CN220058012U - Fertilizer groove backfilling and anti-floating pressure relief observation matching system - Google Patents

Abstract

The utility model discloses a fertilizer tank backfill and anti-floating pressure relief observation matching system, which comprises a basement strip base, a basement retaining wall, a basement top plate, an anti-floating pressure relief device and a foundation pit slope protection surrounding the outer side of the basement, wherein the basement retaining wall is arranged above the basement strip base, and the basement top plate is arranged above the basement retaining wall. The underground retaining wall and the foundation pit slope protection are sequentially provided with a lower impermeable layer, a gravel layer, a plain soil backfill layer and an upper impermeable layer from bottom to top. A drainage ditch is arranged on the surface of the basement strip base, and the drainage ditch is communicated with a water collecting pit in the underground space. The anti-floating pressure relief device comprises a drain pipe and a drain pipe, the lower end of the drain pipe extends into the crushed stone layer, and the upper end of the drain pipe is positioned on the inner side of the underground retaining wall and is provided with an upward opening. The upper end of the drain pipe is connected with one side of the drain pipe, and the lower end of the drain pipe extends into the drain ditch. The utility model can timely drain accumulated water in the fertilizer discharging groove through the anti-floating pressure relief device, thereby avoiding damaging the basement structure, having good economical efficiency, saving the whole period cost of engineering and avoiding anti-floating accidents.

Description

Fertilizer groove backfilling and anti-floating pressure relief observation matching system

Technical Field

The utility model relates to the technical field of building design and construction, in particular to a fertilizer tank backfilling and anti-floating pressure relief observation matching system.

Background

The early stage of project design survey units give out site survey reports, and anti-floating anti-water level data can be reflected in the reports. The anti-floating design is divided into two cases, namely, the seepage of groundwater and the inflow of surface water to the basement. Strictly speaking, the inflow anti-floating of the surface water does not belong to the investigation range, and because the anti-floating accident of the underground garage frequently occurs in recent years, the investigation unit can determine the anti-floating anti-water level by considering the inflow condition of the surface water at the same time.

The anti-floating technical standard of the constructional engineering (JGJ 476-2019) comprehensively considers the double functions of lateral constraint and impermeability, and provides requirements for backfill materials of a fertilizer tank, and adopts layered rammed cohesive soil, gray soil or pouring pre-mixed fluid state solidified soil, plain concrete and other weak water permeability materials. In order to avoid the basin effect, the scheme of pouring the premixed fluid solidified soil and plain concrete is poor in economy, and is not accepted by many owners, the scheme of directly and completely using the layered compacted cohesive soil and gray soil is good in economy, but the impermeability is relatively poor, and the designer feels hidden danger in view of the aspect of control of construction quality.

Besides observing the water level elevation in the investigation stage, after the project is completed and accepted, no condition exists for timely water level observation even in the water-rich stage. When the construction period is in rainy season, once the drainage measures are not finished, anti-floating accidents are easy to occur, even if the scheme of drilling holes on the bottom plate and draining water is adopted, the drainage process is not smooth, sediment can be carried out, and the later-stage plugging of waterproof leakage is also a great engineering problem.

In the project completion use process, the real-time data of the underground water level cannot be obtained, even if a reconnaissance party wants to verify, whether the original reconnaissance anti-floating water data of the project is economical and reliable cannot be judged conveniently, and the effect of the backfilling impermeability of the fertilizer tank cannot be verified for a design party. Even if the anti-floating accident occurs, if a lot of time-consuming and labor-consuming coordination work is not performed, the parties can not accurately judge the reason and give an economic solution.

If no clear condition shows that the anti-floating water level data given by the investigation unit directly and comprehensively considers the inflow hidden danger of the surface water, the anti-floating design is completely carried out by adopting an anti-floating scheme, and the economical efficiency is poor. In order to avoid the 'basin effect', the scheme of pouring ready-mixed fluid solidified soil and plain concrete is poor in economy by directly and fully adopting layered compacted cohesive soil and gray soil, but the impermeability is relatively poor. If the bottom of the fertilizer tank is poured by pre-mixed fluid-state solidified soil and plain concrete with high impermeability and reliability, the penetration of the collected water of the fertilizer tank and possible crack water under the substrate is avoided, a layer of weak permeable sealing belt is arranged on the upper part, the surface of the ground is hardened and drained, the comprehensive consideration of economy is high, but the permeability is not satisfactory, and quantitative judgment is not good.

The anti-floating design of the underground space can cause the waste of underground water and aggravate the load of the drainage equipment if the drainage scheme is adopted; if the scheme of resistance is adopted, the infiltration of surface water is reduced by improving the impermeability of the backfill material of the fertilizer tank, and then the conservation anti-floating water level with extremely low probability is directly resisted, so that the economical efficiency is poor.

During construction, if the top soil of the garage is not backfilled, under the condition that the surface hardening drainage is not available, the temporary drainage can not be timely caused to prevent floating accidents when the rainy season is met. Even if the scheme of drilling and draining the bottom plate is adopted, the drainage smoothness is poor and sediment can be carried out, and the later plugging is waterproof and leakage-resistant, so that the problem of large engineering is solved.

In the project completion use process, groundwater level data cannot be obtained economically and conveniently in real time, whether the anti-floating water data of the existing investigation project is economical and reliable cannot be judged, and the impervious effect of the fertilizer tank backfill scheme cannot be judged. Even if the anti-floating accident occurs, the reason can not be accurately judged, and an economic solution is provided. There is therefore a need for further improvements and enhancements in the art.

Disclosure of Invention

Aiming at the defects of the prior art, the utility model aims to provide a system for observing and matching backfilling and anti-floating pressure relief of a fertilizer tank, which solves the problems that the existing backfilling and anti-seepage performance and economy of the fertilizer tank are poor, the collected water of the fertilizer tank is difficult to discharge in time, and the temporary water discharge can cause anti-floating accidents in time when the rainy season is met.

In order to solve the technical problems, the utility model adopts the following technical scheme:

the utility model provides a fertile groove is backfilled and is anti supporting system of pressure release observation that floats, includes basement strip base, underground retaining wall, basement roof, anti pressure release device that floats and encircle the foundation ditch bank protection in the basement outside, and the underground retaining wall is along the vertical arrangement of the extending direction of basement strip base, and the basement roof sets up in the top of underground retaining wall.

The underground retaining wall and the foundation pit slope protection are sequentially provided with a lower impermeable layer, a gravel layer, an plain soil backfill layer and an upper impermeable layer from bottom to top.

The surface of the basement strip foundation is provided with a drainage ditch which is positioned at the inner side of the underground retaining wall and is arranged along the trend of the underground retaining wall, and the drainage ditch is communicated with a water collecting pit in the underground space.

The anti-floating pressure relief device is at least two and is arranged at intervals along the extending direction of the underground retaining wall, the anti-floating pressure relief device comprises a drain pipe and a drain pipe, the lower end of the drain pipe penetrates through the underground retaining wall to extend into the crushed stone layer, and the upper end of the drain pipe is positioned on the inner side of the underground retaining wall and is provided with an upward opening.

The drain pipe is vertically arranged at one side of the drain pipe, the upper end of the drain pipe is connected and communicated with the upper part of the drain pipe, and the lower end of the drain pipe extends to the drainage ditch.

Further, the bottom of the underground retaining wall is connected with the basement strip base to form an integrated structure, and one side of the basement strip base, which is close to the foundation pit slope protection, protrudes outwards relative to the outer side wall of the underground retaining wall.

The edge of the basement roof is connected with the upper end of the underground retaining wall to form an integrated structure.

Further, the foundation pit slope protection is arranged on one side opposite to the underground retaining wall in an inclined mode and is formed by concrete spraying, and the foundation pit slope protection and the underground retaining wall form a fertilizer groove with wide upper part and narrow lower part.

Further, the lower water-impermeable layer is formed by pouring premixed fluid solidified soil or plain concrete, is filled between the foundation pit slope protection and the basement strip base, and covers the upper surface of the basement strip base.

Further, the drain pipe is the body of L shape structure, and the vertical part of drain pipe is located the inboard of underground retaining wall, and its horizontal part one end links to each other with vertical part lower extreme, and the other end is located the lower part of rubble layer.

The joint of the horizontal part and the vertical part of the blow-down pipe is provided with an inspection port, and the inspection port is provided with a water stop plug which can seal the inspection port.

Further, the other end of the horizontal part of the sewage pipe is wrapped with geotextile, and the geotextile is fastened and fixed on the circumferential outer wall of the sewage pipe.

The outside cover of blow off pipe is equipped with the water-stop ring dish, and the water-stop ring dish is fixed in inside the underground retaining wall with embedded mode, and the outer wall of blow off pipe passes through water-stop ring dish and underground retaining wall sealing fit.

Further, the crushed stone layer is formed by paving graded sand pebbles or broken stones above the lower impermeable layer.

The plain soil backfill layer is formed by backfilling plain soil or clay above the crushed stone layer and tamping the clay layer in a layered manner, and the compaction coefficient of the plain soil backfill layer is K ₁ ，0.94≤K ₁ ＜1。

Further, the upper impermeable layer is formed by pouring concrete on the surface of the plain soil backfill layer, one side of the upper impermeable layer is covered on the surface of the basement roof, and the upper end face of the foundation pit slope protection on the other side of the upper impermeable layer extends outwards.

A backfill layer is paved above the upper impermeable layer and the basement roof, and compacted layer by layer, and the compaction coefficient K of the backfill layer is equal to the compaction coefficient K ₂ ，0.94≤K ₂ ＜1。

By adopting the technical scheme, the utility model has the beneficial technical effects that:

1. the anti-floating drainage caused by stable groundwater is realized, the groundwater level breaks through the design anti-floating water level or the leakage resistance of the fertilizer tank is insufficient, so that surface water flows into the fertilizer tank, and the anti-floating pressure relief device can timely drain, thereby avoiding the damage to the basement structure caused by long-term water storage.

2. Compared with the scheme of filling the fertilizer tank with the pre-mixed fluid cured soil and plain concrete, the method has the advantages of good pouring economy and construction cost saving.

3. The blind ditches are arranged along the through length of the foundation pit fertilizer groove, so that accumulated water can be drained through the blind ditches, and meanwhile, the drain pipe blockage caused by sediment carry-over is avoided.

4. The problem of anti-floating in the construction period can be solved, the occurrence of anti-floating accidents is avoided, and meanwhile, the problem that the plugging is performed by the traditional bottom plate opening pressure relief scheme is solved.

5. The anti-floating pressure relief observation and fertilizer tank backfilling scheme comprehensively considers, observes the groundwater level in real time, and provides resource investigation and design for similar engineering decisions in local areas.

Drawings

FIG. 1 is a schematic diagram of a system for observing and matching backfilling and anti-floating and pressure-releasing of a fertilizer tank.

Detailed Description

The utility model is described in detail below with reference to the attached drawing figures:

embodiment, combine figure 1, a fertile groove is backfilled and is anti to float pressure release observe supporting system, including basement strip base 1, underground retaining wall 2, basement roof 3, anti pressure release device that floats and encircle the foundation ditch bank protection 5 in the basement outside, have the bottom water barrier between basement strip base 1 and the bottom of basement ground and the soil layer of below, the bottom water barrier is by plain concrete, ready mixed flow state solidification soil casting maintenance. The underground retaining wall 2 is vertically arranged along the extending direction of the basement strip base 1. The bottom of the underground retaining wall 2 and the upper surface of the basement strip base 1 are poured into an integral structure, and one side, close to the foundation pit slope protection 5, of the basement strip base 1 protrudes outwards relative to the outer side wall of the underground retaining wall 2.

The basement roof 3 is located the top of the area that the basement retaining wall 2 encloses, the side edge of basement roof 3 pours into an organic whole structure with the inboard of basement retaining wall 2, and basement strip base 1 forms the interior space of basement with basement retaining wall 2, basement ground and basement roof 3.

The foundation pit slope protection 5 is located the opposite one side of the underground retaining wall 2, and the slope arrangement is formed by concrete injection, the foundation pit slope protection 5 forms a fertilizer groove with wide upper part and narrow lower part with the underground retaining wall 2, and after the construction of the basement structure is completed, the fertilizer groove needs to be backfilled, and the construction of the foundation pit slope protection 5 is completed in the foundation pit excavation process.

The underground retaining wall 2 and the foundation pit slope protection 5 are sequentially provided with a lower impermeable layer 61, a gravel layer 62, a plain soil backfill layer 63 and an upper impermeable layer 64 from bottom to top.

The lower water-impermeable layer 61 is formed by pouring premixed fluid solidified soil or plain concrete, is filled between the foundation pit slope protection 5 and the basement strip base 1, and covers the upper surface of the basement strip base 1. The lower impermeable layer 61 is combined with the bottom water barrier layer below the basement membrane 1 to isolate groundwater to some extent. The lower impermeable layer 61 is laid along the trend of the fertilizer tank, and two sides of the lower impermeable layer are respectively combined with the lower parts of the basement strip base 1 and the foundation pit slope protection 5 into a whole. The bottom of the fertilizer tank is poured by premixed fluid-state solidified soil with high impermeability and reliability, so that hidden danger ponding of the fertilizer tank is prevented from being communicated with possible crevice water under the substrate.

The gravel layer 62 is formed by paving graded sand pebbles or broken stones above the lower impermeable layer 61, the thickness of the gravel layer 62 is 750mm, more pores exist between the sand pebbles or broken stones, the gravel layer 62 is used as a water collecting blind ditch arranged along the through length of a foundation pit fertilizer groove, and the gravel layer 62 is wrapped by 400g/m2 of nonwoven geotextile.

The plain soil backfill layer 63 is formed by backfilling plain soil or clay above the crushed stone layer 62 and tamping the clay layer in layers, and the compaction coefficient of the plain soil backfill layer 63 is K ₁ ，0.94≤K ₁ ＜1。

The upper impermeable layer 64 is formed by pouring concrete on the upper surface of the plain soil backfill layer 63, one side of the upper impermeable layer 64 covers the surface of the basement roof 3, and the upper end surface of the foundation pit slope protection 5 on the other side extends outwards.

The backfill layer 65 is paved above the upper impermeable layer 64 and the basement roof 3, the backfill layer 65 is compacted in layers, the compaction coefficient K2 is more than or equal to 0.94 and less than or equal to K2 and 1, and the surface hardening and the organized surface drainage are well performed. The upper impermeable layer 64 is used as a weak permeable sealing belt above the plain soil backfill layer 63, and a water collecting blind ditch is arranged along the full length of the foundation pit fertilizer groove, so that the accumulated water flowing into the fertilizer groove from the earth surface due to insufficient impermeability can be drained in a series manner, and the drain pipe blockage caused by the carrying-out of silt is avoided.

The surface of the basement strip base 1 is provided with a drainage ditch 11, the drainage ditch 11 is positioned at the inner side of the underground retaining wall 2 and is arranged along the trend of the drainage ditch 11, the drainage ditch is communicated with a water collecting pit in an underground space, and the top of the drainage ditch 11 is sequentially connected with a plurality of cover plates 12 along the trend of the drainage ditch.

The anti-floating pressure relief devices are two or more and are arranged at intervals along the extending direction of the underground retaining wall. Under the condition that has a plurality of, all anti pressure release devices that floats are equidistant in proper order along the length direction in fertile groove, and equidistant in proper order along the extending direction in fertile groove promptly, and arbitrary adjacent two anti pressure release devices that floats are spaced a certain distance. The anti-floating pressure relief device comprises a drain pipe 41 and a drain pipe 42, wherein the drain pipe 41 and the drain pipe 42 are made of glass fiber reinforced plastic or stainless steel pipe bodies, the lower end of the drain pipe 41 penetrates through the underground retaining wall 2 to extend into the gravel layer 62, and the upper end of the drain pipe 41 is positioned on the inner side of the underground retaining wall 2 and is opened upwards. Through the principle of hydraulic communicating pipe, the collected groundwater or surface water is flowed into the ponding of the fertilizer groove and communicated with the drain pipe arranged in the underground space, the water level height is measured through the top opening of the drain pipe, if the water level reaches the designed anti-floating water level, the water which is higher up is immediately discharged into the drainage ditch 11 through the drainage pipe 42, and flows into the water collection pit to be discharged by the drainage equipment.

The drain pipe 41 is a pipe body of an L-shaped structure, a vertical portion of the drain pipe 41 is located inside the soil retaining wall 2, one end of a horizontal portion thereof is connected to a lower end of the vertical portion, and the other end thereof is located at a lower portion of the crushed stone layer 62. The joint of the horizontal part and the vertical part of the sewage drain 41 is provided with an inspection opening 43, and the inspection opening 43 is provided with a water stop plug which can seal the inspection opening.

The arrangement of the inspection opening 43 of the glass fiber reinforced plastic or stainless steel drain pipe can firstly drain the aged accumulated water in the blind ditch of the fertilizer tank through the opening of the inspection opening 43, update the aged accumulated water into clean underground water, and can also be used for flushing and cleaning the underground garage after the underground water is filtered and deposited. If the fertilizer groove is backfilled in advance during construction, the counterweight earthing on the garage top is not backfilled yet, and under special conditions of no surface hardening and drainage system, heavy storm weather is met, and accumulated water in the fertilizer groove is timely drained by utilizing a water pump in a water collecting pit through opening a drain pipe inspection port 43, so that timely precipitation is equivalent, and anti-floating accidents caused by insufficient counterweight are avoided.

The guiding survey gives two anti-floating waterproof levels, wherein the first case is to only consider the underground water condition, and the second case is to additionally consider the inflow condition of the surface water. The drain pipe 42 is vertically arranged on one side of the drain pipe 41, the upper end is horizontally bent and is connected and communicated with a certain height of the upper part of the drain pipe 41, the lower end passes through a perforation arranged on the cover plate 12 and extends to the inner side of the drain ditch 11, the joint of the upper end of the drain pipe 42 and the drain pipe 41 is a drain pipe interface elevation 7, the drain pipe interface elevation 7 and groundwater are designed to be anti-floating, no matter whether the groundwater level exceeds the elevation or water with poor seepage resistance of a fertilizer tank under the condition of extremely small probability, and once the water pressure is released by the overflow line, the water can be automatically and timely discharged. The water head resisting the first condition is more safe and reliable through the arrangement of the counterweight and the anti-pulling anchor rod (anti-pulling pile); by timely discharging water flowing in when the groundwater level exceeds the elevation or the seepage resistance of the fertilizer tank is poor under the condition of extremely small probability, compared with the scheme of resisting, the method is more economical and reasonable, and the water head which needs to be resisted is automatically kept unchanged after capping in a short time.

Specifically, geotechnical cloth 44 is wrapped at the other end of the horizontal part of the drain pipe 41, the geotechnical cloth 44 can be fastened and fixed on the circumferential outer wall of the drain pipe 41 by adopting steel wires 46, and the geotechnical cloth 44 can filter sediment in a water collecting blind ditch to prevent the sediment from entering the drain pipe 41 to cause blockage. The outside cover of blow off pipe 41 is equipped with water-stop ring dish 45, and water-stop ring dish 45 is fixed in the underground retaining wall 2 middle part with embedded mode, and the outer wall of blow off pipe 41 passes through water-stop ring dish 45 and underground retaining wall 2 sealing fit.

In the project completion use process, the soft steel scale can be inserted from the top of the sewage pipe at any time to measure the water level elevation. Judging whether the groundwater level breaks through the anti-floating water level or the surface water with insufficient impermeability of the fertilizer tank flows in according to the water outlet condition of the water drain pipe and the weather condition at the corresponding moment. The observation data can be fed back for investigation, so that more scientific and reasonable anti-floating water level can be provided for subsequent projects in the region; the feedback design is used for researching, verifying whether the impermeability of the fertilizer slot backfill layering scheme meets engineering application, and if the reliability is high, the follow-up project can avoid the basin effect and can simply use the layering scheme to carry out fertilizer slot backfill.

The parts not described in the utility model can be realized by adopting or referring to the prior art.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present utility model, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", etc., are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present utility model and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present utility model.

It should be understood that the above description is not intended to limit the utility model to the particular embodiments disclosed, but to limit the utility model to the particular embodiments disclosed, and that the utility model is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the utility model.

Claims (8)

1. The system is characterized by comprising a basement strip base, a basement retaining wall, a basement top plate, an anti-floating pressure relief device and a foundation pit slope protection surrounding the outer side of the basement, wherein the basement retaining wall is vertically arranged along the extending direction of the basement strip base, and the basement top plate is arranged above the basement retaining wall;

the underground retaining wall and the foundation pit slope protection are sequentially provided with a lower impermeable layer, a gravel layer, an plain soil backfill layer and an upper impermeable layer from bottom to top;

the surface of the basement strip base is provided with a drainage ditch which is positioned at the inner side of the underground retaining wall and is arranged along the trend of the underground retaining wall and communicated with a water collecting pit in the underground space;

the anti-floating pressure relief devices are at least two and are arranged at intervals along the extending direction of the underground retaining wall, the anti-floating pressure relief devices comprise a drain pipe and a drain pipe, the lower end of the drain pipe penetrates through the underground retaining wall to extend into the crushed stone layer, and the upper end of the drain pipe is positioned at the inner side of the underground retaining wall and is provided with an upward opening;

the drain pipe is vertically arranged at one side of the drain pipe, the upper end of the drain pipe is connected and communicated with the upper part of the drain pipe, and the lower end of the drain pipe extends to the drainage ditch.

2. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank according to claim 1, wherein the bottom of the underground retaining wall is connected with a basement strip base into an integrated structure, and one side of the basement strip base, which is close to a foundation pit slope protection, protrudes outwards relative to the outer side wall of the underground retaining wall;

the edge of the basement roof is connected with the upper end of the underground retaining wall to form an integrated structure.

3. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank according to claim 1, wherein the foundation pit slope protection is positioned on the opposite side of the underground retaining wall, is obliquely arranged and is formed by concrete spraying, and the foundation pit slope protection and the underground retaining wall form the fertilizer tank with wide upper part and narrow lower part.

4. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank according to claim 2, wherein the lower water-impermeable layer is formed by pouring pre-mixed fluid solidified soil or plain concrete, is filled between the foundation pit slope protection and the basement strip base, and covers the upper surface of the basement strip base.

5. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank according to claim 1, wherein the drain pipe is a pipe body with an L-shaped structure, the vertical part of the drain pipe is positioned on the inner side of the underground retaining wall, one end of the horizontal part of the drain pipe is connected with the lower end of the vertical part, and the other end of the horizontal part of the drain pipe is positioned on the lower part of the crushed stone layer;

the joint of the horizontal part and the vertical part of the blow-down pipe is provided with an inspection port, and the inspection port is provided with a water stop plug which can seal the inspection port.

6. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank as set forth in claim 1, wherein the other end of the horizontal part of the drain pipe is wrapped with geotextile, and the geotextile is fastened and fixed on the circumferential outer wall of the drain pipe;

the outside cover of blow off pipe is equipped with the water-stop ring dish, and the water-stop ring dish is fixed in inside the underground retaining wall with embedded mode, and the outer wall of blow off pipe passes through water-stop ring dish and underground retaining wall sealing fit.

7. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of a fertilizer tank according to claim 1, wherein the crushed stone layer is formed by paving graded sand pebbles or crushed stones above a water-impermeable layer on the lower layer;

the plain soil backfill layer is formed by backfilling plain soil or clay above the crushed stone layer and tamping the clay layer in a layered manner, and the compaction coefficient of the plain soil backfill layer is K ₁ ，0.94≤K ₁ ＜1。

8. The system for observing and matching the backfilling and the anti-floating and pressure-relieving of the fertilizer tank according to claim 1, wherein the upper impermeable layer is formed by pouring concrete on the surface of the plain soil backfilling layer, one side of the upper impermeable layer covers the surface of a top plate of the basement, and the upper end face of a slope protection of a foundation pit on the other side extends outwards;

a backfill layer is paved above the upper impermeable layer and the basement roof, and compacted layer by layer, and the compaction coefficient K of the backfill layer is equal to the compaction coefficient K ₂ ，0.94≤K ₂ ＜1。