Construction method of deep foundation pit of in-situ mucky soil

Abstract

The application discloses a deep foundation pit construction method for in-situ mucky soil, which comprises the following steps: dividing a to-be-processed area into a plurality of square blocks and a plurality of layer step regions; performing the following operations on each step region in the to-be-processed area in sequence from top to bottom: adding a solidifying agent, stirring and standing, digging out the mucky soil after solidification, and setting a protective layer; adding the solidifying agent into the mucky soil at the bottom of the lowermost layer step region, stirring uniformly and standing, and constructing after the mucky soil meets the design requirement of solidification strength. The mucky soil of the foundation pit is solidified by using a soil solidifying agent, and a single process is used for construction, so that the difficulty of excavation is reduced. The deep foundation pit construction method for in-situ mucky soil solidifies the bottom and the slope of the foundation pit, has simple construction technology and convenient on-site construction. The anti-seepage performance of the soil after solidification treatment is obviously improved, and the seepage of the foundation pit can be effectively reduced. The solidified soil has a relatively short setting time, saves the engineering construction period, and has good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit treatment technology, and relates to a method for constructing deep foundation pits in situ with silty soil. Background Technology

[0002] Silt has a high water content and low bearing capacity, making deep foundation pit excavation difficult, especially for pits 10 to 15 meters deep. Common treatment methods include pile foundation, soil replacement, cement mixing, and caisson foundation. These methods often involve high investment, long construction periods, and complex processes. In addition, the slopes of deep foundation pits are prone to collapse and groundwater leakage during excavation, posing a safety threat to workers and buildings inside the pit and affecting project safety.

[0003] In summary, existing technologies suffer from complex processes and high construction costs. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ deep foundation pit construction method for silty soil, which solves the problems of complex processes and high construction costs in the existing technology.

[0005] The technical solution adopted in this invention is an in-situ deep foundation pit construction method for silty soil, comprising the following steps:

[0006] S1. Divide the area to be processed into several square blocks and several stepped areas;

[0007] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0008] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0009] The invention is further characterized by:

[0010] S2 includes the following steps:

[0011] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0012] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0013] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0014] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the stepped area divided in step S1 is completed to the bottom stepped area, proceed to step S2.5; if the stepped area divided in step S1 is not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0015] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the design requirements for curing strength, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0016] Several square blocks are of the same size; several stepped areas are stacked vertically, with a depth of three to five meters. The length and width of the lower stepped area are five to seven meters smaller than those of the upper stepped area.

[0017] The mass ratio of the solidifying agent added to the area to be treated to the silty soil of the area to be treated is 10%-12%.

[0018] The first protective layer is the solidified soil wall retained at the upper outer edge of any stepped area when the solidified soil of that stepped area is excavated.

[0019] The width of the first protective layer is one to two meters; the second protective layer is in contact with the ground or the upper step area on one side, and with the lower step area or the solidified area at the bottom of the foundation pit on the other side.

[0020] The second protective layer is the solidified soil slope retained at the edge of any step area when the solidified soil is excavated; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:(1-1.5).

[0021] The third protective layer is a retaining wall of solidified soil set at the lower inner edge of any stepped area when the solidified soil of that stepped area is excavated.

[0022] The third protective layer is one to one and a half meters high and one to two meters wide. The outer edge of the third protective layer is attached to the second protective layer, and the inner edge is the same size as the lower step area on the horizontal plane. Several anchor rods are installed in the third protective layer for reinforcement. One end of the anchor rod extends out of the third protective layer, and the other end is embedded in the first protective layer of the lower step area.

[0023] The design requirements for solidification strength are as follows: the characteristic value of bearing capacity of solidified silty soil is not less than 200 kPa, the cohesion is not less than 280 kPa, and the permeability coefficient is not greater than 1×10⁻⁶. -8 cm / s, with an internal friction angle of 25 to 29 degrees.

[0024] The beneficial effects of this invention are: using a soil stabilizer to solidify the silty soil in the foundation pit, employing a single construction process, and reducing excavation difficulty; solidifying the bottom and slopes of the foundation pit, the construction process is simple and convenient on-site construction; the impermeability of the soil is significantly improved after solidification treatment, which can effectively reduce water seepage in the foundation pit; the solidified soil has a shorter solidification time, saving the construction period and resulting in better economic benefits. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the deep foundation pit after construction is completed in an embodiment of the present invention.

[0026] In the diagram, 1. Ground surface; 2. First step solidification area; 3. Second step solidification area; 4. Third step solidification area; 5. Anchor bolt; 6. First step solidified soil removal area; 7. Second step solidified soil removal area; 8. Third step solidified soil removal area; 9. Foundation pit bottom solidification operation area; 10. First protective layer; 11. Second protective layer; 12. Third protective layer. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] The in-situ deep foundation pit construction method for silty soil includes the following steps:

[0029] S1. Divide the area to be processed into several square blocks and several stepped areas;

[0030] Several square blocks are of the same size; several stepped areas are stacked vertically, with a depth of three to five meters. The length and width of the lower stepped area are five to seven meters smaller than those of the upper stepped area.

[0031] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0032] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0033] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0034] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0035] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the stepped area divided in step S1 is completed to the bottom stepped area, proceed to step S2.5; if the stepped area divided in step S1 is not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0036] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the design requirements for curing strength, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0037] The design requirements for solidification strength are as follows: the characteristic value of bearing capacity of solidified silty soil is not less than 200 kPa, the cohesion is not less than 280 kPa, and the permeability coefficient is not greater than 1×10⁻⁶. -8 cm / s, with an internal friction angle of 25 to 29 degrees.

[0038] The mass ratio of the solidifying agent added to the area to be treated to the silty soil of the area to be treated is 10%-12%.

[0039] The first protective layer is the solidified soil wall retained at the upper outer edge of any stepped area when the solidified soil of that stepped area is excavated.

[0040] The width of the first protective layer is one to two meters; the second protective layer is in contact with the ground or the upper step area on one side, and with the lower step area or the solidified area at the bottom of the foundation pit on the other side.

[0041] The second protective layer is the solidified soil slope retained at the edge of any stepped area when the solidified soil of that stepped area is excavated.

[0042] The ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:(1-1.5).

[0043] The third protective layer is a retaining wall of solidified soil set at the lower inner edge of any stepped area when the solidified soil of that stepped area is excavated.

[0044] The third protective layer is one to one and a half meters high and one to two meters wide. The outer edge of the third protective layer is attached to the second protective layer, and the inner edge is the same size as the lower step area on the horizontal plane. Several anchor rods are installed in the third protective layer for reinforcement. One end of the anchor rod extends out of the third protective layer, and the other end is embedded in the first protective layer of the lower step area.

[0045] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0046] When dividing the area to be treated into square blocks, if there are areas with large cross-sectional changes, the treatment blocks can be adjusted accordingly to facilitate construction. In this invention, dividing the area to be treated into blocks is beneficial for the arrangement of on-site work sequence, facilitates work control, and avoids repeated or incomplete curing. The amount of curing agent used can be selected after comprehensively considering the water content and silt type of the silty soil in the area to be treated. The anchor parameters are as follows: total height of four meters, plane spacing of two meters, anchor protruding 0.2 meters above the ground, and the diameter of the steel bar can be 20 mm to 25 mm of ribbed grade II steel bar.

[0047] This invention involves adding a certain proportion of soil stabilizer to the silt to perform in-situ stabilization treatment on the silt in the deep foundation pit. After stabilization treatment, the soil in the foundation pit is excavated. During the excavation process, a certain range of stabilized soil at the edge of the foundation pit is retained as a retaining structure, ultimately forming a working environment for the silty soil deep foundation pit, providing a site for the next construction operation. Both stabilization and excavation are carried out in a stepped manner.

[0048] This invention employs a single construction process, reducing construction and excavation difficulties; it significantly improves the seepage prevention performance of the soil surrounding the foundation pit, effectively reducing water seepage and drainage, thus ensuring the safety of the foundation pit; the solidified soil in this invention has a shorter solidification time, saving construction time and resulting in better economic benefits.

[0049] Example 1

[0050] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0051] S1. Divide the area to be processed into several square blocks and four-layer stepped areas;

[0052] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0053] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0054] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0055] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the four stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the four stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0056] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the design requirements for curing strength, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0057] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0058] Example 2

[0059] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0060] S1. Divide the area to be processed into several square blocks and a five-step area;

[0061] Several square blocks are of the same size; five stepped areas are stacked vertically, with a depth of four meters. The length and width of the lower stepped area are six meters smaller than those of the upper stepped area, respectively.

[0062] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0063] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0064] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0065] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0066] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the five stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the five stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0067] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0068] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0069] Example 3

[0070] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0071] S1. Divide the area to be processed into several square blocks and four-layer stepped areas;

[0072] Several square blocks are of the same size; four stepped areas are stacked vertically, with a depth of three meters. The length and width of the lower stepped area are five meters smaller than those of the upper stepped area.

[0073] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0074] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0075] The mass ratio of the solidifying agent added to the area to be treated to the silty soil of the area to be treated is 10%.

[0076] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0077] The width of the first protective layer is one meter; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:1; the height and width of the third protective layer are one meter each.

[0078] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0079] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the four stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the four stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0080] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0081] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0082] Example 4

[0083] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0084] S1. Divide the area to be processed into several square blocks and a six-layer stepped area;

[0085] Several square blocks are of the same size; six layers of stepped areas are stacked vertically, with a depth of five meters. The length and width of the lower layer of stepped areas are seven meters smaller than those of the upper layer of stepped areas, respectively.

[0086] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0087] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0088] The mass ratio of the solidifying agent added to the area to be treated to the silty soil of the area to be treated is 12%.

[0089] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0090] The width of the first protective layer is two meters; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:1.5; the height of the third protective layer is 1.5 meters and the width is two meters.

[0091] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0092] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the six stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the six stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0093] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0094] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0095] Example 5

[0096] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0097] S1. Divide the area to be processed into several square blocks and a five-step area;

[0098] Several square blocks are of the same size; five stepped areas are stacked vertically, with a depth of four meters. The length and width of the lower stepped area are six meters smaller than those of the upper stepped area, respectively.

[0099] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0100] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0101] The mass ratio of the solidifying agent added to the area to be treated to the silty soil in the area to be treated is 11%.

[0102] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0103] The width of the first protective layer is 1.5 meters; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:1.25; the height of the third protective layer is 1.25 meters and the width is 1.5 meters.

[0104] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0105] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the five stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the five stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0106] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0107] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0108] Example 6

[0109] This embodiment proposes an in-situ deep foundation pit construction method for silty soil, including the following steps:

[0110] S1. Divide the area to be processed into several square blocks and three-tiered stepped areas;

[0111] Several square blocks are of the same size; three layers of stepped areas are stacked vertically, with a depth of four meters. The length and width of the lower layer of stepped areas are six meters smaller than those of the upper layer of stepped areas, respectively.

[0112] S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer.

[0113] S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.2.

[0114] The mass ratio of the solidifying agent added to the area to be treated to the silty soil in the area to be treated is 11%.

[0115] S2.2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively;

[0116] The first protective layer is the solidified soil wall retained at the upper outer edge of any stepped area when the solidified soil of any stepped area is excavated;

[0117] The width of the first protective layer is 1.5 meters; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:1.

[0118] The third protective layer is one meter high and two meters wide;

[0119] S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.4.

[0120] The design requirements for solidification strength are: a characteristic value of bearing capacity of 250 kPa, a cohesion of 300 kPa, and a permeability coefficient of 1 × 10⁻⁶ after solidification of the silty soil. -8 cm / s, internal friction angle is 27 degrees;

[0121] S2.4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the three stepped areas divided in step S1 are completed to the bottom stepped area, proceed to step S2.5; if the three stepped areas divided in step S1 are not completed to the bottom stepped area, repeat steps S2.3 to S2.4.

[0122] S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively.

[0123] S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

[0124] like Figure 1 The diagram shows the structure after construction in this embodiment. Starting from the ground 1, three solidified areas are stacked vertically from top to bottom: a first-step solidified area 2, a second-step solidified area 3, and a third-step solidified area 4. Below the third-step solidified area 4 is a foundation pit bottom solidification work area 9. Within the first-step solidified area 2, the second-step solidified area 3, and the third-step solidified area 4, there are respectively a first-step solidified soil excavation area 6, a second-step solidified soil excavation area 7, and a third-step solidified soil excavation area 8. One side of the second protective layer 11 of the first-step solidified area 2 is the first protective layer 10 of the first-step solidified area 2, and the other side of the second protective layer 11 of the first-step solidified area 2 is the third protective layer 12 of the first-step solidified area 2. The first protective layer 10 of the first-step solidified area 2 is flush with the ground 1. Several anchor rods 5 are installed within the third protective layer 12 of the first-step solidified area 2. One end of the anchor rod 5 passes through the third protective layer 12 of the first-step solidified area 2 and is vertically inserted into the first protective layer of the second-step solidified area.

Claims

1. A method for constructing deep foundation pits in silty soil in situ, characterized in that, Includes the following steps: S1. Divide the area to be processed into several square blocks and several stepped areas; Several square blocks are of the same size; several stepped areas are stacked vertically, with a depth of three to five meters, and the length and width of the lower stepped area are five to seven meters smaller than the length and width of the upper stepped area, respectively. S2. For each step area in the area to be treated, perform the following operations in order from top to bottom: add curing agent, stir and let stand, excavate after the silty soil has solidified, and set a protective layer. S2.1 Add the curing agent to the silty soil of the area to be treated, stir evenly and let stand. After the silty soil of the area to be treated meets the design requirements for curing strength, proceed to step S2.

2. The mass ratio of the solidifying agent added to the area to be treated to the silty soil of the area to be treated is 10%-12%. S2.

2. Excavate the solidified soil in the upper step area of ​​the area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer in the upper step area respectively; The first protective layer is the solidified soil wall retained at the upper outer edge of any stepped area when the solidified soil of any stepped area is excavated; the width of the first protective layer is one to two meters; one side of the second protective layer is in contact with the ground or the upper stepped area, and the other side is in contact with the lower stepped area or the solidified area at the bottom of the foundation pit; The second protective layer is the solidified soil slope retained at the edge of any step area when the solidified soil is excavated; the ratio of the vertical height to the horizontal width of the solidified soil slope in the second protective layer is 1:(1-1.5). S2.3 Add the curing agent to the silty soil at the bottom of the excavated step area, stir evenly and let stand. After the silty soil in the area to be treated meets the design requirements for curing strength, proceed to step S2.

4. S2.

4. Excavate the solidified soil in the stepped area to be treated from the center outwards, and set the first protective layer, second protective layer and third protective layer for the stepped area respectively. When the stepped area divided in step S1 is completed to the bottom stepped area, proceed to step S2.5; if the stepped area divided in step S1 is not completed to the bottom stepped area, repeat steps S2.3 to S2.

4. The third protective layer is a retaining wall of solidified soil set at the lower inner edge of any step area when the solidified soil of any step area is excavated. The third protective layer has a height of 1 to 1.5 meters and a width of 1 to 2 meters; the outer edge of the third protective layer is attached to the second protective layer, and the inner edge is the same size as the lower step area on the horizontal plane; several anchor rods are installed in the third protective layer for reinforcement; one end of the anchor rod extends out of the third protective layer, and the other end is embedded in the first protective layer of the lower step area; S2.5 Add the curing agent to the silty soil in the lowest step area, stir evenly and let stand. After the silty soil in the treatment area meets the curing strength design requirements, dig out the cured soil in the lowest step area from the center to the surrounding area, and set the first protective layer and the second protective layer in the lowest step area respectively. The design requirements for the solidification strength are that the characteristic value of the bearing capacity of the solidified silty soil is not less than 200 kPa, the cohesion is not less than 280 kPa, and the permeability coefficient is not greater than 1 × 10⁻⁶. -8 cm / s, with an internal friction angle of 25 to 29 degrees; S3. Add curing agent to the silty soil at the bottom of the lowest step area, stir evenly and let stand. Once the silty soil meets the design requirements for curing strength, the construction is complete.

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