Water stop construction process for foundation pit in offshore boulder backfill area

Abstract

The invention discloses an offshore boulder backfill area foundation pit water stop construction technology, which adopts a cement soil water stop wall and slope excavation foundation pit construction technology to prevent underground water from lateral ocean runoff, and is matched with open drainage to achieve the purpose of reducing the underground water of a foundation pit. And meanwhile, the technical problem that the self-stability of the foundation pit slope in the block stone backfill area is poor is solved through combination of slope making and the cement soil water stop wall, interception and drainage are combined, and underground water in the foundation pit is efficiently reduced. Meanwhile, cement-soil wall construction is simple, rapid and economical, the construction period is greatly shortened, and cost is reduced; the construction site construction face is wide, reasonable construction organization is facilitated, the method is suitable for rock backfill stratums, foundation pits with the excavation depth smaller than 5 m are excavated, and rapid construction of complex underground structures is also facilitated.

Description

Technical Field

[0001] The invention belongs to the field of engineering construction, and in particular relates to a water-stopping construction process for a foundation pit in an offshore large-block rock backfill area. Background Art

[0002] The self-stability of the excavated slope of the foundation pit in the block stone backfill area is poor. In addition, the project is close to the coastline, and under the influence of factors such as strong permeability, high groundwater level, and tides, the water-stopping construction of local deep foundation pits such as the water pool in the offshore foundation has become a major difficulty in offshore foundation construction. At present, existing offshore water-stopping technologies include water-stop curtains in the form of concrete mixing pile retaining structures, cement mixing pile support plus soil nail walls, etc. These technologies all require the use of down-the-hole hammers to drill holes in the blocks and then use mixing pile machines for mixing, which has low efficiency and is prone to hole collapse; soil nail walls require the use of a large amount of steel bars and concrete, which increases construction costs, prolongs construction periods, and has high safety risks. Summary of the invention

[0003] In order to solve the above problems, the present invention discloses a water-stopping construction process for foundation pits in offshore large-block rock backfill areas, which adopts a combination of drainage in the foundation pit and a water-stopping curtain to prevent radial water flow. The process is scientific, the construction period is shortened, the cost is reduced, and a certain strength of support is formed at the same time, avoiding the instability and collapse of the foundation pit in the block rock backfill area due to poor self-stability.

[0004] To achieve the above object, the technical solution of the present invention is as follows: The water-stopping construction technology for the foundation pit in the offshore large rock backfill area includes the following steps: (1) The site is leveled; (2) Positioning and setting out: First determine the slope coefficient for the large stone backfill foundation excavation; after determining the slope coefficient, complete the foundation pit positioning and setting out according to the slope ratio; (3) Guardrail erection: erect guardrails according to the upper opening of the foundation pit according to the positioning and laying out; (4) Slope excavation: Use a multi-level slope excavation method and excavate to the first platform. The height of the first platform is at the original normal water level of the foundation pit. The width of the first platform needs to be greater than the width of the cement water stop wall. (5) Cement soil preparation: According to the mix ratio of cement and clay determined in the test section, the cement soil is prepared by excavator and mixer; (6) Cement soil wall construction: On the first platform, excavation is carried out using an excavator according to the width and depth of the cement soil water stop wall determined in the test section. Because the foundation pit is backfilled with large rocks that are prone to collapse, the prepared cement soil is backfilled in time during excavation, and finally a closed cement soil water stop wall is formed around the foundation pit. (7) Foundation pit drainage: After the cement soil water stop wall reaches a certain strength, it forms a water stop curtain, thereby preventing seawater from flowing radially into the foundation pit; auxiliary drainage is carried out by using a pump to form a water level difference inside and outside the foundation pit; (8) Excavation from the first platform to the bottom of the pit: As the water level in the foundation pit drops, excavation is carried out in layers until the bottom of the foundation pit is reached; (9) Overall acceptance of the slope: After excavation to the bottom of the foundation pit, the slope gradient is corrected using a soil inclinometer and acceptance is carried out in a timely manner; (10) Construction of superstructure: After acceptance, pour the cushion layer in time. When the cushion layer construction is completed and reaches the required strength, complete the superstructure in time.

[0005] As a supplement to the present invention, the cement soil water stop wall in step (5) has a width of 2 meters and a depth of 4 meters.

[0006] As a supplement to the present invention, the mass ratio of cement to clay in step (5) is about 1:6. As a supplement to the present invention, the large rocks used for backfilling the foundation pit in step (6) are construction waste such as fill stones and concrete blocks.

[0007] As a supplement to the present invention, the water level difference between the inside and outside of the foundation pit in step (7) reaches 500 mm.

[0008] As a supplement to the present invention, a drainage ditch is provided on the platform outside the water-stop curtain in step (7).

[0009] As a supplement to the present invention, after the layered excavation in step (8), multiple circles of water-stopping curtains can be set according to actual conditions.

[0010] As a supplement to the present invention, the cushion layer in step (10) can be thickened according to the on-site conditions.

[0011] As a supplement to the present invention, a second drainage ditch is provided on the cushion platform outside the upper project in step (10).

[0012] The beneficial effects of the present invention are: 1. The drainage in the foundation pit and the water-stop curtain formed by the cement water-stop wall are used to prevent the lateral runoff outside the foundation pit. The combination of water-stopping and drainage forms a water level difference inside and outside the foundation pit, so that the groundwater level is reduced to 500㎜ below the excavation surface to complete the foundation pit slope excavation construction of the upper structure.

[0013] 2. It not only eliminates the complicated construction work of drilling holes for concrete pile support and underwater concrete pouring, but also reduces the impact of vibration and noise on nearby buildings by abandoning conventional steel sheet pile support.

[0014] 3. Compared with the above two support methods, it can shorten the construction period and reduce costs while ensuring stability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Example

[0017] Taking the construction of the basement foundation pit and underground structure of a chemical plant's public engineering room, cooling water tank, initial rainwater tank, and accident emergency tank on the ground formed by land reclamation at the seaside as an example, there is a large stone backfill area under the ground, which is an unconventional geological condition. The fill type is block stone fill, which is generally mixed with construction waste and domestic waste such as fill stone and concrete blocks. The overall physical and mechanical properties of the artificial fill layer are poor, and there are obvious unevenness in density and compressibility, which can easily cause ground subsidence and side wall collapse; its self-stabilization ability is poor, which can easily have an adverse effect on the excavation of the foundation pit; and the permeability of artificial fill is relatively strong. If the surrounding pipelines leak or there is heavy rainfall, water bags are easily formed, or fine particles in the soil are carried away by the running water, it is easy to form sinkholes underground and collapse. The excavation depth of the foundation pit is about 4.0m. The water-stop curtain in the form of concrete mixing pile retaining structure, cement mixing pile support plus soil nail wall and other technologies used in the past are not very suitable for this situation (if steel sheet pile support is used, due to the high content of block stones in the foundation and the presence of many blocks of stones with a diameter of about 3 meters, the steel sheet piles cannot be installed at all. If pile-anchor support is used, the pile type is punched pile or rotary pile construction. Because the porosity of the block stone area is large, the self-stabilization is poor, and the groundwater is abundant, the pile construction is extremely difficult and prone to collapse).

[0018] In this case, if Figure 1 As shown, this embodiment adopts a foundation pit water-stopping construction process in the offshore large-rock backfill area, and the overall construction process is: site leveling → positioning and laying out → guardrail erection → earth slope excavation to the first step platform → cement soil preparation → cement soil wall construction → foundation pit dewatering → earth excavation from the platform to the bottom of the pit → overall slope acceptance → pool structure construction → earth backfilling.

[0019] The specific steps are as follows: 1. The site is level.

[0020] 2. Positioning and setting out: Due to unconventional geological conditions, it is necessary to first check the geological survey report, conduct on-site trial excavation, and use the Pinming calculation software to comprehensively determine the slope coefficient of the large stone backfill foundation excavation. After determining the slope coefficient, complete the foundation pit positioning and setting out according to the slope ratio.

[0021] 3. Erection of guardrails: Erection of guardrails starts according to the upper position of the foundation pit where positioning is made.

[0022] 4. Excavation of foundation pit: Use multi-level slope excavation and excavate to the first platform. The height of the first platform is at the original normal water level of the foundation pit. The width of the platform needs to be greater than the width of the cement water stop wall.

[0023] 5. Preparation of cement soil: According to the mix ratio of cement and clay determined in the test section, which is about 1:6 (cement content is about 15%), the preparation of cement soil is completed by excavator and mixer.

[0024] 6. Cement soil wall construction: On the first stage earthwork platform, the width of the cement soil water stop wall is determined to be 2 meters and the depth is 4 meters according to the test section, and excavation is carried out by excavator. Because the foundation pit is backfilled with large stones that are prone to collapse, the prepared cement soil is backfilled in time during excavation, and finally a closed cement soil water stop wall is formed around the foundation pit.

[0025] 7. Dewatering of foundation pit: After the cement soil wall reaches a certain strength, it forms a water-stop curtain, thereby preventing seawater from flowing radially into the foundation pit. Pumping is used to assist in drainage, so that a water level difference is formed inside and outside the foundation pit, and the water level is reduced to 500mm below the bottom of the foundation pit. The cement soil water-stop wall not only forms a water-stop curtain, thereby preventing radial water flow. At the same time, it reaches a certain strength to form support for the foundation pit, avoiding the instability and collapse of the foundation pit in the block stone backfill area due to poor self-stability.

[0026] 8. Excavation from the platform to the bottom of the pit: While maintaining precipitation, excavate in layers to the bottom of the foundation pit.

[0027] 9. Overall acceptance of slope: Use basin excavation method to keep the slope of foundation pit stable. After excavating to the bottom of foundation pit, use soil inclinometer to correct the slope and accept it in time.

[0028] 10. Pool structure construction: After acceptance, pour the cushion layer in time. To avoid excessive water pressure at the bottom of the foundation pit and sudden surges, thicken the cushion layer according to site conditions. When the cushion layer reaches the required strength, complete the superstructure in time.

[0029] During the construction process, the water level changes should be monitored at any time, and data analysis should be provided to analyze the drainage and water stopping effects, so as to ultimately achieve safe and standardized construction of the foundation pit in the offshore large stone backfill area. At the same time, the soil inclinometer should be used to correct the slope of the slope, dynamically repair it, and provide real-time warning.

[0030] The present invention adopts the foundation pit construction technology of cement soil water stop wall plus slope excavation to prevent the lateral ocean runoff of groundwater, and cooperates with open drainage to achieve the purpose of reducing the groundwater in the foundation pit. At the same time, the technical difficulty of poor self-stability of the foundation pit slope in the block stone backfill area is solved by combining slope and cement soil water stop wall, and the groundwater in the foundation pit is effectively reduced by combining interception and drainage. At the same time, the construction of cement soil wall is simple, fast and economical, which greatly shortens the construction period and reduces costs. The on-site work surface is open, which is convenient for the reasonable organization of construction. It is suitable for foundation pits with block stone backfill strata and excavation depth less than 5m, and it is also convenient for the rapid construction of complex underground structures.

[0031] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. The water-stopping construction technology for foundation pit in offshore large rock backfill area is characterized by: The following steps are involved: (1) The site is leveled; (2) Positioning and setting out: First determine the slope coefficient for the large stone backfill foundation excavation; after determining the slope coefficient, complete the foundation pit positioning and setting out according to the slope ratio; (3) Guardrail erection: erect guardrails according to the upper opening of the foundation pit according to the positioning and laying out; (4) Slope excavation: Use a multi-level slope excavation method and excavate to the first platform. The height of the first platform is at the original normal water level of the foundation pit. The width of the first platform needs to be greater than the width of the cement water stop wall. (5) Cement soil preparation: According to the mix ratio of cement and clay determined in the test section, the cement soil is prepared by excavator and mixer; (6) Cement soil wall construction: On the first platform, excavation is carried out using an excavator according to the width and depth of the cement soil water stop wall determined in the test section. Because the foundation pit is backfilled with large rocks that are prone to collapse, the prepared cement soil is backfilled during excavation, and finally a closed cement soil water stop wall is formed around the foundation pit. (7) Foundation pit drainage: After the cement soil water stop wall reaches a certain strength, it forms a water stop curtain, thereby preventing seawater from flowing radially into the foundation pit; pumps are used to assist in drainage, so that a water level difference is formed inside and outside the foundation pit; (8) Excavation from the first platform to the bottom of the pit: As the water level in the foundation pit drops, excavate in layers to the bottom of the foundation pit; (9) Overall acceptance of the slope: After excavation to the bottom of the foundation pit, the slope gradient is corrected using a soil inclinometer and acceptance is carried out in a timely manner; (10) Construction of superstructure: After acceptance, pour the cushion layer in time. When the cushion layer construction is completed and reaches the required strength, complete the superstructure in time.

2. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: The width of the cement soil water stop wall in step (5) is 2 meters and the depth is 4 meters.

3. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: The cement content in the cement soil in step (5) is 15%.

4. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: The large stones used for backfilling the foundation pit in step (6) are filling stones and concrete blocks.

5. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: In step (7), the water level difference between the inside and outside of the foundation pit reaches 500 mm.

6. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: In step (7), a drainage ditch is provided on the platform outside the water-stop curtain.

7. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: After the layered excavation in step (8), the number of water-stop curtains is ≥ 1 circle.

8. The water-stopping construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: The cushion layer in step (10) is a thickened cushion layer.

9. The waterproofing construction process for foundation pit in offshore large rock backfill area according to claim 1 is characterized by: In step (10), a second drainage ditch is provided on the cushion platform outside the upper project.

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