Large-area sludge foundation treatment construction method based on partition treatment

Abstract

The invention discloses a large-area sludge foundation treatment construction method based on zoning treatment, which comprises the following steps: filling a broken stone soil material separation dam (1) shaped like a Chinese character'tian 'on a sludge foundation (8), arranging a geotechnical blind ditch (2) with a trapezoidal section along the middle lower part of the broken stone soil material separation dam (1), and arranging a water collecting well (5) in the geotechnical blind ditch (2) at the joint of the broken stone soil material separation dam (1); the geotechnical blind ditch (2), the permeable pipe and the water collecting well (5) are combined to form a drainage system; geogrids (3) are laid on the surface of the sludge foundation (8) in a layered mode, and loess is backfilled on the geogrids (3) laid in the grids shaped like the Chinese character'tian 'of the sludge foundation (8) to the dam top elevation of the gravel soil material separation dam (1) to form a loess layer (7). The problems that a traditional sludge foundation treatment construction method is high in cost, long in period, low in foundation bearing capacity and difficult to be used for treatment construction of a large-area sludge foundation are effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a composite treatment construction method for a large-area silty soft soil foundation. Background Art

[0002] Silt foundation refers to the foundation soil layer mainly composed of silt (Muck Soil / Silt Soil), which belongs to the typical soft soil foundation type and has the following characteristics: generally formed in a static water or slow-flowing water environment (such as ponds, swamps, depressions, etc.), formed by long-term deposition of fine-grained clay, silt and organic matter, with a natural porosity ratio usually >1.5 and an organic matter content ≥5%. The natural water content is high, the liquid limit is >50%, the plastic limit index is >20, the permeability coefficient is low, and the weight is small. The shear strength is extremely low, the compressibility is high, the rheology is significant, and the thixotropy is sparse. The foundation bearing capacity is insufficient, the post-construction settlement is large and uneven, the drainage and consolidation time is long, and the construction disturbance is easy to cause soil instability.

[0003] Traditional silt foundation treatment often uses replacement method, preloading method or pile foundation reinforcement. The replacement method is suitable for situations where the thickness of the silt layer is relatively thin. The silt layer is replaced with sandy loam, gray soil, coarse sand, and cement soil to treat the foundation; the preloading method uses sand wells, sand well preloading, electroosmosis, etc. to promote soil drainage and consolidation to improve the bearing capacity of the foundation; when the silt layer is thick and it is difficult to carry out deep treatment on a large scale, piling can be used for reinforcement. These traditional methods have the following defects: (1) large-scale treatment requires large amounts of material consumption, high costs, and poor economic efficiency; (2) the drainage consolidation method has a long cycle (3-6 months); (3) pile foundation construction destroys the original soil structure; (4) local uneven bearing capacity leads to differences in post-construction settlement.

[0004] In order to solve the problem of silt foundation treatment, the article "Application of cement soil mixing pile technology in silt foundation treatment" published in the 9th issue of the Chinese journal "Water Conservancy Construction and Management" in 2015 elaborated in detail the determination of cement soil mixing pile construction parameters, construction process flow, construction points and quality control measures under the complex geological conditions of high water content silt soil. However, this silt treatment technology also has the problem of high construction cost, which makes it difficult to use it for large-scale silt foundation treatment construction. Summary of the invention

[0005] The purpose of the present invention is to provide a large-area silt foundation treatment construction method based on zoning disposal to address the problems of high construction cost, long construction period, large material consumption, and uneven local bearing capacity in existing silt foundation treatment technologies.

[0006] To achieve the above-mentioned purpose of the present invention, a large-area silt foundation treatment construction method based on zoning disposal is implemented by the following steps:

[0007] S1 Partition Enclosure: On the silt foundation, divide the treatment area into a "field" - shaped grid. Control the grid cell size within 20m×20m. Use a crawler excavator to fill the "field" - shaped grid with gravel - soil material to form a criss - cross "field" - shaped gravel - soil separation dam.

[0008] S2 Drainage System Setting: Set a trapezoidal cross - section geocomposite drain along the middle - lower part of the gravel - soil separation dam. Lay a Φ75 - 100mm permeable pipe at the bottom of the geocomposite drain, with a longitudinal slope ≥0.5%; Every 40 - 60m, set a sump in the geocomposite drain at the intersection of the gravel - soil separation dams. The geocomposite drain, permeable pipe, and sump jointly form a drainage system.

[0009] S3 Sump Setting: Combine with the elevation characteristics of the site where the silt foundation is located to select a location to build a sump. The sump is connected to the permeable pipe laid at the bottom of the geocomposite drain. Install a lift pump in the sump, and connect the drainage outlet of the lift pump to the external drainage pipe to drain the water flowing into the sump outwards.

[0010] S4 Consolidation Control: Through the combined drainage of the gravel - soil separation dam, geocomposite drain, permeable pipe laid at the bottom, and sump, after the water content of the silt drops below 45%, carry out subsequent construction.

[0011] S5 Reinforcement Treatment: Lay geogrid on the surface of the silt foundation in layers. The laying directions of adjacent layers are orthogonal, and the single - layer tensile strength ≥80kN / m.

[0012] S6 Consolidation and Hardening: Backfill loess on the geogrid laid within the "field" - shaped grid of the silt foundation to the top elevation of the gravel - soil separation dam to form a loess layer, squeezing the water in the lower silt layer to enhance the bearing capacity of the silt foundation.

[0013] Preferably, in step S1, the top width of the gravel - soil separation dam is not less than 3m, and the slope ratio of the slope is controlled between 1:1.5 and 1:2.0.

[0014] Preferably, in step S1, the top elevation of the gravel - soil separation dam is controlled to be 1.3 - 1.6m higher than the surface of the silt foundation. This elevation design comprehensively considers the vertical deformation caused by soil consolidation and compression, reserves enough buffer space, and ensures the operation safety during the process of mud extrusion and up - turning during construction.

[0015] Preferably, in step S2, the geocomposite drain is wrapped with a 160 - 250g / m 2 long - filament geotextile; The permeable pipe laid at the bottom of the geocomposite drain uses a DN75 - DN100 flexible permeable pipe, and the material is high - density polyethylene.

[0016] Preferably, in step S5, the geogrid adopts U-shaped clips, the longitudinal overlap length is ≥300mm, and the transverse overlap length is ≥200mm; the geogrid adopts biaxially oriented polypropylene geogrid, and its longitudinal and transverse tensile strengths are both ≥80kN / m.

[0017] The results of experimental research and application show that the large-area silt foundation treatment construction method based on zoning disposal of the present invention has the following positive effects after adopting the above technical scheme:

[0018] (1) When dealing with large-scale silt foundations, the separation dam method is used, which shortens the treatment cycle by more than 40% (the actual average consolidation time is 28 days), reduces the overall cost by more than 65% (compared with the traditional pile foundation solution), increases the foundation bearing capacity to more than 150 kPa, and effectively controls differential settlement through grid zoning.

[0019] (2) When treating large-area silt foundations, the method of the present invention effectively solves the problems of high cost, long cycle, low foundation bearing capacity, and difficulty in treating large-area silt foundations in traditional silt foundation treatment construction methods, and achieves unexpected technical and economic effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the plan layout of a large-area silt foundation for zoning treatment according to a large-area silt foundation treatment construction method based on zoning treatment of the present invention.

[0021] Figure 2 A cross-sectional view of the internal structure of the dam designed for the present invention.

[0022] Figure numerals: 1-gravel soil separation dam; 2-geotechnical blind ditch; 3-geogrid; 4-water collection pool; 5-water collection well; 6-lifting pump; 6'-external drainage pipe; 7-loess layer; 8-silt foundation. DETAILED DESCRIPTION

[0023] To further describe the present invention, the large-area silt foundation treatment construction method based on zoning disposal of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0024] Depend on Figure 1 The present invention shows a large area of ​​silt foundation treatment construction method based on zoning treatment. The large area of ​​silt foundation plane layout diagram of zoning treatment is combined with Figure 2 It can be seen that in the embodiment of the large-area silt foundation treatment construction method based on zoning disposal of the present invention, the following steps are adopted:

[0025] S1 Partition Enclosure: On the silt foundation 8, divide the treatment area in a "field" - shaped grid, with the grid cell size controlled within 20m×20m; use a crawler excavator to fill and construct a trapezoidal - section operation platform with crushed stone and soil on the "field" - shaped grid, and backfill and compact the crushed stone and soil to form a criss - cross "field" - shaped crushed - stone - and - soil separation dam 1; the top width of the crushed - stone - and - soil separation dam 1 is not less than 3m, and the slope ratio of the slope is controlled between 1:1.5 and 1:2.0 to ensure meeting the requirements of heavy machinery passage and operation. The top elevation of the crushed - stone - and - soil separation dam 1 is controlled at 1.5m above the silt foundation 8 surface. This elevation design comprehensively considers the vertical deformation caused by soil consolidation and compression and reserves sufficient buffer space, while ensuring the operation safety during the process of mud extrusion and up - turning during construction.

[0026] S2 Drainage System Installation: After the "field" - shaped crushed - stone - and - soil separation dam 1 is built, a trapezoidal - section geocomposite drain 2 is set at the middle - lower part of the crushed - stone - and - soil separation dam 1. A flexible drain pipe with a diameter of DN75 - DN100, made of high - density polyethylene, is laid at the bottom of the geocomposite drain 2, and the longitudinal slope of the drain pipe is ≥0.5%; every 40 - 60m, a sump 5 is set in the geocomposite drain 2 at the intersection of the crushed - stone - and - soil separation dams 1; the geocomposite drain 2, the drain pipe, and the sump 5 jointly form a drainage system; the drain pipe is wrapped with 200g / m 2 of filament geotextile (meeting the GB / T17639 standard).

[0027] S3 Sump Installation: Considering the elevation characteristics of the site where the silt foundation 8 is located, select a location to build a sump 4. The sump 4 is connected to the drain pipe laid at the bottom of the geocomposite drain 2. A lift pump 6 is installed in the sump 4, and the drainage outlet of the lift pump 6 is connected to an external drain pipe 6' to drain the water flowing into the sump 4 outwards.

[0028] S4 Consolidation Control: Through the combined drainage of the crushed - stone - and - soil separation dam 1, the geocomposite drain 2, the drain pipe laid at the bottom, and the sump 4, after the water content of the silt drops below 45%, follow - up construction is carried out.

[0029] S5 Reinforcement Treatment: After the water content of the silt drops below 45%, geogrid 3 (TGDG80 type) is laid in layers on the surface of the silt foundation 8. The laying directions of adjacent layers are orthogonal, and the single - layer tensile strength is ≥80kN / m; the geogrid 3 uses U - shaped fasteners, with the longitudinal lap length ≥300mm and the transverse lap length ≥200mm; the geogrid 3 is a biaxial tensile polypropylene geogrid, and its longitudinal and transverse tensile strengths are both ≥80kN / m.

[0030] S6 Consolidation and Hardening: On the geogrid 3 laid in the "field" - shaped grid of the silt foundation 8, backfill loess to the top elevation of the crushed - stone - and - soil separation dam 1 to form a loess layer 7, squeezing the water in the lower silt layer and enhancing the bearing capacity of the silt foundation 8.

[0031] The method of the present invention has been applied in a large-scale silt foundation treatment construction. Compared with the traditional pile foundation reinforcement method, consolidation is completed in an average of 28 days, the treatment cycle is shortened by more than 40%, the comprehensive cost is reduced by more than 65%, and the foundation bearing capacity is increased to more than 150kPa.

Claims

1. A large-area silt foundation treatment construction method based on zoning disposal, characterized in that It is implemented by the following steps: S1 Partition and Enclosure: On the silt foundation (8), divide the treatment area according to the "field" - shaped grid, and control the grid cell size within 20m×20m; Use a crawler excavator to fill the "field" - shaped grid with gravel - soil material to form a criss - cross "field" - shaped gravel - soil separation dam (1); S2 Drainage System Setting: Set a trapezoidal - section geocomposite drain (2) along the middle - lower part of the gravel - soil separation dam (1), lay a Φ75 - 100mm permeable pipe at the bottom of the geocomposite drain (2), and the longitudinal slope ≥0.5%; Every 40 - 60m, set a sump (5) in the geocomposite drain (2) at the intersection of the gravel - soil separation dams (1); The geocomposite drain (2), the permeable pipe, and the sump (5) jointly form a drainage system; S3 Sump Setting: Combine the elevation characteristics of the site where the silt foundation (8) is located to select a location to build a sump (4). The sump (4) is connected to the permeable pipe laid at the bottom of the geocomposite drain (2). A lift pump (6) is installed in the sump (4), and the drainage outlet of the lift pump (6) is connected to an external drainage pipe (6') to drain the water flowing into the sump (4) out; S4 Consolidation Control: Drain jointly through the gravel - soil separation dam (1), the geocomposite drain (2) and the permeable pipe laid at the bottom, and the sump (4). After the moisture content of the silt drops below 45%, carry out subsequent construction; S5 Reinforcement Treatment: Layer - by - layer lay geogrid (3) on the surface of the silt foundation (8), with the laying directions of adjacent layers being orthogonal, and the single - layer tensile strength ≥80kN / m; S6 Consolidation and Hardening: Backfill loess on the geogrid (3) laid within the "field" - shaped grid of the silt foundation (8) to the top elevation of the gravel - soil separation dam (1) to form a loess layer (7), squeeze the moisture of the lower silt layer, and enhance the bearing capacity of the silt foundation (8).

2. A large-area silt foundation treatment construction method based on zoning disposal as claimed in claim 1, characterized in that: In step S1, the top width of the gravel - soil separation dam (1) is not less than 3m, and the slope ratio of the slope is controlled between 1:1.5 and 1:2.

0.

3. A large-area silt foundation treatment construction method based on zoning disposal as claimed in claim 1, characterized in that: In step S1, the top elevation of the gravel - soil separation dam (1) is controlled to be 1.3 - 1.6m higher than the surface of the silt foundation (8).

4. A large-area silt foundation treatment construction method based on zoning disposal as claimed in claim 1, characterized in that: In step S2, the geotechnical blind ditch (2) is coated with 160-250 g / m 2 Filament geotextile.

5. A large-area silt foundation treatment construction method based on zoning disposal as claimed in claim 1, characterized in that: In step S2, the permeable pipe laid at the bottom of the geocomposite drain (2) uses a DN75 - DN100 flexible permeable pipe, and the material is high - density polyethylene.

6. A large-area silt foundation treatment construction method based on zoning treatment as claimed in claim 1, 2, 3, 4 or 5, characterized in that: In step S5, the geogrid (3) uses U - shaped buckles, the longitudinal lap length ≥300mm, and the transverse lap length ≥200mm.

7. A large-area silt foundation treatment construction method based on zoning treatment as claimed in claim 6, characterized in that: In step S5, the geogrid (3) uses a biaxially oriented polypropylene geogrid, and its longitudinal and transverse tensile strengths are both ≥80kN / m.

8. A large-area silt foundation treatment construction method based on zoning disposal as claimed in claim 2, characterized in that: In step S1, the dam top elevation of the gravel soil separation dam (1) is controlled to be 1.3-1.6 m above the silt foundation (8); in step S2, the geotechnical blind ditch (2) is coated with 160-250 g / m 2 The filament geotextile is used, and the permeable pipe laid at the bottom of the geotechnical blind ditch (2) is a DN75-DN100 soft permeable pipe made of high-density polyethylene; in step S5, the geogrid (3) uses a U-shaped buckle, the longitudinal overlap length is ≥300mm, and the transverse overlap length is ≥200mm. The geogrid (3) uses a biaxially oriented polypropylene geogrid, and its longitudinal and transverse tensile strengths are both ≥80kN / m.

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