Foundation pit supporting method for sludge-polluted site in complex environment and sludge soil cleaning and excavating method

Abstract

The invention provides a foundation pit supporting method and a sludge soil cleaning and excavating method for a complex environment sludge pollution site. The purpose of foundation pit supporting is achieved by arranging intermediary piles in a foundation pit. Supporting piles arranged in rows are arranged on the outer side of the foundation pit, and the intermediate piles are arranged in the middle area, away from the edge, of the foundation pit. The intermediate piles are parallel to the support piles on the outer side of the foundation pit; the foundation pit area is separated to form a plurality of independent areas; the tops of the outer side supporting piles and the tops of the intermediate piles are connected through steel supports or concrete supports. According to the foundation pit supporting technology and the soil cleaning and excavating method for achieving deformation control by arranging the intermediary piles, the method has the beneficial effects of being safe, reliable, small in secondary pollution risk, small in influence on future plot development and good in comprehensive benefit.

Description

Technical Field

[0001] The present invention belongs to the field of sludge treatment, and in particular relates to a foundation pit support method and a sludge and soil excavation method for a sludge-polluted site in a complex environment. Background Art

[0002] During the annual production process of some old industrial plants, for various reasons, the soil and groundwater will be polluted. With the industrial upgrading and urban land transfer following industrial development, it is necessary to repair and treat the polluted soil and groundwater to ensure that the repaired land can be safely used without posing a safety risk to human health.

[0003] The ex-situ remediation technology is a technology that excavates polluted soil from its original polluted location and transports or transfers it to other places or positions for treatment and remediation. Foundation pit support is often involved in the process of excavating polluted soil. The selection of foundation pit support technology needs to be comprehensively considered according to different excavation depths and surrounding environments. According to relevant statistical research in the industry, the foundation pit depths for ex-situ disposal of polluted soil are mostly from several meters to more than ten meters. When the pollution depth is too large, other disposal methods are usually considered due to the high investment in foundation pit support.

[0004] However, the pollution soil treatment projects in the above-mentioned old industrial plants often face relatively complex environmental conditions. First, the plant area is large, and the pollution shows regional or local dispersion; second, the pollution boundary crosses the planned red line of the plot, and it is not clear whether there is pollution outside the boundary; third, there are buildings or underground pipelines sensitive to deformation at the repair boundary; fourth, the plot is often located in the central city or the new city around the city, with high land added value, and the demand for land turnover and development and utilization is urgent, resulting in a tight schedule for polluted soil remediation; Finally, when carrying out foundation pit support in sludge and soil, the following aspects should be mainly considered: (1) Because of the deformation control of the foundation pit support system, it should meet the deformation control requirements of the surrounding environment, especially sensitive buildings and underground pipelines, etc. Using slope or conventional steel members for support, the deformation and stiffness cannot meet the requirements; (2) During the construction process of the foundation pit support system, potential secondary pollution problems of polluted soil should be avoided. For example, when using common bored piles, diaphragm walls and other methods, during the process of implementing the process, polluted soil is converted into slurry, which is not conducive to subsequent treatment; (3) In a site with groundwater pollution, good curtain blocking measures are required, which should not only block the pollution diffusion caused by the seepage of polluted groundwater, but also ensure reasonable and efficient volume and efficiency when treating polluted groundwater.

[0005] (4) The foundation pit support system is a temporary protective measure for the excavation of contaminated soil. After the soil treatment is completed, the materials and components related to the support system should not only be recycled as much as possible for secondary use to improve the comprehensive benefits, but also reduce the potential adverse impacts of the remaining components for single use on the subsequent development and utilization of the plot. Summary of the Invention

[0006] In view of this, the present invention aims to provide a foundation pit support method and a sludge soil excavation method for a sludge-contaminated site in a complex environment. By setting intermediate piles, a foundation pit support technology and a soil excavation method for deformation control are realized. This method has the characteristics of safety and reliability, low risk of secondary pollution, small impact on the future plot development, and good comprehensive benefits.

[0007] To achieve the above object, the technical solution of the present invention is realized as follows: A foundation pit support method and a sludge soil excavation method for a sludge-contaminated site in a complex environment, achieving the purpose of foundation pit support by setting intermediate piles in the foundation pit; a row of support piles are arranged on the outside of the foundation pit, The intermediate piles are arranged in the middle area far from the edge of the foundation pit; the intermediate piles are arranged parallel to the support piles on the outside of the foundation pit; to divide the foundation pit area and form several independent areas; The tops of the outer support piles and the tops of the intermediate piles are connected by steel supports or concrete supports; It includes the following steps: S1. Level the site; S2. Construct the outer cement-soil mixing piles; S3. Construct the outer support piles and the intermediate piles; S4. Construct the concrete capping beam and the steel pipe supports; S5. Excavate the sludge soil in the contaminated site within the range of the intermediate piles; S6. Excavate the sludge soil in the contaminated site outside the intermediate piles.

[0008] Furthermore, the intermediate piles and the support piles divide the foundation pit from the outside to the inside into a first area, a second area, and a third area; the first area is the site outside the foundation pit, and the second area and the third area are contaminated sites; The steel supports or the concrete supports also divide the second area into several second sub-areas.

[0009] Furthermore, the intermediate piles are SMW method piles.

[0010] Furthermore, the distance between the intermediate piles and the outer support piles is set between 10 - 20 m.

[0011] Furthermore, cement mixing piles are continuously arranged outside the support piles as a water stop curtain to prevent leakage and stop the spread of pollution caused by the flow of groundwater.

[0012] Furthermore, the form of the cement mixing pile is a double-axis, or a triple-axis, or a continuous cement soil wall with equal thickness.

[0013] Furthermore, the method for excavating the contaminated soil in the foundation pit is as follows: First, determine the excavation sequence as follows: clean the second area first, and then clean the third area; Second, after excavation to the required depth, take samples for testing. After passing the test, backfill with clean native soil, and the required compaction degree of the backfill shall not be less than 95%; Finally, excavate the third area again.

[0014] Compared with the prior art, the foundation pit support method and the sludge soil excavation method for the sludge-polluted site in a complex environment of the present invention have the following advantages: (1) For the foundation pit support method and the sludge soil excavation method for the sludge-polluted site in a complex environment of the present invention, the intermediate piles can be flexibly arranged according to different excavation depths and site conditions; for shallow foundation pits, a cantilever support form can be adopted, and the stiffness and water-stop effect of the intermediate piles are utilized, which is both economical and environmentally friendly; for deep foundation pits, the intermediate piles can be combined with the support system to provide additional support force to ensure the stability of the foundation pit.

[0015] (2) For the foundation pit support method and the sludge soil excavation method for the sludge-polluted site in a complex environment of the present invention, the SMW method piles are adopted for the intermediate piles. This pile type has a high cost performance. The H-shaped steel can be pulled out and reused after the construction is completed, reducing material waste and meeting the requirements of sustainable development. In addition, the curtain formed by the cement mixing pile can effectively block groundwater and reduce the risk of pollution diffusion.

[0016] (3) For the foundation pit support method and the sludge soil excavation method for the sludge-polluted site in a complex environment of the present invention, the intermediate piles can effectively control the deformation of the foundation pit support system, especially in the case where there are sensitive buildings or underground pipelines around; through reasonable design and construction, the impact of foundation pit excavation on the surrounding environment can be significantly reduced.

[0017] (4) For the foundation pit support method and the sludge soil excavation method for the sludge-polluted site in a complex environment of the present invention, the intermediate piles divide the foundation pit into different areas, allowing staged excavation; this way of block excavation can ensure that the soil mass in each area is effectively supported during the excavation process, avoiding deformation and collapse caused by soil stress release.

[0018] (5) For the foundation pit support method and sludge soil excavation method for sludge-polluted sites in complex environments of the present invention, during the excavation of polluted soil, the use of intermediate piles in combination with support piles can reduce the problem of slurry pollution that may occur in traditional construction methods; through reasonable support design and construction management, the diffusion of polluted soil can be effectively controlled, and the surrounding environment can be protected.

[0019] (6) For the foundation pit support method and sludge soil excavation method for sludge-polluted sites in complex environments of the present invention, the second area and the third area of the foundation pit are excavated in sequence to avoid soil stress concentration caused by large-area excavation, provide reaction force for the intermediate piles, reduce the lateral displacement impact on surrounding buildings and pipelines during the excavation of the second area, and thus ensure the stability of the support system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a top view schematic diagram of the foundation pit of the polluted site described in the embodiment of the present invention; Figure 2 is a side view schematic diagram of the foundation pit of the polluted site described in the embodiment of the present invention; Figure 3 is a schematic diagram of the excavation of polluted soil in the second area described in the embodiment of the present invention; Figure 4 is a schematic diagram of the excavation of polluted soil in the third area described in the embodiment of the present invention.

[0021] Description of the reference numerals in the drawings: 1, support pile; 2, intermediate pile; 3, waterproof curtain; 4, steel support; 5, first area; 6, second area; 7, third area. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0023] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0024] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0025] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0026] Foundation pit support method and sludge and soil excavation method for sludge-polluted sites in complex environments, as Figures 1-4 shown, the purpose of foundation pit support is achieved by setting intermediate piles 2 in the foundation pit; a row of support piles 1 are provided outside the foundation pit, the intermediate piles 2 are arranged in the middle area of the foundation pit far from the edge; the intermediate piles 2 are arranged parallel to the support piles 1 outside the foundation pit; the foundation pit area is divided to form several independent areas; The tops of the outer support piles 1 and the tops of the intermediate piles 2 are connected by steel supports 4 or concrete supports; It includes the following steps: S1. Level the site; S2. Construct the outer cement-soil mixing piles; S3. Construct the outer support piles and intermediate piles; S4. Construct the concrete capping beam and steel pipe supports; S5. Excavate the sludge and soil in the polluted site within the range of the intermediate piles; S6. Excavate the sludge and soil in the polluted site outside the intermediate piles.

[0027] The steel support 4 is usually a steel pipe. The minimum specification that meets the requirements is calculated according to the stiffness requirements, and then it is generally selected from 400 - 1000 according to the national standard hardware standard specifications. In the case project, it is a φ = 426 / 609 spiral welded steel pipe; The reinforced concrete support is usually of rectangular cross-section. The most suitable one is selected after cross-section calculation, and there are cases such as 1200×900, 1200×700, 900×700, 900×800, etc.; The plane spacing of the supports is generally about 8m apart.

[0028] Preferably, the intermediate pile 2 and the retaining pile 1 divide the foundation pit into a first area 5, a second area 6, and a third area 7 from the outside to the inside; The first area 5 is the site outside the foundation pit, and the second area 6 and the third area 7 are polluted sites; The steel support 4 or the concrete support also divides the second area 6 into several second sub-areas.

[0029] Preferably, the intermediate pile 2 is an SMW method pile, and a comparison study is carried out during the selection of such a retaining form for the intermediate pile 2; a Slope; Vertical excavation of deep pits is not applicable; b Soil nail wall and shotcrete; Greatly affected by the soil layer, poor applicability, large deformation, and additional treatment is required to provide reaction force for the outer retaining pile 1; c Pile-anchor support; The anchor occupies underground space; And it cannot achieve the two-way resistance effect of different working conditions of the intermediate pile 2 (when excavating the second area 6, it blocks the earth pressure of the right third area 7, and when excavating the third area 7, it blocks the pressure of the backfill soil of the left second area 6); d Precast pile / Steel pile; The pile body characteristics result in limited applicability for pit depth and slightly larger deformation; e Cast-in-place row piles; The polluted soil slurry formed during pile formation will cause difficulties in subsequent harmless treatment. In water-rich areas, the cost of all-steel casing is too high, the process is complex, and the waste piles affect subsequent development; f Diaphragm wall; The slurry is difficult to treat and the cost is high; Compared with the above methods, using the SMW method pile has excellent effects, mainly manifested as: (1) The process is relatively mature and the cost is low; (2) It has a certain stiffness, can resist earth pressure and provide a certain reaction force; (3) The cement soil forms a curtain barrier to achieve groundwater barrier and zoning, which is convenient for treatment; (4) It can achieve two-way resistance to earth pressure. When excavating the second area 6, it blocks the earth pressure of the right third area 7, and when excavating the third area 7, it blocks the backfill soil pressure of the left second area 6; (5) The H-shaped steel can be pulled out after construction and reused, and the remaining cement soil piles have less impact on subsequent development.

[0030] Preferably, the distance between the intermediate pile 2 and the outer retaining pile 1 is set between 10 - 20 m.

[0031] Preferably, a cement mixing pile is further arranged outside the retaining pile 1 as a water stop curtain 3 to protect against leakage and prevent the spread of pollution caused by groundwater flow.

[0032] Preferably, the form of the cement mixing pile is a double - axis, or a triple - axis, or an equal - thickness cement - soil continuous wall; (1) Double - axis, generally φ700@900, φ700@1000 (two intersecting circles with a diameter of 700, the center - to - center distance between groups is 1000, that is, the length of the intersecting part of the axis is 200); (2) Triple - axis, generally φ650@900, φ850@1200; (3) Equal - thickness cement - soil continuous wall (TRD / CSM method), generally with a wall thickness of 600 - 800 mm; The difference from the construction method pile is that there is no need to insert H - shaped steel, and it is a cement - soil component formed by mixing soil and cement slurry with corresponding equipment.

[0033] In summary, the foundation pit support method of this application realizes the support purpose through the mutual cooperation of three support forms; The first is realized through the retaining pile; The second is the support form of the cooperation between the retaining pile and the intermediate pile; The third is to add the form of a cement mixing pile water stop curtain on the basis of the second support form.

[0034] Preferably, the method for excavating contaminated soil in the foundation pit is as follows: First, determine the excavation sequence as follows: clean area 6 of the second area first, and then clean area 7 of the third area; Regarding the above - mentioned excavation sequence, we have also verified it; If the sequence is not in accordance with the above - mentioned sequence of area 6 of the second area first and then area 7 of the third area, but in the sequence of area 7 of the third area first and then area 6 of the second area, since the soil mass in area 7 of the third area bears the structural reaction force during the excavation of area 6 of the second area, it is necessary to ensure that the clean soil backfilled after the excavation of area 7 of the third area is compacted. Otherwise, it will affect the reaction force effect of the intermediate pile 2. That is to say, the denser the soil at the position of area 7 of the third area, the greater the system stiffness with the intermediate pile 2, and the greater the reaction force that can be provided to the retaining pile 1. When excavating area 6 of the second area in the field, the deformation of area 5 of the first area in the direction of area 6 of the second area will be smaller, which is more conducive to the protection of the buildings and municipal pipelines in area 5 of the first area.

[0035] Therefore, to avoid potential hazards caused by improper backfilling in Area 7 of Region 3, it is recommended to excavate Area 6 of Region 2 first and then Area 7 of Region 3. For the excavation of Area 6 of Region 2, a small excavator is used to transfer the contaminated soil within the area of the intermediate pile 2 within this range and concentrate it in one place, and then an excavator and a transport vehicle are used for cleaning and transportation. For the excavation of Area 7 of Region 3, a stepped excavation method is adopted, as Figure 3 Figure 4 shown.

[0036] Secondly, after the excavation reaches the required depth, sampling and testing are carried out. After passing the test, clean native soil is backfilled, and the required backfill compaction degree is not less than 95%. Finally, Area 7 of Region 3 is excavated again.

[0037] The retaining pile 1 is also an SMW method pile. For conventional shallow foundation pit contaminated sites (0 - 4m), a cantilever retaining form is adopted, and SMW method piles are set outside the foundation pit. This retaining form can play a role in water stop and can also act as a retaining wall to play a retaining role, and has the advantages of low cost, environmental protection and recyclability, and short construction period, and is suitable for various shallow foundation pits in soil remediation projects.

[0038] In particular, core sampling tests should be carried out on the cement soil used to make the retaining pile 1, and the test method is the toxicity leaching test (acid leaching method) to ensure that the pollutants in the cement soil pile will not precipitate due to time effect under the condition of cement solidification.

[0039] It is not suitable to adopt retaining forms such as cast-in-place piles for contaminated plots, while traditional method piles have certain applicability. Coupled with the strict requirements for deformation control of the surrounding environment, the retaining form combining the intermediate pile 2 and the retaining pile 1 is innovated.

[0040] Generally, groundwater and soil pollution are divided into three categories: heavy metal pollution, organic matter pollution, and composite pollution (heavy metals and organic matter); no matter which type of pollution, once the contaminated soil is repaired off-site (not treated in situ), it will involve foundation pit engineering. Just like the four difficult problems involved in the four related works described in the background technology, this retaining technology has a strong space for development.

[0041] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A foundation pit support method and a sludge soil excavation method for a complex environmental sludge contaminated site, characterized by: The following steps are involved: S1. Level the site; S2, construction of cement soil mixing piles on the outside; S3, construction of outer supporting piles and intermediate piles; S4, concrete cap beam and steel pipe support construction; S5. Excavation of sludge and soil from contaminated sites within the scope of the intermediate piles; S6. Excavation of sludge and soil from the contaminated area outside the intermediate pile; The purpose of supporting the foundation pit is achieved by setting intermediate piles in the foundation pit; supporting piles arranged in rows are arranged outside the foundation pit. The intermediate piles are arranged in the middle area of ​​the foundation pit away from the edge; the intermediate piles are arranged in parallel with the supporting piles outside the foundation pit; the foundation pit area is separated to form several independent areas; The top of the outer supporting pile and the top of the intermediate pile are connected by steel support or concrete support.

2. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 1, characterized in that: Intermediate piles and support piles divide the foundation pit into Area 1, Area 2 and Area 3 from the outside to the inside; Area 1 is the site outside the foundation pit, and Areas 2 and 3 are contaminated sites; The steel support or concrete support also divides the No. 2 area into a number of No. 2 sub-areas.

3. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 1, characterized in that: The intermediate pile is an SMW method pile.

4. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 1, characterized in that: The distance between the intermediate pile and the outer supporting pile is set between 10-20m.

5. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 1, characterized in that: Cement mixing piles are further set on the outside of the supporting piles as a water-stop curtain to protect against leakage and prevent groundwater flow and pollution spread.

6. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 5, characterized in that: The cement mixing piles are in the form of biaxial, triaxial, or equal-thickness cement-soil continuous walls.

7. The method for supporting foundation pits and clearing sludge soil in a complex environment sludge contaminated site according to claim 1, characterized in that: The method of clearing contaminated soil in the foundation pit includes the following steps: First, determine the excavation order: clean up area No. 2 first, then clean up area No. 3; Secondly, after the excavation is completed, sampling and testing are carried out. After the test is qualified, clean soil is backfilled, and the backfill compaction degree is required to be no less than 95%; Finally, area No. 3 is excavated.

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