CN112012790A - Groundwater seepage control method for water-rich soft plastic loess tunnel based on drainage of dewatering well - Google Patents

Abstract

The invention relates to a method for controlling groundwater seepage in a water-rich soft-plastic loess tunnel based on the pumping and draining of a water-rich soft-plastic loess tunnel. The dewatering well is regularly pumped to reduce the moisture content of the soil layer and achieve the purpose of controlling the groundwater seepage in the water-rich soft plastic loess tunnel. This method solves the problem that groundwater seepage seriously affects the construction of water-rich loess tunnels, and determines the key parameters of the surface dewatering well layout process. It ensures the normal construction of the loess tunnel and achieves the purpose of safe and efficient construction.

Description

Groundwater seepage control method for water-rich soft plastic loess tunnel based on drainage well

technical field

The invention relates to the technical field of groundwater seepage control in tunnels, in particular to a water-rich soft plastic loess tunnel groundwater seepage control method based on pumping and draining of dewatering wells.

Background technique

At present, the following problems exist in the construction of water-rich soft plastic loess tunnels:

1. In the working conditions where the long section of the tunnel is below the groundwater level, due to the influence of soft plastic loess and groundwater, problems such as seepage of water, softening of the tunnel bottom, and collapse and instability of the tunnel face will occur during the construction of the tunnel, which will seriously affect the construction. Safety and progress.

2. The measures in the cave have great construction interference, and it is difficult to ensure the construction progress and safety.

3. Surface precipitation has the characteristics of thick loess aquifer, relatively poor permeability, long pre-precipitation time and large drawdown.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a water-rich soft plastic loess tunnel groundwater seepage control method based on dewatering well pumping and drainage, which solves the problem that groundwater seepage seriously affects the water-rich loess tunnel construction, and determines the key parameters of the surface dewatering well arrangement process, Through surface precipitation, the groundwater seepage flow in the water-rich soft plastic loess tunnel is reduced, the moisture content of the loess is reduced, the normal construction of the loess tunnel is ensured, and the purpose of safe and efficient construction is achieved.

The technical scheme adopted in the present invention is:

A method for controlling groundwater seepage in a water-rich soft plastic loess tunnel based on pumping and draining of a dewatering well, which is characterized by:

The method includes the following steps:

S1: Dewatering wells are arranged in rows on both sides of the water-rich soft plastic loess tunnel;

S2: Clean the well after the dewatering well is completed;

S3: Through the regular pumping operation of the dewatering well, the moisture content of the soil layer is reduced, and the purpose of controlling the groundwater seepage of the water-rich soft-plastic loess tunnel is achieved.

The process of dewatering well construction is as follows:

The borehole is fully drilled with large aperture without core, the borehole diameter is 600mm, and the diameter of the drilled well is 325mm. After the hole depth reaches the design depth, the well pipe determined according to the drainage plan is run in sequence; above the groundwater level, backfill cementing with clay; The well pipe adopts Ф325*6 steel coiled pipe, and the well pipe connection method is welding.

A water filter pipe is installed in the well pipe, which is a Ф325*6 bridge type water filter pipe. The water filter pipe is put into the prepared specification gravel according to the predetermined position, with a diameter of 2-5mm, and the gravel is filled between the well hole and the water filter pipe, and the thickness of the gravel is 200-300mm. , The method of throwing gravel is the method of throwing gravel in still water, and a layer of 100-mesh nylon mesh is wrapped around the water filter pipe.

The precipitation well is equipped with a submersible pump for pumping and draining precipitation: the flow rate is 10-20m3/h; the hole depth is ≤100m, and the lift is greater than 150m; the hole depth is greater than 100m, and the lift is greater than 200m.

The longitudinal spacing of the dewatering wells is 20-25m, and they are arranged at 4m on the left and right sides of the outer edge of the outline of the main hole.

The diameter of the dewatering well is 325mm, and the depth of the dewatering well is 15-25m below the elevation of the soft plastic layer.

The bottom of the dewatering well is a sand tube with a length of 5m.

The well is cleaned immediately after the pipe down and packing are completed.

Staged time-sharing pumping is adopted, and the final water level of the dewatering well is drawn to a depth of 5m from the bottom of the hole, or drainage and precipitation are adopted.

The present invention has the following advantages:

1. The first application of surface deep well dewatering in mountain loess tunnels with rich water.

2. Through the surface precipitation, the water output in the tunnel is greatly reduced, and the problems of strand-shaped water output and water gushing in the tunnel are solved. The loess in the construction area is basically free of water seepage, which improves the tunnel construction and tunnel face driving conditions and reduces the cost of water flow. construction safety risks.

3. Surface precipitation has changed the water content and physical properties of the loess in the tunnel body, and the water content and liquid index of the loess have decreased significantly, which has improved the stability of the loess surrounding rock in the tunnel body. The accumulated settlement and deformation rate were significantly reduced, which provided the basis for the adjustment of the tunnel construction method.

Description of drawings

Figure 1: Schematic diagram of the dewatering well structure.

In the figure, 1-solid pipe, 2-filter pipe, 3-precipitation pipe.

Figure 2: Schematic diagram of the layout of the dewatering wells.

Figure 3: The relationship between the surface pumping water volume and the water output volume in the tunnel cavity and time.

Figure 4: Diurnal variation of loess moisture content on the face of the inclined shaft.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments.

The invention relates to a method for controlling groundwater seepage in a water-rich soft plastic loess tunnel based on pumping and draining of a dewatering well. The method comprises the following steps:

S1: Dewatering wells are arranged in rows on both sides of the water-rich soft plastic loess tunnel;

S2: Clean the well after the dewatering well is completed;

S3: Through the regular pumping operation of the dewatering well, the moisture content of the soil layer is reduced, and the purpose of controlling the groundwater seepage of the water-rich soft-plastic loess tunnel is achieved.

The process of dewatering well construction is as follows:

The borehole is fully drilled with large aperture without core, the borehole diameter is 600mm, and the diameter of the drilled well is 325mm. After the hole depth reaches the design depth, the well pipe determined according to the drainage plan is run in sequence; above the groundwater level, backfill cementing with clay; The well pipe adopts Ф325*6 steel coiled pipe, and the well pipe connection method is welding.

A water filter pipe (ie filter) is set in the well pipe, which is a Ф325*6 bridge water filter pipe. The water filter pipe is put into the prepared specification gravel according to the predetermined position, with a diameter of 2-5mm, and the gravel is filled between the well hole and the water filter pipe. The thickness of the gravel is 200-300mm, and the method of throwing the gravel is the static water throwing method, and the water filter pipe is covered with a layer of 100-mesh nylon mesh.

The precipitation well is equipped with a submersible pump for pumping and draining precipitation: the flow rate is 10-20m3/h; the hole depth is ≤100m, and the lift is greater than 150m; the hole depth is greater than 100m, and the lift is greater than 200m.

According to the hydrogeological conditions, the distribution of the aquifer in the water-rich soft plastic loess tunnel is analyzed, and the section of the soft plastic layer where the tunnel body is located and the thickness of the aquifer are determined, so as to determine the layout plan and key parameters of the dewatering well. The longitudinal spacing of the dewatering wells is 20-25m, and they are arranged at 4m on the left and right sides of the outer edge of the outline of the main hole. The diameter of the dewatering well is 325mm, the depth of the dewatering well is 15-25m below the elevation of the soft plastic layer, and the thickness of the gravel is 200-300mm. The bottom of the dewatering well is a sand tube with a length of 5m.

Below in conjunction with embodiment, the method of the present invention is described in further detail:

Example: Yinxi High-speed Railway Yima No. 1 Tunnel

Step S1: Design parameters of surface precipitation

1. Types of aquifers: submerged aquifers dominated by clayey loess.

2. According to the analysis and calculation results, the spacing of the dewatering wells is considered as 20-25m, the left and right sides of the tunnel are symmetrically arranged, and the terrain fluctuations and the distance between the gully positions are slightly adjusted.

3. Surface dewatering wells are arranged at 4m from the left and right sides of the outer edge of the outline of the main hole (Figure 2).

4. The diameter of the dewatering well is 325mm, the depth of the dewatering well is 15-25m below the elevation of the soft plastic layer, and the thickness of the gravel is 200-300mm;

5. The location of the filter: within the range from the static water level to 5m from the bottom of the hole, determined according to the loess aquifer revealed by the completion of the well.

6. The groundwater level is based on the groundwater level during the survey period, and the variation range is considered as 1-2m.

7. Submersible pump: equipped with a submersible pump with a flow rate of 10-20m ³ /h, a hole depth ≤ 100m, a lift greater than 150m, a hole depth greater than 100m, and a lift greater than 200m.

The structure of the dewatering well is as follows: the borehole is fully drilled with large aperture without core, the borehole diameter is 600mm, the diameter of the drilled well is 325mm, and after the hole depth reaches the design depth, the well pipe determined according to the drainage plan is run in sequence. Above the groundwater level, backfill and cement with clayey soil. The well pipe adopts Ф325*6 steel coil pipe, the water filter pipe is Ф325*6 bridge-type water filter pipe, and the well pipe connection method is welding.

Step S2: Implementation and effect analysis of dewatering wells

1. Well completion process and method requirements

(1) In order to ensure the quality of the well completed, the design of the structure, process, well cleaning, and testing of the dewatering well should be carried out according to the main technical parameters of the dewatering well before construction;

(2) The dewatering well should be kept as vertical as possible. When the hole deviation is inclined to the left and right sides of the inclined well, the deviation should be corrected in time to ensure that the dewatering well has no influence on the construction of the inclined well or the dewatering effect will be affected when it deviates far from the inclined well;

(3) It is recommended to use a combination of reverse circulation and positive circulation to complete the well;

(4) The length of the designed sand chamber is 5m;

(5) Accurately measure the initial water level and static water level during the drilling process.

(6) The gravel in the aquifer section should have a certain degree of roundness, the mud content (including stone powder) of the gravel should be ≤3%, and the particle size should be 2-5mm;

(7) To avoid the phenomenon of filter tube offset and filter material bridging in the hole caused by excessively fast or uneven filling speed, the filter material should be replenished in time after the well is washed, and the actual amount of filler should not be less than 95% of the theoretical calculation. quantity.

2. Well cleaning requirements

(1) The requirement of well cleaning to achieve "clean water and sand";

(2) Well flushing should be carried out immediately after the completion of pipe laying and packing, and the maximum time interval between well completion and well flushing should not exceed 8 hours;

(3) When using mud drilling, the combined well washing methods of mechanical, chemical and air compressors are used to achieve the purpose of breaking the mud wall of the well hole, removing the mud and sand in the hole, and dredging the waterway;

(4) Well washing, water pumping test, water level observation, etc. shall be carried out in strict accordance with the requirements of "Code for Hydrogeological Investigation of Railway Engineering" (TB10049-2014) and "Code for Hydrogeological Investigation of Water Supply" (GB5007-2016).

(5) Acceptance criteria

1) The sand content before the well flushing is not more than 1/20000 (volume ratio);

2) The steady water output of the dewatering well or the continuous water output for one week reaches 5m ³ /h, and the flow is continuous.

(6) Maintain groundwater observation during precipitation period

1) During the maintenance precipitation period, the dynamics of groundwater should be observed, and the dynamic changes of groundwater should be analyzed in time;

2) When the groundwater level changes sharply, the reasons should be analyzed in time (such as water pump damage or regional groundwater level rise, etc.), and corresponding measures should be taken;

3) After the construction of the dewatering well, the static water level should be measured before the formal pumping. Before the water level within the precipitation range drops to the design drawdown, the observation frequency should be no less than 3 times a day. When the water level reaches the design drawdown, And when the water level does not change much, it can be observed once a day;

4) The final water level of the dewatering well shall be drawn down to 5m from the bottom of the hole, or the dewatering shall be taken.

3. Analysis of the effect of the test section

(1) Tunnel groundwater level drops

The intersection mileage of the No. 1 inclined shaft and the main hole is DK256+520. Combined with the progress of the construction of the inclined shaft roof, the dewatering well started the construction of the test dewatering well near the No. 1 inclined shaft on September 15, 2017, and the test pumping was carried out. . After the official water pumping started, the average water inflow of the 10 group wells after pumping stabilized was 31-91m3/d, the dynamic water level in each well was basically the same as that of the test pumping, reaching 86-92m, and the drawdown in the hole was 42.2-45.2m. Slightly lower than the formal pumping, lower than the depth of the tunnel bottom. According to the pumping conditions of the No. 1 inclined well and the DK256+510~DK256+680 precipitation test wells in the main hole, the static water level of the groundwater is between 47m and 54m. It is 42.2 to 45.2m, with an average of 40.5m.

(2) The water output in the tunnel is reduced

From March to September 2017, after the inclined shaft of Yima Tunnel No. 1 entered the soft plastic soil layer in the body of X0+235~+385, the water content gradually increased, and the water seepage developed into a local strand-shaped water outlet. The maximum concentration of water can be It reaches 400～600m ³ /d, and then gradually decays. The decay period is about half a month, and the stable water volume is generally between 200～300m ³ /d. During the construction process, water gushing appeared in some areas. Under normal circumstances, 6 dewatering wells on both sides of the tunnel body work at the same time, the surface precipitation reaches more than 400m ³ /d, the precipitation is about 40 days, the water output in the tunnel is reduced to about 70m ³ /d, and the tunnel face is basically free of water seepage. The effluent in the tunnel is mainly the seepage of the rear initial support and the drainage of the secondary lining blind pipe.

(4) Changes in physical properties of loess on the palm face

Table 1 reflects the test results of the physical properties of the loess surrounding rock during the surface precipitation test of the Yima No. 1 tunnel. It can be seen that before the surface precipitation of the Yima No. 1 tunnel, the average moisture content of the loess is 31.2%, and the liquid limit is 31.2%. The average is 33%, the average plastic limit is 18.75, the average liquid index is 0.84, and the average plastic index is 14.28. After a long period of surface precipitation, the physical properties of the loess on the tunnel face have been improved to a certain extent, and the moisture content, liquidity index and plasticity index have all declined to a certain extent. The index decreased obviously. After about 40 days, the changes of water content and liquid index of loess decreased, and the values tended to be stable. In general, the average water content decreased from 34.4% to 27.3%, and the minimum reached 23.6%; the average liquid index also decreased from 0.84 to 0.6, and the minimum reached 0.3. Some test results showed that the loess was in a hard plastic state; the plasticity index The average dropped from 14.28 to 10.6, with a minimum of 10.2. At the same time, the liquid limit and plastic limit of loess have not changed significantly, and the average value is relatively close, which indicates that surface precipitation has not changed the basic characteristics of loess, but mainly changed the water content of loess, and the plastic state of loess has also changed to a certain extent. The stability is obviously enhanced, the properties of the loess surrounding rock in the tunnel body are improved, and the effect of surface precipitation is obvious.

The Yima No. 1 tunnel was implemented in accordance with the principle of early precipitation. The pumping time began on October 22, 2017 (experimental well), and ended on July 10, 2019. On July 18, 2019, the Yima No. 1 tunnel was fully completed. DK255+880~DK257+596 section has a total of 135 wells, and the actual number of dewatering wells is 14920m/135. The main principles of surface precipitation are as follows:

1. The construction sections that need dewatering should be carried out in advance, and the water will be pumped intermittently immediately after the well is completed to ensure the normal operation of the dewatering well.

2. According to the construction progress, the water is pumped in sections and time-sharing.

3. There are 6 to 8 precipitation wells near each face to ensure simultaneous precipitation. The pre-precipitation time of the precipitation well is 1-2 months.

4. In principle, the working time of a single well is 120 to 150 days. In case of special circumstances such as roofing, assembling trolleys, working face penetration, landslide treatment, etc., real-time dewatering is required according to work needs, and the working time of dewatering wells is extended.

The average pumping of a single well is 251d.

The single well pumping capacity is 34-127m³/d, the average single well pumping capacity is 84m³/d, and the total pumping volume is 2,691,141m³. For specific pumping time, pumping amount, and pumping drawdown, please refer to the appendix: Checklist for Surface Wells Constructed in Sections DK255+880~DK257+596 of Yima No. 1 Tunnel.

After the surface precipitation was carried out, the improvement effect of the surrounding rock in the cave was obvious, and the situation of strand water and seepage water was basically eliminated. Mainly, the moisture content is about 23%. There is a small amount of water seepage on the face of the tunnel in the direction of Xi'an and Yinchuan, and there is no strand or linear water outlet. The surrounding rock is mainly hard plastic, with soft plastic in some parts, and the moisture content is about 27%. The effect of precipitation is obvious, the moisture content is reduced from 31% (average) to 25% (average), the fissure water is basically drained, and the tunneling environment is improved significantly, as shown in the table below.

The content of the present invention is not limited to those listed in the embodiments, and any equivalent transformations taken by those of ordinary skill in the art to the technical solutions of the present invention by reading the description of the present invention are covered by the claims of the present invention.

Claims (9)

1. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on drainage of the dewatering well is characterized by comprising the following steps of:

the method comprises the following steps:

s1: arranging precipitation wells on the ground surfaces on two sides of the water-rich soft plastic loess tunnel in rows;

s2: washing the well after the dewatering well is constructed;

s3: the water content of the soil layer is reduced through the regular pumping operation of the dewatering well, and the purpose of controlling the groundwater seepage of the water-rich soft plastic loess tunnel is achieved.

2. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 1, wherein:

the construction process of the dewatering well comprises the following steps:

drilling holes by adopting large-aperture core-free comprehensive drilling, wherein the hole diameter of each drilled hole is 600mm, the diameter of each drilled hole is 325mm, and well pipes determined according to a drainage scheme are sequentially put into the drilled holes after the hole depth reaches the design depth; backfilling and cementing the well by using cohesive soil above the underground water level; the well pipe adopts a phi 325 and 6 steel coiled pipe, and the connection mode of the well pipe is welding.

3. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 2, wherein:

and arranging filter pipes in the well pipe, wherein the filter pipes are phi 325 & 6 bridge type filter pipes, the filter pipes are filled with prepared gravel materials with the specification according to preset positions, the diameter of the gravel materials is 2-5 mm, gravel is filled between the well hole and the filter pipes, the thickness of the filled gravel is 200-300 mm, a still water gravel filling method is adopted in the gravel filling method, and a nylon net layer with 100 meshes is coated outside the filter pipes.

4. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 3, wherein:

be provided with the immersible pump that is used for pump drainage precipitation in the precipitation well: configuring the flow rate to be 10-20 m 3/h; the hole depth is less than or equal to 100m, and the lift is more than 150 m; the hole depth is more than 100m, and the head is more than 200 m.

5. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 4, wherein:

the longitudinal distance of the dewatering wells is 20-25 m, and the dewatering wells are arranged at the positions 4m on the left side and the right side of the outer edge of the main tunnel contour line.

6. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 5, wherein:

the diameter of the dewatering well is 325mm, and the depth of the dewatering well is 15-25 m below the elevation of the soft plastic layer.

7. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 6, wherein:

the bottom in the dewatering well is a sand setting pipe with the length of 5 m.

8. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 7, wherein:

and (5) immediately washing the well after the pipe lowering and the filling are finished, and washing the well by adopting a water pump suction combined well washing method.

9. The groundwater seepage control method of the water-rich soft plastic loess tunnel based on dewatering well drainage of claim 8, wherein:

and (3) pumping water in a segmented and time-sharing manner, and finally lowering the water level of the dewatering well to 5m from the bottom of the hole or dewatering.

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