Seasonal permafrost region pile foundation structure

Abstract

The utility model discloses a seasonal frozen soil area pile foundation structure and a construction method thereof, relates to the field of foundations, and solves the problem that an existing seasonal frozen soil area pile foundation structure is not beneficial for backfill to release frost heaving force through deformation. According to the technical scheme, the seasonal frozen soil area pile foundation structure comprises a pile body, the pile body is sequentially divided into an upper pile body section, a middle pile body section and a lower pile body section from top to bottom, the upper pile body section is exposed out of the ground, the middle pile body section is located in a thawing and freezing layer, the lower pile body section is located in a permanent freezing layer, and deformable backfill is arranged on the periphery of the middle pile body section. The deformable backfill material is sealed through the sealing layer or sealed through the sealing layer and the pile body. The sealing layer can prevent rainfall, underground water and other natural water from permeating into the deformable backfill material, so that the deformable backfill material can be kept dry for a long time and can keep deformability for a long time, and therefore the deformable backfill material can effectively release frost heaving force of a thawing and freezing layer around the middle-section pile body through deformation. The photovoltaic pile foundation is used as a photovoltaic pile foundation.

Description

TECHNICAL FIELD

[0001] The utility model relates to basic field, concretely is a kind of pile foundation structure in seasonal frozen soil area, and the construction method of the pile foundation structure. BACKGROUND

[0002] Northwest region is vast, sunshine time is high, population is less, and it is the main concentration area of photovoltaic construction. Northwest region is located in mid-latitude zone, cold in winter, and it is the main distribution area of frozen soil region in China. Seasonal frozen soil often leads to photovoltaic pile foundation frost heaving and thawing sinking, tilting and local damage with temperature change, which greatly threatens the safety of photovoltaic power station.

[0003] For the treatment of seasonal frozen soil area pile foundation, there are currently hot stick, hot pile foundation and other methods, but the cost is high, and the process is relatively complex. Patent with authorized announcement number CN 204982931 U discloses an anti-frost heaving photovoltaic support foundation, which comprises a foundation hole and a steel pipe pile. The lower part of the foundation hole extends below the frost heaving line, and the steel pipe pile is arranged in the foundation hole. The outer periphery of the steel pipe pile is filled with backfill material between the foundation hole. The backfill material is a non-frost heaving material, that is, a material that does not frost heave under frozen soil environmental conditions. The backfill material plays a buffering role in the transmission of frost cutting force, reduces the frost cutting force on the steel pipe pile, and prevents the frost cutting force on the foundation from being too large. Because of the water in nature such as precipitation and groundwater will enter the backfill material, the backfill material becomes frozen soil or a material equivalent to frozen soil, so that the backfill material partially loses or completely loses the buffering effect. In addition, the backfill material is in the form of a cylinder and is distributed around the outer periphery of the steel pipe pile and in abutment with the hole wall of the foundation hole. When frost heaving occurs, it is not conducive to the release of frost heaving force by the upward deformation of the backfill material. CONTENT OF UTILITY MODEL

[0004] The utility model provides a seasonal frozen soil area pile foundation structure first, solves the problem that the existing seasonal frozen soil area pile foundation structure is not conducive to the release of frost heaving force by the deformation of backfill material.

[0005] The technical scheme adopted by the utility model is as follows: a seasonal frozen soil area pile foundation structure, which comprises a pile body. The pile body is sequentially divided into an upper segment pile body, a middle segment pile body and a lower segment pile body from top to bottom. The upper segment pile body is exposed on the ground. The middle segment pile body is located in the thawing and freezing layer. The lower segment pile body is located in the permafrost layer. A deformable backfill material is arranged around the outer periphery of the middle segment pile body. The deformable backfill material is closed by a sealing layer or closed by the sealing layer and the pile body.

[0006] In order to facilitate the upward deformation of the deformable backfill material and reduce the extrusion of frost heaving force on the pile body, further, the outer contour of the deformable backfill material is in the form of a circular truncated cone with a small lower part and a large upper part.

[0007] In order to facilitate the upward deformation of the deformable backfill material around the outer periphery of the middle segment pile body, further, the middle segment pile body is in the form of a necked segment with a large lower part and a small upper part, or the middle segment pile body and the upper segment pile body are in the form of necked segments with a large lower part and a small upper part.

[0008] In order to facilitate the pile construction and ensure the stress of the pile, specifically: the outer contour of the pile at any horizontal section is circular, and the lower section of the pile is cylindrical.

[0009] The pile can be a prefabricated pile or a cast-in-place pile, and the pile can be a steel structure or a reinforced concrete structure. Specifically: the pile is a steel structure or a reinforced concrete structure.

[0010] The deformable backfill material can deform upwards when frost heaving occurs in the thawed layer, and can deform downwards and reset after the thawed layer melts. Specifically: the deformable backfill material is coarse gravel, and the particle size of the coarse gravel is 20mm-50mm.

[0011] In order to avoid the precipitation from gathering above the sealing layer on the top of the deformable backfill material, further: the sealing layer on the top of the deformable backfill material is higher than the ground and is arranged downwardly along the radial direction of the pile.

[0012] The sealing layer plays a role in blocking the infiltration of natural water bodies into the deformable backfill material, and the sealing layer can be a structural layer or a waterproof roll material. Specifically: the sealing layer is geotextile.

[0013] In order to avoid the geotextile from being blown away or damaged due to direct exposure, further: a cover layer is provided on the top of the sealing layer on the top of the deformable backfill material. For example, the cover layer is coarse gravel, and the particle size of the coarse gravel is 20mm-50mm.

[0014] The utility model also provides a kind of construction method of seasonal frozen soil area pile foundation structure, construction obtains any seasonal frozen soil area pile foundation structure described above, also solve the problem that the pile foundation structure of existing seasonal frozen soil area is not conducive to backfill material to release frost heaving force by deformation.Seasonal frozen soil area pile foundation structure construction method includes the following steps:

[0015] S1, level the site and excavate the foundation pit, the bottom of the foundation pit is located in the permafrost layer.

[0016] In order to facilitate the excavation construction of the foundation pit, and also to facilitate the upward deformation of the deformable backfill material for subsequent construction, thereby reducing the extrusion of the pile by frost heaving force, further: the foundation pit is in the shape of a circular truncated cone with the top larger than the bottom.

[0017] S2, construct the pile at the bottom of the foundation pit, the pile is sequentially divided into upper section, middle section and lower section from top to bottom, wherein the upper section is above the ground, the middle section is in the thawed layer, and the lower section is in the permafrost layer.

[0018] In order to facilitate the upward deformation of the deformable backfill material around the middle section of the pile, further: the middle section of the pile is a necked section with the bottom larger than the top, or the middle section and the upper section of the pile are necked sections with the bottom larger than the top.

[0019] In order to facilitate the pile body construction and ensure the stress of the pile body, specifically: the outer contour of the pile body at any horizontal section is circular, and the lower section of the pile body is in a cylindrical shape.

[0020] The pile body can be a prefabricated pile or a cast-in-place pile, and the pile body can be a steel structure or a reinforced concrete structure. Further, when the pile body is constructed, the pile hole is first constructed and the lower section of the pile body is inserted into the permafrost layer, or the lower section of the pile body is directly inserted into the permafrost layer without constructing the pile hole, and then the middle section of the pile body is connected to the top of the lower section of the pile body by a sleeve, and the middle section of the pile body and the upper section of the pile body are an integral whole or are connected by the sleeve; or, when the pile body is constructed, the pile hole is first constructed at the bottom of the foundation pit, then the formwork is supported, the steel reinforcement cage of the middle section of the pile body and the lower section of the pile body is placed, the middle section of the pile body and the lower section of the pile body are poured, the pile head is chiseled, the steel reinforcement of the upper section of the pile body is bound, the formwork is supported again, and finally the upper section of the pile body is poured, and finally curing and form removal are performed.

[0021] S3, a sealing layer is constructed at the bottom and around the foundation pit.

[0022] The sealing layer plays a role in blocking the infiltration of water bodies in nature into the deformable backfill material, and the sealing layer can be a structural layer or a waterproof roll material. Specifically, the sealing layer is a geotextile.

[0023] S4, the deformable backfill material is backfilled into the foundation pit, and a sealing layer is constructed on the top of the deformable backfill material, so that the deformable backfill material is closed by the sealing layer or by the sealing layer and the pile body.

[0024] The deformable backfill material can deform upward when frost heaving occurs in the thawing layer, and can deform downward and reset after the thawing layer melts. Specifically, the deformable backfill material is coarse gravel with a particle size of 20mm to 50mm.

[0025] In order to avoid precipitation from gathering above the sealing layer on the top of the deformable backfill material, further, the sealing layer on the top of the deformable backfill material is higher than the ground and is arranged downward along the radial direction of the pile body.

[0026] In order to avoid the geotextile from being blown away or damaged due to direct exposure, further, step S5 is included, S5, a cover layer is laid on the top of the geotextile on the top of the deformable backfill material. For example, the cover layer is coarse gravel with a particle size of 20mm to 50mm.

[0027] The utility model discloses beneficial effect is: deformable backfill is closed through sealing layer, and sealing layer can block the water of nature such as precipitation, groundwater and infiltrate into deformable backfill, make deformable backfill can keep dry for a long time, make deformable backfill keep deformation ability for a long time, thereby make deformable backfill can be through deformation effective release the frost heaving force of the thawed layer around middle section pile body. Seasonal frozen soil area pile foundation structure is safe and reliable, and the cost is low, and the structure is simple, and the influence of the frost heaving force of thawed layer to pile body is little, and the influence of seasonal frozen soil to pile body is adapted well, especially suitable for being used as photovoltaic pile foundation, can guarantee the safety of photovoltaic power station, improve the yield of photovoltaic power station, provide new thought for the construction of photovoltaic power station in frozen soil area, and the construction method of seasonal frozen soil area pile foundation structure has simple process, low construction difficulty and high construction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is the schematic diagram of the utility model seasonal frozen soil area pile foundation structure.

[0029] The figure mark: pile body 1, upper section pile body 1-1, middle section pile body 1-2, lower section pile body 1-3, deformable backfill 2, sealing layer 3, cover layer 4. DETAILED DESCRIPTION

[0030] The utility model will be further explained in connection with the drawings.

[0031] The stratum of seasonal frozen soil area can be divided into upper layer and lower layer, and the upper layer is thawed layer, and the upper surface of thawed layer is ground surface, and the lower layer is permafrost layer. Figure 1 As shown in the utility model seasonal frozen soil area pile foundation structure includes pile body 1, and pile body 1 is sequentially divided into upper section pile body 1-1, middle section pile body 1-2 and lower section pile body 1-3 from top to bottom, and upper section pile body 1-1, middle section pile body 1-2 and lower section pile body 1-3 are an entirety or fixedly connected. Among them, upper section pile body 1-1 emerges on the ground surface, middle section pile body 1-2 is located in the thawed layer, and lower section pile body 1-3 is located in the permafrost layer. Pile body 1 is cylindrical or prismatic, and the outer contour of pile body 1 at any horizontal section is circular or polygonal. In order to facilitate the construction of pile body 1 and ensure the stress of pile body 1, the outer contour of pile body 1 at any horizontal section is generally circular. The length and shape of pile body 1 are determined according to the bearing capacity requirement and geological conditions. Pile body 1 can be a prefabricated pile or a cast-in-place pile, and pile body 1 can be a steel structure or a reinforced concrete structure, and pile body 1 can be an entirety or fixedly connected between each section.

[0032] Deformable backfill material 2 is provided around the outer periphery of the middle section pile 1-2, and directly abuts against the middle section pile 1-2. The deformable backfill material 2 is located in the thaw layer. When frost heave occurs in the thaw layer, the deformable backfill material 2 deforms upwards, reducing the pressure of frost heave on the pile 1. After the thaw layer melts, the deformable backfill material 2 can deform downwards and return to its original position. For example, the deformable backfill material 2 is crushed stone and coarse sand, with a particle size of 20mm to 50mm. To make it easier for the deformable backfill material 2 to deform upwards after being subjected to frost heave, thereby releasing the frost heave force and reducing the pressure of frost heave on the pile 1, the outer contour of the deformable backfill material 2 is a frustum shape, smaller at the bottom and larger at the top, such as... Figure 1 As shown. Additionally, to facilitate the upward deformation of the deformable backfill material 2 around the outer periphery of the middle pile 1-2, the middle pile 1-2 is a constricted section with a larger diameter at the bottom and a smaller diameter at the top, meaning the pile diameter of the middle pile 1-2 gradually decreases from bottom to top; or the middle pile 1-2 and the upper pile 1-1 are constricted sections with a larger diameter at the bottom and a smaller diameter at the top, meaning the pile diameter of the middle pile 1-2 and the upper pile 1-1 gradually decreases from bottom to top. The lower pile 1-3 of pile 1 is located in the permafrost layer and is generally cylindrical. The pile bottom elevation of pile 1 is determined based on geological conditions, load, pile diameter, etc., while the pile top elevation of pile 1 is determined based on the photovoltaic panel installation design height.

[0033] Theoretically, the formula for frost shear force is F = τ * s, where τ is the tangential force and s is the pile circumference. When frost heave occurs, using crushed stone and coarse sand, which are not sensitive to temperature, as deformable backfill material 2 can reduce τ. The middle section of pile 1-2 is a constricted section with a larger bottom and a smaller top; after frost heave, the circumference of the pile body in contact with it decreases, which can reduce the frost shear force F. Compared to a pile with a constant diameter, the middle section of pile 1-2 and the upper section of pile 1-1, being constricted sections with a larger bottom and a smaller top, are more conducive to the upward movement of the deformable backfill material 2 around pile 1, reducing the compression on pile 1. After the temperature rises, the frost heave force disappears, and the deformable backfill material 2 around pile 1 falls back and returns to its original position.

[0034] The deformable backfill material 2 is sealed by the sealing layer 3, meaning the deformable backfill material 2 is completely sealed by the sealing layer 3; or, it is sealed by the sealing layer 3 and the pile body 1, meaning the sealing layer 3 and the pile body 1 together seal the deformable backfill material 2. The sealing layer 3 serves to prevent water from seeping into the deformable backfill material 2. The sealing layer 3 can be a structural layer or a flexible waterproof material such as a waterproof membrane. For example, the sealing layer 3 is geotextile. When the sealing layer 3 is a structural layer, it only needs to function as a waterproof barrier.

[0035] In order to avoid the problem that the precipitation is gathered above the sealing layer 3 on the top of the deformable backfill 2 and then seeps into the deformable backfill 2, the sealing layer 3 on the top of the deformable backfill 2 is higher than the ground and is arranged downward along the radial direction of the pile body 1, so that the precipitation can be automatically discharged. The outer edge of the sealing layer 3 on the top of the deformable backfill 2 extends out of the deformable backfill 2, for example, the outward extension distance is more than 5 times the particle size of the gravel in the deformable backfill 2, to prevent the water body from seeping into the deformable backfill 2.

[0036] In order to avoid that the geotextile is blown away and damaged due to direct exposure, the sealing layer 3 on the top of the deformable backfill 2 can be further provided with a covering layer 4. The covering layer 4 plays a protective role for the sealing layer 3, for example, the covering layer 4 is gravel coarse sand, and the coarse sand particle size is 20mm-50mm.

[0037] The utility model also provides a kind of construction method of seasonal frozen soil area pile foundation structure, and construction obtains above-mentioned seasonal frozen soil area pile foundation structure.The construction method of seasonal frozen soil area pile foundation structure includes the following steps.

[0038] S1, level the site and excavate the foundation pit, and the bottom of the foundation pit is located in the permafrost layer.

[0039] The center position of the foundation pit is the position of the pile body 1. In order to facilitate the excavation construction of the foundation pit, and also to facilitate the upward deformation of the deformable backfill 2 in subsequent construction, thereby reducing the extrusion of the pile body 1 by the frost heaving force, the foundation pit is in the shape of a circular truncated cone with the upper part larger and the lower part smaller.

[0040] S2, construct the pile body 1 at the bottom of the foundation pit.

[0041] The pile body 1 is sequentially divided into an upper section pile body 1-1, a middle section pile body 1-2 and a lower section pile body 1-3 from top to bottom, wherein: after construction is completed, the upper section pile body 1-1 is located above the ground, the middle section pile body 1-2 is located in the thawing layer, and the lower section pile body 1-3 is located in the permafrost layer. The pile body 1 is in the shape of a cylinder or a prism, and the outer contour of the pile body 1 at any horizontal section is in the shape of a circle or a polygon. In order to facilitate the construction of the pile body 1 and ensure the stress of the pile body 1, the outer contour of the pile body 1 at any horizontal section is generally in the shape of a circle. The length and shape of the pile body 1 are determined according to the bearing capacity requirement and the geological condition. The pile body 1 can be a prefabricated pile or a cast-in-place pile, can be a steel structure or a reinforced concrete structure, and can be an integral whole or fixedly connected between sections.

[0042] In order to facilitate the deformation of the deformable backfill 2 on the outer periphery of the middle section pile body 1-2, the middle section pile body 1-2 is a necked section with a large diameter at the bottom and a small diameter at the top, that is, the diameter of the middle section pile body 1-2 gradually decreases from bottom to top; or the middle section pile body 1-2 and the upper section pile body 1-1 are necked sections with a large diameter at the bottom and a small diameter at the top, that is, the diameters of the middle section pile body 1-2 and the upper section pile body 1-1 gradually decrease from bottom to top. The lower section pile body 1-3 of the pile body 1 is located in the permafrost layer, and is generally in a cylindrical shape. The bottom elevation of the pile body 1 is determined according to the geology, load, pile diameter, etc., and the top elevation of the pile body 1 is determined according to the design height of the photovoltaic panel installation.

[0043] The pile body 1 is a steel structure. When the pile body 1 is constructed, the pile hole is first constructed and the lower section pile body 1-3 is inserted into the permafrost layer. The lower section pile body 1-3 can also be directly inserted into the permafrost layer without constructing a pile hole. Then, the middle section pile body 1-2 is connected to the top of the lower section pile body 1-3 by a sleeve. The middle section pile body 1-2 and the upper section pile body 1-1 are an integral whole or are connected by a sleeve.

[0044] The pile body 1 is a reinforced concrete structure. When the pile body 1 is constructed, the pile hole is first constructed at the bottom of the foundation pit, then the formwork is supported, the reinforcement cages of the middle section pile body 1-2 and the lower section pile body 1-3 are placed, the middle section pile body 1-2 and the lower section pile body 1-3 are poured, the middle section pile body 1-2 and the lower section pile body 1-3 are an integral whole, the pile head is chiseled, the reinforcement of the upper section pile body 1-1 is bound, the formwork is supported again, and finally the upper section pile body 1-1 is poured. Finally, maintenance and form removal are performed. In addition, the pile body 1 can also be a prefabricated reinforced concrete structure.

[0045] S3, constructing a sealing layer 3 at the bottom and around the foundation pit.

[0046] The sealing layer 3 blocks the infiltration of water bodies in nature into the deformable backfill 2. The sealing layer 3 can be a structural layer or a flexible waterproof material such as a waterproof roll material. For example, the sealing layer 3 is a geotextile, which can be directly laid during construction. When the sealing layer 3 is a structural layer, the structural layer only needs to have a water-blocking function.

[0047] S4, backfilling the deformable backfill 2 into the foundation pit, and constructing a sealing layer 3 on the top of the deformable backfill 2, so that the deformable backfill 2 is closed by the sealing layer 3 or by the sealing layer 3 and the pile body 1.

[0048] The deformable backfill material 2 can deform upwards when frost heave occurs in the thaw layer, and can deform downwards and return to its original position after the thaw layer melts. Specifically, the deformable backfill material 2 is composed of crushed stone and coarse sand with a particle size of 20mm to 50mm. The deformable backfill material 2 directly abuts against the middle pile body 1-2. Located in the thaw layer, when frost heave occurs in the thaw layer, the deformable backfill material 2 deforms upwards, reducing the pressure of frost heave on the pile body 1. After the thaw layer melts, the deformable backfill material 2 can deform downwards and return to its original position. For example, the deformable backfill material 2 is composed of crushed stone and coarse sand with a particle size of 20mm to 50mm. Since the foundation pit is shaped like a frustum with a larger top and a smaller bottom, the outer contour of the deformable backfill material 2 is also shaped like a frustum with a larger top and a smaller bottom. The deformable backfill material 2 is more likely to deform upwards after being subjected to frost heave, thereby releasing the frost heave force and reducing the pressure of frost heave on the pile body 1. Figure 1 As shown. To prevent rainwater from accumulating above the sealing layer 3 on top of the deformable backfill material 2 and subsequently seeping into the deformable backfill material 2, the sealing layer 3 on top of the deformable backfill material 2 is arranged above the ground and radially downwards along the pile body 1, allowing rainwater to drain automatically. The outer edge of the sealing layer 3 on top of the deformable backfill material 2 extends beyond the deformable backfill material 2, for example, by a distance more than 5 times the particle size of the crushed stone in the deformable backfill material 2, to prevent water from seeping into the deformable backfill material 2.

[0049] To prevent the geotextile from being blown away or damaged due to direct exposure, the construction method for pile foundation structures in seasonally frozen soil areas also includes step S5. S5: Lay a cover layer 4 on top of the geotextile at the top of the deformable backfill material 2. The cover layer 4 protects the sealing layer 3; for example, the cover layer 4 is composed of crushed stone and coarse sand with a particle size of 20mm to 50mm.

Claims

1. A pile foundation structure in a seasonally frozen ground region, comprising a pile body (1), the pile body (1) being sequentially divided into an upper section pile body (1-1), a middle section pile body (1-2) and a lower section pile body (1-3) from top to bottom, wherein the upper section pile body (1-1) is exposed to the ground surface, the middle section pile body (1-2) is located in a thawed frozen layer, and the lower section pile body (1-3) is located in a permafrost layer, and a deformable backfill material (2) is provided on the outer periphery of the middle section pile body (1-2), characterized in that: The deformable backfill (2) is enclosed by the sealing layer (3), or by the sealing layer (3) and the pile body (1). ​ 2. The pile foundation structure in the seasonally frozen ground region according to claim 1, characterized by: The outer contour of the deformable backfill (2) is a circular truncated cone with a small lower part and a large upper part.

3. The pile foundation structure in a seasonally frozen ground region according to Claim 1, characterized by: The middle section pile body (1-2) is a necked section with a large lower part and a small upper part, or the middle section pile body (1-2) and the upper section pile body (1-1) are necked sections with a large lower part and a small upper part.

4. The pile foundation structure in a seasonally frozen ground region according to Claim 1, wherein: The outer contour of the pile body (1) at any horizontal section is circular, and the lower section pile body (1-3) is cylindrical.

5. The pile foundation structure in a seasonally frozen ground region according to Claim 1, wherein: The pile body (1) is a steel structure or a reinforced concrete structure.

6. The pile foundation structure in a seasonally frozen ground region according to Claim 1, wherein: The deformable backfill (2) is gravelly coarse sand, and the coarse sand has a particle size of 20mm-50mm.

7. The pile foundation structure in a seasonally frozen ground region according to Claim 1, characterized by: The sealing layer (3) on the top of the deformable backfill (2) is higher than the ground and is arranged downward along the radial direction of the pile body (1).

8. The pile foundation structure in the seasonally frozen ground region according to any one of claims 1 to 7, characterized by: The sealing layer (3) is geotextile.

9. The seasonally frozen ground area pile foundation structure according to claim 8, characterized by: The top of the sealing layer (3) on the top of the deformable backfill (2) is provided with a cover layer (4).

10. The pile foundation structure in a seasonally frozen ground region according to Claim 9, characterized by: The cover layer (4) is gravelly coarse sand, and the coarse sand has a particle size of 20mm-50mm.

Images