Square well foundation pit supporting method for soft stratum

Abstract

The application provides a square well foundation pit supporting method for soft stratum, which comprises the following steps: obtaining geological parameters of the periphery of a corresponding square well; determining a foundation pit supporting and excavation range according to the geological parameters; sequentially driving a plurality of steel pipes along the periphery of the foundation pit to form a steel pipe row; performing foundation pit excavation construction, and driving a steel plate retaining wall outside the steel pipe row according to the excavation depth of the foundation pit to form a support for the foundation pit; pouring concrete at the bottom of the foundation pit to form a square well bottom plate; setting a steel formwork inside the steel pipe row to form a pouring space between the steel plate retaining wall and the steel formwork, and pouring concrete in the pouring space to form a square well wall.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil drilling, and particularly relates to a square well foundation pit supporting method for soft stratum. BACKGROUND

[0002] The square well of oil drilling is built under the derrick before land drilling to provide space for the wellhead device. The main function of the square well is to provide operation space for the wellhead device in the process of drilling and completion, and the depth of the square well is generally 2-4.5 m.

[0003] At present, the square well structure used in the process of land natural gas exploration and development is generally divided into brick masonry structure, reinforced concrete structure or mixed structure. These square wells need to be excavated to form a foundation pit first, and then built in the foundation pit. If these square wells encounter soft stratum such as high water content quicksand layer during excavation, the foundation pit will collapse, the square well cannot be normally constructed, and even the already poured derrick foundation will be unstable.

[0004] In the prior art, the square well foundation pit is mainly excavated by natural slope, and the stability of the rock-soil layer is relied on. For the square well with small depth, it is not easy to collapse, however, for the deep foundation pit with a depth of about 4 m, if there is a soft underlying layer, the probability of instability is extremely high, especially when the derrick foundation is poured first and then the square well is constructed, the stability of the derrick foundation cannot be ensured, and there is a safety problem, which is easy to damage the foundation of the derrick foundation. SUMMARY

[0005] In view of the above technical problems, the present application aims to provide a square well foundation pit supporting method for soft stratum, which adopts the method of supporting first and then excavating, can quickly form the square well foundation pit, effectively improve the construction efficiency, reduce the construction cost, effectively avoid damaging the foundation of the derrick foundation, avoid foundation treatment, and is simple and convenient to construct, and has strong practicality.

[0006] Therefore, according to the present application, a square well foundation pit supporting method for soft stratum is provided, which comprises the following steps: obtaining the geological parameters of the corresponding square well periphery; determining the foundation pit supporting and excavation range according to the geological parameters; sequentially driving a plurality of steel pipes along the periphery of the foundation pit to form a steel pipe row; performing foundation pit excavation construction, and lowering a steel plate retaining wall outside the steel pipe row according to the foundation pit excavation depth to form a support for the foundation pit; pouring concrete at the bottom of the foundation pit to form a square well bottom plate; setting a steel formwork inside the steel pipe row to form a pouring space between the steel plate retaining wall and the steel formwork, and pouring concrete in the pouring space to form a square well wall.

[0007] In one embodiment, before pouring the square well bottom plate, a guide pipe is pre-buried in the well center.

[0008] In one embodiment, the thickness of the square well bottom plate is not less than 300 mm, and the vertical length of the conduit is not less than 1500 mm.

[0009] In one embodiment, the plurality of steel pipes are uniformly spaced to form the steel pipe row.

[0010] In one embodiment, the depth of the steel pipe into the gravel layer at the bottom of the foundation pit is not less than 300 mm.

[0011] In one embodiment, the top square pipe, the middle square pipe and the bottom square pipe are spaced on the inner side of the steel pipe row, and the top square pipe, the middle square pipe and the bottom square pipe are connected to the steel pipe row by welding.

[0012] In one embodiment, the top square pipe, the middle square pipe and the bottom square pipe are sequentially welded to the steel pipe row according to the excavation depth of the foundation pit.

[0013] In one embodiment, the steel plate retaining wall is uniformly lowered into the stratum in a step-by-step layered manner according to the excavation depth of the foundation pit.

[0014] In one embodiment, the steel plate retaining walls of adjacent layers are connected by full welding.

[0015] In one embodiment, the thickness of the square well wall is not less than 350 mm.

[0016] Compared with the prior art, the application has the following advantages:

[0017] The square well foundation pit supporting method for soft stratum according to the application adopts a construction method of supporting first and then excavating, which can not only rapidly form the square well foundation pit and significantly improve the construction efficiency, but also use the steel pipe row and the steel plate retaining wall as the outer formwork of the square well and use the steel formwork as the inner formwork, thereby forming a pouring space and pouring concrete in the pouring space to form the square well wall, which not only effectively avoids damaging the wellhead foundation and processing the foundation, thereby enhancing the safety of the wellhead foundation, but also reduces the construction cost. In addition, the square well foundation pit supporting method is simple and convenient to construct and has strong practicability, and can be applied to land oil and gas wells, especially to sites with quicksand and other collapsible strata, and has strong applicability. BRIEF DESCRIPTION OF DRAWINGS

[0018] The application will be described below with reference to the drawings.

[0019] Figure 1 is a schematic diagram of the construction steps of the square well foundation pit supporting method for soft stratum according to the application.

[0020] Figure 2The distribution of the steel pipes is shown schematically.

[0021] Figure 3 is a sectional view of the square well foundation pit before the construction of the square well wall.

[0022] Figure 4 The square well floor structure is shown.

[0023] Figure 5 is a sectional view of the square well foundation pit after the construction of the square well wall.

[0024] In the present application, all the drawings are schematic drawings for illustrating the principles of the present application only and are not drawn to scale. DETAILED DESCRIPTION

[0025] The present application will be described below with reference to the drawings.

[0026] Figure 1 is a schematic view of the construction steps of the square well foundation pit supporting method for soft strata according to the present application.

[0027] As shown in Figure 1 , first, the geological parameters of the strata region around the corresponding square well foundation pit 100 are obtained, as step S01. Next, the square well foundation pit supporting and excavation range are determined according to the obtained geological parameters, as step S02. Then, as shown in Figure 2 , a plurality of steel pipes 1 are sequentially driven along the periphery of the foundation pit to form a steel pipe row, as step S03. After that, the foundation pit excavation construction is carried out, and the steel plate retaining wall 2 is lowered outside the steel pipe row according to the excavation depth of the foundation pit to form support for the foundation pit, as step S04. After that, concrete is poured at the bottom of the foundation pit to form a square well floor 3 (see Figure 5 ), as step S05. Finally, as shown in Figure 4 and 5 , a steel formwork 4 is arranged inside the steel pipe row to form a pouring space 41 between the steel plate retaining wall 2 and the steel formwork 4, and concrete is poured in the pouring space 41 to form a square well wall 5, as step S06. Thus, the square well foundation pit supporting construction for soft strata is completed.

[0028] Thus, the square well foundation pit supporting method adopts a construction method of supporting first and then excavating, which can not only quickly form the square well foundation pit 100 and significantly improve the construction efficiency, but also use the steel pipe row and the steel plate retaining wall 2 as the outer formwork of the square well and the steel formwork 4 as the inner formwork to form the pouring space 41 and then pour concrete in the pouring space 41 to form the square well wall 5, which not only effectively avoids damaging the foundation of the derrick 101, avoids foundation treatment, and enhances the safety of the derrick foundation 101, but also significantly reduces the construction cost.

[0029] Specifically, before construction, the surrounding stratum area of the square well foundation pit 100 is subjected to geotechnical engineering investigation or field pit exploration to understand the geological parameters such as the properties and thickness of the surrounding stratum of the square well, so as to obtain the corresponding geological parameters of the surrounding stratum of the square well, so as to determine the excavation mode of the square well foundation pit of the corresponding stratum. This helps to provide guidance for the excavation and subsequent construction of the square well foundation pit 100. For example, the excavation of the square well foundation pit with soft and collapsible stratum needs to be conducted with wall protection.

[0030] The foundation pit support and excavation range are determined according to the obtained geological parameters. The foundation pit support and excavation range need to be greater than the net size of the square well foundation pit. For example, taking a square well with a length of 4000 mm, a width of 4000 mm, and a depth of 4000 mm as an example, the length and width of the determined foundation pit support and excavation range are both 4734 mm, which is the total size of the net size of the square well and the reserved wall thickness and steel formwork thickness. In an embodiment, the wall thickness can be set to 350 mm, and the thickness of the steel formwork on the inside and outside can be set to 12 mm and 5 mm, respectively.

[0031] Then, a plurality of steel pipes 1 are sequentially driven along the periphery of the foundation pit to form a steel pipe row, as shown in Figure 2 The plurality of steel pipes 1 are uniformly spaced apart to form a steel pipe row, and the spacing between adjacent steel pipes 1 is preferably set to 1000 mm. The depth of the bottom of the steel pipe 1 into the pebble layer 31 (see Figure 5 ) at the bottom of the foundation pit is not less than 300 mm. This is beneficial to ensure the stability of the steel pipe 1.

[0032] According to an embodiment of the present application, the forming process of the steel pipe row is as follows: first, drive the steel pipes at the positions of the four corners, and then sequentially drive the steel pipes from the middle of each side to the four corners. The steel pipes at the four corners can serve as point control and temporary support, and can detect the degree of difficulty and depth of driving, while preventing the foundation pit from collapsing due to uneven stress during the driving of the steel pipes.

[0033] In an embodiment, the steel pipe 1 adopts a steel pipe with a model number of D50, and the length of the steel pipe 1 is 4312 mm.

[0034] Then, the foundation pit excavation construction is conducted. As shown in Figure 3 During the excavation process, the steel plate wall protection 2 is lowered outside the four sides of the steel pipe row according to the excavation depth of the foundation pit, thereby forming support for the entire square well foundation pit 100. In an embodiment, the length of the steel plate wall protection 2 is 4734 mm, the width is 1000 mm, and the thickness is 5 mm. Thus, a plurality of steel plate wall protections 2 are sequentially and continuously lowered into the stratum outside the four sides of the steel pipe row.

[0035] According to the present application, the multiple steel sheet walls 2 are uniformly lowered into the stratum in a step-by-step layering manner according to the excavation depth of the foundation pit. Specifically, for example, after the first layer of steel sheet walls 2 is lowered into position, the second layer of steel sheet walls 2 is lowered, and so on until the fourth layer of steel sheet walls 2 is lowered, thereby supporting the entire square shaft foundation pit 100. This lowering manner of the steel sheet walls 2 not only reduces the resistance of the stratum into which the steel sheet walls 2 are lowered, thereby improving the efficiency of the lowering construction, but also facilitates the formation of support for the square shaft foundation pit, thereby reducing the influence of the excavation process on the foundation pit.

[0036] Preferably, the interlayer seams of the steel sheet walls 2 are full-welded. This not only ensures the stability of the connection between the steel sheet walls 2, but also ensures the sealing of the connection between the two adjacent steel sheet walls 2, thereby facilitating the subsequent grouting construction.

[0037] After the steel sheet walls 2 are lowered, cement slurry is injected between the steel sheet walls 2 and the foundation pit wall, thereby sealing the gaps between the steel sheet walls 2 and the foundation pit wall, thereby ensuring the stability of the steel sheet walls 2. At the same time, it facilitates the subsequent grouting construction, and can ensure the integrity of the pouring space formed by the steel sheet walls 2 and the steel formwork 4, thereby facilitating the improvement of the structural integrity and stiffness performance of the square shaft wall 5 formed by pouring.

[0038] According to the present application, as shown in Figure 3 , in order to ensure the extrusion resistance of the steel pipe row, top square pipes 7, middle square pipes 8, and bottom square pipes 9 are respectively arranged in the top region, middle region, and bottom region of the inner side of the steel pipe row. The top square pipes 7, middle square pipes 8, and bottom square pipes 9 are uniformly spaced apart in the vertical direction. In one embodiment, the top square pipes 7, middle square pipes 8, and bottom square pipes 9 are made of the same pipe material, for example, all are made of rectangular pipe material with a cross-sectional size of 100mm long and 100mm wide, and a thickness of 6mm. Preferably, the top square pipes 7, middle square pipes 8, and bottom square pipes 9 can be connected to the steel pipe row by welding. During the excavation of the foundation pit, the top square pipes 7 are first welded, and then the middle square pipes 8 and bottom square pipes 9 are welded according to the excavation depth. The top square pipes 7, middle square pipes 8, and bottom square pipes 9 can effectively improve the extrusion resistance of the steel pipe row, and can effectively ensure the stability performance of the steel pipe row, which is very beneficial to the subsequent grouting construction. In the present application, the term "vertical" refers to the vertical direction in Figure 3 .

[0039] After that, concrete is poured at the bottom of the square shaft foundation pit 100, thereby forming a square shaft bottom plate 3 (see Figure 5 ). The thickness of the square shaft bottom plate 30 is not less than 300mm. In one embodiment, the square shaft bottom plate 3 is formed by pouring 300mm thick C20 concrete. The square shaft bottom plate 3, as the bottom plate of the foundation pit, can effectively seal the quicksand layer, prevent the quicksand layer from entering the square shaft, thereby effectively preventing the square shaft from sinking, and ensuring the stability of the square shaft.

[0040] Before pouring concrete to form the bottom slab 3 of the square well, such as Figures 3 to 5 As shown, a conduit 6 is pre-embedded in the center of the wellbore to seal the lower aquifer. The vertical length of the conduit 6 is not less than 1500mm. After the square well bottom slab 3 is poured, the lower end of the conduit 6 extends into the square well bottom slab 3 and is integrally connected with the square well bottom slab 3. Sealing the conduit 6 can effectively prevent groundwater from seeping into the pool.

[0041] like Figure 4 and Figure 5 As shown, after the concrete is poured and the square well bottom slab 3 is formed, a steel formwork 4 is installed inside the steel pipe row. The steel formwork 4 is separated from the steel pipe row by one end, and the distance between the steel formwork 4 and the steel plate retaining wall 2 is not less than 350mm, thus forming a pouring space 41 between the steel plate retaining wall 2 and the steel formwork 4. Therefore, by using the steel pipe row and steel plate retaining wall 2 as the outer formwork of the square well, and using the steel formwork 4 as the inner formwork, the pouring space 41 is formed, and the thickness of the formed pouring space 41 is not less than 350mm. Then, concrete is poured into the pouring space 41 to form the square well wall 5. The thickness of the formed square well wall 5 is not less than 350mm.

[0042] In one embodiment, the grade of the concrete to be poured is not lower than C20, and the workability, cohesiveness, and fluidity of the concrete must be guaranteed. When pouring concrete, it is preferable to use a tremie pipe, guide pipe, or chute to pour from bottom to top, inserting a vibrator while pouring. The vibrator should be inserted quickly and withdrawn slowly to ensure uniform compaction. The concrete pouring should be continuous and completed within two hours to ensure the pouring quality and thus improve the rigidity of the well wall.

[0043] Furthermore, the steel pipe array, the top square tube 7, the middle square tube 8, and the bottom square tube 9 are all formed inside the square well wall 5, thus becoming an integral part of the square well wall 5. This structure effectively enhances the rigidity of the square well wall 5, which is highly beneficial for improving the stability of the square well.

[0044] According to the present invention, during the excavation of the foundation pit, temporary dewatering measures can be taken to dewater the bottom of the foundation pit using wellpoint dewatering. Depending on the water volume, 4-6 wellpoints can be set up, with a dewatering depth of 10m and a pipe diameter of 150mm, to prevent groundwater from seeping into the square well pool.

[0045] The square well foundation pit supporting method for soft stratum according to the present application adopts a construction mode of supporting first and then excavating, which can not only make the square well foundation pit form quickly and significantly improve the construction efficiency, but also form a pouring space 41 by using a steel pipe row and a steel plate wall 2 as a square well outside formwork and a steel formwork 4 as an inside formwork, and then pour concrete in the pouring space 41 to form a square well wall 5, which not only effectively avoids damaging the foundation 101 of the derrick and processing the foundation, and enhances the safety of the foundation 101 of the derrick, but also reduces the construction cost. In addition, the square well foundation pit supporting method is simple and convenient in construction, and has strong practicability, and can be applied to land oil and gas wells, especially to sites with collapsible stratum such as quicksand layer, and has strong applicability.

[0046] Finally, it should be noted that the above only describes the preferred embodiments of the present application and does not constitute any limitation on the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or replace some technical features equivalently. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for supporting square well foundation pits in soft strata, comprising the following steps: Obtain the relevant geological parameters around the square well; The foundation pit support and excavation range are determined based on the geological parameters. Multiple steel pipes (1) are driven into the periphery of the foundation pit next to the derrick foundation to form a steel pipe row; Excavation of the foundation pit is carried out, and steel plate retaining wall (2) is inserted on the outside of the steel pipe row according to the excavation depth of the foundation pit to form support for the foundation pit; Cement grout is injected between the steel plate retaining wall (2) and the side wall of the foundation pit; Concrete is poured at the bottom of the foundation pit to form a square well bottom slab (3). Before pouring the square well bottom slab, a guide pipe (6) is pre-embedded in the center of the well. A steel template (4) is installed on the inner side of the steel pipe bank, thereby forming a pouring space (41) between the steel plate wall and the steel template. Concrete is poured in the pouring space to form a square well wall (5).

2. The method for supporting square well foundation pits according to claim 1, characterized in that, The thickness of the bottom plate of the square well is not less than 300mm, and the vertical length of the guide tube is not less than 1500mm.

3. The method for supporting square well foundation pits according to claim 1, characterized in that, The steel pipes are evenly spaced apart to form the steel pipe row.

4. The method for supporting square well foundation pits according to claim 1 or 3, characterized in that, The depth to which the steel pipe enters the pebble layer (31) at the bottom of the foundation pit is not less than 300 mm.

5. The method for supporting square well foundation pits according to claim 1 or 3, characterized in that, A top square tube (7), a middle square tube (8), and a bottom square tube (9) are spaced apart on the inner side of the steel pipe bank. The top square tube, the middle square tube, and the bottom square tube are all connected to the steel pipe bank by welding.

6. The method for supporting square well foundation pits according to claim 5, characterized in that, The top square tube, the middle square tube, and the bottom square tube are welded to the steel pipe row in sequence according to the excavation depth of the foundation pit.

7. The method for supporting square well foundation pits according to claim 1, characterized in that, The steel plate retaining wall is uniformly lowered into the strata in a step-by-step, layered manner according to the excavation depth of the foundation pit.

8. The method for supporting square well foundation pits according to claim 7, characterized in that, The steel plate retaining walls of adjacent layers are connected by full welding.

9. The method for supporting square well foundation pits according to claim 1, characterized in that, The thickness of the well wall is not less than 350 mm.

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