Construction method based on prefabricated gravel mixed pile

Abstract

The construction method comprises the following steps that 1, soil layer attributes of a target foundation to be constructed are determined, the corresponding gravel mixed piles are manufactured on the basis of the soil layer attributes, and the different soil layer attributes correspond to the gravel mixed piles composed of different pile cores; and 2, the manufactured sand-gravel mixed piles are put into corresponding pile holes in all positions of a target foundation, the corresponding sand-gravel mixed piles are put according to attributes of soil layers of different depths of the pile holes, all the sand-gravel mixed piles are spliced together in the depth direction of the pile holes, the sand-gravel mixed piles are tamped, and construction is completed. The drainage and bearing functions are both considered, the method can adapt to complex geological layering, the cost is low, and the green and low-carbon construction concept is met.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology, specifically a construction method based on prefabricated sand and gravel mixed piles. Background Art

[0002] In foundation treatment, the geological strata involved are complex. For example, a certain stratum may contain both weak underlying layers and localized liquefaction layers. For foundation treatment involving such complex strata, existing foundation treatment technologies still have the following shortcomings: 1. It is difficult to balance drainage and load-bearing functions. Although traditional crushed stone piles have drainage capabilities, their load-bearing capacity is limited and cannot meet the requirements of complex loads; although concrete piles have strong load-bearing capacity, their drainage performance is poor and is not conducive to the anti-liquefaction treatment of sandy soil foundations.

[0003] 2. Not suitable for complex geological stratification. The properties of soil layers at different depths vary greatly, and conventional single-material piles are difficult to match the needs of each layer, thus limiting bearing capacity and drainage efficiency.

[0004] 3. High cost. When treating foundations with weak interlayers, traditional single foundation treatment methods need to be applied at the full depth, which is costly.

[0005] 4. Insufficient green and low-carbon construction concepts. Existing technologies have low utilization rates of construction waste and recycled materials, resulting in significant material waste and environmental burden. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a construction method based on prefabricated sand and gravel mixed piles, which can solve the problems described in the background art.

[0007] The technical solution to achieve the objective of this invention is: a construction method based on precast aggregate piles, comprising the following steps: Step 1: Determine the soil properties of the target foundation to be constructed, and construct corresponding sand and gravel mixed piles based on the soil properties. Different soil properties correspond to sand and gravel mixed piles composed of different pile cores. Step 2: Place the prepared sand and gravel mixed piles into the corresponding pile holes at various locations of the target foundation. According to the soil properties at different depths of the pile holes, place the corresponding sand and gravel mixed piles. Join the sand and gravel mixed piles together along the depth direction of the pile holes and compact the sand and gravel mixed piles to complete the construction.

[0008] Furthermore, the sand and gravel mixed pile is a columnar structure with concave and convex structures at both ends, so that two sand and gravel mixed piles can be self-locking and centered through the concave and convex structures.

[0009] Furthermore, the soil properties are determined based on the soil type, liquidity index, permeability, and fine particle content, and then the corresponding sand and gravel mixed piles are determined based on the soil properties. The sand and gravel mixed piles include at least a geotextile layer.

[0010] Furthermore, when the soil layer is determined to be a soft cohesive soil layer, the sand and gravel mixed piles are arranged in the following order from the outside to the inside: a geotextile layer, a medium-coarse sand pile core, a crushed stone pile core, and a concrete pile core. The concrete pile core is used to provide bearing capacity, the medium-coarse sand pile core is used to provide a filter layer, and the crushed stone pile core is used to provide a drainage channel.

[0011] Furthermore, when the soil layer is determined to be a hard cohesive soil layer, the sand and gravel mixed piles are arranged in order from the outside to the inside, including a geotextile layer, a medium-coarse sand core, and a crushed stone core. The medium-coarse sand core is used to provide a filter layer, and the crushed stone core is used to provide drainage channels and bearing capacity.

[0012] Furthermore, when the soil layer is determined to be a medium-coarse sand layer, the sand and gravel mixed piles are arranged from the outside to the inside, including a geotextile layer and a medium-coarse sand pile core, which is used to provide load transfer and compaction.

[0013] Furthermore, when the soil layer is determined to be a silty fine sand layer, the sand and gravel mixed piles are arranged in order from the outside to the inside, including a geotextile layer, a medium-coarse sand pile core, and a crushed stone pile core. The medium-coarse sand pile core is used to provide a filter layer, and the crushed stone pile core is used to provide a drainage channel.

[0014] Furthermore, if condition one is met, the soil layer is determined to be a soft cohesive soil layer; if condition two is met, the soil layer is determined to be a hard cohesive soil layer; if condition three is met, the soil layer is determined to be a medium-coarse sandy soil layer; and if condition four is met, the soil layer is determined to be a silty fine sandy soil layer. Condition 1: Fine particle content (FC) > 15%, Liquidity index <0.25, permeability coefficient k < ; Condition 2: Fine particle content (FC) > 15%, Liquidity index >0.25, permeability coefficient k < ; Condition 3: Fine particle content FC < 15%, permeability coefficient k > ; Condition 4: Fine particle content FC > 15%, permeability coefficient k > .

[0015] Furthermore, the soil properties are determined based on the soil type, liquidity index, permeability, and fine particle content. The corresponding sand-gravel mixed piles are then determined based on these properties. The specific implementation method includes the following steps: Step S1: Determine whether the current soil layer is cohesive soil. If yes, proceed to step S2; otherwise, proceed to step S3. Step S2: Determine whether the liquidity index of the current soil layer is less than the preset liquidity index threshold. If yes, proceed to step S4; otherwise, proceed to step S5. Step S3: Determine whether the permeability coefficient of the current soil layer is less than the preset permeability coefficient threshold. If yes, proceed to step S5; otherwise, proceed to step S6. Step S4: The sand and gravel mixed pile includes a concrete pile core and proceeds to step S5; Step S5: The sand and gravel mixed pile includes a crushed stone pile core, that is, a crushed stone pile core needs to be configured, and then proceed to step S6; Step S6: The sand and gravel mixed pile includes a medium-coarse sand pile core, thereby determining the sand and gravel mixed pile.

[0016] Furthermore, prior to step 1, the following steps are also included: Step a: Excavate a foundation pit at the target site to accommodate the sand and gravel piles; Step b: Place a ring-shaped steel mesh at the bottom of the pit and a steel casing on the side wall of the pit to protect the side wall. The ring-shaped steel mesh is attached to the bottom of the pit and the steel casing is attached to the side wall. Step c: Lay geotextile on the annular steel mesh, with the geotextile adhering at least to the sidewall of the pit to form a geotextile layer. Step d: Fabricate the pile cores sequentially from the inside out, and fill the foundation pit with the corresponding materials to obtain reinforced concrete pile cores, crushed stone pile cores, or medium-coarse sand pile cores. After each pile core is fabricated, a ring-shaped steel mesh is installed around its perimeter. The ring-shaped steel mesh is spaced apart from the already fabricated pile cores, forming a ring-shaped cavity. The corresponding material is then filled into the ring-shaped cavity to create the next pile core. After the pile core corresponding to the current annular cavity is made, the corresponding annular steel mesh is extracted to recover the annular steel mesh, and the next pile core is made until all the pile cores are made, thus obtaining a sand and gravel mixed pile, and making the sand and gravel mixed pile fill the foundation pit. Step e: Compact each pile core to obtain the final sand and gravel mixed pile.

[0017] The beneficial effects of this invention are: This invention balances drainage and load-bearing functions, can adapt to complex geological stratification, is low-cost, and conforms to the concept of green and low-carbon construction. More specifically, it has the following advantages: 1. Enables rapid and efficient construction: The use of prefabricated segmented construction and rapid compaction technology greatly shortens the construction cycle and improves construction efficiency, making it particularly suitable for large-area foundation reinforcement projects.

[0018] 2. Layered structure with multiple functions: The inner concrete core provides the main bearing capacity, the crushed stone layer forms a drainage channel, the medium and coarse sand layer acts as a filter, and the geotextile wrapping prevents particle leakage, thus realizing the integration of multiple functions of the pile body: bearing capacity, drainage, filtration and forming.

[0019] 3. Adaptable to complex geological environments: The internal material ratio can be adjusted according to the mechanical and permeability characteristics of soil layers at different depths to form corresponding pile cores, thereby improving the pile's adaptability to complex geological conditions and its overall stability.

[0020] 4. Reliable connection and strong integrity: The ends of the pile segments are equipped with interlocking structures to improve the connection strength and load transfer capacity between pile segments, and significantly enhance the shear and pull-out resistance.

[0021] 5. Green and environmentally friendly, with renewable materials: Supports the use of recycled aggregates, construction waste and inert fillers, reducing raw material energy consumption and construction carbon emissions, which is in line with the current development trend of green construction.

[0022] 6. Controllable quality throughout the entire process: A real-time monitoring and data feedback mechanism is introduced during the construction process to ensure that the compaction, connection accuracy and construction quality of each pile segment meet the design standards. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating a preferred embodiment of the present invention (the annular suction cup is in a separated state). Figure 2 This is a schematic diagram of a sand and gravel mixed pile consisting of three different types of pile cores; Figures 3-5 This is a schematic diagram of the corresponding processes in steps a-e before step 1. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: like Figures 1-5 As shown, a construction method based on precast aggregate piles includes the following steps: Step 1: Determine the soil properties of the target foundation to be constructed, and construct corresponding sand and gravel mixed piles based on the soil properties. Different soil properties correspond to sand and gravel mixed piles composed of different pile cores.

[0025] It is understood that the sand and gravel mixed pile is a columnar structure, for example, a cylindrical structure. It may include multiple sand and gravel mixed piles, which are stacked and connected together in sequence and buried in the pile holes of the target foundation, thereby installing the sand and gravel mixed piles on the target foundation to realize construction.

[0026] Understandably, the soil properties at different locations within the target foundation area can be determined, allowing for the installation of corresponding gravel-mixed piles at locations with different soil properties. Alternatively, at a current location within the target foundation area, corresponding gravel-mixed piles can be installed based on the soil properties determined at different pile hole depths, thus enabling the installation of different gravel-mixed piles at different depths.

[0027] For example, soil properties are determined based on soil type, liquidity index, permeability, and fine particle content, and then the corresponding sand and gravel mixed piles are determined based on the soil properties. The sand and gravel mixed piles include at least a geotextile layer.

[0028] When the soil layer is determined to be a weak cohesive soil layer, the sand and gravel mixed piles, from the outside to the inside, sequentially include a geotextile layer, a medium-coarse sand core, a crushed stone core, and a concrete core. The concrete core provides bearing capacity, the medium-coarse sand core provides a filter layer, and the crushed stone core provides drainage channels.

[0029] When the soil layer is determined to be a hard cohesive soil layer, the sand and gravel mixed piles, from the outside to the inside, sequentially include a geotextile layer, a medium-coarse sand core, and a crushed stone core. The medium-coarse sand core is used to provide a filter layer, and the crushed stone core is used to provide drainage channels and bearing capacity.

[0030] When the soil layer is determined to be medium-coarse sand, the sand-gravel composite pile, from the outside in, consists of a geotextile layer and a medium-coarse sand core. The medium-coarse sand core is used to provide load transfer and compaction.

[0031] When the soil layer is determined to be silty fine sand, the sand and gravel mixed piles, from the outside to the inside, sequentially include a geotextile layer, a medium-coarse sand core, and a crushed stone core. The medium-coarse sand core is used to provide a filter layer, and the crushed stone core is used to provide a drainage channel.

[0032] For example, the soil layer can be determined to be a soft cohesive soil layer when condition one is met. The soil layer can be determined to be a hard cohesive soil layer when condition two is met. The soil layer can be determined to be a medium-coarse sandy soil layer when condition three is met. The soil layer can be determined to be a silty fine sandy soil layer when condition four is met.

[0033] Condition 1: Fine particle content (FC) > 15%, Liquidity index <0.25, permeability coefficient k < .

[0034] Condition 2: Fine particle content (FC) > 15%, Liquidity index >0.25, permeability coefficient k < .

[0035] Condition 3: Fine particle content FC < 15%, permeability coefficient k > .

[0036] Condition 4: Fine particle content FC > 15%, permeability coefficient k > .

[0037] If the fine particle content (FC) is less than 15%, the soil layer can be considered to be cohesive soil; if the fine particle content (FC) is greater than 15%, the soil layer can be considered to be non-cohesive soil.

[0038] Geotextile layers are used within the pile core to prevent leakage of the pile core and to control the overall shape of the sand and gravel pile. Filter layers improve drainage and prevent clogging.

[0039] Understandably, the composition and structure of gravel-soil composite piles differ depending on the soil properties, and even pile cores made of the same material can serve different functions. For example, in gravel-soil composite piles corresponding to soft cohesive soil layers, the gravel core acts as a drainage channel; however, in gravel-soil composite piles corresponding to hard cohesive soil layers, the gravel core, in addition to serving as a drainage channel, also provides bearing capacity.

[0040] For example, soil properties are determined based on soil type, liquidity index, permeability, and fine particle content. The corresponding sand-gravel mixed pile is then determined based on these properties. This can be achieved using a specific implementation method. Alternatively, other methods can be employed, such as the following steps: Step S1: Determine whether the current soil layer is cohesive soil. If yes, proceed to step S2; otherwise, proceed to step S3.

[0041] Step S2: Determine whether the current soil liquidity index is less than the preset liquidity index threshold. If yes, proceed to step S4; otherwise, proceed to step S5.

[0042] The preset liquid index threshold can be determined according to the actual situation; different preset liquid index thresholds can be determined for different situations. In this embodiment, the preset liquid index threshold is 0.25.

[0043] Step S3: Determine whether the permeability coefficient of the current soil layer is less than the preset permeability coefficient threshold. If yes, proceed to step S5; otherwise, proceed to step S6.

[0044] The preset permeability coefficient threshold can be determined based on actual conditions; different preset permeability coefficient thresholds can be set for different situations. In this embodiment, the preset permeability coefficient threshold is [value missing]. .

[0045] Step S4: The sand and gravel mixed pile includes a concrete pile core, that is, a concrete pile core needs to be configured, and then proceed to step S5.

[0046] Step S5: The sand and gravel mixed pile includes a crushed stone pile core, that is, a crushed stone pile core needs to be configured, and then proceed to step S6.

[0047] Step S6: The sand and gravel mixed pile includes a medium-coarse sand pile core, that is, a medium-coarse sand pile core needs to be configured to determine the sand and gravel mixed pile.

[0048] It is understood that, from the outside in, the sand and gravel mixed pile consists of a geotextile layer, a medium-coarse sand core, a crushed stone core, and a concrete core. That is, after determining the geotextile layer, medium-coarse sand core, crushed stone core, and concrete core of the sand and gravel mixed pile based on the soil properties, the structure of the sand and gravel mixed pile is: from the outside in, a geotextile layer, a medium-coarse sand core, a crushed stone core, and a concrete core. When, based on the soil properties, it is determined that a concrete core is not included, then, from the outside in, the sand and gravel mixed pile consists of a geotextile layer, a medium-coarse sand core, and a crushed stone core. Similarly, when, based on the soil properties, it is determined that neither a concrete core nor a crushed stone core is included, then, from the outside in, the sand and gravel mixed pile consists of a geotextile layer and a medium-coarse sand core.

[0049] As can be seen from the above steps, the liquidity index and permeability coefficient are determined through each step, thereby determining which pile cores are included in the sand and gravel mixed pile.

[0050] For example, prior to step 1, the following steps are also included: Step a: Excavate a foundation pit at the target site to accommodate the sand and gravel piles.

[0051] Step b: Place a ring-shaped steel mesh at the bottom of the pit and place steel casings on the sidewalls of the pit to protect them. The ring-shaped steel mesh is attached to the bottom of the pit and the steel casings are attached to the sidewalls.

[0052] Step c: Lay geotextile on the annular steel mesh, with the geotextile adhering at least to the sidewalls of the pit to form a geotextile layer.

[0053] Step d: Construct pile cores sequentially from the inside out, filling the foundation pit with the appropriate materials to obtain reinforced concrete, crushed stone, or medium-coarse sand pile cores. After each pile core is constructed, a ring-shaped steel mesh is installed around its perimeter. The ring-shaped steel mesh is spaced apart from the already constructed pile cores, forming a ring-shaped cavity. The appropriate material is filled into the ring-shaped cavity to construct the next pile core. After constructing the pile core corresponding to the current ring-shaped cavity, the corresponding ring-shaped steel mesh is removed for recycling. Continue constructing the next pile core until all pile cores are constructed, resulting in a sand and gravel mixed pile that fills the foundation pit.

[0054] Step e: Compact each pile core to obtain the final sand and gravel mixed pile, which completes the production of the sand and gravel mixed pile.

[0055] Step 2: Place the prepared sand and gravel mixed piles into the corresponding pile holes at various locations of the target foundation. According to the soil properties at different depths of the pile holes, place the corresponding sand and gravel mixed piles. Join the sand and gravel mixed piles together along the depth direction of the pile holes and compact the sand and gravel mixed piles to complete the construction.

[0056] In this process, the sand and gravel mixed piles are inserted vertically into the pre-dug pile holes and compacted in sections, so that each sand and gravel mixed pile can be tightly bonded to the surrounding soil, thereby forming a continuous pile body.

[0057] It is understandable that two adjacent sand and gravel mixed piles can be connected through a concave-convex interlocking structure. That is, concave-convex interlocking interfaces are set at both ends of the sand and gravel mixed pile, so that another sand and gravel mixed pile can be connected to the current sand and gravel mixed pile through the concave-convex interlocking structure. In other words, the two sand and gravel mixed piles achieve self-locking and centering connection through the concave-convex structure. Centering means that the central axes of the two sand and gravel mixed piles can be aligned, thereby ensuring that the pile segments (corresponding to one sand and gravel mixed pile) achieve self-locking and effective load transfer during mechanical connection, and further improve the shear and pull-out resistance of the overall pile body (all sand and gravel mixed piles).

[0058] Among them, the crushed stone pile core and / or medium-coarse sand pile core can be made of one or more of recycled crushed stone, inert materials and construction waste to reduce raw material energy consumption and environmental impact, while reducing material waste by optimizing the mixing ratio.

[0059] Sand and gravel mixed piles can be made using a rapid on-site compaction method.

[0060] When designing the pile core, the dimensions of the concrete pile core, crushed stone pile core, and medium-coarse sand pile core should be determined sequentially according to the principle of economy. If the pile core section includes a concrete pile core, the minimum required concrete pile core size should be calculated using the composite foundation design bearing capacity calculation method, referring to the specifications. If the pile core section includes a crushed stone pile core, the minimum required crushed stone pile size should be calculated using the composite foundation drainage and liquefaction resistance calculation method, referring to the specifications. Finally, the size of the medium-coarse sand pile core should be calculated by subtracting the concrete pile core (if any) from the total pile diameter and then subtracting the crushed stone pile core (if any).

[0061] The embodiments disclosed in this specification are merely illustrative of one aspect of the invention, and the scope of protection of the invention is not limited to these embodiments. Any other functionally equivalent embodiments fall within the scope of protection of the invention. Those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the scope of protection of the claims of this invention.

Claims

1. A construction method based on precast aggregate piles, characterized in that, The following steps are involved: Step 1: Determine the soil properties of the target foundation to be constructed, and construct corresponding sand and gravel mixed piles based on the soil properties. Different soil properties correspond to sand and gravel mixed piles composed of different pile cores. Step 2: Place the prepared sand and gravel mixed piles into the corresponding pile holes at various locations of the target foundation. According to the soil properties at different depths of the pile holes, place the corresponding sand and gravel mixed piles. Join the sand and gravel mixed piles together along the depth direction of the pile holes and compact the sand and gravel mixed piles to complete the construction.

2. The construction method based on precast aggregate piles according to claim 1, characterized in that, The sand and gravel mixed pile is a columnar structure with concave and convex structures at both ends, so that two sand and gravel mixed piles can be self-locking and centered through the concave and convex structures.

3. The construction method based on precast aggregate piles according to claim 1, characterized in that, Soil properties are determined based on soil type, liquidity index, permeability, and fine particle content. Then, based on these properties, the corresponding sand and gravel mixed piles are determined. Sand and gravel mixed piles include at least a geotextile layer.

4. The construction method based on precast aggregate piles according to claim 3, characterized in that, When the soil layer is determined to be a soft cohesive soil layer, the sand and gravel mixed piles are arranged in the following order from the outside to the inside: geotextile layer, medium-coarse sand core, crushed stone core and concrete core. The concrete core is used to provide bearing capacity, the medium-coarse sand core is used to provide a filter layer, and the crushed stone core is used to provide a drainage channel.

5. The construction method based on precast aggregate piles according to claim 4, characterized in that, When the soil layer is determined to be a hard cohesive soil layer, the sand and gravel mixed piles are arranged in the following order from the outside to the inside: a geotextile layer, a medium-coarse sand core, and a crushed stone core. The medium-coarse sand core is used to provide a filter layer, and the crushed stone core is used to provide drainage channels and bearing capacity.

6. The construction method based on precast aggregate piles according to claim 5, characterized in that, When the soil layer is determined to be a medium-coarse sand layer, the sand and gravel mixed piles are arranged from the outside to the inside, including a geotextile layer and a medium-coarse sand pile core, which is used to provide load transfer and compaction.

7. The construction method based on precast aggregate piles according to claim 6, characterized in that, When the soil layer is determined to be a silty fine sand layer, the sand and gravel mixed piles are arranged from the outside to the inside, including a geotextile layer, a medium-coarse sand pile core, and a crushed stone pile core. The medium-coarse sand pile core is used to provide a filter layer, and the crushed stone pile core is used to provide a drainage channel.

8. The construction method based on precast aggregate piles according to claim 7, characterized in that, The soil layer is classified as a soft cohesive soil layer if condition one is met; a hard cohesive soil layer if condition two is met; a medium-coarse sandy soil layer if condition three is met; and a silty fine sandy soil layer if condition four is met. Condition 1: Fine particle content (FC) > 15%, Liquidity index <0.25, permeability coefficient k < ; Condition 2: Fine particle content (FC) > 15%, Liquidity index >0.25, permeability coefficient k < ; Condition 3: Fine particle content FC < 15%, permeability coefficient k > ; Condition 4: Fine particle content FC > 15%, permeability coefficient k > .

9. The construction method based on precast aggregate piles according to claim 7, characterized in that, Soil properties are determined based on soil type, liquidity index, permeability, and fine particle content. The corresponding sand-gravel mixed piles are then determined based on these properties. The specific implementation method includes the following steps: Step S1: Determine whether the current soil layer is cohesive soil. If yes, proceed to step S2; otherwise, proceed to step S3. Step S2: Determine whether the liquidity index of the current soil layer is less than the preset liquidity index threshold. If yes, proceed to step S4; otherwise, proceed to step S5. Step S3: Determine whether the permeability coefficient of the current soil layer is less than the preset permeability coefficient threshold. If yes, proceed to step S5; otherwise, proceed to step S6. Step S4: The sand and gravel mixed pile includes a concrete pile core and proceeds to step S5; Step S5: The sand and gravel mixed pile includes a crushed stone pile core, that is, a crushed stone pile core needs to be configured, and then proceed to step S6; Step S6: The sand and gravel mixed pile includes a medium-coarse sand pile core, thereby determining the sand and gravel mixed pile.

10. The construction method based on precast aggregate piles according to claim 1, characterized in that, Before step 1, the following steps are also included: Step a: Excavate a foundation pit at the target site to accommodate the sand and gravel piles; Step b: Place a ring-shaped steel mesh at the bottom of the pit and a steel casing on the side wall of the pit to protect the side wall. The ring-shaped steel mesh is attached to the bottom of the pit and the steel casing is attached to the side wall. Step c: Lay geotextile on the annular steel mesh, with the geotextile adhering at least to the sidewall of the pit to form a geotextile layer. Step d: Fabricate the pile cores sequentially from the inside out, and fill the foundation pit with the corresponding materials to obtain reinforced concrete pile cores, crushed stone pile cores, or medium-coarse sand pile cores. After each pile core is fabricated, a ring-shaped steel mesh is installed around its perimeter. The ring-shaped steel mesh is spaced apart from the already fabricated pile cores, forming a ring-shaped cavity. The corresponding material is then filled into the ring-shaped cavity to create the next pile core. After the pile core corresponding to the current annular cavity is made, the corresponding annular steel mesh is extracted to recover the annular steel mesh, and the next pile core is made until all the pile cores are made, thus obtaining a sand and gravel mixed pile, and making the sand and gravel mixed pile fill the foundation pit. Step e: Compact each pile core to obtain the final sand and gravel mixed pile.

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