to backfill the drilled sections, cross-hole phenomena can occur during adjacent pile hole construction, causing all backfill material to flow into adjacent holes. This not only increases the workload of drilling and cleaning, but also leads to the leakage of backfill material, exposing the pile holes and creating new safety hazards.

[0004] Therefore, there is a need to provide a method for constructing retaining piles for deep foundation pits within pits, which can solve the problems of high cost of plain concrete backfilling of empty drilled sections and easy cross-hole problems of plain soil or yellow sand backfilling of empty drilled sections in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing retaining piles for deep foundation pits, which can solve the problems of high cost of plain concrete backfilling of empty drilled sections and easy cross-hole problems of plain soil or yellow sand backfilling of empty drilled sections in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for constructing retaining piles for a deep foundation pit includes the following steps:

[0008] Step 1: Conduct planar and elevation measurements and layout of the retaining pile positions in the pit-in-pit, mark the pile positions, and determine the construction sequence of each pile, forming several sets of construction sequence groups;

[0009] Step 2: For the preliminary construction group among several construction sequence groups, excavate the guide trench of the pile body and install the casing in sequence according to the construction sequence, and prepare for mud circulation.

[0010] Step 3: For the pile locations where the guide trench was excavated and the casing was installed in Step 2, construct the pile holes sequentially according to the construction sequence; each pile hole includes a dry drilling section and an effective pile length section;

[0011] Step 4: Connect the bottom of the simple hoisting cage of the empty drilling section to the steel cage of the effective pile length section, lower the simple hoisting cage and steel cage into the pile hole, and connect the top of the simple hoisting cage to the pile hole opening for fixation.

[0012] Step 5: For each pile hole in the pre-construction group after the steel cage and simple hoist cage have been installed, the grouting pipe is lowered according to the construction sequence, and underwater concrete is poured. After the underwater concrete is poured to the top of the pile top of the effective pile length section, the grouting pipe is pulled out and the fluidized solidified soil is immediately poured to fill the empty drill section. The empty drill section is filled to the ground elevation to form a continuous rigid protective wall isolation body.

[0013] Step 6: Repeat steps 2 to 5 to construct each pile of the subsequent construction group in several construction sequence groups to form a pit-in-pit retaining pile.

[0014] Step 7: Curing the underwater concrete poured into the pile body of the retaining piles of the pit-in-pit. After the curing meets the standards, the foundation pit is excavated and the pit-in-pit is constructed.

[0015] Step 8: Construct a water-stop curtain on the outside of the retaining piles of the pit-within-the-pit. The water-stop curtain and the retaining piles of the pit-within-the-pit together form a closed soil-retaining and water-stopping system.

[0016] In step 1, several piles of the pit-within-a-pit retaining piles are arranged around the perimeter of the pit within the deep foundation pit. The piles are marked as several construction sequence groups, namely the first construction sequence group, the second construction sequence group, ..., the nth construction sequence group.

[0017] Each construction sequence group includes multiple piles, which are constructed using a combination of skip-driving and sequential construction methods, forming a pre-construction group and a subsequent construction group. The piles in the pre-construction group are staggered with the piles in the subsequent construction group.

[0018] In step 2, during the installation of the casing, multiple casings of the preceding construction group are installed in one go according to the construction sequence, and the deviation between the center of the casing and the center of the pile position is no more than 50mm.

[0019] The top of the effective pile length section is located in the deep foundation pit. The effective pile length section uses a steel cage, while the empty drilling section uses a simple hoisting cage. The top elevation of the empty drilling section is consistent with the ground elevation.

[0020] The steel cage includes several main bars arranged vertically at intervals, spiral stirrups surrounding the outside of the main bars, and multiple reinforcing stirrups arranged at intervals along the axial direction of the main bars. The main bars are anchored upwards into the simple hanging cage.

[0021] The simple suspended cage includes several vertically spaced lifting rods and multiple reinforcing hoops spaced along the axial direction of the lifting rods.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention uses a simple cage with a rigid frame and steel lifting rings to fix the steel cage, which can ensure the placement accuracy of the steel cage, prevent the steel cage from falling apart, deforming, having excessive elevation control deviation, and solve problems such as the steel cage getting stuck in the grouting pipe during installation.

[0024] 2. This invention adopts a construction sequence of skip-driving and sequential construction, and backfills the empty drilled section with fluidized solidified soil. This avoids risks such as cross-hole, hole collapse, drill hole tilting, and rebar cage installation deviation during the construction of adjacent piles. It solves the cost waste problem caused by conventional concrete backfilling of empty drilled sections and the construction quality problem of deep foundation pit retaining piles. It greatly reduces the construction safety risk after pile hole backfilling, increases the safety guarantee during the construction of deep foundation pit retaining piles, and reduces the amount of excess concrete pile heads to be removed during foundation pit excavation.

[0025] 3. The construction method of the present invention is simple to operate and easy to implement. It is suitable for complex environments in water-rich areas and for retaining pile construction in areas that require the excavation of deep foundation pits and pits within pits (such as elevator shafts, ultra-deep water collection wells, underground treasure troves, and underground laboratories). Attached Figure Description

[0026] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0027] Figure 1 This is a schematic cross-sectional view of the construction method for the retaining pile construction of deep foundation pits in this invention.

[0028] Figure 2 This is a schematic diagram of the steel cage and simple hoisting cage in the construction method of retaining piles for deep foundation pits in this invention;

[0029] Figure 3 A schematic diagram of the construction sequence in the construction method of retaining piles for deep foundation pits in this invention.

[0030] In the diagram, 1 is underwater concrete, 2 is fluidized solidified soil, 3 is a steel cage, 4 is a simple hoisting cage, 5 is a steel lifting ring, 6 is a steel cage reinforcing stirrup, 7 is a main reinforcement bar, 8 is a spiral stirrup, and 9 is a water-stop curtain. Detailed Implementation

[0031] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the reinforced structure and construction method for the top water-resistant structure of an explosion-proof wall proposed in this invention. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0032] A method for constructing retaining piles for a deep foundation pit includes the following steps:

[0033] Please see the appendix Figure 1 Step 1: Conduct planar and elevation measurements and layout of the retaining pile positions in the pit-in-pit, mark the pile positions, and determine the construction sequence of each pile, forming several construction sequence groups.

[0034] In the construction method of retaining piles for deep foundation pits in this invention, the excavation depth of the foundation pit is L2, the excavation depth of the pit within the pit is L3, and the pile diameter of the retaining piles within the pit is determined according to the design value; before construction, site leveling, drawing review and technical briefing are completed.

[0035] In step 1, several piles of the pit-within-a-pit retaining piles are arranged around the perimeter of the pit-within-a-pit of the deep foundation pit. The piles are marked as several construction sequence groups, namely the first construction sequence group, the second construction sequence group, ..., the nth construction sequence group (n is a natural number).

[0036] Please see the appendix Figure 3 Each construction sequence group includes multiple piles, which are constructed using a combination of skip-driving and sequential construction to form a pre-construction group and a subsequent construction group. The piles in the pre-construction group are staggered with the piles in the subsequent construction group.

[0037] For example: Each construction sequence group includes 5 piles in sequence. The first pile is marked as I, the third pile as II, and the fifth pile as III. I, II, and III are the first construction groups. The second pile is marked as IV and the fourth pile as V. IV and V are the subsequent construction groups.

[0038] Step 2: For the first construction group among several construction sequence groups, excavate the guide trench of the pile body and install the casing in sequence according to the construction sequence, and prepare for mud circulation.

[0039] During the installation of casings, multiple casings of the preceding construction group should be installed in the order of construction I, II, and III. The deviation between the center of the casing and the center of the pile position should not exceed 50mm. The installation depth of the casing should meet the requirements of borehole stability and mud slurry backflow.

[0040] A mud circulation system was established to prepare mud that meets the requirements for wall protection. The mud's specific gravity, viscosity, and sand content meet the drilling specifications for complex formations.

[0041] Excavation of the guide trench, installation of the casing, and construction of the mud circulation system are all standard construction procedures in this field and will not be described in detail here.

[0042] Step 3: For the pile positions where the guide trench was excavated and the casing was installed in Step 2, construct the pile holes in sequence according to the construction order; each pile hole includes an empty drilling section (length L4) and an effective pile length section (length L5), the hole depth L1=L4+L5, and the hole interval meets the requirements of initial setting of concrete and consolidation of fluidized solidified soil.

[0043] Referring to relevant specifications, the construction testing time for adjacent pile holes should not be less than 36 hours, or the distance between pile holes should not be less than 4 times the pile diameter. Therefore, the construction sequence of each pile hole should be determined first, and then the pile hole construction should proceed to avoid simultaneous drilling of adjacent piles, which could lead to cross-hole formation or collapse. Preferably, the pile holes can be constructed using the existing mud-wall drilling and grouting pile construction technology; the construction process will not be elaborated here.

[0044] The top of the effective pile length section is located in the deep foundation pit, and the elevation of the top of the effective pile length section is slightly higher than the bottom elevation of the foundation pit. The effective pile length section adopts the steel cage 3 required by the design, and the empty drilling section adopts the simple hoisting cage 4. The top elevation of the empty drilling section is consistent with the ground elevation to ensure that the steel cage 3 is installed smoothly and the elevation is fixed.

[0045] The empty drilled section needs to be removed during the deep foundation pit excavation, and the effective pile length section belongs to the pile body stress section.

[0046] Please see the appendix Figure 2 Step 4: The bottom of the simple cage 4 of the empty drilling section is connected to the steel cage 3 of the effective pile length section. The simple cage 4 and the steel cage 3 are lowered into the pile hole. The top of the simple cage 4 is connected to the pile hole opening and fixed by the steel lifting ring 5.

[0047] Preferably, the top of the simple cage 4 is welded and locked to the steel reinforcement ring 5, which can accurately control the pile top elevation and prevent the steel reinforcement cage 3 from floating, sinking, deviating or getting stuck.

[0048] The steel cage 3 includes several main bars 7 arranged vertically at intervals, spiral stirrups 8 arranged around the outside of the main bars 7, and multiple steel cage reinforcing stirrups 6 arranged at intervals along the axial direction of the main bars 7. The main bars 7 are anchored upwards (anchorage length of L6) into the simple hanging cage 4.

[0049] Preferably, the main reinforcement 7 extends upward into the simple cage 4 and is fixed by lap welding to ensure that the bottom of the simple cage 4 is reliably connected to the top of the steel cage 3.

[0050] The simple suspended cage 4 includes several vertically spaced lifting rods and multiple cage reinforcing hoops spaced along the axial direction of the lifting rods.

[0051] Preferably, the lifting bars can be made of φ14~φ18 steel bars, with four lifting bars arranged at equal intervals. The four lifting bars are welded and fixed to the steel lifting rings 5. The length of the lifting bars and the length of the steel lifting rings 5 ​​meet the anti-buoyancy and elevation stability requirements of the steel cage 3. The reinforcing hoops of the cage can be made of φ14~φ18 steel bars, with one reinforcing hoop every 2~3m. The lifting bars and the reinforcing hoops of the cage form a rigid skeleton. The length of the simple cage 4 is determined according to the length L4 of the empty drilling section. When transportation or installation is inconvenient, it can be manufactured in sections and installed by connecting sections.

[0052] Step 5: For each pile hole in the pre-construction group after the installation of the reinforcing cage 3 and the simple hoisting cage 4, lower the grouting pipe according to the construction sequence and pour underwater concrete 1. After the underwater concrete 1 is poured to the top of the pile over-grouting section of the effective pile length, the grouting pipe must be pulled out to prevent the subsequent grouting of fluidized solidified soil from mixing into the underwater concrete of the effective pile length and forming quality hazards such as mud inclusion. Immediately pour fluidized solidified soil 2 to fill the empty drill section. Fill the empty drill section to the ground elevation to form a continuous rigid protective wall isolation body to prevent cross-hole, hole collapse, drilling deviation, and reinforcing cage installation deviation during the construction of the subsequent construction group (i.e., piles IV and V).

[0053] The unfilled section can be selectively filled with fluidized solidified soil according to site geology, schedule, and cost requirements. It can be backfilled in its entirety or partially, and the backfill density meets safety requirements. The fluidized solidified soil backfill is continuous and dense, without voids or segregation, and the final setting time is controlled within 6-12 hours. The 24-hour strength meets the requirements for subsequent construction disturbance.

[0054] The fluidized solidified soil hardens basically at room temperature in 24 hours. After 24 hours, the fluidized solidified soil backfilled by the preceding construction group is not affected by the operation of operators and small machinery and equipment, and can meet the pile hole construction conditions of the subsequent construction group.

[0055] Step 6: Repeat steps 2 to 5 to construct the piles of the subsequent construction groups in several construction sequence groups to form a pit-in-pit retaining pile.

[0056] Steps 2 to 5 complete the pile construction of multiple piles (i.e., piles marked I, II, and III) in each preliminary construction group. In step 6, the same process as for piles I, II, and III is used to complete the pile construction of piles marked IV and V. The pile construction process of piles IV and V will not be described again here.

[0057] Step 7: Curing the underwater concrete 1 poured into the pile body of the retaining piles of the pit-in-pit. After the curing meets the standards, the deep foundation pit excavation and pit-in-pit construction are carried out.

[0058] During the excavation of the foundation pit and the construction of the pit within the pit, the fluidized solidified soil in the empty drilling section is easy to remove, avoiding the chiseling operation of the concrete pile head in the existing technology, which can effectively reduce costs and construction period.

[0059] Step 8: Construct a water-stop curtain 9 on the outside of the retaining piles of the pit-in-pit. The water-stop curtain 9 and the retaining piles of the pit-in-pit together form a closed soil retaining and water-stopping system, which is suitable for pit-in-pit construction conditions such as water-rich, soft soil, and complex geology, and improves the overall stability and seepage prevention capacity.

[0060] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for constructing retaining piles for a deep foundation pit within a pit, characterized in that, Includes the following steps: Step 1: Conduct planar and elevation measurements and layout of the retaining pile positions in the pit-in-pit, mark the pile positions, and determine the construction sequence of each pile, forming several sets of construction sequence groups; Step 2: For the preliminary construction group among several construction sequence groups, excavate the guide trench of the pile body and install the casing in sequence according to the construction sequence, and prepare for mud circulation. Step 3: For the pile locations where the guide trench was excavated and the casing was installed in Step 2, construct the pile holes sequentially according to the construction sequence; each pile hole includes a dry drilling section and an effective pile length section; Step 4: The bottom of the simple hoisting cage (4) of the empty drilling section is connected to the steel cage (3) of the effective pile length section. The simple hoisting cage (4) and the steel cage (3) are lowered into the pile hole. The top of the simple hoisting cage (4) is connected to the pile hole opening and fixed. Step 5: For each pile hole in the pre-construction group where the steel cage (3) and simple hoist cage (4) have been installed, the grouting pipe is lowered according to the construction sequence, and underwater concrete (1) is poured. After the underwater concrete (1) is poured to the top of the pile top of the effective pile length section, the grouting pipe is pulled out and the fluidized solidified soil (2) is poured immediately to fill the empty drill section. The empty drill section is filled to the ground elevation to form a continuous rigid protective wall isolation body. Step 6: Repeat steps 2 to 5 to construct each pile of the subsequent construction group in several construction sequence groups to form a pit-in-pit retaining pile. Step 7: Curing the underwater concrete (1) poured into the pile body of the retaining piles of the pit-in-pit. After the curing meets the standards, the foundation pit is excavated and the pit-in-pit is constructed. Step 8: Install a water-stop curtain (9) on the outside of the retaining piles of the pit-in-pit. The water-stop curtain (9) and the retaining piles of the pit-in-pit together form a closed soil retaining and water-stopping system.

2. The method of claim 1, wherein the method further comprises: In step 1, several piles of the pit-within-a-pit retaining piles are arranged around the perimeter of the pit within the deep foundation pit. The piles are marked as several construction sequence groups, namely the first construction sequence group, the second construction sequence group, ..., the nth construction sequence group.

3. The method of claim 2, wherein the method further comprises: Each construction sequence group includes multiple piles, which are constructed using a combination of skip-driving and sequential construction methods, forming a pre-construction group and a subsequent construction group. The piles in the pre-construction group are staggered with the piles in the subsequent construction group.

4. The method of claim 1, wherein the method further comprises: In step 2, during the installation of the casing, multiple casings of the preceding construction group are installed in one go according to the construction sequence, and the deviation between the center of the casing and the center of the pile position is no more than 50mm.

5. The method of claim 1, wherein the method further comprises: The top of the effective pile length section is located in the deep foundation pit. The effective pile length section adopts a steel cage (3), and the empty drilling section adopts a simple hoisting cage (4). The top elevation of the empty drilling section is consistent with the ground elevation.

6. The method of claim 1 or 5, wherein The steel cage (3) includes several main bars (7) arranged vertically at intervals, spiral stirrups (8) arranged around the outside of the main bars (7), and multiple steel cage reinforcing stirrups (6) arranged at intervals along the axial direction of the main bars (7). The main bars (7) are anchored upwards into the simple hanging cage (4).

7. The method of claim 1 or 5, wherein The simple hanging cage (4) includes several vertically spaced hanging bars and multiple hanging cage reinforcing hoops spaced along the axial direction of the hanging bars.

Images