CN112144559B - Well construction method in high-water-rich loess sand pebble stratum pressure-variable pipe well - Google Patents

Abstract

The invention provides a method for constructing a transformer well in a high-water-rich loess sand and gravel formation, which includes the following steps: excavating a sink hole, making a caisson in the sink hole, and reserving holes for the main pipeline to pass through on the side walls of the caisson; pushing out the pipe sections of the two main pipelines from the holes of the caisson respectively; measuring and positioning; inspecting the construction of the lower shaft of the well; backfilling around the lower shaft of the well; inspecting the construction and backfilling of the upper shaft of the well; when the caisson is backfilled to the top surface of the roadbed, the roadbed in the caisson is backfilled and constructed together with the base of the entire road; preparing slurry and grouting reinforcement; using a spiral drill rotary drilling machine for hole formation; mixing cement: water glass: water in a mass ratio of 1:0.1:1 to form a double slurry, and mixing the double slurry evenly and filtering it through a screen before use. The advantages of this method are: shortening the construction period of the inspection well and pipeline, reducing the disturbance of jacking, and avoiding direct impact on the ground buildings, providing a guarantee for the early penetration of the road, and greatly improving the overall quality of the project.

Description

Construction method of transformer well in water-rich loess sandy gravel stratum

Technical Field

The invention relates to a method for constructing a transformer-tube well in a water-rich loess sand-pebble formation.

Background Art

"Well in a well" refers to an inspection well that is made secondary in a caisson. The traditional municipal road "well in a well" construction is to build a sintered brick or cast reinforced concrete well in the caisson and complete the backfill around the well. However, in the high-water-rich loess-sand and gravel area transformer pipe (due to the long-term abnormal operation of the downstream outlet sewage treatment plant, resulting in changes in head pressure in the pipe), the inspection well made in the deep well (>10m) caisson is affected by the difficulty of conventional machine head jacking, the large disturbance of the formation, the poor sealing performance of the two materials of the inspection well shaft, and the irregular changes in the head difference in the pipe. As a result, the joints of the well shaft, pipe body and pipe mouth are easily affected by the impact, which causes gaps. Under the action of unbalanced water pressure inside and outside, the deep sand and soil outside the pipe are hollowed out, and the loess sinks, resulting in uneven settlement of the road surface in the later period.

Due to the characteristics of the regional soil layer and the fact that the caisson structure of large-diameter sewage and wastewater pipes (1.5-3.0m) is generally large, it cannot be used directly as an inspection well. There is a lack of a method for constructing a transformer well in a high-water-rich loess sand and gravel stratum.

Summary of the invention

The technical problem to be solved by the present invention is to provide a method for constructing a transformer well in a water-rich loess sand and gravel formation with reasonable process and convenient construction.

In order to solve the above technical problems, the present invention provides a method for constructing a transformer well in a water-rich loess sand and gravel formation, comprising the following steps:

a) Caisson construction

Digging a countersink at a predetermined location, the depth of the countersink exceeding the predetermined depth of the main pipeline;

A reinforced concrete caisson is made on the four walls and bottom wall of the shaft at the bottom of the sink hole according to the construction drawing. The caisson adopts a non-drained bottom seal. The caisson is made and sunk multiple times. Holes are reserved on the side walls on both sides of the caisson for the passage of the main pipeline.

b) Pipe jacking construction

The pipe sections of the main pipeline are hoisted into the caisson in sequence, and the pipe sections of the two main pipelines are pushed out from the opening of the caisson respectively by the jacking equipment, with a gap between the pipe sections of the two main pipelines;

c) Measurement and positioning

According to the center coordinates of the inspection well in the drawing, the coordinates of the four corners of the caisson can be calculated through the structural dimensions and layout of the caisson;

d) Inspection of the lower shaft construction

The on-site construction is carried out in stages. The first step is to construct the well chamber floor, the second step is to construct the well chamber wall, and the third step is to construct the reinforced concrete well shaft.

Roughen the bottom plate of the caisson, then pour the bottom plate concrete of the inspection well, and embed the well wall steel bars when pouring the bottom plate concrete;

Before the construction of the inspection well wall, the pipeline is cut according to the distance between the caisson and the inspection well, the pipeline is openly connected on both sides, and the foundation is poured. At the same time, the outer wall of the pipeline is roughened, and then the template and steel bars are processed. The steel bars of the wellbore are pre-embedded on the upper end face of the well chamber wall;

The wellbore is a square wellbore, with supports erected from bottom to top to provide a working platform for operators. The place where the pipeline passes through the well wall is filled with oil hemp asphalt sand, and the water-facing surface is sealed with polysulfide sealing paste;

e) Backfill around the lower shaft of the inspection well

The backfill around the well is made of sand from the water drop site. When there are no more tiny bubbles on the backfill surface, water injection can be stopped.

After the on-site water drop is completed, the ring knife is sampled in time at the site, and the relevant data is obtained by using the balance and microwave drying method to measure the compaction degree;

The external platform of the wellbore can backfill the soil around the well chamber to a certain height in advance. After backfilling to the branch pipe elevation, install the branch pipe and protect the finished product when backfilling the branch pipe.

f) Inspection well upper shaft construction and backfilling

The upper shaft structure of the inspection well is brickwork. After the reinforced concrete shaft is completed, it is backfilled to the top of the reinforced concrete shaft;

g) Road subgrade and subbase construction

Since the inspection well is within the roadbed, when the caisson is backfilled to the top surface of the roadbed, the roadbed inside the caisson is backfilled and constructed together with the base of the entire road;

h) Preparation of slurry and grouting reinforcement

The plane position of the drill hole should be consistent with the plane position of the weak parts inside and outside the caisson, and multiple points should be selected to arrange the grouting holes, with the distance between points ≤ 1.0m;

The hole is drilled with a spiral rotary drill, the hole diameter is 70mm~110mm, the verticality tolerance is ±1%, and the hole depth is from the roadbed to the top pipe or weak parts;

Mix cement, water glass and water in a mass ratio of 1:0.1:1 to form a double-liquid slurry. Mix the double-liquid slurry evenly and filter it through a sieve before use.

The double grout is poured through the grouting pipe. Before pouring, cement mortar is used to seal the gap between the outside of the grouting pipe and the orifice. After the sealed mud solidifies, the flexible plug of the grouting pipe is poked out. The injection pressure is 0.4Mpa. During the grouting process, the double grout is stirred slowly and continuously. The stirring time is less than the initial setting time. The grouting flow rate is 5-10L/min, the water temperature is controlled between 0℃ and 30℃, and the initial setting time of the double grout is 55min.

i) Maintenance and inspection and acceptance

Closed traffic management is adopted in the area where grouting is completed, and large-scale machinery and vibrating machinery are prohibited from passing through the surrounding construction areas;

Inspection will be carried out 28 days after the completion of grouting, and the standard penetration method will be used for testing. The grouting inspection point is 3% of the number of grouting holes. When the qualified rate is less than 80%, repeated grouting will be implemented.

As a preferred embodiment of the present method, in step d), the lower shaft of the inspection well is constructed, and the lower shaft is cast to a height of about 3m at a time, and can be constructed in sections if the height is greater than 3m.

As a preferred embodiment of the present method, in the step e), the upper shaft of the inspection well is constructed, and the inner and outer walls of the shaft are plastered with 1:2 cement mortar plus 5% waterproofing agent with a thickness of 20 mm.

As a preferred embodiment of the present method, in the step h) of preparing the slurry and grouting reinforcement, the stirring time in the preparation of the cement slurry should be greater than 2 minutes, the water-cement ratio is controlled at 0.8-1, and then a certain amount of water glass solution is added into the mixing barrel according to the volume of the mud mixing barrel and stirred evenly, and the volume ratio of water glass to cement slurry is controlled between 0.5 and 0.8.

As a preferred embodiment of the present method, in step h) slurry preparation and grouting reinforcement, grouting holes are arranged in a plum blossom shape according to the caisson area, the hole depth is from the roadbed to the pipe section, and spiral drilling is used. The hole diameter is 70mm to 110mm, and the allowable verticality deviation is ±1%.

As a preferred embodiment of the present method, a caisson cover is prefabricated, and a through hole for the top of the inspection well is reserved on the caisson cover. After h) the preparation of the slurry and the grouting reinforcement, the caisson cover is covered on the upper side of the caisson.

As a preferred embodiment of the present method, in the step h), the grouting pipes are divided into a plurality of first grouting pipes and a plurality of second grouting pipes, the plurality of first grouting pipes are divided into two groups, the two groups of first grouting pipes correspond to the pipe sections on both sides, the lower end of each group of first grouting pipes extends to the upper sides of the pipe sections on the inner and outer sides of the caisson; the lower ends of the plurality of second grouting pipes extend to the surroundings of the connection between the upper shaft and the lower shaft of the inspection well.

After adopting this method, the jacking technology can be used to carry out pipeline laying without affecting the ground facilities, avoiding the direct impact of the operation on the ground buildings or structures, and through active grouting reinforcement measures, the possibility of ground subsidence is reduced to the greatest extent.

After ensuring the quality of the caisson and checking the quality of the caisson bottom plate, start to support the formwork and tie the steel bars according to the position of the pipeline, and pour the lower concrete inspection well chamber. After the lower well chamber is completed, the upper well chamber is built. The backfill material between the lower caisson and the inspection well is the original medium-coarse sand, and the layered (20cm) water-drop sand inserted vibrator tamping method is used for backfilling. The caisson is equipped with a sand-free filter pipe wrapped with geotextile to pump out water to form a water circulation. The sand density must meet the dense requirements; 3:7 ash soil is used to evenly backfill the surroundings of the upper caisson and the inspection well.

After the completion of the roadbed and subbase, holes are left in the ground through a spiral drill, and the elevation and coordinates are controlled. The outlet of the directional grouting pipe is placed at the junction of the brickwork and the concrete top plate under construction, the reserved hole of the caisson, the weak point of the pipeline, and the pipeline between the caisson and the inspection well. Through pressure grouting, the double slurry is injected into the stratum through the grouting pipe through the surrounding soil to inject the strongly solidified slurry into the stratum. The slurry squeezes out the moisture and air in the soil particles by filling, infiltration, compaction and splitting, and then occupies their position. After solidification, the slurry binds the originally loose soil particles or cracks into a whole, and expands to form inclusions through penetration, filling and compaction.

Since the gravel layer and the medium and coarse sand in the stratum have pores, a certain amount of slurry is injected into the soil layer under pressure through drilling, and the soil around the grouting port is squeezed and filled to form a plastic inclusion area. The soil far away from the slurry undergoes elastic deformation, and the overall density of the soil around the grouting port is improved. This inclusion forms a combination with the compacted foundation soil, which together play the role of rapid reinforcement, filling voids and cracks, and blocking cracks caused by hydraulic impact.

Through the combined effects of dense backfilling of materials in the upper and lower shaft parts and grouting reinforcement of weak points, problems such as collapse of the road surface around the well caused by the "water hammer effect", unbalanced internal and external water pressure, and road surface load at weak points were overcome.

The advantages of this transformer well construction method in high water-rich loess sand and gravel strata are: shortening the construction period of inspection wells and pipelines, avoiding direct impact on ground buildings while reducing jacking disturbance, and minimizing the possibility of ground settlement. It provides a guarantee for the early completion of the road, and at the same time greatly improves the overall quality of the project, providing a lot of good reference for the implementation of similar domestic projects in the future, and producing significant social benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic elevation view of an embodiment of a method for constructing a transformer well in a water-rich loess sand and gravel stratum.

Figure 2 is a process flow diagram of an embodiment of the transformer well construction method in a high water-rich loess sand and gravel formation.

DETAILED DESCRIPTION

As shown in Figures 1 to 2

Taking the construction of the top pipe well in the municipal road of Fengxi New City as an example, the upper geology here is a high water-rich loess layer, and the lower geology is a sand and gravel layer. The construction method of the transformer pipe well in the high water-rich loess sand and gravel layer includes the following steps:

a) Caisson construction

Digging a countersink at a predetermined location, the depth of the countersink exceeding the predetermined depth of the main pipeline;

A reinforced concrete caisson 2 is made on the four walls and the bottom wall of the wellbore at the bottom of the sink hole according to the construction drawing. The caisson 2 adopts a non-drained bottom sealing method. The caisson 2 is made and sunk multiple times. Holes are reserved on both sides of the caisson 2 for the main pipeline to pass through.

Before pouring concrete, the formwork size, embedded parts position and formwork sealing are inspected. After the formwork is removed and meets the requirements, it is lowered. During the on-site process, process control checks are carried out on site for deviations.

b) Pipe jacking construction

The pipe sections 11 of the main pipeline are hoisted into the caisson 2 in sequence, installed through guide rails, back wall production, jacking equipment installation, the jacking machine head in place, the machine head into the hole, the pipe sections 11 and the jacking iron are placed, jacking and deviation correction are performed, and the pipe sections 11 of the two main pipelines are respectively pushed out from the hole of the caisson 2 through the jacking equipment. There is a certain distance between the pipe sections 11 of the two main pipelines. During the jacking operation, the deviation of the jacking pipe is observed through the ground jacking main console to prevent the machine head from swinging left and right, increase the disturbance to the sand and gravel layer, and form a larger cavity outside the pipe wall. When it is 5m away from the receiving well, control the machine head out-of-hole speed and the center axis of the hole, slowly push the machine head into the receiving well, use a car crane to lift the jacking machine head, and continue to jack the pipe to the predetermined position.

c) Measurement and positioning

According to the center coordinates of the inspection well in the drawing, the coordinates of the four corners of caisson 2 are calculated through the structural dimensions and layout of caisson 2. The coordinate points are laid out on site using an ink fountain and marked with wooden stakes.

d) Inspection of the lower shaft 33

According to the designed structure of the inspection well, the on-site construction is carried out in steps. The first step is to construct the well chamber bottom plate 34, the second step is to construct the well chamber wall and top plate, and the third step is to construct the reinforced concrete well shaft.

After the pipe jacking is completed, the debris and silt in the caisson 2 are cleaned, the bottom plate of the caisson 2 below the inspection well chamber is roughened, and then the bottom plate concrete of the inspection well is poured. When pouring the concrete of the inspection well bottom plate 34, the well wall steel bars are embedded in advance. If the steel bar is required to be planted, the pull-out test is performed after the steel bar is planted;

Before the construction of the inspection well wall, the pipeline is cut according to the distance between caisson 2 and the inspection well, the pipeline is openly connected on both sides, and the foundation is poured. At the same time, the outer wall of the pipeline is roughened, and then the template and steel bars are processed, and the ladder is pre-buried. The required materials are transported vertically by a truck crane. When pouring concrete, a pump truck is used for transportation and a vibrating rod is used for vibration. The chute concrete is poured together with the well wall, and the steel bars of the well shaft are pre-buried on the top plate;

The lower shaft 33 of the inspection well is a square shaft of 1m*1m. The casting height of the lower shaft 33 is about 3m at one time. The height greater than 3m can be constructed in sections. The main difficulty in the construction of the shaft of the inspection well is that the installation space of the inner template is limited. Only one person can work in the shaft. By pre-embedding steel bars at the well chamber opening and setting up supports from bottom to top, a working platform is provided for the operator. The place where the pipeline passes through the well wall is filled with linseed asphalt sand with a seam width of 50mm, and the water-facing surface is sealed with polysulfide sealant.

e) Check the backfilling of the lower shaft of the well 33 times

The backfill around the well is filled with sand from the site of water-falling sand (i.e. the caisson backfill area 52). The soil is lifted by a car and leveled manually. The thickness of each layer is not more than 30 cm (virtual thickness). When the elevation of the outer wall of the inspection well is marked, the water is injected 20 cm higher than the filling height, and the water head is maintained. When the water surface sinks slowly and there are no more tiny bubbles on the backfill surface, the water injection can be stopped;

After the water drop on site is completed, take samples in time at the site using a knife ring, use a balance and microwave oven drying method to obtain relevant data, and measure the compaction degree, specifically:

The outer part of the wellbore 33 in the lower part of the well is backfilled with medium-coarse sand at the same time, and the thickness of each backfill layer is not more than 20cm. The elevation is marked on the outer wall of the inspection well, and the water is injected 20cm higher than the fill height to maintain the water head. When the water surface sinks slowly and no fine bubbles emerge from the backfill surface, the water injection can be stopped. During the water injection process, an inserted vibrator is used for tamping. A sand-free water filter pipe wrapped with geotextile is installed in the caisson to pump out water to form a water flow cycle. The sand density must meet the dense requirements. Samples are taken on site in time with a ring knife. Relevant data are obtained using a balance and a microwave oven drying method to measure the compaction degree.

The external platform of the wellbore can backfill the soil around the well chamber to a certain height in advance. After backfilling to the elevation of branch pipe 35, branch pipe 35 is installed, and the finished product is well protected when branch pipe 35 is backfilled.

f) Construction and backfilling of the upper shaft 32 of the inspection well

The structure of the upper shaft 32 of the inspection well is brickwork. After the shaft of the inspection well is completed, the inner and outer walls of the upper shaft 32 of the inspection well are plastered with 1:2 cement mortar plus 5% waterproofing agent with a thickness of 20mm, and the top of the inspection well is provided with an upper cover 31;

The brick-built inspection well is backfilled with 3:7 ash soil evenly around the well, then compacted with a small rammer, backfilled and compacted layer by layer, and the thickness of each layer of backfill is not more than 15cm.

g) Road subgrade and subbase construction

Then backfill the area around the upper shaft of the inspection well (i.e., the roadbed backfill area 51). Since the inspection well is within the roadbed range of the road, after backfilling to the top surface of the road bed, the roadbed in the caisson 2 is backfilled and constructed together with the base of the entire road.

h) Preparation of slurry and grouting reinforcement

Taking into account the characteristics of the double-liquid slurry with a fast setting time, the initial and final setting time of the slurry needs to be measured on-site to ensure that the time from the preparation of the slurry to its use does not exceed its initial setting time. The water glass is stored in a closed container, and the double-liquid slurry is prepared by mixing cement: water glass: water in a mass ratio of 1:0.1:1. A movable steel mixing bucket is set up on-site to prepare the slurry. The bucket capacity is ≥800L. The double slurry is evenly mixed and filtered through a sieve before use.

The plane position of the drilled hole should be consistent with the plane position of the weak and vulnerable parts inside and outside the caisson 2, and multiple points should be selected to arrange the grouting holes, with the distance between points ≤1.0m.

The holes are drilled with a spiral rotary drill rig, with a hole diameter of 70mm to 110mm, an allowable verticality deviation of ±1%, and a hole depth from the roadbed to the jacking pipe or soft and weak parts.

The double grout is poured through a grouting pipe with a hole diameter of 50mm. Before pouring, cement mortar is used to seal the gap between the outside of the grouting pipe and the hole. After the sealed mud solidifies, the active plug of the grouting pipe is poked out. The injection pressure is 0.4Mpa. During the grouting process, the double grout is stirred slowly and continuously. The stirring time is less than the initial setting time. The grouting flow rate is 5-10L/min, the water temperature is controlled between 0℃ and 30℃, and the initial setting time of the double grout is 55min.

When the final hole requirement is met, crushed stone and gravel are filled into the grouting borehole and cement-water glass slurry is added to form a micropile body, and the hole mouth is restored with cold patch material.

The grouting pipes are divided into a plurality of first grouting pipes 41 and a plurality of second grouting pipes 42. The plurality of first grouting pipes 41 are divided into two groups. The two groups of first grouting pipes 41 correspond to the pipe sections 11 at both sides. The lower end of each group of first grouting pipes 41 extends to the upper side of the pipe sections 11 on the inner and outer sides of the caisson 2; the lower ends of the plurality of second grouting pipes 42 extend to the surrounding areas of the connection between the upper shaft 32 and the lower shaft 33 of the inspection well.

The grouting borehole is filled with crushed stone and gravel and supplemented with cement/water glass slurry to form micro-inclusions, and the hole mouth is restored with cold patch material.

A prefabricated caisson cover plate 21 is provided with a through hole at the top of the inspection well. After h) the preparation of the slurry and grouting reinforcement, the caisson cover plate 21 is covered on the upper side of the caisson 2.

i) Maintenance and inspection and acceptance

Closed traffic management is adopted in the area where grouting is completed, and large-scale machinery and vibrating machinery in the surrounding area are prohibited from passing through for construction.

Inspection shall be carried out 28 days after the completion of grouting, and the standard penetration method shall be used for testing; the grouting inspection point is 3% of the number of grouting holes. When the qualified rate is less than 80%, repeated grouting shall be implemented.

This transformer well-in-well construction method in high-water-rich loess sand and gravel strata is convenient, safe and reliable. The caisson serves as the working surface of the construction inspection well, which can effectively reduce the precipitation in the later construction process, so that the pipeline project and the "well-in-well" construction can be carried out under dry conditions, ensuring the safety of operators during the construction process and improving the construction quality of the "well-in-well".

In addition, the construction method of the transformer pipe well in the high-water-rich loess sand and gravel stratum has good sealing quality and improves the durability of the weak structure. Double-liquid grouting is carried out at the stress-maximum locations such as the well body, pipe body and pipe mouth joints to fully wrap and reinforce the weak locations where fatigue gaps occur. This ensures that even if the downstream sewage treatment plant is operating abnormally for a long time and the pipe body is subjected to alternating water hammer pressure and pipeline vibration, no cracks will occur in the pipe wall and the inspection well body, leading to infiltration of water and sand outside the well, thereby causing the collapse of the drainage system around the well, resulting in hollowing out of deep sand and soil, subsidence of loess, and collapse of the road surface around the well.

The above is only one embodiment of the present invention. It should be pointed out that a person skilled in the art may make several modifications and improvements without departing from the principle of the present invention, and these should also be regarded as falling within the scope of protection of the present invention.

Claims (7)

1. A method for constructing a transformer well in a water-rich loess sand and gravel formation, comprising the following steps: a) Caisson construction Digging a countersink at a predetermined location, the depth of the countersink exceeding the predetermined depth of the main pipeline; A reinforced concrete caisson is made on the four walls and bottom wall of the shaft at the bottom of the sink hole according to the construction drawing. The caisson adopts a non-drained bottom seal. The caisson is made and sunk multiple times. Holes are reserved on the side walls on both sides of the caisson for the passage of the main pipeline. b) Pipe jacking construction The pipe sections of the main pipeline are hoisted into the caisson in sequence, and the pipe sections of the two main pipelines are pushed out from the opening of the caisson respectively by the jacking equipment, with a gap between the pipe sections of the two main pipelines; c) Measurement and positioning According to the center coordinates of the inspection well in the drawing, the coordinates of the four corners of the caisson can be calculated through the structural dimensions and layout of the caisson; d) Inspection of the lower shaft construction The on-site construction is carried out in stages. The first step is to construct the well chamber floor, the second step is to construct the well chamber wall, and the third step is to construct the reinforced concrete well shaft. Roughen the bottom plate of the caisson, then pour the bottom plate concrete of the inspection well, and embed the well wall steel bars when pouring the bottom plate concrete; Before the construction of the inspection well wall, the pipeline is cut according to the distance between the caisson and the inspection well, the pipeline is openly connected on both sides, and the foundation is poured. At the same time, the outer wall of the pipeline is roughened, and then the template and steel bars are processed. The steel bars of the wellbore are pre-embedded on the upper end face of the well chamber wall; The wellbore is a square wellbore, with supports erected from bottom to top to provide a working platform for operators. The place where the pipeline passes through the well wall is filled with oil hemp asphalt sand, and the water-facing surface is sealed with polysulfide sealing paste; e) Backfill around the lower shaft of the inspection well The backfill around the well is made of sand from the water drop site. When there are no more tiny bubbles on the backfill surface, stop water injection. After the on-site water sand fall is completed, the ring knife is sampled on site in time, and the relevant data is obtained by using the balance and microwave drying method to measure the compaction degree; The external platform of the wellbore can backfill the soil around the well chamber to a certain height in advance. After backfilling to the branch pipe elevation, install the branch pipe and protect the finished product when backfilling the branch pipe. f) Inspection well upper shaft construction and backfilling The upper shaft structure of the inspection well is brickwork. After the reinforced concrete shaft is completed, it is backfilled to the top of the reinforced concrete shaft; g) Road subgrade and subbase construction Since the inspection well is within the roadbed, when the caisson is backfilled to the top surface of the roadbed, the roadbed inside the caisson is backfilled and constructed together with the base of the entire road; h) Preparation of slurry and grouting reinforcement The plane position of the drill hole should be consistent with the plane position of the weak parts inside and outside the caisson, and multiple points should be selected to arrange the grouting holes, with the distance between points ≤1.0m; The hole is drilled with a spiral rotary drill, the hole diameter is 70mm~110mm, the verticality tolerance is ±1%, and the hole depth is from the roadbed to the top pipe or weak parts; Cement: water glass: water in a mass ratio of 1:0.1:1 to prepare a double-liquid slurry. Before use, the double-liquid slurry is evenly mixed and filtered through a sieve; The double grout is poured through the grouting pipe. Before pouring, cement mortar is used to seal the gap between the outside of the grouting pipe and the orifice. After the sealed mud solidifies, the flexible plug of the grouting pipe is poked out. The injection pressure is 0.4Mpa. During the grouting process, the double grout is stirred slowly and continuously. The stirring time is less than the initial setting time. The grouting flow rate is 5-10L/min, the water temperature is controlled between 0℃ and 30℃, and the initial setting time of the double grout is 55min. i) Maintenance and inspection and acceptance Closed traffic management is adopted in the area where grouting is completed, and large-scale machinery and vibrating machinery are prohibited from passing through the surrounding construction areas; The grouting will be inspected 28 days after completion, with the standard penetration method being used for testing. The grouting inspection points will be 3% of the number of grouting holes. When the qualified rate is less than 80%, repeated grouting will be implemented. 2. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: The step d) checks the construction of the lower shaft of the well. The lower shaft is cast to a height of about 3m at a time, and can be constructed in sections if it is greater than 3m. 3. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: In the step e), the upper shaft of the inspection well is constructed, and the inner and outer walls of the upper shaft are plastered with 1:2 cement mortar plus 5% waterproofing agent with a thickness of 20 mm. 4. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: In the step h) of preparing the slurry and grouting reinforcement, the stirring time in preparing the cement slurry should be greater than 2 minutes, and the water-cement ratio is controlled at 0.8-1. Then, a certain amount of water glass solution is added into the mixing barrel according to the volume of the mud mixing barrel and stirred evenly. The volume ratio of water glass to cement slurry is controlled between 0.5 and 0.8. 5. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: In the step h) of preparing the slurry and grouting reinforcement, the grouting holes are arranged in a plum blossom shape according to the area of the caisson, the hole depth is from the roadbed to the pipe section, and the spiral drill is used for rotary drilling. The hole diameter is 70mm to 110mm, and the verticality allowable deviation is ±1%. 6. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: The caisson cover is prefabricated, and a through hole for the top of the inspection well is reserved on the caisson cover. After h) the preparation of the slurry and grouting reinforcement, the caisson cover is covered on the upper side of the caisson. 7. The method for constructing a transformer well in a water-rich loess sand and gravel formation according to claim 1 is characterized by: In the step h), the grouting pipes are divided into a plurality of first grouting pipes and a plurality of second grouting pipes, the plurality of first grouting pipes are divided into two groups, the two groups of first grouting pipes correspond to the pipe sections on both sides, the lower end of each group of first grouting pipes extends to the upper side of the pipe sections on the inner and outer sides of the caisson; the lower ends of the plurality of second grouting pipes extend to the surroundings of the connection between the upper shaft and the lower shaft of the inspection well.