JP7475208B2 - How to build a water barrier - Google Patents

Description

The present invention relates to a method for constructing a waterproof wall.

Methods for identifying strata are known (see, for example, Patent Documents 1 and 2)

JP 2020-007815 A JP 2017-115457 A

When constructing a waterproof wall on the ground, the depth of the waterproof wall is set based on the depth of the impermeable layer (depth information) obtained from a boring survey, so that the lower end of the waterproof wall is embedded in the impermeable layer of the ground.

However, if there are unevenness on the surface of the impermeable layer, the depth of the impermeable layer in the construction area of the impermeable wall may be deeper than the depth of the impermeable layer obtained from the boring survey. In this case, there is a risk that the lower end of the impermeable wall will not reach the impermeable layer and will not be embedded in it.

Taking the above facts into consideration, the present invention aims to ensure that the lower end of a water barrier is firmly embedded in a low-permeability layer.

The method for constructing a watertight wall in the first embodiment comprises a hole drilling step of using a drilling machine to drill holes in the ground while pumping drilling water, and causing the holes to reach a low-permeability layer in the ground based on drilling data acquired during drilling, and an injection material injection step of injecting injection material into the drilled holes to form a ground improvement body in the ground.The hole drilling step and the injection material injection step are repeated to form a watertight wall by connecting the ground improvement body in a wall shape.

According to the method for constructing a water impermeable wall according to the first aspect , in the hole drilling step, a drilling machine is used to drill holes in the ground while supplying drilling water, and the drilled holes are made to reach a low-permeability layer in the ground based on drilling data acquired during drilling. In addition, in the grouting material injection step, grouting material is injected into the drilled holes to form a ground improvement body in the ground. The hole drilling step and the grouting material injection step are repeated to form a wall-like continuous ground improvement body, thereby forming a water impermeable wall.

As described above, in the hole drilling process, the holes are drilled to reach the impermeable layer of the ground based on the drilling data acquired during drilling. This allows the holes to reach the impermeable layer even if there are unevenness on the surface of the impermeable layer. By injecting injection material into the drilled holes, the bottom end of the ground improvement body, i.e., the bottom end of the water shielding wall, can be firmly embedded in the impermeable layer.

The method for constructing a watertight wall according to the second aspect is the method for constructing a watertight wall according to the first aspect , wherein the ground at a position where the depth of the impermeable layer has been obtained is drilled using a drilling machine while supplying drilling water, and a reference drilling water pressure value is set as the drilling water pressure value when the drilling reaches the impermeable layer, the drilling data includes a drilling water pressure value of drilling water to be supplied to the drilling hole during drilling, and in the drilling process, it is determined that the drilling has reached the impermeable layer when the drilling water pressure value reaches the reference drilling water pressure value.

According to the method for constructing a water impermeable wall of the second aspect , a drilling machine is used to drill a hole in the ground at a position where the depth of the impermeable layer has been acquired while supplying drilling water, and the drilling water supply pressure value when the drilling reaches the impermeable layer is set as a reference drilling water supply pressure value. The drilling data includes a drilling water supply pressure value of the drilling water supplied to the hole during drilling. Then, in the drilling process, it is determined that the drilling has reached the impermeable layer when the drilling water supply pressure value reaches the reference drilling water supply pressure value.

Here, the permeability coefficient of the impermeable layer is, for example, smaller than the permeable layer. Therefore, the drilling water supply pressure value during drilling is higher for the impermeable layer than for the permeable layer. Therefore, by monitoring the drilling water supply pressure value during drilling, it is possible to determine whether or not drilling has reached the impermeable layer.

As described above, in the present invention, the ground is excavated at a position where the depth of the impermeable layer has been obtained from a ground survey or the like, and the drilling water supply pressure value when the drilling reaches the impermeable layer is set as the reference drilling water supply pressure value. Then, in the drilling process, the drilling water supply pressure value obtained during drilling is compared with the reference drilling water supply pressure value, thereby improving the accuracy of determining whether or not the drilling has reached the impermeable layer.

A third aspect of the watertight wall construction method is the watertight wall construction method of the second aspect , in which, in the hole-drilling process, it is determined that the hole-drilling has reached the impermeable layer when the hole-drilling water supply pressure value reaches the standard hole-drilling water supply pressure value and is maintained at or above the standard hole-drilling water supply pressure value for a predetermined period of time.

According to the method for constructing a watertight wall relating to the third aspect , in the drilling process, it is determined that the drilling has reached the impermeable layer when the drilling water supply pressure value reaches the standard drilling water supply pressure value and is maintained at or above the standard drilling water supply pressure value for a predetermined period of time.

Here, if rocks or the like are buried in the ground, the drilling water supply pressure value may temporarily become high even before the drilling reaches the impermeable layer. To address this issue, the present invention determines that drilling has reached the impermeable layer not only when the drilling water supply pressure value reaches the standard drilling water supply pressure value, but also when the drilling water supply pressure value remains equal to or higher than the standard drilling water supply pressure value for a predetermined period of time. This further improves the accuracy of determining whether drilling has reached the impermeable layer.

As explained above, according to the present invention, the lower end of the water shielding wall can be securely embedded in the impermeable layer.

1 is a cross-sectional view showing a watertight wall constructed by a watertight wall construction method according to one embodiment. FIG. 2A is an enlarged cross-sectional view of FIG. 1 showing a test process of a drilling test according to one embodiment, and FIG. 2B is a graph showing an example of a drilling water supply pressure value obtained from the drilling test. 1A to 1D are cross-sectional views showing a construction process of a water shield wall construction step according to one embodiment. 13 is a graph showing an example of a drilling water supply pressure value acquired in a drilling process according to one embodiment. FIG. 2 is a cross-sectional view showing a water impermeable wall constructed by a water impermeable wall construction method according to a comparative example. FIG. 2 is a cross-sectional view showing a water impermeable wall constructed by a water impermeable wall construction method according to a comparative example. 1 is a cross-sectional view showing a watertight wall constructed by a watertight wall construction method according to one embodiment. FIG.

Below, we will explain a method for constructing a waterproof wall according to one embodiment, with reference to the drawings.

(Method of constructing water impermeable walls)
The method for constructing a water impermeable wall according to this embodiment includes a hole drilling test step and a water impermeable wall construction step, and forms a water impermeable wall 40 in a predetermined region (hereinafter referred to as "construction region R2") of ground 10, as shown in Fig. 1. The water impermeable wall 40 is for blocking groundwater, and has a lower end 42L embedded in a low permeability layer 10X of the ground 10.

Here, the impermeable layer 10X refers to a layer through which water does not easily permeate and has a small permeability coefficient k (m/s). The impermeable layer 10X includes, for example, a layer having a permeability coefficient k of ^10-5 or less. The impermeable layer 10X also includes, for example, a clayey soil layer, a fine sand layer, and a silt layer.

On the other hand, a permeable layer means a layer through which water easily permeates and has a large permeability coefficient k (m/s). For example, the permeable layer includes a layer having a permeability coefficient k of more than ^10-5 . In addition, the permeable layer includes, for example, a sand layer and a gravel layer. In addition, a fine sand layer and a silt layer having a permeability coefficient k of more than ^10-5 are also included in the permeable layer.

As mentioned above, the permeability coefficient k of the impermeable layer 10X is smaller than the permeability coefficient k of the permeable layer. Therefore, when drilling the ground 10 while pumping drilling water, the water supply pressure value of the drilling water (hereinafter referred to as the "drilling water supply pressure value") is higher for the impermeable layer 10X than for the permeable layer.

Therefore, in this embodiment, first, as shown in Figures 2(A) and 2(B), in the hole drilling test process, the water supply pressure value (hole drilling water supply pressure value _P1 ) when the hole drilling 30 (tip 24T of the rod 24) reaches the impermeable layer 10X is measured in advance, and the measured hole drilling water supply pressure value is set as the reference hole drilling water supply pressure value _PX . Next, as shown in Figures 3(A) and 4, in the waterproof wall construction process, the drilling depth in the ground 10 is determined based on the reference hole drilling water supply pressure value, and the lower end 42L of the waterproof wall 40 is embedded in the impermeable layer 10X. Each step of the hole drilling test process and the waterproof wall construction process will be specifically described below.

(Drilling test process)
As shown in Figure 1, in the drilling test process, a drilling test is performed in a construction area R2 of the ground 10 or in a surrounding area where a ground investigation (stratum investigation) has been carried out (hereinafter referred to as the "test area R1").

As shown in FIG. 2(A), in this embodiment, a boring survey is performed as a ground survey, for example. In the boring survey, a hole is drilled at a predetermined position (survey position) V in the ground 10, and a standard penetration test is performed at each predetermined depth to measure the strength (hardness) of the ground. In addition, the geology and depth of the strata (strata boundary) are surveyed from the collected excavated soil. This boring survey provides the depth (depth information, etc.) of the surface 10X1 of the impermeable layer 10X in the ground 10, and more specifically, the depth of the strata boundary between the impermeable layer 10X and the strata directly above the impermeable layer 10X.

The test area R1 is a concept that includes position V of the ground 10 and the surroundings of position V. The results of the boring survey are summarized, for example, in a ground survey report.

In the drilling test, a drilling machine 20 is used to drill a test area R1 of the ground 10. In this embodiment, as described below, a water shielding wall 40 (see FIG. 1) is constructed in the construction area R2 of the ground 10 using a double pipe strainer construction method or the like. Therefore, the drilling test also uses a drilling machine 20 that is used for the double pipe strainer construction method or the like.

The drilling machine 20 has a drilling machine body 22, a rod 24 supported by the drilling machine body 22 and drilling a hole in the ground 10, a water pump 26 that delivers drilling water to the rod 24 via a water supply pipe or the like, and a water pressure gauge 28 that is attached to the water supply pipe or the like and measures the water supply pressure value of the drilling water. The rod (injection rod) 24 is, for example, a double pipe with a tip device attached to the tip (lower end) 24T.

The drilling machine 20 drills the ground 10 while spraying drilling water from the tip 24T of the rod 24 until the tip 24T of the rod 24 reaches the impermeable layer 10X. At this time, the water pressure value of the drilling water (hereinafter referred to as the "drilling water pressure value P ₁ ") is measured by the water pressure gauge 28. The drilling water pressure value P ₁ when the tip 24T of the rod 24 reaches the impermeable layer 10X is set as the reference drilling water pressure value P _X.

Fig. 2(B) shows an example of the stratum of the test area R1 obtained from the boring survey and the drilling water supply pressure value _P1 obtained from the drilling test. As can be seen from Fig. 2(B), the ground 10 includes, from the surface, a fill soil layer 10A, a clay layer 10B, a sand layer 10C, and a low-permeability layer 10X.

2B, when the tip 24T of the rod 24 reaches the clay layer 10B, the drilling water supply pressure value _P1 increases. Next, when the tip 24T of the rod 24 reaches the sand layer 10C, the drilling water supply pressure value _P1 decreases. Next, as the tip 24T of the rod 24 approaches the impermeable layer 10X, the drilling water supply pressure value _P1 increases, and when the tip 24T of the rod 24 reaches the impermeable layer 10X, the drilling water supply pressure value _P1 becomes maximum. In this way, the drilling water supply pressure value _P1 varies depending on the stratum, so the impermeable layer 10X can be identified by the drilling water supply pressure value _P1 .

In this embodiment, for example, the impermeable layer 10X is drilled to a predetermined depth, and the average value of multiple drilling water supply pressure values measured while drilling the impermeable layer 10X is set as the reference drilling water supply pressure value.

In addition, the reference drilling water supply pressure value P _X is not limited to the average value of multiple drilling water supply pressure values as described above, but may be, for example, the maximum or minimum value of multiple drilling water supply pressure values measured while drilling the impermeable layer 10X.

For example, it is desirable to use a high-precision pressure gauge for the water supply pressure gauge 28. A high-precision pressure gauge includes, for example, a pressure gauge with a measurement accuracy of 0.000 MPa or more and a measurement pitch of 10 Hz or more. The water supply pressure value measured by the water supply pressure gauge 28 is recorded by a recording device such as a data logger. The process of measuring the drilling water supply pressure value when the tip 24T of the rod 24 has reached the impermeable layer 10X can be considered as a reference drilling water supply pressure value acquisition process.

(Waterproof wall construction process)
1 , in the impermeable wall construction process, a water impermeable wall 40 having a lower end 42L embedded in a low permeability layer 10X is constructed in a construction region R2 of the ground 10. In this embodiment, the water impermeable wall 40 is constructed in the construction region R2 by, for example, a double pipe strainer method among chemical injection methods. This water impermeable wall construction process includes a hole drilling step and a grouting material injection step, and the water impermeable wall 40 is formed in the construction region R2 of the ground 10 by repeating these hole drilling step and grouting material injection step.

(Drilling process)
As shown in Fig. 3(A), in the drilling step, the drilling machine 20 described above is used to drill the construction area R2 of the ground 10. As in the excavation test step, the drilling machine 20 drills the construction area R2 of the ground 10 while injecting drilling water from the tip 24T of the rod 24, and forms a drilling hole 30 in the construction area R2. At this time, the drilling water supply pressure value of the drilling water is measured by the water supply pressure gauge 28. Then, for example, as shown in Fig. 4, when the drilling water supply pressure value _P2 reaches the reference drilling water supply pressure value _PX , it is determined that the drilling hole 30 has reached the impermeable layer 10X, and the drilling by the drilling machine 20 is stopped.

For example, in order to ensure the embedment depth of the drilling 30 into the impermeable layer 10X, the impermeable layer 10X may be further drilled after the drilling water supply pressure value reaches the reference drilling water supply pressure value P _X. The drilling water supply pressure value is an example of drilling data acquired during drilling.

(Injection process)
Next, in the injection step, as shown in Fig. 3B, the injection material 32 is jetted from the tip 24T of the rod 24 in the radial direction with the tip 24T of the rod 24 reaching the impermeable layer 10X, and the injection material 32 is injected into the soil around the tip 24T. The injection material 32 penetrates into the gaps between the soil particles around the tip 24T of the rod 24, and bonds the soil particles together. As a result, the soil around the tip 24T of the rod 24 solidifies, and a cylindrical ground improvement portion 42S is formed. The injection material 32 is, for example, a solvent (solution) containing water glass.

Next, as shown in FIG. 3(C), with the rod 24 raised a predetermined amount, the injection material 32 is sprayed radially from the tip 24T of the rod 24, and the injection material 32 is injected into the soil around the tip 24T. This causes the soil around the tip 24T of the rod 24 to solidify, forming a cylindrical ground improvement section 42S. At this time, the amount by which the rod 24 is raised is adjusted so that the vertically adjacent ground improvement sections 42S are continuous.

In this way, by injecting the injection material 32 into the construction area R2 of the ground 10 while pulling up the rod 24 by a predetermined amount at a time, multiple ground improvement sections 42S are made continuous in the vertical direction (depth direction) as shown in FIG. 3(D). This forms a cylindrical ground improvement body 42 that extends from the impermeable layer 10X to the ground surface and has its lower end 42L embedded in the impermeable layer 10X.

Then, the above-mentioned hole drilling process and injection material injection process are repeated to overlap adjacent ground improvement bodies 42 in a plan view as shown in Figure 1, thereby forming a wall-shaped water shielding wall 40 (see Figure 1).

(effect)
Next, the effects of this embodiment will be described.

First, a method for constructing a water-impermeable wall according to a comparative example will be described. FIG. 5 shows a water-impermeable wall 100 constructed by the method for constructing a water-impermeable wall according to a comparative example. In the method for constructing a water-impermeable wall according to the comparative example, when drilling a construction area R2 of the ground 10, it is determined whether or not the drilling 30 has reached the impermeable layer 10X based on the depth of the surface 10X1 of the impermeable layer 10X obtained from a boring survey.

5, the surface 10X1 of the impermeable layer 10X is uneven, and the depth of the surface 10X1 of the impermeable layer 10X in the construction area R2 is deeper than the depth of the surface 10X1 of the impermeable layer 10X in the test area R1 where the boring survey was conducted. In this case, as in the construction method of the impermeable wall according to the comparative example, when constructing the impermeable wall 100 in the construction area R2, if it is determined whether the drilling 30 has reached the impermeable layer 10X based on the depth of the surface 10X1 of the impermeable layer 10X obtained from the boring survey, the lower end 100L of the impermeable wall 100 will not reach the impermeable layer 10X, and the lower end 100L of the impermeable wall 100 will not be embedded in the impermeable layer 10X.

In contrast, according to the construction method of a water impermeable wall according to the present embodiment, in a drilling test step, as shown in Fig. 2(A), a test area R1 of the ground 10, in which the depth of the impermeable layer 10X has been obtained by a boring survey, is drilled using a drilling machine 20. At this time, the test area R1 is drilled while drilling water is fed from the tip 24T of the rod 24, and the drilling water supply pressure value when the drilling hole 30 reaches the impermeable layer 10X is set as a reference drilling water supply pressure value P _X. Then, as shown in Fig. 3(A), in the drilling step, it is determined that the drilling hole 30 has reached the impermeable layer 10X when the drilling water supply pressure value P ₂ obtained during drilling reaches the reference drilling water supply pressure value P _X.

As a result, as shown in FIG. 1, even if there are unevenness on the surface (layer boundary) 10X1 of the impermeable layer 10X, the drilled hole 30 can reach the impermeable layer 10X. In addition, in the injection material injection process, the injection material 32 is injected into the drilled hole 30, so that the lower end of the ground improvement body 42 can be embedded in the impermeable layer 10X. Therefore, the lower end 42L of the water shielding wall 40 can be embedded more reliably in the impermeable layer 10X.

In addition, for example, as in the comparative example shown in Figure 6, if the lower end 100L of the water shielding wall 100 does not reach the impermeable layer 10X, groundwater may flow into the inside of the water shielding wall 100 between the lower end 100L of the water shielding wall 100 and the impermeable layer 10X, as shown by arrow a, and the amount of water pumped from the pumping well 50 may increase, as shown by arrow b.

In contrast, in this embodiment, as shown in FIG. 7, the lower end 42L of the impermeable wall 40 is embedded in the impermeable layer 10X, so that groundwater is prevented from flowing into the inside of the impermeable wall 40 from between the lower end 42L of the impermeable wall 40 and the impermeable layer 10X. Therefore, in this embodiment, the amount of water pumped from the pumping well 50 (arrow b) can be reduced compared to the impermeable wall 40 in the comparative example.

In addition, the symbol _WL0 shown in Figs. 6 and 7 is an example of a natural groundwater level, and the symbol _WL1 is an example of a groundwater level after pumping.

In addition, in this embodiment, the waterproof wall 40 is constructed using a chemical injection method. Therefore, in this embodiment, compared to the soil cement column wall method (SMW method), the waterproof wall 40 can be constructed using small heavy machinery (hole drilling machine 20). In addition, in this embodiment, for example, as shown in FIG. 7, when the waterproof wall 40 is constructed from above the existing pressure plate 52, the diameter of the working hole 54 formed in the existing pressure plate 52 can be made smaller than in the soil cement column wall method. Therefore, construction costs can be reduced.

(Modification)
Next, a modification of the above embodiment will be described.

In the above embodiment, in the drilling process, it is determined that the drilling 30 has reached the impermeable layer 10X of the construction area R2 when the drilling water supply pressure value _P2 reaches the reference drilling water supply pressure value P _X. However, for example, it may be determined that the drilling ₃₀ has reached the impermeable layer 10X of the construction area R2 not only when the drilling water supply pressure value _P2 reaches the reference drilling water supply pressure value P _X , but also when the drilling water supply pressure value P2 is maintained at or above _the reference drilling water supply pressure value P X for a predetermined time.

Here, when rocks or the like are buried in the ground 10, there is a possibility that the drilling water supply pressure value _P2 may become temporarily high even before the drilling 30 reaches the impermeable layer 10X. In this case, as described above, by determining that the drilling ₃₀ has reached the impermeable layer _10X not only when the drilling water supply pressure value _P2 reaches the reference drilling water supply pressure value PX, but also when the drilling water supply pressure value P2 maintains the reference drilling water supply pressure value _PX or more for a predetermined time, it is possible to improve the accuracy of determining whether the drilling 30 has reached the impermeable layer 10X.

In addition, in the above embodiment, the same drilling machine 20 was used in the drilling test process and the drilling process. However, different drilling machines may be used in the drilling test process and the drilling process.

In the above embodiment, the water shielding wall 40 was constructed using the double-pipe strainer method. However, it is also possible to construct the water shielding wall 40 using, for example, the double-pipe double packer method.

In the above embodiment, the water impermeable wall 40 was constructed using a chemical injection method. However, the water impermeable wall may also be constructed using, for example, a soil cement column wall method (SMW method). In this case, for example, in the drilling process, when the drilling water supply pressure value obtained during drilling of the soil cement column reaches the reference drilling water supply pressure value, it may be determined that the drilling of each soil cement column has reached the low permeability layer.

In the above embodiment, the drilling data is the drilling water supply pressure value _P2 of the drilling water supplied to the drilling hole 30 during drilling. However, the drilling data is not limited to the drilling water supply pressure value, and may be, for example, the rotation torque or drilling speed of the bit that excavates the ground, or a combination of the drilling water supply pressure value, the rotation torque of the bit, and the drilling speed.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and one embodiment and various modified examples may be used in appropriate combination, and the present invention may of course be embodied in various forms without departing from the spirit of the present invention.

10 Ground 10X Impermeable layer 20 Drilling machine 30 Drilling hole 32 Injection material 40 Impermeable wall 42 Ground improvement body V Position of ground

Claims (2)

a drilling step of drilling a hole in the ground while feeding drilling water using a drilling machine and causing the hole to reach a low-permeability layer of the ground based on drilling data acquired during the drilling;
A grout injection process for injecting grout into the drilled hole to form a ground improvement body in the ground;
Equipped with
The drilling data includes a drilling water supply pressure value of drilling water supplied to the drilling hole during drilling,
A drilling machine is used to drill a hole in the ground at a position where the depth of the impermeable layer has been obtained, while supplying drilling water, and the drilling water supply pressure value when the drilling reaches the impermeable layer is set as a reference drilling water supply pressure value;
In the drilling step, when the drilling water supply pressure value reaches the reference drilling water supply pressure value, it is determined that the drilling has reached the impermeable layer;
The drilling step and the injection step are repeated to form a water impermeable wall by connecting the ground improvement body in a wall shape.
How to build a watertight wall. In the drilling step, when the drilling water supply pressure value reaches the reference drilling water supply pressure value and is maintained at or above the reference drilling water supply pressure value for a predetermined period of time, it is determined that the drilling has reached the impermeable layer.
A method for constructing a water impermeable wall according to claim 1.