Ground improvement method after removing existing piles

Abstract

To provide a ground improvement method by which strength characteristics of a backfilled ground in which a pile hole is backfilled and strength characteristics of a surrounding ground are made approximately equal to each other.SOLUTION: A ground improvement method after removal of an existing pile 10 comprises: a water content setting step of setting a water content of mud 150 stirred and mixed with an injection material 120 by an auger screw 200 by regarding that water 124 is filled into a pile hole 50 after removal; a test step of producing an adjusted test mud, a specimen with a changed mixture ratio of the injection material 120 and a water-cement ratio of the injection material 120 and performing a test including measurement of uniaxial compressive strength; an injection material setting step of setting the water-cement ratio of the injection material 120 and an injection amount of the injection material 120 based on test results in the test step so that strength characteristics of a backfilled ground 130 in which the pile hole 50 is backfilled is made approximately equal to strength characteristics of a surrounding ground 102; and a backfilling step of injecting the injection material 120 with the set water-cement ratio so as to be the injection amount and stirring and mixing by the auger screw 200 to backfill the hole.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for improving ground after removal of existing piles. [Background technology]

[0002] Cited Document 1 discloses a pile extraction method and device suitable for extracting existing foundation piles from the ground when rebuilding a building, and technology related to an improved ground and ground improvement method suitable for filling holes after extracting foundation piles. In this prior art, high-pressure water is sprayed from a high-pressure water jetting device in a concentric circle around the foundation pile to soften the ground around the foundation pile, making it easier to remove the foundation pile. After the pile extraction hole is filled with soil or coarse sand from the surrounding ground, cement, bentonite, and water are injected and mixed with the soil around the hole to adjust the compressive strength to be equal to that of the surrounding ground.

[0003] Patent Document 2 relates to a reinforced backfilled ground and a method for constructing the same, and discloses a technique for a reinforced backfilled ground and a method for constructing the same, in which a ground reinforcement structure using a backfill material obtained by adding a cement-based solidification material to a predetermined coarse-grained material and solidifying it is laid in the backfilled ground to prevent displacement such as subsidence of the surrounding ground of the backfilled ground. In this prior art, a reinforced backfilled ground is created by filling a backfilled space partitioned by an earth retaining wall with a backfill material, and a ground reinforcement structure is provided in the backfilled ground to ensure ground strength. The ground reinforcement structure is made of an improved ground material obtained by mixing and solidifying a coarse-grained material, a hydraulic solidification material, and water, and the improved ground material is laid in a predetermined layer thickness in the general backfill soil layer backfilled in the backfilled space, near a depth corresponding to the position of the struts placed in the original backfilled space, to suppress deformation of the earth retaining wall toward the backfilled ground side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-147771 A [Patent Document 2] JP 2007-154528 A Summary of the Invention [Problem to be solved by the invention]

[0005] When pulling out an existing pile, it is common to inject water into the hole to keep the water level constant, in order to prevent the wall of the hole from collapsing due to negative pressure. Therefore, the hole is filled with water after the existing pile is removed.

[0006] However, in the conventional construction methods such as the cited document 1, when backfilling pile holes after removing existing piles to improve the ground, the water filled in the pile holes is not taken into consideration, and basically even the water content of the original ground alone is not taken into consideration. Even if it is taken into consideration, if the water-cement ratio of the injection material and the injection amount of the injection material are set without reflecting the actual phenomenon, there is a risk that the strength characteristics of the backfilled ground after backfilling the pile holes will be significantly different from the strength characteristics of the surrounding ground.

[0007] In view of the above, an object of the present invention is to improve the accuracy of equalizing the strength characteristics of the backfilled ground after backfilling a pile hole with the strength characteristics of the surrounding ground. [Means for solving the problem]

[0008] The first aspect is a ground improvement method after removal of an existing pile, comprising: a water content setting step of setting the water content of the mud to be mixed with the injection material by an auger screw as if the pile hole was filled with water after the existing pile was removed; a test step of preparing a plurality of types of samples in which the mixing ratio of the injection material and the test mud adjusted to the water content of the mud set in the water content setting step and the water-cement ratio of the injection material are changed, and a test including measurement of the uniaxial compressive strength of the samples is carried out; an injection material setting step of setting the water-cement ratio of the injection material and the injection amount of the injection material based on the test results of the test step so that the strength characteristics of the backfilled ground obtained by backfilling the pile hole are equivalent to the strength characteristics of the surrounding ground; and a backfilling step of injecting the injection material having the water-cement ratio set in the injection material setting step to the injection amount, mixing and stirring with the auger screw to backfill the pile hole.

[0009] In the first embodiment of the ground improvement method after removal of existing piles, the moisture content of the test mud in the testing process is adjusted to the moisture content of the mud that is set in the moisture content setting process to reflect the actual phenomenon of water filling the pile hole after the existing pile is removed, so the moisture content of the test mud can be reproduced with higher accuracy compared to cases where the moisture content of only the original ground is not even taken into account, or where even if it is taken into account, the actual phenomenon is not reflected.

[0010] Therefore, compared to when the water-cement ratio of the injection material and the injection amount of the injection material are set without taking into account actual phenomena, the accuracy of making the strength characteristics of the backfilled ground after the pile hole is backfilled equivalent to the strength characteristics of the surrounding ground is improved.

[0011] A second aspect is a ground improvement method after removal of an existing pile as described in the first aspect, in which, in the moisture content setting step, the moisture content of the mud is set using the volume ratio between the volume of water filled in the pile hole and the volume of the soil mass around the existing pile.

[0012] In the second embodiment of the method for improving ground after removal of existing piles, the moisture content of the mud in the moisture content setting step is set using the volume ratio of the water filled in the pile hole to the volume of the soil mass around the existing pile. Therefore, the moisture content of the mud can be set more easily than when it is actually measured.

[0013] A third aspect is the ground improvement method after removal of existing piles described in the second aspect, in which the volume ratio is calculated using the pile diameter of the existing pile and the screw diameter of the auger screw in the water content setting step.

[0014] In the third aspect of the ground improvement method after removal of existing piles, the volume ratio of the existing pile volume to the soil mass surrounding the existing pile in the moisture content setting process can be easily set using the pile diameter of the existing pile and the screw diameter of the auger screw. Effect of the Invention

[0015] According to the present invention, it is possible to improve the accuracy of making the strength characteristics of the backfilled ground after the pile hole is backfilled equal to the strength characteristics of the surrounding ground, compared to a case where the moisture content of only the original ground is not taken into consideration, or where the consideration does not reflect actual phenomena. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a process diagram showing the ground improvement process after removing existing piles in the embodiment of the present invention in order from (A) to (F). [Diagram 2] FIG. 1 is an explanatory diagram showing the internal soil water pressure and the external soil water pressure. (A) is an explanatory diagram of the state in which the existing pile is buried, (B) is an explanatory diagram of the water level dropping after the existing pile is pulled out, and (C) is an explanatory diagram of the state in which the pile hole is filled with water. [Diagram 3] FIG. 2A is a graph showing the relationship between unconfined compressive strength, water-cement ratio (w / c), and mix volume ratio, and FIG. 2B is an explanatory diagram for explaining the mix volume ratio. [Figure 4] FIG. 1 is a schematic diagram illustrating the relationship between the diameter of the existing pile and the diameter of the auger screw, the pile hole filled with water, the soil mass around the pile, and the volume ratio. [Diagram 5] (A) is an explanatory diagram explaining the movement of the excavation rod in a construction trouble where the strength characteristics of the backfilled ground are too greater than the strength characteristics of the surrounding ground and excavation accuracy cannot be maintained, and (B) is an explanatory diagram explaining the movement of the excavation rod in a construction trouble where the strength characteristics of the backfilled ground are too smaller than the strength characteristics of the surrounding ground and excavation accuracy cannot be maintained. [Figure 6] 1 is a graph showing the relationship between the unconfined compressive strength of samples prepared by changing the volume ratio in an indoor mix test and the unconfined compressive strength of samples taken from backfilled ground. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Embodiment> A method for improving ground after removing existing piles according to one embodiment of the present invention will be described.

[0018] [Soil improvement process] First, an example of a process for improving the ground by removing existing piles and backfilling the pile holes will be described.

[0019] As shown in FIG. 1(A), an existing pile 10 is buried in an original ground 100 . As shown in Fig. 1(B), a cylindrical casing material 12 is inserted around the buried existing pile 10 to separate the existing pile 10 from the surrounding ground 102. The soil around the existing pile 10 is referred to as a pile surrounding soil mass 110. The pile surrounding soil mass 110 is the ground to be stirred and mixed by an auger screw 200 (see Figs. 1(E) and 1(F)) which will be described later.

[0020] As shown in Fig. 1(C) and Fig. 1(D), after the casing material 12 is pulled out, the existing pile 10 is pulled out using a wire 20 or the like. When pulling out the existing pile 10, in order to prevent the wall 52 of the pile hole 50 from collapsing due to the generation of negative pressure, the existing pile 10 is pulled out while injecting water 124 so that the water level in the pile hole 50 remains constant. The generation of negative pressure will be described later.

[0021] As shown in Figures 1(E) and 1(F), while injecting the injection material 120, the soil mass 110 around the pile and the water 124 filled in the pile hole 50 are stirred and mixed with the auger screw 200 to backfill the pile hole 50, thereby constructing the backfilled ground 130 (see Figure 1(F)). The soil mass 110 around the pile and the water 124 filled in the pile hole 50 are stirred and mixed to form mud 150 (see Figure 1(E)).

[0022] Here, we will explain how, when pulling out the existing pile 10 described above, in order to prevent the wall 52 of the pile hole 50 from collapsing due to the generation of negative pressure, the existing pile 10 is pulled out while injecting water 124 so that the water level in the pile hole 50 remains constant.

[0023] As shown in FIG. 2(A), when the existing pile 10 is buried, the soil water pressure 60 in the pile hole 50 and the soil water pressure 70 outside the hole are the same pressure.

[0024] However, as shown in Fig. 2(B), when the existing pile 10 is pulled out, the water level in the pile hole 50 drops, so that the soil water pressure 60 in the hole becomes smaller than the soil water pressure 70 outside the hole. This increases the risk of collapse of the wall 52 of the pile hole 50, boiling, etc.

[0025] Therefore, as shown in FIG. 2(C), the pile hole 50 is filled with water so that the soil water pressure 60 inside the hole and the soil water pressure 70 outside the hole become equal.

[0026] Therefore, when backfilling the pile hole 50 in the process of FIG. 1(E), the pile hole 50 is filled with water 124, and this water 124 and the soil mass 110 around the pile are stirred and mixed together by the auger screw 200.

[0027] [Setting the water-cement ratio and injection amount of the injection material] Next, a method for setting the water-cement ratio and injection amount of the injection material 120 injected in the step of FIG. 1(E) will be described.

[0028] The injection material 120 is composed of water, cement, and other additives. The other additives include bentonite, a thickener, and soda ash. The water-cement ratio of the injection material 120 refers to the volume ratio of the water and cement contained in the injection material 120.

[0029] (First step) In the step of Fig. 1(E), the moisture content of the mud 150 to be mixed with the injection material 120 by the auger screw 200 is set. As described above, the "mud 150" refers to the soil around the pile hole 50, that is, the soil around the pile hole 50, mixed with the water 124 in the pile hole 50. The method for setting the moisture content of the mud 150 will be described later in detail.

[0030] (Second process) A test mud adjusted to the water content set in the first step is prepared. A plurality of test grout materials 120 are also prepared by varying the water-cement ratio and the amounts of other mix materials. Then, for each of the plurality of grout materials 120, a plurality of types of samples are prepared by varying the mixing ratio (mixing volume ratio) of the grout material 120 and the test mud.

[0031] (Third step) Tests are performed on the multiple types of samples prepared in the second step, including measurement of uniaxial compressive strength as an example of strength characteristics.

[0032] Then, based on the test results, the water-cement ratio and the mixing ratio (mixing volume ratio) of the injection material are set so as to have the same strength characteristics as the surrounding ground 102 (see FIG. 1).

[0033] Here, an example of a method for setting the water-cement ratio and mixture proportion of the injection material that are equivalent to the strength characteristics of the surrounding ground 102 (see FIG. 1) based on the test results will be described.

[0034] Fig. 3(A) is a graph showing the relationship between the unconfined compressive strength, the water-cement ratio (w / c), and the mixing volume ratio (mixing proportion) of the injection material 120. The target strength in Fig. 3(A) is the unconfined compressive strength that is equivalent to the strength characteristics of the surrounding ground 102 (see Fig. 1). Then, from this graph, the water-cement ratio (w / c) and the mixing volume ratio (mixing proportion) of the injection material 120 that will result in the target strength are obtained.

[0035] 3(B) is an explanatory diagram for explaining the mixing volume ratio (mixing proportion) of the injection material 120. That is, when the ratio of the injection material 120 to the mud 150 is 2:1, the mixing volume ratio of the injection material 120 is 67%, when the ratio of the injection material 120 to the mud 150 is 1:1, the mixing volume ratio of the injection material 120 is 50%, and when the ratio of the injection material 120 to the mud 150 is 1:2, the mixing volume ratio of the injection material 120 is 33%.

[0036] The target strength is set based on the construction conditions and the strength characteristics of the surrounding ground 102 based on past ground investigations, such as the uniaxial compressive strength, N value, and deformation coefficient.

[0037] (Fourth step) The water-cement ratio and injection amount of the injection material 120 to be injected in Fig. 1(E) are set based on the water-cement ratio and the mixing ratio set in the third step. The injection amount of the injection material 120 can be calculated from the mixing ratio (mixing volume ratio) of the injection material 120 and the test mud and the volume of the pile surrounding soil mass 110 (see Fig. 1) to be mixed and stirred by the auger screw 200.

[0038] (Details of mud moisture content) Next, a method for setting the water content of the mud 150 (see FIG. 1) will be described in detail.

[0039] First, a moisture content ω0 of the pile surrounding soil mass 110 (see FIG. 1) surrounding the existing pile 10 is set. Note that any method may be used to set the moisture content ω0 of the pile surrounding soil mass 110, and an example thereof will be described below.

[0040] A wet density test is performed on a sampling sample taken from the pile surrounding soil mass 110 around the existing pile 10 to set the wet density ρt of the pile surrounding soil mass 110. Note that the surrounding ground 102 (see FIG. 1) may be taken as the sampling sample instead of the pile surrounding soil mass 110. If a wet density test cannot be performed, the wet density ρt is set based on the N value of the sampling depth of the sampling sample.

[0041] A soil particle density test is performed on the sample to set the particle density ρs of the soil mass around the pile 110. If a soil particle density test is not possible, a soil particle density value of 2.6 to 2.7 g / cm for general soil is used. 3 will be adopted.

[0042] From the wet density ρt and the particle density ρs, the water content ω0 of the soil mass around the pile 110 is set assuming that the degree of saturation Sr is 100%. The wet density ρt can be expressed by the following [Equation 1].

[0043]

number

[0044] [Number 1] ρw (density of water) = 1g / cm 3 Sr=100 Substituting, If we rearrange the left side with ω0, we get the following [Equation 2].

[0045]

number

[0046] Then, by inputting the wet density ρt and particle density ρs of the soil mass 110 around the pile into the above [Equation 2], the moisture content ω0 of the soil mass 110 around the pile can be obtained.

[0047] Next, the volume ratio A / B of the volume A of the water filled in the pile hole 50 (see FIG. 1) to the volume B of the soil mass 110 surrounding the pile is calculated from the pile diameter φ1 of the existing pile 10 and the auger screw diameter φ2 of the auger screw 200 (see FIG. 4).

[0048] If the ground being stirred and mixed by the auger screw 200 is the soil mass around the pile 110, and the pile diameter φ1 of the pile 10 is constant in the depth direction, A / B can be calculated by the following [Equation 3].

[0049]

number

[0050] If the pile diameter is not constant in the depth direction because the bottom end of the existing pile 10 has expanded in diameter, etc., calculations should be made as appropriate. For example, find the volume A of the water to be filled after pulling out the existing pile 10 whose pile diameter is not constant in the depth direction. Subtract volume A from the range stirred and mixed by the auger screw 200 to find the volume B of the soil mass 110 around the pile. From these, find the volume ratio A / B.

[0051] Using the volume ratio A / B between the volume A of the water 124 filled in the pile hole 50 and the volume B of the soil mass around the pile 110, the moisture content ω1 of the mud 150 when the water equivalent to the volume of the existing pile 10 is filled in the pile hole 50 is calculated and set using the following [Equation 4].

[0052]

number

[0053] <Action and Effects> Next, the operation and effects of this embodiment will be described.

[0054] The test mud for measuring uniaxial compressive strength is adjusted to the moisture content ω1 of the mud 150, which is set assuming that water 124 is filled into the pile hole 50 after the existing pile 10 is removed. Therefore, the moisture content ω1 of the test mud can be reproduced with higher accuracy than when the test mud is adjusted to the moisture content ω0 of the soil mass 110 around the pile or the surrounding ground 102.

[0055] Therefore, the accuracy of equalizing the uniaxial compressive strength of the backfilled ground 130 in which the pile hole 50 is backfilled and the strength characteristics of the surrounding ground 102 is improved.

[0056] In addition, by using the pile diameter φ1 of the existing pile 10 and the screw diameter φ2 of the auger screw 200, the volume ratio A / B of the volume A of the water 124 and the volume B of the soil mass 110 around the existing pile 10 can be easily set.

[0057] Here, Fig. 4(A) and Fig. 4(B) show an example in which the volume ratio A / B between the volume A of the water 124 filled in the pile hole 50 and the volume B of the pile surrounding soil mass 110 of the existing pile 10 is different. Therefore, if only the moisture content ω0 of the pile surrounding soil mass 110 is used, the moisture content ω1 of the mud 150 cannot be set accurately. If the moisture content ω1 is different, the uniaxial compressive strength changes even if the mixture and injection rate of the injection material are the same. Therefore, there is a risk that the strength characteristics of the backfilled ground 130 (see Fig. 1) will ultimately be significantly different from the strength characteristics of the surrounding ground 102.

[0058] Therefore, when drilling with the drilling rod 220 to drive new piles near the backfilled ground 130, if the strength characteristics of the temporary backfilled ground 130 are greater than the strength characteristics of the surrounding ground 102 as shown in Fig. 5(A), there is a risk that the drilling rod 220 will deviate from the backfilled ground 130 and the drilling accuracy will decrease. Alternatively, if the strength characteristics of the temporary backfilled ground 130 are smaller than the strength characteristics of the surrounding ground 102 as shown in Fig. 5(B), there is a risk that the drilling rod 220 will move closer to the backfilled ground 130 and the drilling accuracy will decrease.

[0059] In contrast, in this embodiment, there is a high degree of precision in making the strength characteristics of the backfilled ground 130 and the strength characteristics of the surrounding ground 102 equivalent, so that when excavating with the excavation rod 220 to drive new piles near the backfilled ground 130, there is no or only a small risk that the excavation rod 220 will deviate from the backfilled ground 130 as shown in Figure 5(A) or move toward the backfilled ground 130 as shown in Figure 5(B).

[0060] FIG. 6 shows the relationship between the uniaxial strength of samples SA, SB, and SC, which were prepared by adjusting the mud 150 to ω1 set as if the pile hole 50 was filled with water 124 as in this embodiment and changing the volume ratio A / B, and the uniaxial compressive strength of samples No. 1 to No. 6, which were obtained by sampling the backfilled ground 130.

[0061] The volume ratio A / B of sample SA was set to 0.16, which is the same as that of the actual construction. The volumes A / B of sample SA and sample SB were set to 0.31 and 1.1, which are different from those of the actual construction. Samples No. 1 to No. 6 were collected from the backfill ground 130 at a depth of about 3 m underground.

[0062] As shown in Fig. 6, samples No. 1 to No. 6 taken at a depth of about 3 m underground of the backfilled ground 130 are concentrated near sample SA, although there is some variation. Therefore, it is understood that the uniaxial compressive strength of the backfilled ground 130 can be more accurately equalized by not only setting the pile hole 50 as filled with water 124 but also combining the volume ratio A / B with the actual construction.

[0063] <Other> The "strength characteristics of the backfilled ground and the surrounding ground after the pile hole is backfilled" are characteristics indicated by uniaxial compressive strength, N value, deformation coefficient, etc. Also, "same strength characteristics" means that there is no difference or the difference is small between the strength characteristics of the two, and that no defects caused by the difference in the strength characteristics of the two occur, or even if they do occur, the impact is small. One example of a defect caused by the difference in strength characteristics of the two is that the drilling rod 220 deviates from the backfilled ground 130 as shown in Figure 5(A) above, or the drilling rod 220 approaches the backfilled ground 130 as shown in Figure 5(B), resulting in a decrease in drilling accuracy.

[0064] The present invention is not limited to the above embodiment.

[0065] For example, in the above embodiment, the volume ratio A / B of the volume A of the water 124 filled in the pile hole 50 to the volume B of the soil mass 110 around the existing pile 10 is calculated from the pile diameter φ1 of the existing pile 10 and the auger screw diameter φ2 of the auger screw 200, but is not limited to this. For example, the volume of the water 124 may be calculated by actually measuring the diameter of the pile hole 50 after the existing pile 10 is pulled out.

[0066] In the above embodiment, the water content of the mud 150 obtained by mixing the water 124 and the soil mass 110 around the pile is calculated using the volume ratio A / B between the volume A of the water 124 filled in the pile hole 50 and the volume B of the soil mass 110 around the pile of the existing pile 10, but the water content may be determined by taking into consideration the groundwater level, the saturation level of the ground, and the permeability of the ground.

[0067] Furthermore, for example, the injection material may be a cement bentonite liquid or liquefied treated soil.

[0068] Furthermore, for example, the method of injecting the injection material is not limited to the above embodiment. For example, the injection material may be injected from above without using an auger screw, and then mixed and stirred with an auger screw.

[0069] Furthermore, the present invention can be embodied in various forms without departing from the spirit and scope of the present invention. A plurality of embodiments and modifications can be implemented in appropriate combination. [Explanation of symbols]

[0070] 10 Existing piles 50 Pilehole 102 Surrounding ground 110 Pile surrounding soil mass 120 Injection material 124 Water 130 Backfill ground 150 Mud 200 Auger screw

Claims

1. A water content setting process for setting in advance the water content of mud composed of water filled in a pile hole after the existing pile is removed and the pile surrounding soil mass around the pile hole which is stirred and mixed with an auger screw when backfilling the pile hole; A test process in which a plurality of types of samples are prepared by varying the mixing ratio of the test mud adjusted to the water content of the mud set in the water content setting process and the injection material, and the water-cement ratio of the injection material, and a test including measurement of the uniaxial compressive strength of the samples is carried out; An injection material setting process for setting the water-cement ratio of the injection material and the injection amount of the injection material when backfilling the pile hole so that the strength characteristics of the backfilled ground obtained by backfilling the pile hole are equivalent to the strength characteristics of the surrounding ground based on the test results of the test process; A backfilling process in which the injection material having the water-cement ratio set in the injection material setting process is injected into the pile hole from which the existing pile was removed so as to reach the injection amount, and the pile surrounding soil mass and the water filled in the pile hole are stirred and mixed with the auger screw to backfill the pile hole; A method for improving ground after removing existing piles.

2. In the water content setting step, the water content of the mud is set using a volume ratio between the volume of water filled in the pile hole and the volume of the soil around the existing pile. A method for improving ground after removal of existing piles according to claim 1.

3. In the water content setting step, the volume ratio is calculated using the pile diameter of the existing pile and the screw diameter of the auger screw. A method for improving ground after removal of existing piles according to claim 2.

4. A water content setting process for setting the water content of the mud to be mixed with the injection material by the auger screw as if the pile hole had been filled with water after the existing pile was removed; A test process in which a plurality of types of samples are prepared by varying the mixing ratio of the test mud adjusted to the water content of the mud set in the water content setting process and the injection material, and the water-cement ratio of the injection material, and a test is carried out including measuring the uniaxial compressive strength of the samples; An injection material setting process for setting the water-cement ratio of the injection material and the injection amount of the injection material so that the strength characteristics of the backfilled ground obtained by backfilling the pile hole are equivalent to the strength characteristics of the surrounding ground based on the test results of the test process; A backfilling process in which the injection material having the water-cement ratio set in the injection material setting process is injected to the injection amount, stirred and mixed with the auger screw, and the pile hole is backfilled; Equipped with In the water content setting step, the water content of the mud is set using a volume ratio between the volume of water filled in the pile hole and the volume of the soil around the existing pile. A method for improving ground after removing existing piles.

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