Steel sheet pile support construction method for soft soil layer

Abstract

The invention provides a steel sheet pile support construction method for a soft soil layer, which comprises the following steps of: preparing a slurry discharge ditch and a slurry pit in advance before construction, preparing cement slurry, drilling, and respectively performing high-pressure jet grouting from the middle of each side of a foundation pit to two sides to form a cement soil enclosure wall as a waterproof curtain; the field is leveled to the top elevation of the supporting piles, a foundation pit is excavated to 0.5 m below the top elevation of the supporting piles, and Larsen steel sheet pile construction is conducted; and after the concrete cushion layer and the bottom plate are poured and the main body structure is constructed to the horizontal construction joint, a plain concrete support replacement belt is arranged between the construction body and the fender post, the second support and the waist beam are dismantled, construction of the main body structure continues after dismantling, soil body backfilling is conducted, the first support and the waist beam are dismantled, backfilling continues to be conducted to the ground elevation, and the steel sheet piles are pulled out. The method is suitable for foundation pit supporting construction of the water-rich soft soil layer.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, and in particular to a steel sheet pile support construction method for a soft soil layer. Background Art

[0002] Foundation pit engineering is highly regional. For example, foundation pit engineering in foundations with different engineering geological and hydrogeological conditions such as soft clay foundation and loess foundation is very different. Foundation pit engineering mainly includes two parts: support system design and earth excavation. The design and construction of the support system and earth excavation should be adapted to local conditions and carried out according to local conditions. Whether the construction organization of earth excavation is reasonable will play an important role in the success of the support system.

[0003] Soft soil refers to soil areas with high natural water content, low shear strength and high compressibility. Such soil layers usually have weak bearing capacity, which affects the stability and safety of building structures. How to efficiently handle soft soil layers and support them while ensuring construction efficiency has become a key link in ensuring building stability and safety. Pile-anchor support can utilize the gripping and friction between cement slurry anchor bodies and rock and soil bodies. Therefore, it is widely used in foundation pit support projects and has become a relatively mature technology in foundation pit support in recent years. However, there are also shortcomings in anchor cable construction. For example, in silt soil layers, anchor cables are prone to hole collapse and neck shrinkage during construction, and the construction quality is difficult to guarantee; the lateral friction resistance provided by silt soil is small, resulting in insufficient anchoring force for the anchor cables, which in turn causes a large loss of prestress, resulting in large deformation of the foundation pit support and risks. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a steel sheet pile support construction method for soft soil layers. The steel sheet pile support construction speed is fast and has strong pressure bearing capacity. At the same time, high-pressure jet grouting piles are used to reinforce the foundation pit foundation and improve the stability of the foundation pit support.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] A steel sheet pile support construction method for soft soil layer, comprising the following steps:

[0007] A. Jet grouting pile foundation reinforcement

[0008] Before construction, prepare drainage trenches and mud pools, prepare cement slurry, drill holes according to control piles and design drawings, and perform high-pressure jet grouting from the middle of each side of the foundation pit to both sides to form a cement soil retaining wall as a water-proof curtain with a permeability coefficient of no more than 10 -4 cm / s;

[0009] B. Steel sheet pile driving and foundation pit excavation

[0010] Level the site to the top elevation of the support piles, excavate the foundation pit to 0.5m below the top elevation of the support piles, first construct the Larsen steel sheet piles on the side close to the building, and then construct the Larsen steel sheet piles on the other side; excavate to 0.5m below the bottom elevation of the first support, construct the first support, excavate to 0.5m below the bottom elevation of the second support, and construct the second support; excavate the earth to the bottom of the pit, and dig a drainage ditch on the side close to the foundation pit;

[0011] C. Demolition

[0012] After pouring the concrete cushion layer and bottom plate, and constructing the main structure to the horizontal construction joint, a plain concrete support strip is placed between the construction body and the retaining piles. After the strength of the main structure and the plain concrete reaches 75% of the design strength, the second support and waist beam are removed, and the construction of the main structure is continued after the removal. After the concrete strength of the main structure reaches 75% of the design strength, the soil is backfilled to the bottom of the first support, the first support and waist beam are removed, and the backfill is continued to the ground elevation, and the steel sheet piles are removed.

[0013] The foundation pit excavation of the present invention should be symmetrically excavated in layers, advanced in layers, and the layer height should not exceed 1m. The soft soil layer is mostly silt and organic soil, and the structure is unstable, so it is suitable to excavate in layers and the layer height should not exceed 1m.

[0014] In step C of the present invention, the first support is backfilled with lime soil at a ratio of 2:8, and the first support is backfilled with plain soil to the ground level. After the backfill soil is accepted, the steel sheet piles are removed. The stability and bearing capacity requirements below the first support are higher, and the lime soil backfill is 2:8.

[0015] Preferably, during the construction of the tunnel foundation pit, the ordinary section of the foundation pit backfill material above the first support is made of plain soil, and the 500mm range on the side wall and top plate of the crossing section is made of medium-coarse sand, and the backfill density is not less than 0.94. Since it is difficult to ensure that the compaction degree of the 500mm backfill range on the side wall and top plate meets the design requirements, the use of medium-coarse sand in the 500mm range can ensure the compaction degree and prevent subsequent cracking of the restored road surface.

[0016] In the construction project of the rotary jet grouting of the present invention, the abandoned slurry is discharged into the mud pool, and after sedimentation and condensation, it is transported to the outside for storage or abandonment.

[0017] The overlap spacing between the jet grouting piles of the present invention is not less than 200mm, and the spacing between the jet grouting piles and the Larsen steel sheet piles is 1m. If the overlap spacing is too large, it will lead to the failure to form a complete reinforcement system between the piles, which is prone to uneven settlement, and the water-stop curtain will also lose its due anti-seepage function. The overlap spacing between the piles is not less than 200mm, and the spacing between the jet grouting piles and the Larsen steel sheet piles is 1m, which is conducive to the stability of the foundation pit.

[0018] The water-cement ratio of the cement slurry of the present invention is 1.0, and the cement content is not less than 580kg / m 3 , slurry density 1.5kg / l. Make the permeability coefficient no greater than 10 -4 cm / s.

[0019] During the grouting process, the cement slurry should be prevented from settling to reduce its concentration. Preferably, the mixing time after each feeding should not be less than 3 minutes, and the slurry should be poured into the collection hopper before grouting, and the cement slurry should be used as soon as it is mixed.

[0020] Preferably, the compressed air pressure for spraying is 0.5-0.7 MPa, the air volume is 1500-3000 l / min, the nozzle diameter is 2.1 mm, the drill rod lifting speed is 10-15 cm / min, and the slurry volume is 60-70 l / min.

[0021] In step C of the present invention, the piles are pulled out at intervals with a spacing of not less than 2 m, and the gaps left by the pile pulling are promptly filled with 1:1 cement mortar.

[0022] After the steel sheet piles have completed their supporting functions, they need to be pulled out and reused, so the pores left in the soil need to be backfilled. In foundation pit projects with high requirements for surrounding environmental protection, the backfill quality requirements are high, and the post-processing is also more troublesome. Preferably, the cement of the cement mortar uses silicate cement with a strength grade not lower than PO 42.5, a water-cement ratio of 0.55, and a grouting pressure of no more than 0.1MPa, which is conducive to the stability of the soil. The grouting slurry is added with an accelerator accounting for 2% of the total mass, and the grouting is done while pulling out and pouring.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention takes both retaining and water-stopping into consideration, and adopts the combined effect of steel sheet support piles and rotary jet grouting water-stopping curtains. The composite support structure of Larsen steel sheet piles and high-pressure rotary jet grouting piles effectively solves the water-stopping problem in the foundation pit support and construction process, and is suitable for the foundation pit support structure in water-rich soft soil layers.

[0025] 2. The water-cement ratio of the cement slurry prepared by the present invention for rotary jet grouting is 1.0, and the cement content is not less than 580kg / m 3 , slurry density 1.5kg / l. Make the permeability coefficient no greater than 10 -4 cm / s; strictly control the spraying speed and air pressure to form a cement soil retaining wall as a waterproof curtain, with a permeability coefficient of no more than 10 -4 cm / s, stably strengthening the foundation.

[0026] 3. Due to the higher requirements for stability and bearing capacity under the first support, 2:8 lime soil backfill is used. During the construction of the tunnel foundation pit, since it is difficult to ensure that the compaction degree of the 500mm backfill range on the side wall and the top plate meets the design requirements, the ordinary section of the foundation pit backfill material above the first support is plain soil, and the 500mm range on the side wall and the top plate of the crossing section structure is medium-coarse sand. The backfill density is not less than 0.94, which ensures the structural stability of the tunnel foundation pit in the water-rich soft soil layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the support structure layout of the soft soil layer of the present invention. DETAILED DESCRIPTION

[0028] In order to more clearly and in detail illustrate the technical solution of the present invention, the present invention is further described below through relevant embodiments. The following embodiments are only for specific explanation of the implementation method of the present invention, and do not limit the protection scope of the present invention.

[0029] Example 1

[0030] A steel sheet pile support construction method for soft soil layer, comprising the following steps:

[0031] A. Jet grouting pile foundation reinforcement

[0032] Before construction, prepare drainage trenches and mud pools, prepare cement slurry, drill holes according to control piles and design drawings, and perform high-pressure jet grouting from the middle of each side of the foundation pit to both sides to form a cement soil retaining wall as a water-proof curtain with a permeability coefficient of no more than 10 -4 cm / s.

[0033] B. Steel sheet pile driving and foundation pit excavation

[0034] Level the site to the top elevation of the support piles, excavate the foundation pit to 0.5m below the top elevation of the support piles, first construct the Larsen steel sheet piles on the side close to the building, and then construct the Larsen steel sheet piles on the other side; excavate to 0.5m below the bottom elevation of the first support, construct the first support, excavate to 0.5m below the bottom elevation of the second support, and construct the second support; excavate the earth to the bottom of the pit, and dig a drainage ditch on the side close to the foundation pit;

[0035] C. Demolition

[0036] After pouring the concrete cushion layer and bottom plate, and constructing the main structure to the horizontal construction joint, a plain concrete support strip is placed between the construction body and the retaining piles. After the strength of the main structure and the plain concrete reaches 75% of the design strength, the second support and waist beam are removed, and the construction of the main structure is continued after the removal. After the concrete strength of the main structure reaches 75% of the design strength, the soil is backfilled to the bottom of the first support, the first support and waist beam are removed, and the backfill is continued to the ground elevation, and the steel sheet piles are removed.

[0037] Example 2

[0038] This embodiment is based on embodiment 1:

[0039] The foundation pit excavation should be carried out symmetrically in layers, with the layer height not exceeding 1m.

[0040] In the above step C, the soil below the first support is backfilled with 2:8, and the soil above the first support is backfilled to the ground level. After the backfill soil is accepted, the steel sheet piles are removed. The stability and bearing capacity requirements below the first support are higher, and the soil backfill is 2:8.

[0041] Example 3

[0042] This embodiment is based on embodiment 1:

[0043] The foundation pit excavation should be carried out symmetrically in layers, with the layer height not exceeding 1m.

[0044] During the construction of the tunnel foundation pit, 2:8 gray soil backfill is used under the first support, plain soil is used for the ordinary section of the foundation pit backfill material above the first support, and medium-coarse sand is used within 500mm on the side walls and top plate of the crossing section structure. The density of the backfill is not less than 0.94.

[0045] Example 4

[0046] This embodiment is based on embodiment 1:

[0047] During the construction of rotary jet grouting, the waste slurry is discharged into the mud pool, and after sedimentation and condensation, it is transported to off-site storage or disposal.

[0048] The overlap spacing between the jet grouting piles is not less than 200 mm, and the spacing between the jet grouting piles and the Larsen steel sheet piles is 1 m.

[0049] The water-cement ratio of the cement slurry is 1.0, and the cement content is not less than 580kg / m 3 , pulp density 1.5kg / l.

[0050] The mixing time after each addition of materials shall not be less than 3 minutes. Pour the slurry into the collecting hopper before grouting and the cement slurry can be used as soon as it is mixed.

[0051] The compressed air pressure for spraying is 0.5-0.7 MPa, the air volume is 1500-3000 l / min, the nozzle diameter is 2.1 mm, the lifting speed is 10-15 cm / min, and the slurry volume is 60-70 l / min.

[0052] Example 5

[0053] This embodiment is based on embodiment 1:

[0054] In the above-mentioned step C, the piles are pulled out at intervals with a spacing of not less than 2m, and the gaps left by the piles are promptly filled with 1:1 cement mortar.

[0055] The cement of the cement mortar is silicate cement with a strength grade not lower than PO 42.5, the grouting pressure is not greater than 0.1MPa, and the grouting slurry is added with an accelerating agent accounting for 2% of the total mass, and the grouting is performed while pulling.

[0056] Example 6

[0057] The steel sheet pile support construction method of the present invention is used to construct the supporting overhead pipe gallery project for the high-voltage line channel in the east and west areas of Jiangyin. The starting point is located at the open space outside the wall of the built 220KV Chicuo substation, and the end point is at the open space outside the wall of the built 220KV Shunbao substation. The construction scale of the cable civil engineering channel of this project is 10 220kV lines and 8 110kV lines. The length of the newly built cable line is 7000 meters. The entire line is constructed with overhead pipe gallery, open-cut cable tunnel and top-pipe tunnel. The open-cut tunnel laying path is 700 meters long, the top-pipe tunnel laying path is 150 meters long, and the overhead pipe gallery path is 6150 meters long.

[0058] Larsen steel sheet piles are produced by roller cold bending. The steel sheet piles are driven into the foundation by a pile driver to connect them to form a steel sheet pile wall, which is used to retain soil and water. The support effect is reliable, the construction method is simple, and the operation is convenient. High-pressure rotary jet piles are used to reinforce the silt below the base elevation in the foundation pit to improve the stability of the foundation pit support. During the support removal process, 2:8 gray soil is used for backfilling below the first support, and plain soil is used for the ordinary section of the foundation pit backfill material above the first support. Medium-coarse sand is used within 500mm on the side wall and top plate of the crossing section structure, and the backfill density is not less than 0.94. This construction method reduces the project cycle, reduces the construction cost, and improves the construction efficiency.

[0059] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A steel sheet pile support construction method for soft soil layer, characterized in that: The following steps are involved: A. Jet grouting pile foundation reinforcement Before construction, prepare drainage trenches and mud pools, prepare cement slurry, drill holes according to control piles and design drawings, and perform high-pressure jet grouting from the middle of each side of the foundation pit to both sides to form a cement soil retaining wall as a water-proof curtain with a permeability coefficient of no more than 10 -4 cm / s. B. Steel sheet pile driving and foundation pit excavation Level the site to the top elevation of the support piles, excavate the foundation pit to 0.5m below the top elevation of the support piles, first construct the Larsen steel sheet piles on the side close to the building, and then construct the Larsen steel sheet piles on the other side; excavate to 0.5m below the bottom elevation of the first support, construct the first support, excavate to 0.5m below the bottom elevation of the second support, and construct the second support; excavate the earth to the bottom of the pit, and dig a drainage ditch on the side close to the foundation pit; C. Demolition After pouring the concrete cushion layer and bottom plate, and constructing the main structure to the horizontal construction joint, a plain concrete support strip is placed between the construction body and the retaining piles. After the strength of the main structure and the plain concrete reaches 75% of the design strength, the second support and waist beam are removed, and the construction of the main structure is continued after the removal. After the concrete strength of the main structure reaches 75% of the design strength, the soil is backfilled to the bottom of the first support, the first support and waist beam are removed, and the backfill is continued to the ground elevation, and the steel sheet piles are removed.

2. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: The foundation pit excavation should be carried out symmetrically in layers, with the layer height not exceeding 1m.

3. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: In the above step C, the bottom of the first support is backfilled with 2:8 gray soil, and the top of the first support is backfilled with plain soil to the ground elevation. After the backfill soil is accepted and qualified, the steel sheet piles are removed.

4. The steel sheet pile support construction method for soft soil layer according to claim 3 is characterized in that: During tunnel foundation pit construction, plain soil is used as the backfill material for the ordinary section above the first support, and medium-coarse sand is used within 500mm on the side walls and top plate of the crossing section structure. The density of the backfill is not less than 0.

94.

5. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: During the construction of rotary jet grouting, the waste slurry is discharged into the mud pool, and after sedimentation and condensation, it is transported to off-site storage or disposal.

6. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: The overlap spacing between the jet grouting piles is not less than 200mm, and the spacing between the jet grouting piles and the Larsen steel sheet piles is 1m.

7. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: The water-cement ratio of the cement slurry is 1.0, and the cement content is not less than 580kg / m 3 The slurry specific gravity is 1.5kg / l. The mixing time after each feeding shall not be less than 3min. Pour the slurry into the collecting hopper before grouting. The cement slurry can be used as soon as it is mixed.

8. The steel sheet pile support construction method for soft soil layer according to claim 7 is characterized in that: The compressed air pressure for spraying is 0.5-0.7 MPa, the air volume is 1500-3000 l / min, the nozzle diameter is 2.1 mm, the lifting speed is 10-15 cm / min, and the slurry volume is 60-70 l / min.

9. The steel sheet pile support construction method for soft soil layer according to claim 1 is characterized in that: In the above-mentioned step C, the piles are pulled out at intervals with a spacing of not less than 2m, and the gaps left by the piles are promptly filled with 1:1 cement mortar.

10. The steel sheet pile support construction method for soft soil layer according to claim 9 is characterized in that: The cement of the cement mortar is silicate cement with a strength grade not lower than PO 42.5, the grouting pressure is not greater than 0.1MPa, and the grouting slurry is added with an accelerating agent accounting for 2% of the total mass, and the grouting is performed while pulling.

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