JP7824809B2 - Watertight method for anchor hole opening - Google Patents

Description

This invention relates to a method for waterproofing the mouth of an anchor hole, and in particular to technology for preventing soil and groundwater from gushing out of the anchor hole when the casing pipe is pulled out during ground anchor installation under high water pressure.

Ground anchor installation is generally carried out in the following steps:
First, attach a water stop box to the core material of the retaining wall.
Next, the leading casing, which has a ring bit with a check valve attached to the tip, is inserted into the opening of the water stop box.
A packer (water stop device) attached to the casing is connected to this water stop box to prevent water leakage from the outer surface of the casing. However, a prepender may be used instead of the packer.

Next, the drilling machine rotates or strikes the casing while driving it into the ground, and drilling begins. During this process, drilling water is supplied into the casing, and the drainage water (drilling mud) travels through the gap between the casing and the anchor hole to the water stop box, where it is discharged and treated through a drainage valve attached to the water stop box.
Drilling continues by adding casing until the required depth is reached.

When the tip of the casing reaches the required depth, the drain valve of the water stop box is closed.
Next, a grout hose is inserted into the casing and filled with cement milk.
Next, tendons (steel wires) are inserted into the casing, and a casing packer is inserted into the casing located at the rearmost end, ensuring watertightness inside the casing.
After this, the bit is detached and the casings are pulled out one by one from the back. When the front casing is pulled up to a position where it can be removed (a position inside the watertight box), the casing packer is pushed into the next casing with the inner rod, maintaining watertightness inside the casing.

Figure 1 shows the state when the tip 10a of the last casing 10 has reached the water stop box 12, with the reference numeral 36 indicating the packer, the reference numeral 38 indicating the casing packer, the reference numeral 14 indicating the drain valve, the reference numeral 18 indicating the anchor hole, the reference numeral 16 indicating the guide pipe buried in the soil wall 22, the reference numeral 40 indicating the tendon, and the reference numeral 34 indicating the ground.
As shown in the figure, the anchor hole 18, the guide pipe 16, the water stop box 12 and the casing 10 are filled with cement milk 42.

If time passes in this state, the cement milk 42 will harden, making it difficult to clean or reuse the water stop box 12 and the casing 10.
For this reason, conventionally, as shown in Figure 12, a water-stopping material 80 such as LW (water glass + cement milk) is pressed into the water-stopping box 12 through an injection port (not shown) provided on the side of the water-stopping box 12, and after water is stopped inside the water-stopping box 12, the casing 10, and the guide pipe 16, the water-stopping box 12, the packer 36, the casing 10, and the casing packer 38 are removed.

As shown in Figure 13, even if the water stop box 12 etc. is removed, the inside of the guide pipe 16 and the upper end of the anchor hole 18 are filled with gelled water stop material 80, so that soil and groundwater are effectively prevented from gushing out onto the ground.
Furthermore, since the gelled water-stop material 80 can be removed by washing or the like, the water-stop box 12 and the casing 10 can be reused.
JP 4-198522 JP 10-280855 JP 2006-161345 JP 2009-68285

However, the waterproofing process using the waterproof material 80 itself is a relatively difficult task, and failures due to insufficient hardening or strength are likely to occur. In such cases, it is necessary to review the formulation and hardening confirmation time and start the work over from scratch.
Furthermore, the water glass and cement milk used as the water-stopping material 80 had to be procured separately, and the time and effort required to install and move dedicated equipment, such as a pump for pumping the water glass and a pump for pumping the cement milk, to the site was also required.
Furthermore, although the water stop box 12 and the casing 10 can be reused, cleaning the gel water stop material 80 requires considerable effort.
Furthermore, since friction between the water-stopping material 80 and the soil wall 22 is poor, there is a risk of water leakage due to the water-stopping material 80 coming loose.

This invention was devised in light of this current situation, and aims to provide a technology that can more easily and stably achieve waterproofing at the mouth of an anchor hole, as an alternative to conventional waterproofing methods that use water-stopping materials.

To achieve the above objective, the anchor hole watertightness method described in claim 1 is a ground anchor construction method in which multiple casings are inserted sequentially into a watertight box connected to the outer surface of a retaining wall to drill anchor holes in the ground, cement milk is filled into the anchor holes and a tendon is inserted, and the casings are then pulled out sequentially from the back while additional cement milk is added. When the tip of the last casing reaches the watertight box, a predetermined amount of liquid (e.g., water) is injected from the rear end opening of the casing packer loaded inside the casing at an injection pressure higher than the pressurized water generated in the injection port, forcing the cement milk filled inside the casings and watertight box into the anchor hole. After the cement milk in the anchor hole has solidified, the watertight box and casings are removed and the liquid inside is discarded.

The method for waterproofing the mouth of an anchor hole described in claim 2 is the method described in claim 1, characterized in that the liquid is supplied from the rear end opening of a casing packer loaded inside the casing.

The anchor hole mouth waterstop method described in claim 3 is the method described in claim 2, characterized in that the amount of liquid is set by subtracting the volume of the casing packer and tendon from the volume from the tip of the waterstop box to the rear end of the casing.

According to the method for watertightness at the mouth of an anchor hole of this invention, simply filling a predetermined amount of liquid (water, etc.) with an injection pressure higher than the pressurized water generated in the injection port causes the cement milk in the casing and the watertight box to move toward the anchor hole, reliably achieving watertightness at the mouth, eliminating the need for rework due to failure and improving construction efficiency.
In addition, it is no longer necessary to prepare water glass or cement milk when stopping water leakage, as was previously done, and to install devices to pump each of them into the water leakage box, thereby reducing the costs and effort required.
Furthermore, after the water stop is completed, the liquid supplied to the casing and water stop box can be simply discarded, eliminating the need to clean the inside of the water stop box or the casing, thereby improving their reusability.
Furthermore, because cement has good friction with the soil wall, it is possible to prevent the water-stopping material from coming loose when pressurized water acts as an external force after installation, as occurs with conventional water-stopping materials (water glass + cement milk), so there is no risk of water leakage.

This is a cross-sectional view showing the state in which the tip of the last casing has reached the water stop box during the casing extraction process of the ground anchor method. This is a plan view showing the state in which a mouth plate is installed between a pair of core materials of a soil wall. FIG. 10 is a cross-sectional view showing how water is poured into the casing and the water stop box. 10 is a cross-sectional view showing the mouth of the anchor hole when the water stop box and casing are removed. FIG. 1 is a cross-sectional view showing an experimental device prepared for verifying the effectiveness of the water stopping method according to the present invention. FIG. FIG. 10 is a cross-sectional view showing the state in which cement milk is filled in the experimental apparatus. FIG. 10 is a cross-sectional view showing the state in which water is poured into the experimental device. FIG. 10 is a cross-sectional view showing the state after water injection into the experimental apparatus is completed. 10 is a graph showing the change in density over time inside the water stop box measured by a density meter. This is a cross-sectional view showing the experimental apparatus after the guide pipe, water stop box, and casing have been removed and the filled water has been discarded. FIG. 10 is a diagram comparing measurement results of the height h of a void formed in a housing. FIG. 1 is a cross-sectional view showing a conventional water blocking method. 1 is a cross-sectional view showing the mouth of an anchor hole when a waterstop box and a casing are removed in a conventional waterstop method. FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
As mentioned above, FIG. 1 is a cross-sectional view of the casing pulling-out process in the ground anchor construction method, more specifically, the point in time when the tip 10 a of the last casing 10 has reached the water stop box 12 .

The water stop box 12 includes a cylindrical storage pipe 12a, a first flange 12b, a second flange 12c, and a branch pipe 12d. A drain valve 14 is connected to the branch pipe 12d. A transparent window may be provided to visualize the replacement of cement milk with water inside the water stop box 12 or the branch pipe 12d.
The water stop box 12 is connected to a guide pipe 16 .

The guide tube 16 has a cylindrical body 16a and a flange 16b, and the body 16a and flange 16b are designed to intersect at an angle corresponding to the inclination angle of the anchor hole 18.

Reference numeral 20 in the figure denotes a core material (H-shaped steel) of the soil wall 22, and as shown in FIG. 2, a steel mouth plate 24 is welded between a pair of core materials 20.
A circular through-hole 24 a is formed in the center of this mouth plate 24 , and the main body 16 a of the guide pipe 16 is embedded in the soil wall 22 through this through-hole 24 a.
Reference numeral 26 in the figure denotes a bracket welded between the core members 20 to support the mouth plate 24 .

The guide pipe 16 and the water stop box 12 are fixed by overlapping their respective flanges 16b, 12b, inserting bolts 28 erected on the mouth plate 24 into their respective through holes, and fastening them together with nuts 30. As a result, the storage pipe 12a of the water stop box 12 and the main body 16a of the guide pipe 16 are in a state of communication.
Reference numeral 32 in FIG. 1 denotes cement milk filled in the gap between the mouth plate 24 and the core material 20 .
When forming the anchor holes 18 in the ground 34, a plurality of casings are inserted in sequence from the storage pipe 12a of the water stop box 12 to the main body 16a of the guide pipe 16.

A packer 36 is attached to the outer peripheral surface of the casing 10.
The packer 36 has the function of closing the gap between the outer peripheral surface of the casing 10 and itself.
The flange 36 c of the packer 36 is connected to the second flange 12 c of the water stop box 12 via the bolts 28 and nuts 30 .

A casing packer 38 is loaded into the rear end opening 10b of the casing 10.
The casing packer 38 has a check valve inside consisting of a ball and a spring, and fluid flowing in from the rear end opening 38a is released directly from the front end opening 38b, but fluid attempting to flow in from the front end opening 38b is blocked by the check valve.
The reference numeral 40 in the drawing indicates a tendon (steel wire) that was inserted into the anchor hole 18 from the rear end of the casing in the preceding step.

The casing 10, the water stop box 12, the guide pipe 16, and the anchor hole 18 are filled with cement milk 42 that was filled in the previous process.
If time continues like this, the cement milk 42 inside the water stop box 12 and the casing 10 will harden, making it difficult to reuse the water stop box 12 and the casing 10.Therefore, in this invention, a process is carried out to replace the cement milk 42 with water before it hardens.

That is, as shown in FIG. 3, a head cap 44 is attached to the rear end opening 10b of the casing 10, and a predetermined amount of water 48 is injected into the casing 10 via a hose 46 at an injection pressure higher than the pressure of the pressurized water generated in the injection port.
As a result, the cement milk 42 in the casing packer 38, the casing 10, the water stop box 12 and the guide pipe 16 is pushed toward the anchor hole 18 under water pressure.

This state is maintained for several to several dozen hours, and after waiting for the cement milk 42 in the anchor hole 18 to solidify, the water stop box 12 and casing 10 are removed, and the water in the guide pipe 16, water stop box 12, and casing 10 is discarded.

Even in this case, as shown in Figure 4, the upper end of the anchor hole 18 and part of the guide pipe 16 are blocked by hardened cement milk 42, ensuring watertightness, preventing soil and groundwater from flowing into the work area.
After this, a fixing portion consisting of a bracket, wale, base, etc. is provided on the core material 20, and the rear end of the tendon 40 is fixed in a tensioned state.

This watertight method has the following advantages:
(1) By simply filling the casing 10, water stop box 12, and guide pipe 16 with a pre-calculated amount of water, the cement milk 42 moves into the anchor hole 18, ensuring watertightness at the opening, eliminating the need for rework due to failure and improving construction efficiency.
(2) It is only necessary to supply water 48 into the casing 10, the water stop box 12, and the guide pipe 16, and it is no longer necessary to prepare water glass or cement milk when stopping water and to install devices to pump each of them into the water stop box 12, as was done in the past, thereby reducing costs and labor.
(3) After the water stoppage is completed, the water 48 can be simply discarded, and cleaning of the inside of the water stoppage box 12 and the casing 10 is not required, which improves the reusability of these components.
(4) The cement 42 has good friction with the soil wall 22, and unlike conventional water-stopping materials, it can prevent the water-stopping material from coming loose due to the external force of pressurized water, so there is no risk of water leakage.

In the above, an example is shown in which water 48 is supplied from the rear end opening 10b of the casing 10, but the present invention is not limited to this, and for example, water can also be supplied into the water stop box 12, the casing 10, and the guide pipe 16 from an inlet provided on the side of the water stop box 12.
In addition, in the above example, the guide pipe 16 is buried in the soil wall 22 and forms part of the anchor hole 18, but the installation of the guide pipe 16 may be omitted.
Instead of the water 48, other liquids having a lower specific gravity than the cement milk may be used.

FIG. 5 shows an experimental device 50 prepared for verifying the effectiveness of the water stopping method according to the present invention.
The experimental apparatus 50 comprises a steel housing 52, a guide pipe 16 attached to an opening 52a of the housing 52, a water stop box 12 connected to the guide pipe 16, a casing 10 inserted into the water stop box 12, and a packer 36 attached to the outer surface of the casing 10.
Reference numeral 53 in the drawing denotes a check valve that functions as a drain port of the housing 52 .

The flange 16 b of the guide pipe 16 and the first flange 12 b of the water stop box 12 are fixed to the housing 52 via bolts 28 and nuts 30 that are provided on the outer surface of the housing 52 .
The dimension from the rear end of the packer 36 to the rear end of the casing 10 is set to 750 mm.
The tip 10 a of the casing 10 is inserted into the water stop box 12 .
A non-contact density meter (not shown) is installed on the side of the water stop box 12, making it possible to measure changes in the density of the liquid (e.g., cement milk or water) inside the water stop box 12 in real time.
Since the purpose of the experiment was not to actually install anchors but to confirm their water-stopping effect, the insertion of tendons and the installation of drainage valves were omitted.

Prior to the start of the experiment, as shown in FIG. 6, cement milk 42 is supplied from the rear end opening 10b of the casing 10 and filled into the housing 52, guide pipe 16, water stop box 12 and casing 10.
A casing packer 38 is loaded into the rear end opening 10b of the casing 10.

Next, as shown in Figure 7, a head cap 44 is attached to the rear end opening 10b of the casing 10, and water 48 is supplied from a water source at a predetermined pressure. The water is then poured into the casing 10 through the tip opening 38b of the casing packer 38, and the cement milk 42 inside the casing 10 is pushed toward the housing 52.
When the water supply is stopped after a preset amount of water 48 has been injected, the cement milk 42 in the casing 10 and the water stop box 12 is replaced with water 48, as shown in FIG.

FIG. 9 is a graph showing the change over time in density inside the water stop box 12 measured by a density meter, with density on the vertical axis and time on the horizontal axis.
As shown in the figure, the density of the material in the watertight box 12 increases as soon as the filling of the cement milk 42 begins, and at the time of completion of filling, a value of 1.84 g/cm3, which corresponds to the density of the cement milk, is recorded.
After this, the density of the material in the water stop box 12 begins to decrease as soon as the water injection starts, and at the end of the water injection, a value of 1.00 g/cm3, which corresponds to the density of water, is recorded.
From this result, it was confirmed that the substance in the water stop box 12 was replaced by water 48 from cement milk 42 by pouring water.

Figure 10 is a cross-sectional view showing the state after the guide pipe 16, water stop box 12, and casing 10 have been removed from the housing 52 and the filled water 48 has been discarded, showing that a void 54 where no cement 42 is present has been formed within the housing 52.
The relationship between the height h from the bottom to the top of the space 54 and the amount of water poured will be examined below.

First, two experimental devices 50A and 50B having common specifications are prepared, and the volumes of the water stop boxes 12 and casings 10 of each are measured.
Here, the volume of each of the experimental devices 50A and 50B was 16.9 L, but since the volume of the casing packer 38 was 2.0 L, this was subtracted to obtain the reference water volume W, 15.0 L.
Next, 15 L of water (1.0 times the standard water volume W) is poured into one water stop device 50A, and 18 L of water (1.2 times the standard water volume W) is poured into the other water stop device 50B.
After a 16-hour curing period until the cement milk 42 solidified, the water stop box 12 and the casing 10 were removed from each housing 52, the injected water was discarded, and the height h of each cavity 54 was measured.

FIG. 11 shows the results, where h=14 cm for the experimental device 50A and h=16.5 cm for the experimental device 50B.
In other words, when the amount of water injected into the experimental device 50 is increased, the height h of the void 54 also increases proportionally (the amount of sinking of the solidified surface of the cement 42 increases), and it was confirmed that the injected water 48 and the cement milk 42 do not become cloudy, and the effect of pushing the cement milk 42 toward the housing 52 increases.
This means that as long as the amount of water injected is correct, the cement milk 42 can be removed from the casing 10 and the water stop box 12 without any problems.

10 Casing
12 Water stop box
14 Drain valve
16 Guide tube
18 Anchor holes
20 Core material
22 Soil Wall
24 Mouth plate
34 Ground
36 Packer
38 Casing Packer
40 Tendon
42 Cement Milk
44 Head Cap
46 Hose
48 water
50 Experimental Equipment
52 Case
53 Check valve
54 Vacant Space

Claims (2)

In a ground anchor construction method, a plurality of casings are inserted in sequence into a water stop box connected to the outer surface of an earth retaining wall to drill anchor holes in the ground, and cement milk is filled into the anchor holes while a tendon is inserted. After that, the casings are successively pulled out from the back while supplementary filling of cement milk is carried out.
When the tip of the last casing reaches the inside of the water stop box, a predetermined amount of water is injected into the casing and the water stop box at an injection pressure higher than the pressurized water generated in the injection port, and the cement milk filled in the casing and the water stop box is pushed toward the anchor hole.
a step of removing the water stop box and the casing after the cement milk in the anchor hole has solidified, and disposing of the water therein for reuse of the water stop box and the casing ;
wherein the water is supplied from a rear end opening of a casing packer loaded in the rear end opening of the casing . 2. The anchor hole watertight method according to claim 1, wherein the amount of water is set by subtracting the volume of the casing packer and tendon from the volume from the tip of the watertight box to the rear end of the casing.