JP2000240049A - Estimating method for finished shape of natural ground improved body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high-reliability estimated information about the finished shape of an improved body. SOLUTION: An electrode fitting body 14 is installed for estimating a diameter DX. The fitting body 14 is provided with current electrodes PI and potential electrodes PV. An arithmetic means 20 determines the measured resistance value Rreal per unit length of an improved body 12 from the potential difference V when a current I flows between the current electrodes PI. The relation between the resistance value R and diameter D per unit length of a simulated improved body is obtained based on the specific resistances ρ1 of improved bodies of multiple kinds and the specific resistance ρ2 of the natural ground by the two-dimensional axisymmetric finite element method with the ratio between the specific resistances ρ1, ρ2 used as a factor. When the measured specific resistance ρ1 real of the improved body 12 and the measured specific resistance ρ2 real of the natural ground 10 are obtained, the factor which is the ratio between the specific resistances ρ1, ρ2 is selected from the ratio between them, thereby the relation between the resistance value R and diameter D of the simulated improved body is specified, and the diameter DX can be estimated by collating the measured resistance value Rreal with this relation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a finished shape of an improved body formed in the ground.

[0002]

2. Description of the Related Art In some cases, an improved body is formed in the ground for the purpose of improving the ground or receiving a tunnel. This type of ground improvement body is, for example, in the ground improvement method of improving soft ground, while rotating the injection nozzle, high-pressure injection of a hardening agent such as cement milk into the ground, the hardening agent Injection into the ground is performed, and the injection energy is used to cut the ground and mix with the ground to create a high-pressure injection stirring method.

According to such a method, a pile-shaped ground improvement body can be formed in a soft ground by hardening a hardening agent. Also, in the mountain tunnel construction method, prior to the excavation of the tunnel, a tunnel front receiving method (fore piling method) in which a ground improvement body is formed in an arch shape around the tunnel to be excavated, is known. For example, the pile-shaped ground improvement body can reinforce the ground in front of the face.

[0004] Incidentally, after improving the ground or the ground by such a construction method, estimating or confirming the completed shape of the formed improved body is a very important management for judging the success or failure of the construction. Matters.

[0005] However, conventionally, as such a method, prior to actual construction, a test construction is performed, an improved body formed by the test construction is dug up, the completed shape is confirmed, and the actual construction is confirmed. The finished shape of the improved body in was estimated.

However, the method for estimating the finished shape of such an improved body has the following technical problems.

[0007]

That is, in the above-described method for estimating the finished shape of the improved body based on the test work,
Although the reliability of the completed shape is higher than the on-site measurement method using an elastic wave, an ultrasonic wave, or the like, there is a problem that the test work is disadvantageous in terms of a construction period and a construction cost.

[0008] Further, when there is not enough room at the construction site and the test construction cannot be performed at the construction site, the geology at the test construction site and the construction site do not always match, so that only low-precision estimation can be performed. could not.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a ground improvement method capable of obtaining highly reliable estimated information without performing test work. It is an object of the present invention to provide a method for estimating a finished shape of a body.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an electrode mounting body installed along the longitudinal direction of an improved body formed in the ground, and a longitudinal direction of the electrode mounting body. When a predetermined current flows between a pair of current electrodes attached at a predetermined interval along the pair, a pair of potential electrodes installed at a predetermined interval between the current electrodes, and the current electrode Further comprising calculating means for detecting a potential difference between the potential electrodes and obtaining an actually measured resistance value per unit length of the improved body, based on the specific resistance of each of the plurality of types of ground and the simulated improved body. , By the two-dimensional axisymmetric finite element method,
Using the ratio of the specific resistance as a factor, the relationship between the resistance value per unit length and the diameter of the simulated improved body is determined in advance, the factor is selected from the measured specific resistance of the ground and the improved body, and the measured resistance is selected. By comparing the value with the relationship between the resistance value per unit length and the diameter of the simulated improved body,
The diameter of the improved body was estimated. According to the method for estimating the completed shape of the ground improvement body thus configured, highly reliable information can be obtained without performing test work, as is clear from the principle explanation and the verification experiment described later. In the estimation method of the present invention, it is preferable that the ratio between the length and the diameter of the improved body is in the range of 0.07 to 0.16. If the shape of the improved body is within such a range, the current density is considered to be uniform even if the electrode for passing the predetermined current between the current electrodes is not a diploma, so that highly accurate estimation becomes possible. . Further, in the estimation method of the present invention, the ratio of the specific resistance of the ground and the improved body is:
Desirably, it is 50 times or more. If the specific resistance of the ground and the specific resistance of the improved body greatly differ from each other in this manner, highly accurate estimation becomes possible, as will be apparent from the following description.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2 show an embodiment of a method for estimating a finished shape of a mountain improved body according to the present invention.

The estimating method shown in FIG. 1 is an improved body 1 which is located in the ground 10 in front of a face and is formed in a substantially cylindrical shape so as to be directed obliquely upward for the purpose of receiving a tunnel.
2 illustrates an example in which the present invention is applied when estimating the diameter Dx of a fore-pile structure.

When estimating the diameter Dx of the improved body 12,
Before the improved body 12 is cured, the electrode mounting body 14 is inserted and installed therein. As shown in detail in FIG. 2, the electrode mounting body 14 has a rod-shaped main body 14a and a main body 14a.
Along the longitudinal direction, a pair of current electrodes P _I placed at a predetermined interval, in time for the current electrode P _I, along the longitudinal direction of the main body 14a, is disposed at a predetermined interval L a pair of and a potential electrode P _V were.

[0014] body 14a is internally configured with an electrical insulator, such as hollow PVC pipe, and a current electrode P _I and the potential electrodes P _V made of an annular metal ring which is fixed to the outer periphery thereof.

One end of a lead wire is connected to each of the current electrode P _I and the potential electrode P _V, and the other end of the lead wire on the current electrode P _I side is connected to a DC power supply 16. The other end of the _V- side lead wire is connected to the voltmeter 18.

[0016] DC power supply 16, a voltmeter 18, its operation is controlled by the computing means 20 constituted by a microcomputer or the like, the calculating means 20, via a DC power source 16, current electrode P _I given current I between when a current of, reads the potential difference V between the potential electrode P _V from the voltmeter 18, V / (I ×
L) is calculated, and the measured resistance value Rreal (Ω / m) per unit length of the improved body 12 is obtained.

Meanwhile, the estimation method of the present invention, in advance, the specific resistance [rho ₁ of a plurality of types of simulation improved body, and resistivity [rho ₂ of a plurality of types of natural ground is selected, by a two-dimensional axisymmetric finite element method The relationship between the resistance value R per unit length and the diameter D of the simulated improved body is determined using the ratio of these specific resistances ρ ₁ and ρ ₂ as a factor. This relationship can be stored as a table in the memory of the arithmetic unit 20, for example.

The measured specific resistance ρ ₁ real of the improved body 12 actually formed and the measured specific resistance ρ ₂ real of the ground 10 are
It is measured by an electric potential measurement method, a Wenner method, or the like described later.

Then, the measured specific resistance ρ ₁ real and the ground 10
Once the measured specific resistance ρ ₂ real is obtained, these ratios are calculated.First, a factor that is the ratio of the specific resistances ρ ₁ and ρ ₂ of the relationship obtained by the two-dimensional axisymmetric finite element method is selected. You.

When this factor is selected, the relationship between the resistance value R per unit length and the diameter D of the simulated improved body is specified, and the measured resistance value Rreal (Ω / m)
Can be estimated, the diameter Dx of the improved body 12 can be estimated.

The contents of the present invention will be described in more detail below based on the estimation principle of the estimation method of the present invention performed as described above, and a verification experiment conducted to confirm its effectiveness.

Basic Principle of the Estimating Method of the Present Invention The estimating method of the present invention uses the electric potential method as its basic principle. In general, when an electric current is applied to an underground medium, it is known that the following generalized Ohm's law (extended Ohm's law) holds even when the current density in the medium is not uniform. Have been.

E = ρi (1) where, E: Equivalent to the potential difference per unit length in the direction of the force applied to the charged particles by the strength of the electric field, i: Current density in the direction of the electric field, ρ: Specific resistance (specific to the material) resistance)

Consider a tiny cube dxdydz in an infinite medium,
The current density in the x, y and z directions of the current entering the cube is i_x, I
_y, I_zAnd the electric potential is V, x, y, z
E_x, E _y, E_zFrom equation (1), E_x=-(∂V / ∂x) = ρ_xi_x E_y= − (∂V / ∂y) = ρ_yi_y E_z= − (∂V / ∂z) = ρ_zi_z (2) and the outgoing current density i_x', I_y', I_z'Is the next
Become like

[0025] _{i x '= i x + (} ∂i x / ∂x) dx i y' = i y + (∂i y / ∂y) dy i z '= i z + (∂i z / ∂z) dz (3)

Thus, the difference in current in each direction, Δ
i _x, Δi _y, Δi _{z is, Δi x = i x 'dydz} -i x dydz = (∂i x / ∂x) dxdydz Δi y = (∂i y / ∂y) dxdydz Δi z = (∂i z / ∂z) dxdydz (4). Here, since the current flowing into the cube and the current flowing out are equal, Δi _x + Δi _y + Δi _z = 0 (5)

[0027] Therefore, _{(∂i x / ∂x) + (} ∂i y / ∂y) + (∂i z / ∂z) = 0 (6). When the specific resistances ρ _x , ρ _y , and ρ _z are uniform and equal to ρ, that is, in an isotropic homogeneous medium, equation (7) is obtained by substituting equation (2) into equation (6). ^{(∂ 2 V / ∂x 2)} + (∂ 2 V / ∂y 2) + (∂ 2 V / ∂z 2) = 0 (7)

This relational expression is an equation serving as a basis of the electric potential method for analyzing the structure of an underground medium or the like, and is a Laplace's equation relating to the potential V. In an actual problem, the equation (7) is set so as to satisfy the given boundary condition. ). Specific resistance of the substance

The specific resistance value of the material constituting the ground (ground) is
A wide range of good conductors (ρ <10 ⁻⁵ Ω · m), semiconductors (10
^-5 ≦ ρ ≦ 10 ⁷ Ω · m) and defective conductor (insulator) (ρ> 10 ⁷ Ω · m)
m).

Quartz and feldspar crystals, which are typical rock-forming minerals, are insulators. The specific resistance of rocks and sands composed of these insulator particles is determined by the bonding material, cracks and cracks between the mineral particles. It is lowered by moisture existing in the gap.

Normally, the specific resistance of a rock or the like has a value as shown in FIG. 3, but the specific resistance decreases as the number of cracks and gaps in the rock increases. The resistivity of groundwater is lower than that of surrounding materials, and seawater is treated as 0.3Ω · m.

Here, as shown in FIG.
(m ² ), a material having a length L (m) is considered, the current density i is made uniform, the potential difference between both ends of the material is V (V), and the applied current is I
Assuming (A), E = V / L (8) i = I / S (9) holds, and V = (ρL / S) I = RI (10) holds. Here, R is resistance (Ω), ρ corresponds to the resistance of the substance per unit volume, and the unit is Ω · m.

From equation (10), when the surrounding is an insulator, R = ρL / S (11) holds, and if ρ of the substance is constant, the resistance of the substance is measured by the following equation, and By determining the gradient, the cross-sectional area of the substance can be obtained. S = ρ / (R / L) (12)

When the specific resistance of the improved body during construction and the specific resistance of the ground are constant, that is, when the current source is a plane, the cross-sectional area of the substance can be obtained by equation (12). If it is cylindrical, the diameter can be determined.

However, as shown in FIGS. 1 and 2, in the case of the improved body 12 such as a fore-pile structure during construction, since the surrounding ground 10 around the improved body 12 is not an insulator, the end of the improved body 12 When the vicinity of the part is measured as a current source,
There is a current flowing to the zero side, and the finished shape of the improved body 12 (cross-sectional area) is improved by the specific resistance ρ ₁ of the mixture (hardened material and earth and sand) of the improved body 12, the specific resistance ρ ₂ of the surrounding ground 10 and the resistance. Must be considered as a function of the gradient R / L.

Therefore, the improved body (hardening material and earth and sand) 12
The need to measure the specific resistance [rho ₂ real specific resistance [rho ₁ real and natural ground 10, the specific resistance [rho ₁ real improvement body 12, wherein the potential measured by the experimental apparatus described later (FIG. 6) (11 ).

On the other hand, the specific resistance ρ ₂ real of the ground 10 is shown in FIG.
As shown partially in FIG. 2, since the distribution range of the specific resistance value is wide even in the same type of ground 10, it is necessary to actually measure the surrounding ground 10 and actually measure it.

The method for measuring the specific resistance [rho ₂ real of natural ground 10 is, for example, the specific resistance [rho ₂ real of natural ground 10, there is a method of measuring the land surface of the field, the current shown in FIG. 5 electrodes ( C1,
2) and the potential electrodes (P1, 2),
It can be obtained by the Wenner method of symmetrically arranging such that the electrode intervals between C1, P1, P1, 2 and P2, C2 are equal to a. The specific resistance ρ ₂ r of the ground 10 at this time
eal is represented by the following equation. ρ ₂ real = G (V / I) (13) Here, G = 2πa.

Laboratory experiment in which the current source is not planar and the surroundings are insulated (1) Outline An experimental apparatus shown in the figure, in which a cylinder whose wall is insulated is filled with water, and this is regarded as a simulated fore pile Was used to measure the electric potential between the electrodes.

At this time, since the current source is not planar,
As shown, the current density flowing between the electrodes is not uniform in each cross section. Therefore, it is not considered that equation (12) holds as it is. Therefore, it considered that the specific resistance [rho _'1 the apparent resistivity measured by this method, it was confirmed whether the formula (14) below is established. (R / L) · S = ρ ′ ₁ (constant)

(2) Experimental Method and Procedure The experiment was performed using the apparatus shown in FIG. 6 according to the following procedure. a) A vinyl chloride cylinder was prepared, one end was closed so that water did not leak, and the inside was filled with water to obtain a simulated improved body. b) The electrodes (current electrodes C ₁ , C ₂ , voltage electrodes P ₁ , P ₂ ) are placed in a cylinder with the electrode rods arranged as shown in the figure, and a DC current of 1 mA is applied from the current electrode C ₁ to the same C _2. Electric current was applied. c) The electric potential (potential difference) between the electrodes was measured using the potential electrodes P ₁ and P ₂ for measuring the electric potential. In addition,
The interval between the potential electrodes P ₁ and P ₂ was 5 cm. Also, set the water depth to 6
When 0 cm, the cylinder diameter is 4 cm, 5 cm and 6.5 cm, and when the water depth is 40 cm, the cylinder diameter is 5 cm,
6.5 cm and 34 cm.

(3) Experimental Results FIGS. 8 and 9 show the relationship between the measured resistance value per unit length and the electric potential measurement position in the longitudinal direction of the simulated fore pile.
Shown in In the drawings, the vertical axis represents the resistance per unit length (Ω / m), the horizontal axis represents the distance to the measuring position from the electrode C ₁ to (m).

[0043] From FIGS. 8 and 9, the unit resistance per length is found to be substantially constant regardless of the distance from the measurement position that is C _1. Also, the resistance per unit length decreases as the diameter of the cylinder (diameter of the simulated improved body) increases.

Here, how the apparent specific resistance ρ ′ ₁ obtained as the product of the resistance R / L per unit length and the cross-sectional area S of the cylinder (simulated improved body) changes with the diameter of the cylinder will be examined. Was.

The results are shown in FIGS. In the figure, the vertical axis represents the resistance per unit length R / L (Ω · m) × the cross-sectional area S of the cylinder (simulated improved body), and the horizontal axis represents the diameter (cm) of the cylinder.

[0046] As can be seen, when the depth 60cm (distance between the electrodes C ₁ and the electrode C ₂ is 60cm) and depth 40 cm (electrode C ₁ and the electrode
In the case where the distance between C ₂ is 40 cm) and the cylinder diameter is 5 cm or 6.5 cm, the product of the resistance R / L per unit length and the cross-sectional area S of the cylinder (simulated improved body), that is, the apparent specific resistance ρ ′ ₁ Is almost constant. On the other hand, when the water depth is 40 cm and the cylinder diameter is 34 cm, the apparent specific resistance ρ ′ ₁ is extremely large.

[0047] Considering the ratio of the cylinder of diameter D and depth (distance between the electrodes C ₁ and the electrode C ₂₎ H at this time, in the former case, D /
H = 0.07 to 0.16, and in the latter case, D / H = 0.88.

In the latter case, when the diameter becomes extremely large,
It is considered that the point R was in the state of the point current source, the current density was largely different in the simulated fore pile having a cylindrical shape, and at the same time, the current flowing to the outside was small, so that the resistance R was large.

From the above experimental results, when the periphery is an insulator, the current density is considered to be substantially uniform even if the current source is not planar, that is, D / H = 0.07 to 0. .
In a state where 16 is satisfied, equation (14) holds,
Apparent resistivity [rho _'1 is consistent with the specific resistance [rho _1, the resistivity of the mixture of hardeners and the sediment constituting the resistance value R obtained from the measurement of the electric potential measuring electrode interval L and improved body 12 [rho ₁ It can be seen from real that the diameter Dx of the cylindrical improved body 12 can be estimated.

Electric Potential Analysis by Axisymmetric Finite Element Method (1) Introduction When the periphery of the improved body 12 is an insulator, the diameter Dx of the cylindrical improved body 12 can be estimated from the equation (14). However, since the surrounding ground 10 of the actual improved body 12 is not an insulator, the finished shape of the improved body 12 has a specific resistance ρ ₁ real of the mixture (hardening material and earth and sand) in the improved body 12 and the surrounding ground 10 It is necessary to consider the following function affected by the specific resistance ρ ₂ real and the resistance gradient R / L. S = F (R / L, ρ 2 / ρ 1) (15)

Therefore, in the present invention, the improved body 12 was modeled as a cylinder vertically buried in a semi-infinite medium, and a numerical analysis was performed by a two-dimensional axisymmetric finite element method to investigate the relationship.

(2) Axisymmetric Finite Element Method Analysis When dealing with a potential field of an electrostatic field, the governing equation is 1 / ρ (∂ ² V / ∂x ² + ∂) at the boundary surface (z axis and ground surface). ² V / ∂y ² ) = − i (16), and the Poisson equation for the scalar potential V is solved. In the case of the axially symmetric analysis, the equation (16) becomes the following Poisson equation. 1 / ρ (∂ ² V / ∂r ² + 1 / r∂V / ∂r + ∂ ² V / ∂z ² ) + i = 0 (17) where ρ is a specific resistance, V is a potential (scalar potential), i Is the current density.

The boundary condition regarding the potential V when numerically analyzing the equation (17) using the finite element method is as follows: ∂V / ∂n = 0 (6.18), where n is a unit normal vector of the boundary surface. is there.

(3) Simulation Model and Numerical Analysis Considering the simulation model shown in FIG. 12, an element is divided as shown in FIG. 13 on an axisymmetric analysis plane, and a potential (potential potential) distribution is obtained by a finite element method. Was.

Here, ρ ₁ is the specific resistance of the simulated improved body, ρ ₂
The specific resistance of the surrounding natural ground, r _p is the radius of the electrode, r _m is the radius of the simulated improvement body, r _r is the radius of the peripheral natural ground.

As shown in FIG. 12, the analysis was performed on the assumption that a simulated improved body was formed vertically in the surrounding ground.

At this time, the specific resistance of the simulated improved body was 1 Ω · m
The resistivity of the surrounding ground was changed to 10, 20, 50, 100, and ∞Ω · m. The current was set to 1 mA, the current was passed from the bottom electrode of the simulated improved body to the ground surface electrode, and the potential difference was determined by a potential measurement electrode arranged therebetween. The interval between the current electrodes of the simulated improved body was 1.2 m.

(4) Results of Numerical Analysis FIG. 14 shows the diameter Dm (m) of the simulated improved body on the horizontal axis and the resistance per unit length (Ω / m) on the vertical axis. This is a plot in which the specific resistance ratios ρ ₁ and ρ ₂ of the mountain are used as parameters.

From the figure, it can be seen that the larger the specific resistance ρ _{2 of the} surrounding ground is, the larger the value of the resistance per unit length (resistance gradient) is, compared to the specific resistance ρ ₁ of the simulated improved body. I understand.

From this, it can be considered that the more the resistivity of the surrounding ground and the resistivity of the fore pile greatly differ, the more accurately the finished shape of the improved body 12 can be estimated.

From the results of the above laboratory experiments and numerical analysis,
Based on the resistivity ρ ₁ of the simulated improved body and the resistivity ρ _{2 of the} ground in advance, the ratio of these resistivity ρ ₁ and ρ ₂ is used as a factor by a two-dimensional axisymmetric finite element method as shown in FIG. The relationship between the resistance value R per unit length and the diameter D of the simulated improved body is determined in advance, and the measured specific resistance ρ ₁ real of the improved body 12 is obtained.
The measured specific resistance ρ ₂ real of the surrounding ground 10 and the measured resistance value R real (Ω / m) per unit length of the improved body 12 were measured, and the measured specific resistance ρ ₁ real and the measured specific resistance ρ ₂ real were calculated. From the ratio, the factor in FIG. 14 is selected, one of the curves is specified, the measured resistance value Rreal (Ω / m) is applied to the vertical axis of the curve, and the horizontal axis indicates the improved body 12.
It can be understood that the cross-sectional area (diameter Dx) can be estimated.

According to such estimation, highly reliable information can be obtained without performing test work.

At this time, the ratio of the length to the diameter of the improved body 12 is preferably in the range of 0.07 to 0.16. If the shape of the improved body 12 is in such a range, the current density is considered to be uniform even if the current electrode P _I through which the predetermined current I flows is not planar, so that highly accurate estimation is possible. become.

It is desirable that the ratio of the measured specific resistances ρ ₁ real and ρ ₂ real of the ground 10 and the improved body 12 be 50 times or more. The measured resistivity ρ ₁ real and the measured resistivity ρ ₂ real are
Such a large difference enables highly accurate estimation.

That is, in FIG. 14, the diameter of the simulated improved body is 40
When comparing the case of cm and the case of 60 cm, in the latter case, ρ ₂ / ρ ₁
When the diameter of the improved body 12 actually exceeds 60 cm, the diameter Dx of the improved body 12 can be calculated from the resistance value per unit length Rreal even if the value of It is difficult to estimate.

[0066] Also, as can be seen in the case of ρ ₂ / ρ ₁ = 10, when the specific resistance [rho ₂ of the resistivity [rho ₁ and the peripheral natural ground simulated improvement body is not much different, the diameter of simulated improved body Even if it changes, the change in specific resistance per unit length becomes small,
Cannot be measured accurately.

Therefore, from the result of the numerical analysis at the distance between the current electrodes of 1.2 m, the diameter Dx of the improved body 12 is 50 cm or less, ρ
_{If 2} / ρ ₁ = 50 or more, it can be said that effective measurement can be performed.

From this, the diameter Dx of the improved body 12 is
At about 2/5 or less of the distance between the current electrodes P _I , ρ ₂ / ρ ₁ = 50
In the above, the completed shape of the improved body 12 can be estimated by this method. Considering that the specific resistance ratio of the water measured in the demonstration experiment and the simulated improved body is 60 or more, the surrounding ground It can be said that a practical diameter for construction can be identified even when is saturated with water.

Demonstration experiment of effectiveness of estimation method of the present invention (1) Outline of demonstration experiment a) Date of demonstration experiment April 23 and 24, 1998 b) Location of demonstration experiment 1-1, Hasuikecho, Nagata-ku, Kobe-shi Hanshin Expressway Nagata tunnel construction c) Demonstration experiment method

The measured resistivity ρ ₁ real of the simulated fore pile
Is a slime discharged from a fore pile currently being constructed on site by inserting a vinyl chloride pipe (inner diameter: 14.5, 24 cm) as an insulator into a hole about 1.5 m deep drilled in the ground Was measured.

The measuring method is the same as the method shown in FIG.
Current flows from the C _2, it was decided to measure the potential of the tube portion at each electrode of the electrode rod. C ₁ and P ₂ were changed according to the actual depth of the measurement hole. In addition, the actual resistivity ρ ₂ real
Was determined by the Wenner method described above.

In the demonstration experiment, holes with nominal diameters of 20 cm and 30 cm were drilled in the ground, and the holes were filled with the above-mentioned slime to form a simulated fore pile. The potential inside the simulated fore pile was measured as shown in FIGS. The measurement was carried out in the same manner as described above.

The simulation was performed by the axisymmetric finite element method described above, and the relationship between the resistance per unit length and the diameter of the simulated fore pile was determined using the resistivity of the ground as a parameter.

From the comparison between the diameter of the simulated fore pile obtained from the measurement of the electric potential and the simulation result and the completed shape (diameter) of the simulated fore pile dug out after curing, the shape of the completed shape using the electric potential method was determined. The validity of the estimation method was verified.

(2) Results of Demonstration Test a) Specific Resistance of Simulated Fore Pile and Specific Resistance of Ground The specific resistance of the simulated fore pile is calculated by using the equation (11) from the potential measurement result measured by changing the tube diameter and current. Ρ ₁
= 0.9Ω · m.

On the other hand, the measured specific resistance of the ground was ρ ₂ = 58 Ω · m as a result of measuring the electrode spacing a by the Wener method described above with 0.5 cm and 0.55 m. b) Measurement result of electric potential (potential) of simulated fore pile

Demonstration measurement of the simulated fore pile was carried out for the nominal diameters of the drilled holes of 20 cm and 30 cm, and the resulting resistance value per unit length was 14.8 Ω / m at the nominal diameter of 20 cm.
It became 9 Ω / m at the nominal diameter of 30 cm.

C) Simulation Results The simulation by the finite element method using the axisymmetric model was performed for each of the simulated fore pile diameters of 20 cm, 30 cm and 40 cm using the resistivity of the ground as a parameter. Table 1 shows the results. At this time, the specific resistance of the simulated fore pile was a value obtained from the above measurement, ρ ₁ = 0.9Ω · m. The current was 1 mA.

The results were obtained by comparing the ground resistivity of 58 Ω · m and 300 Ω · m.
When the relationship between the fore pile diameter and the resistance per unit length is plotted for each of m and ∞Ω · m, FIG.
It becomes as shown in.

[0080]

[Table 1]

D) Result of Excavation of Simulated Fore Pile The simulated fore pile was excavated after curing, and the actual completed shape was measured. Here, it is a simulated fore pile made by drilling with a nominal diameter of 20 cm, but it has collapsed near the mouth between potential measurement and hardening, and it is not possible to compare the result of measurement of the completed shape with the simulation result It was judged inappropriate.

The results of the measurement of the shape of the two simulated fore piles having a nominal diameter of 30 cm are shown in Tables 2 and 3, respectively, but there is no possibility of collapse between the time of potential measurement and the time of excavation (potential measurement). (The shape of the clay at the time of excavation coincides with the shape at the time of excavation).

[0083]

[Table 2]

[0084]

[Table 3]

From the results of the above-mentioned demonstration experiments, simulation results in which the resistivity of the ground was 58 Ω · m, which is the actual measurement value, were obtained, and the unit length of the simulated fore pile with a nominal diameter of 30 cm obtained from the electric potential measurement was obtained. When the resistance value of 9 Ω / m is applied, the diameter of the simulated fore pile is approximately 28 cm from FIG.
Becomes

On the other hand, the diameter of the simulated fore pile that was dug out and measured was 28 to 33 cm as a value at a reliable portion as described above.

As is clear from the results of this demonstration experiment, the specific resistance value of the fore pile and the specific resistance value of the ground are expressed by the following equation (1).
It is possible to estimate the finished shape of the improved body by comparing the resistance per unit length obtained from the measurement results of the fore pile potential with the simulation result by the axisymmetric finite element method performed in consideration of 5). , Which almost coincides with the actual shape of the improved body, and it can be said that the estimation method of the present invention is effective.

[0088]

As described above in detail in the embodiments,
ADVANTAGE OF THE INVENTION According to the estimation method of the completed shape of a ground improvement body concerning this invention, highly reliable estimation information is obtained without performing a test construction.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an improved body to which a method for estimating a completed shape of a ground improvement body according to the present invention is applied.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a graph showing a specific resistance value of a rock or the like.

FIG. 4 is a diagram illustrating a case where a current flows through a substance so that a current density becomes uniform.

FIG. 5 is an explanatory diagram when measuring a specific resistance by the Wiener method.

FIG. 6 is an explanatory diagram when measuring a specific resistance by an electric potential method.

FIG. 7 is an explanatory diagram of a case where a current flows through a substance so that a current density becomes non-uniform.

FIG. 8 is a graph showing the measurement results of FIG.

FIG. 9 is a graph showing the measurement results of FIG.

FIG. 10 is a graph showing the measurement results of FIG.

FIG. 11 is a graph showing the measurement results of FIG.

FIG. 12 is an explanatory diagram of a simulation model of a two-dimensional axisymmetric finite element method.

FIG. 13 is a development view of FIG.

14 is a graph showing an analysis result of the model shown in FIG. 12 by a two-dimensional axisymmetric finite element method.

FIG. 15 is a graph showing an analysis result by a two-dimensional axisymmetric finite element method in a demonstration experiment of the present invention.

[Explanation of symbols]

10 natural ground 12 improved 14 electrode mounting member 14a body 16 DC power supply 18 voltmeter 20 calculating unit P _I current electrode P _V potential electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2D040 AB03 AC05 BB09 BD05 CA01 CB03 GA02 2F063 AA19 AA41 BA30 DA05 FA10 KA01 2G060 AA14 AE40 AF02 AF07 AG11 EA06 EA07 HA01 HC10 KA09

Claims (3)

[Claims] 1. An electrode mounting body installed along the longitudinal direction of an improved body formed in the ground, and a pair of current electrodes mounted at a predetermined interval along the longitudinal direction of the electrode mounting body. And a pair of potential electrodes provided at a predetermined interval between the current electrodes, and when a predetermined current flows between the current electrodes, a potential difference between the potential electrodes is detected, and the improved body is detected. Calculating means for obtaining an actual measured resistance value per unit length of, based on the specific resistance of each of the plurality of types of ground and the simulated improved body, the two-dimensional axisymmetric finite element method, the ratio of the specific resistance As a factor, the relationship between the resistance value per unit length and the diameter of the simulated improved body is determined in advance, the factor is selected from the measured resistivity of the ground and the improved body, and the measured resistance value is calculated by the simulated improvement. The resistance per unit length of the body and By matching the relationship between the diameter, the method of estimating the finished shape of the natural ground improvement body characterized by estimating the diameter of Construction has been the improved body. 2. The improvement according to claim 1, wherein the ratio between the length and the diameter of the improved body is 0.
The method for estimating the finished shape of a ground improvement body according to claim 1, wherein the estimated shape is in the range of 07 to 0.16. 3. The specific resistance ratio between the ground and the improved body is as follows:
2. The method for estimating the completed shape of a ground improvement body according to claim 1, wherein the number is 50 times or more.