A method for constructing a pipeline in an expansive soil layer

Abstract

The present invention relates to the field of pipeline construction, and in particular to a method for pipeline construction in an expansive soil layer, which comprises the following steps: drainage and interception of water supply and drainage measures around the construction area to reduce water flow to the construction area; drainage structures are arranged on both sides of the length direction of the foundation pit; foundation pit is excavated, and slopes are laid on both sides of the length direction of the foundation pit; after the slope construction is completed, steel sheet pile construction is carried out, and after the steel sheet pile construction is completed, the foundation pit is excavated to reach the designed depth; a crushed stone layer is laid at the bottom of the foundation pit, a waterproof membrane is laid on the slope of the foundation pit, a base is cast on the crushed stone layer, and support piles are cast between the inner side wall of the foundation pit and the side wall of the base. The present invention has the effect of facilitating the lifting of pipelines into the foundation pit and improving the construction efficiency of the foundation pit.

Description

Technical Field

[0001] The invention relates to the field of pipeline construction, in particular to a pipeline construction method in an expansive soil layer. Background Art

[0002] Expansive soil is a clay soil that expands dramatically after being soaked in water and shrinks significantly after losing water. Since the soil contains a lot of clay minerals such as montmorillonite and illite, it is very hydrophilic. When the natural water content is high, the expansion amount and expansion force after soaking in water are small, while the shrinkage amount and shrinkage force after losing water are large; when the natural porosity is larger, the expansion amount and expansion force are smaller, and the shrinkage amount and shrinkage force are larger. Therefore, when constructing in the expansive soil layer, the construction work is difficult and greatly affects the construction progress.

[0003] When laying large diameter (greater than 1.5m in diameter) pipelines in expansive soil layers, steel sheet piles are generally used to support the slope construction first, and steel sheet piles are set in the foundation pit to support the inner wall of the foundation pit, and internal supports are set to support the steel sheet piles. However, due to the large diameter of the laid pipeline, the foundation pit is deep, and the internal support is in the middle part of the foundation pit and close to the ground, which further makes it difficult to lift the pipeline into the foundation pit, further reducing the construction progress. Summary of the invention

[0004] In order to facilitate the lifting of pipelines into a foundation pit and improve the construction efficiency of the foundation pit, the present invention provides a pipeline construction method in an expansive soil layer.

[0005] The present invention provides a method for constructing a pipeline in an expansive soil layer, which adopts the following technical solution:

[0006] A method for constructing a pipeline in an expansive soil layer comprises the following steps:

[0007] Divert or intercept water supply and drainage measures around the construction area to reduce water flow to the construction area;

[0008] Drainage structures are set up on both sides of the foundation pit length direction;

[0009] Excavation of foundation pit, slopes on both sides of the length of the foundation pit; after the slope construction is completed, steel sheet pile construction is carried out. After the steel sheet pile construction is completed, the foundation pit is excavated to the designed depth;

[0010] A gravel layer is laid at the bottom of the foundation pit, a waterproof membrane is laid on the slope of the foundation pit, a base is poured on the gravel layer, and supporting piles are poured between the inner wall of the foundation pit and the side wall of the base.

[0011] In a specific feasible implementation scheme, the drainage structure includes a drainage pipe and a drainage well. The drainage pipe extends along the length direction of the foundation pit. The drainage pipe is arranged on both sides of the length direction of the foundation pit. The drainage pipe is arranged underground outside the foundation pit. The drainage pipe is a mesh permeable pipe. The drainage pipe is wrapped with geotextile. The drainage well is arranged outside the foundation pit, and the drainage pipe is connected to the drainage well.

[0012] In a specific feasible implementation scheme, after the pipeline laying in the foundation pit is completed, partitioned backfilling is adopted when backfilling the foundation pit.

[0013] In a specific implementation scheme, the partition backfilling method is:

[0014] The area between the foundation pit base and the top surface of the foundation is divided into Zone A; the area between the top surface of the foundation and 450-550mm above the pipe is divided into Zone B, and the area between the top of Zone B and the ground is Zone C;

[0015] Backfill area A with clay soil, with each layer 245-255mm thick and compacted, and control the thickness after compaction to be 190-210mm, and backfill until area A is filled;

[0016] Backfill area B with clay soil, with each layer 295-305mm thick and compacted, and control the thickness after compaction to be 245-255mm, and backfill until area B is filled;

[0017] The C area is backfilled with original soil, each layer is 295-305mm thick and compacted, and the thickness after compaction is controlled to be 245-255mm. The backfill is until it is 450-550mm away from the top surface of the C area; the area 450-550mm away from the top surface of the C area is backfilled with original soil and then naturally settled.

[0018] In a specific feasible implementation plan, the slope coefficient of the slope on both sides of the foundation pit is 1.5;

[0019] A reinforcing rib connected to the steel sheet pile is arranged on the top surface of the supporting pile; a guide plate is arranged on the reinforcing rib, and one end of the guide plate extends to the top of the base.

[0020] In a specific possible implementation manner, a connecting block is provided between adjacent bases, and both ends of the connecting block are connected to the bases.

[0021] In a specific possible implementation scheme, a floating ball is arranged in the drainage well, a mark rod is arranged on the floating ball, and an end of the mark rod away from the floating ball extends out of the drainage well;

[0022] Determine the groundwater situation by observing the length of the pole extending from the drainage well:

[0023] If the extension length of the benchmark exceeds the preset first threshold, it indicates that there is a lot of groundwater, the expansive soil may absorb water and swell, and the groundwater needs to be pumped out;

[0024] If the extension length of the benchmark is less than the preset second threshold, it indicates that there is less groundwater, the expansive soil may lose water and shrink, and water needs to be supplemented;

[0025] Otherwise, it indicates that the groundwater is normal and remains the same.

[0026] In a specific possible implementation scheme, a sponge layer is provided between the waterproof membrane and the slope, and air holes are provided on the waterproof membrane;

[0027] Under normal conditions, the air pores are closed; when there is a lot of groundwater, the air pores are opened and the sponge layer evaporates water to the outside.

[0028] In a specific possible implementation scheme, an anchor rod is provided at one end of the steel sheet pile close to the ground;

[0029] An elastic layer is provided between the crushed stone layer and the bottom surface of the foundation pit;

[0030] A support column is arranged on the bottom surface of the base, and the support column extends underground in a vertical direction.

[0031] In a specific possible implementation scheme, a connecting hole is provided in the support column, and a spray hole connected to the connecting hole is provided on the side wall of the support column at one end away from the base;

[0032] Before setting up the base, the support column is first inserted into the ground, and cement slurry is injected into the connection hole so that the injection hole sprays cement slurry to the surrounding area. After the cement slurry solidifies, a blocking platform is formed; then the base is poured on the top of the support column.

[0033] In summary, the present invention includes at least one of the following beneficial technical effects:

[0034] 1. Reduce water flow to the construction area through drainage and interception, and reduce water entering the land around the foundation pit through waterproof membrane, reduce the expansion of expansive soil, and improve the stability of the inner wall of the foundation pit. Through further support of supporting piles and bases, the stability of steel sheet piles in the foundation pit is improved, so that internal support between steel sheet piles can be omitted, which is convenient for lifting pipes into the foundation pit and improving construction efficiency.

[0035] 2. When backfilling the foundation pit, backfill different soils in Area A, Area B and Area C. This will not only improve the bearing capacity of the foundation, but also reduce the squeezing of the pipes buried in the foundation pit and avoid damage to the pipes. Backfilling the original soil can recycle and reuse earthwork resources and reduce the consumption of natural resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of Example 1.

[0037] Figure 2 It is a top view of the foundation pit in Example 1.

[0038] Figure 3 It is a structural schematic diagram of Example 2.

[0039] Figure 4 It is a top view of the foundation pit in Example 2.

[0040] Figure 5 It is a schematic diagram of the overall structure of the support column.

[0041] Explanation of the accompanying reference numerals: 1. Steel sheet pile; 2. Elastic layer; 3. Gravel layer; 4. Reinforcement ribs; 5. Guide plate; 6. Anchor rod; 7. Support pile; 8. Connecting block; 9. Support column; 10. Injection hole; 11. Connecting hole; 12. Base. DETAILED DESCRIPTION

[0042] The following is combined with Figure 1-5 The present invention is described in further detail.

[0043] Embodiment 1:

[0044] Reference Figure 1 and Figure 2 The pipeline construction method for the expansive soil layer includes the following steps:

[0045] S100, divert and intercept water supply and drainage measures around the construction area to reduce the flow of water to the construction area.

[0046] Investigate the water supply and drainage measures of farmland, canals, etc. around the construction area in advance, and set up pipes or dig ditches to divert water, or dig intercepting ditches to intercept water, so as to reduce the flow of water to the area where the foundation pit is to be excavated.

[0047] Waterproof tape and other anti-seepage treatments are applied to the bottom of the canals around the construction area to reduce water penetration into the construction area, avoid the adverse effects of water swelling caused by expansive soil, and ensure the safety of the construction area.

[0048] A drainage structure (not shown in the figure) is laid in the soil layer outside the foundation pit. The drainage structure includes a drainage pipe and a drainage well. The drainage pipe extends along the length of the foundation pit. The drainage pipe is a mesh permeable pipe. The outer wall of the drainage pipe is wrapped with a geotextile. The drainage well is connected to one end of the drainage pipe in the length direction. Water in the soil layer penetrates through the geotextile into the drainage pipe, and the drainage pipe discharges the water into the drainage well. By observing the water level in the drainage well, the groundwater situation is timely understood, and the groundwater is pumped out in time to reduce the water absorption of the expansive soil, avoid the obvious expansion and contraction of the expansive soil due to water absorption, and ensure the safety of the construction area.

[0049] S200, foundation pit excavation.

[0050] The slope is cut on both sides of the foundation pit in the length direction, 1:1.5 on one side and 1:1.5 on the other side. In the actual construction process, the slope ratio can be adjusted according to the construction needs. After the slope construction is completed, the steel sheet piles 1 are constructed, and the foundation pit is further excavated in the area surrounded by the steel sheet piles 1. Since there is no internal support between the steel sheet piles 1, the soil can be easily transported out of the foundation pit during the foundation pit excavation process, which increases the excavation speed of the foundation pit and improves the construction efficiency.

[0051] During the excavation of the foundation pit, a transparent waterproof membrane (not shown in the figure) is covered on the slope of the foundation pit, that is, the slope formed by the slope is covered with a waterproof membrane. The waterproof membrane blocks rainwater, and the slope condition can be observed through the waterproof membrane, so that the soil layer changes can be observed in real time, and the soil layer can be avoided as much as possible from significantly expanding or shrinking in volume after being soaked in rainy weather, thereby improving the stability of the slope and the safety of construction.

[0052] S300 , pouring the base 12 , and laying pipes on the base 12 .

[0053] A crushed stone layer 3 is laid on the inner bottom surface of the foundation pit, and a base 12 is cast on the crushed stone layer 3. The base 12 is used to stably support the pipes to be laid and fix the pipes. At the same time, the base 12 is made of concrete, which can apply a large pressure to the soil layer, thereby preventing the buoyancy caused by the swelling of the expansive soil after absorbing water. Support piles 7 are cast between the inner wall of the foundation pit and the side wall of the base 12. The support piles 7 prevent the deformation of the steel sheet piles 1 caused by the swelling of the expansive soil, etc., to ensure the safety and stability of the project.

[0054] S400, foundation pit backfill.

[0055] After completing the laying of pipes in the foundation pit, the foundation pit is backfilled by using the partitioned backfill method.

[0056] The area between the foundation pit base and the top surface of the base 12 is divided into zone A, the area between the top surface of the base 12 and 450-550mm above the pipeline is divided into zone B, and the area between the top of zone B and the ground is zone C.

[0057] Backfill area A with clay soil, with each layer 245-255mm thick, and use impact rammer to compact the soil to increase the compaction degree of the soil in the limited space. Control the thickness after compaction to 190-210mm, and backfill until area A is filled.

[0058] Backfill the clay soil in area B, with each layer 295-305mm thick, and use a small 800kg roller to compact it to avoid damaging the pipeline during the compaction process. The thickness after compaction is controlled to be 245-255mm, and backfill until area B is filled;

[0059] Backfill the original soil in area C, with each layer 295-305mm thick, and compact it with a small 800kg roller to control the thickness after compaction to 245-255mm. Backfill until it is 450-550mm away from the top surface of area C; the area 450-550mm away from the top surface of area C is backfilled with original soil and then settled naturally.

[0060] Backfilling clay soil in Area A and Area B can reinforce the pipeline and prevent the extrusion of the pipeline by expansive soil. Layered backfilling can effectively improve the bearing capacity and stability of the foundation, reduce foundation settlement and deformation, and improve the safety and reliability of the project. Backfilling the original soil in Area C is conducive to reducing transportation time and transportation costs, and can adapt well to the surrounding environment to prevent affecting soil quality and the arable layer environment. It is conducive to reducing the degree of damage to the environment caused by excavation construction and reducing the removal and destruction of soil. It can effectively recycle and reuse earthwork resources, reduce the consumption of natural resources, and help promote green construction and resource recycling.

[0061] Embodiment 2:

[0062] Reference Figure 3 and Figure 4 The difference between Example 2 and Example 1 is that: in step S100, a float is provided in the drainage well, a pole is fixed on the float, an end of the pole away from the float extends out of the drainage well, and a scale is provided on the side wall of the pole.

[0063] By reading the scale reading on the pole, that is, the length of the pole extending out of the drainage well, the situation of groundwater in the drainage well can be understood. When the length of the pole extending out of the drainage well exceeds the preset first threshold, it indicates that there is a lot of groundwater, and there is a hidden danger of obvious swelling due to water absorption by the expansive soil, and it is necessary to pump out the groundwater; when the length of the pole extending out of the drainage well is less than the preset second threshold, it indicates that there is a little groundwater, and there is a hidden danger of obvious shrinkage due to water loss by the expansive soil, and it is necessary to replenish groundwater; otherwise, it indicates that the groundwater is within a safe range and monitoring is sufficient.

[0064] In step S200, before laying the waterproof membrane, a sponge layer is first laid on the surface of the slope, and then a waterproof membrane is laid on the surface of the sponge layer, and a plurality of air holes are provided on the waterproof membrane. Normally, the air holes are in a closed state to prevent rainwater from entering the waterproof membrane through the air holes and being absorbed by the soil layer. The sponge layer has good water absorption and water storage capacity, can attract moisture in the soil layer, thereby absorbing groundwater, and delaying the expansion of expansive soil due to the increase of groundwater. By opening the air holes in sunny weather, the sponge layer can be connected to the external environment, and the water in the sponge layer can be quickly volatilized through air flow, which assists in the discharge of groundwater. When the amount of groundwater is significantly reduced, the sponge layer can be squeezed so that the water in the sponge layer is squeezed out and absorbed by the expansive soil, thereby stabilizing the volume of the expansive soil.

[0065] Reference Figure 5 In step S300, before laying the gravel layer 3, a support column 9 is vertically inserted into the foundation pit. A connection hole 11 extending along the length direction of the support column 9 is provided on the support column 9. A plurality of injection holes 10 connected to the connection hole 11 are provided on the side wall of the support column 9. The injection hole 10 is arranged at one end of the support column 9 underground. By connecting the grouting equipment with the connection hole 11, cement slurry is injected into the connection hole 11, and the cement slurry is sprayed into the soil layer below the foundation pit through the injection hole 10, and forms a blocking platform after solidification. The blocking platform blocks the support column 9 from settling underground, thereby improving the stability of the support column 9 in the soil layer.

[0066] First, an elastic layer 2 is laid on the inner bottom surface of the foundation pit, and then a crushed stone layer 3 is laid on the elastic layer 2. The top of the support column 9 is flush with or protrudes from the top surface of the crushed stone layer 3. Concrete is poured on the crushed stone layer 3 to form a base 12, and the base 12 is poured on the top of the support column 9. After the base 12 is formed, the base 12 is fixedly connected to the support column 9. Since the expansion force is anisotropic when the expansive soil absorbs water and expands, the base 12 is fixedly connected to the support column 9, that is, the base 12 is fixedly connected to the blocking platform. When the expansive soil expands, the anisotropy of the expansive soil will cause the base 12 and the blocking platform to be subjected to thrusts in different directions, and there is a situation of mutual offset, thereby reducing the influence of the expansion of the expansive soil on the stability of the base 12. At the same time, the elastic layer 2 offsets a part of the thrust applied by the expansive soil to the base 12 by its own deformation, further alleviating the influence of the expansion of the expansive soil on the base 12.

[0067] Multiple bases 12 are arranged at intervals along the length direction of the foundation pit, and adjacent bases 12 are fixedly connected to each other by connecting blocks 8. Multiple bases 12 are connected to each other by connecting blocks 8. When a base 12 floats due to the thrust of the expansive soil, the connecting blocks 8 transfer the thrust to the surrounding bases 12, thereby dispersing the thrust, blocking the floating of the base 12, and further improving the stability of the base 12.

[0068] A plurality of anchor rods 6 are arranged at the top of the steel sheet pile 1, which fix the steel sheet pile 1 and the soil layer, thereby improving the stability of the connection between the steel sheet pile 1 and the soil layer, reducing the support for the steel sheet pile 1, and allowing for a larger space between the steel sheet piles 1, thereby facilitating the lifting of the pipeline.

[0069] The reinforcing rib 4 is fixed on the top surface of the supporting pile 7, and the reinforcing rib 4 is fixedly connected to the steel sheet pile 1. The reinforcing rib 4 and the supporting pile 7 further support the steel sheet pile 1, prevent the deformation of the steel sheet pile 1 caused by the expansion of the expansive soil, and ensure the safety and stability of the project. A guide plate 5 is fixed on the reinforcing rib 4, and one end of the guide plate 5 extends to the top of the base 12. In the process of lifting the pipeline, due to the large diameter of the pipeline, there is a problem of position deviation when the pipeline is placed in the base 12, and due to the limited space in the foundation pit, it is difficult to intuitively make accurate adjustment instructions for the deflection direction and distance. The guide plate 5 supports the pipeline. Since the guide plate 5 is inclined on one side facing the base 12, the pipeline has a tendency to roll into the base 12 on the guide plate 5, thereby guiding the lifting of the pipeline and facilitating the quick completion of the setting of the pipeline.

[0070] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a pipeline in an expansive soil layer, characterized in that: The steps include: Divert or intercept water supply and drainage measures around the construction area to reduce water flow to the construction area; Drainage structures are set up on both sides of the foundation pit length direction; The foundation pit is excavated, and slopes are laid on both sides of the length direction of the foundation pit; after the slope construction is completed, the steel sheet pile (1) is constructed, and after the steel sheet pile (1) is constructed, the foundation pit is excavated to the designed depth; Laying a crushed stone layer (3) at the bottom of the foundation pit, laying a waterproof membrane on the slope of the foundation pit, pouring a base (12) on the crushed stone layer (3), and pouring support piles (7) between the inner wall of the foundation pit and the side wall of the base (12); The slope coefficient of the slope on both sides of the foundation pit is 1.5; A reinforcing rib (4) connected to the steel sheet pile (1) is provided on the top surface of the supporting pile (7); a guide plate (5) is provided on the reinforcing rib (4), and one end of the guide plate (5) extends to the top of the base (12); An anchor rod (6) is arranged at one end of the steel sheet pile (1) close to the ground; An elastic layer (2) is provided between the crushed stone layer (3) and the bottom surface of the foundation pit; A support column (9) is provided on the bottom surface of the base (12), and the support column (9) extends vertically toward the ground; A connecting hole (11) is provided in the support column (9), and a spray hole (10) connected to the connecting hole (11) is provided on a side wall of an end of the support column (9) away from the base (12); Before setting the base (12), the support column (9) is first inserted into the ground, and cement slurry is injected into the connection hole (11), so that the injection hole (10) sprays cement slurry to the surrounding area, and after the cement slurry solidifies, a blocking platform is formed; and then the base (12) is poured on the top of the support column (9).

2. The method for constructing a pipeline in an expansive soil layer according to claim 1, characterized in that: The drainage structure includes a drainage pipe and a drainage well. The drainage pipe extends along the length of the foundation pit. The drainage pipe is arranged on both sides of the length of the foundation pit. The drainage pipe is arranged underground outside the foundation pit. The drainage pipe is a mesh permeable pipe. The drainage pipe is wrapped with geotextile. The drainage well is arranged outside the foundation pit, and the drainage pipe is connected to the drainage well.

3. The method for constructing a pipeline in an expansive soil layer according to claim 1, characterized in that: After completing the laying of pipes in the foundation pit, the foundation pit is backfilled in sections.

4. The method for constructing a pipeline in an expansive soil layer according to claim 3, characterized in that: The partition backfill method is: The area between the foundation pit base and the top surface of the base (12) is divided into zone A; the area between the top surface of the base (12) and 450-550 mm above the pipeline is divided into zone B; and the area between the top of zone B and the ground is zone C; Backfill area A with clay soil, with each layer 245-255mm thick and compacted, and control the thickness after compaction to be 190-210mm, and backfill until area A is filled; Backfill area B with clay soil, with each layer 295-305mm thick and compacted, and control the thickness after compaction to be 245-255mm, and backfill until area B is filled; The C area is backfilled with original soil, each layer is 295-305mm thick and compacted, and the thickness after compaction is controlled to be 245-255mm. The backfill is until it is 450-550mm away from the top surface of the C area; the area 450-550mm away from the top surface of the C area is backfilled with original soil and then naturally settled.

5. The method for constructing a pipeline in an expansive soil layer according to claim 1, characterized in that: A connecting block (8) is provided between adjacent bases (12), and both ends of the connecting block (8) are connected to the base (12).

6. The method for constructing a pipeline in an expansive soil layer according to claim 2, characterized in that: A floating ball is arranged in the drainage well, and a pole is arranged on the floating ball, and an end of the pole away from the floating ball extends out of the drainage well; Determine the groundwater situation by observing the length of the pole extending from the drainage well: If the extension length of the benchmark exceeds the preset first threshold, it indicates that there is a lot of groundwater, the expansive soil may absorb water and swell, and the groundwater needs to be pumped out; If the extension length of the benchmark is less than the preset second threshold, it indicates that there is less groundwater, the expansive soil may lose water and shrink, and water needs to be supplemented; Otherwise, it indicates that the groundwater is normal and remains the same.

7. A method for constructing a pipeline in an expansive soil layer according to claim 6, characterized in that: A sponge layer is arranged between the waterproof membrane and the slope, and air holes are provided on the waterproof membrane; Under normal conditions, the air pores are closed; when there is a lot of groundwater, the air pores are opened and the sponge layer evaporates water to the outside.

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