JP2023102428A - Soil cement compression strength evaluation method and device for the same - Google Patents

Abstract

To provide a soil cement compression strength evaluation method capable of quickly and precisely evaluating compression strength of soil cement after hardening in an unconsolidated state, and a device for the same.SOLUTION: A soil cement compression strength evaluation method includes: a setup step to determine soil cement compression strength and a correlation between an effective cement-water ratio and electric resistivity; a construction step to build the soil cement with the effective cement-water ratio obtained by mixing cement milk injected into a drilling hole and soil and sand in the drilling hole; a measurement step to measure the electric resistivity of the soil cement in an unconsolidated state in the drilling hole; and an evaluation step to estimate a strength property of the soil cement after hardening on the basis of the correlation between the effective cement-water ratio and the electric resistivity.SELECTED DRAWING: Figure 1

Description

The present invention relates to a soil cement compressive strength evaluation method and apparatus for evaluating the compressive strength of soil cement after hardening.

Conventionally, when burying prefabricated concrete piles, for example, foot protection is constructed at the deepest part of the piles in order to transmit the load of the superstructure through the piles to a wide range of the supporting layer. The excavated hole of the foot protection part is excavated one size larger than the outer diameter of the pile in order to secure a larger bearing capacity, and the gap between the pile and the excavated hole is filled with soil cement. Soil cement is formed by mixing and stirring earth and sand in a borehole and cement milk injected into the ground from the ground.

In order to determine whether or not the foot protection portion satisfies a predetermined strength, there are a method of measuring the strength of a specimen prepared by directly collecting cement milk from a mixing plant during pile construction, a method of confirming the strength by collecting an unsolidified sample (soil cement) during pile construction (see, for example, Patent Document 1), and a method of directly collecting a specimen using a boring machine after the soil cement has hardened.

JP 2009-102817 A

However, in all of these methods, confirmation is required after some time has passed since the construction, so if deficiencies are found as a result of confirmation, it will be difficult to re-construct the piles.

In the case of the method of measuring the strength of a test piece made by directly extracting cement milk from a mixing plant, it is only a measurement of the consolidation strength of the hardening part used at the time of pile construction, and it does not confirm the strength of soil cement, which is a mixture of in-situ soil and cement milk, and lacks reliability as a method for checking the strength of the hardening part.

In the case of the method of confirming the strength by collecting an unconsolidated sample (soil cement), after excavating a pile hole, cement milk is injected, and the soil cement after mixing and stirring with the soil inside is collected by a dedicated sampler from a dedicated hole formed separately from the pile hole to be actually constructed, and a compression test is performed after a certain age period (3 to 28 days) to confirm the quality. It is difficult to say that the overall evaluation is carried out because the evaluation is local, in which samples are taken from a part of the foot protection part.

In the case of core boring surveys, in which a test piece is taken using a boring machine after the soil cement has hardened, cement milk is poured after excavating the pile hole, mixed with the soil and sand inside, and then the pile is inserted. It is costly because it is necessary to drill a borehole for the installation of the sampling device. In addition, since this is a local evaluation in which samples are collected from a part of the foot protection part, it is difficult to say that the overall evaluation is performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for evaluating the compressive strength of soil cement that can accurately evaluate the compressive strength of soil cement after hardening in an unsolidified state in a short period of time.

The method for evaluating compressive strength of soil cement according to claim 1 is a method for evaluating compressive strength of soil cement formed by mixing a cementitious material, a soil material, and water, and estimating the strength characteristics of the soil cement after hardening, comprising: a setting step of obtaining a correlation between the compressive strength of the soil cement, an effective cement-water ratio, and an electrical resistivity; and an evaluation step of estimating the strength characteristics of the soil cement after curing from the correlation from the effective cement water ratio and the electrical resistivity.

The method for evaluating compressive strength of soil cement according to claim 2 is the method for evaluating compressive strength of soil cement according to claim 1, wherein in the measuring step, a resistivity measuring means having a plurality of current electrodes and a plurality of voltage electrodes is used, a voltage value applied to the voltage electrode is measured by passing a current through the current electrode, and the electrical resistivity is calculated based on the current value, the voltage value, and the electrode spacing between the current electrode and the voltage electrode.

The method for evaluating compressive strength of soil cement according to claim 3 is the method for evaluating compressive strength of soil cement according to claim 1 or 2, wherein in the evaluation step, a chart in which compressive strength, effective cement water ratio, and a plurality of control standard values are entered is used, and a value obtained from the measured electrical resistivity of soil cement in an unsolidified state and the effective cement water ratio of the soil cement is plotted on the chart to evaluate whether the compressive strength after hardening of the soil cement satisfies the required strength. .

The soil cement compressive strength evaluation apparatus according to claim 4 is a soil cement compressive strength evaluation apparatus for estimating the strength characteristics after hardening of soil cement formed by mixing a cementitious material, a soil material, and water. and evaluation means for estimating the strength properties of the soil cement after hardening based on the correlation.

The apparatus for evaluating compressive strength of soil cement according to claim 5 is the apparatus for evaluating compressive strength of soil cement according to claim 4, wherein the evaluation means comprises a plurality of management reference values for the electrical resistivity of soil cement preset based on the electrical resistivity of the unsolidified soil cement measured by the resistivity measuring means, the compressive strength of the cured soil cement, and the effective cement water ratio of the unsolidified soil cement. It is evaluated whether or not the compressive strength of the soil cement after hardening satisfies the required strength by comparing the value corresponding to the strength.

The apparatus for evaluating compressive strength of soil cement according to claim 6 is the apparatus for evaluating compressive strength of soil cement according to claim 4 or 5, wherein the resistivity measuring means has a plurality of current electrodes and a plurality of voltage electrodes, and measures the value of voltage applied to the voltage electrodes by causing current to flow through the current electrodes, and calculates the electrical resistivity based on the value of the current, the value of the voltage, and the electrode spacing between the current electrode and the voltage electrode.

ADVANTAGE OF THE INVENTION According to this invention, the compressive strength after hardening of soil cement can be evaluated accurately in a short time under an unsolidified state.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the compressive strength evaluation apparatus of one embodiment of this invention. (a) is a schematic diagram showing a state in which the excavating device is excavating the ground, (b) is a schematic diagram showing a state in which the excavating device is pulled out from the excavation hole, and (c) is a schematic diagram showing a state in which a prefabricated concrete pile is buried in the excavation hole. It is a schematic diagram which shows a specific resistance measuring means (electrode arrangement) of a compressive strength evaluation apparatus same as the above. Fig. 2 is a flow chart showing a method for evaluating compressive strength of the same soil cement after hardening. 4 is a chart showing the relationship between the compressive strength of soil-cement conditioned soil and the effective cement water ratio. 4 is a chart showing the relationship between the approximate linear gradient recalculated with an effective cement water ratio of 40% as a base point and the electrical resistivity. 4 is a chart showing the relationship between compressive strength, effective cement water ratio, and electrical resistivity using a plurality of root hardening solutions mixed at a plurality of different mixing ratios as samples. 4 is a chart in which control standard values for evaluating the compressive strength after hardening of soil cement of the same compressive strength evaluation apparatus are entered. 4 is a chart showing the relationship between compressive strength, effective cement water ratio, and electrical resistivity in this example.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a compressive strength evaluation device. The compressive strength evaluation device 1 estimates and evaluates the compressive strength after hardening based on the electrical resistivity in the unhardened (unhardened) state of the soil cement 3 that supports the ready-made concrete pile 2, which is a ready-made pile. The compressive strength evaluation device 1 may be applied to any device as long as it can reach the soil cement 3 in the ground, but in the present embodiment, for example, it is applied to an excavator 5 such as an auger that can inject a hardening liquid such as cement milk while excavating the ground to the support layer.

As shown in FIG. 2( a ), the excavator 5 has an excavation head 6 as an excavation unit body that excavates the ground in the advancing direction, and an excavation wing 7 that can excavate the ground together with the excavation head 6 .

The excavation wing 7 is rotatably provided so that the tip portion thereof can come into contact with and separate from the excavation head 6 . That is, the excavating blade 7 is rotatably supported on the excavating head 6 at its base end portion, and is rotatable at its tip portion around the pivotally supported portion.

The excavator 5 can excavate the ground in either a normal state in which the excavating blade 7 approaches the excavating head 6 or an expanded state in which the excavating blade 7 is spaced outward from the excavating head 6 . That is, the excavating device 5 excavates the ground to a predetermined depth (supporting layer) with the excavating head 6 and the excavating blades 7 in a normal state, thereby forming the upper excavated portion 10 in the excavated hole 8 . Further, by excavating in an enlarged state after reaching the support layer, an enlarged excavated portion 11 is formed in the excavated hole 8 . A foot protection portion 12 ( FIG. 2( c )) is formed at the position of the enlarged excavation portion 11 .

As shown in FIG. 1 , the compressive strength evaluation device 1 has a resistivity measuring means (electrical resistance measuring device) 15 for measuring the electrical resistivity of the uncured soil cement 3 . The resistivity measuring means 15 may be arranged at any position in the excavator 5, but for example, the excavation head 6 shown in FIG.

The resistivity measuring means 15 shown in FIG. 1 may be of any configuration capable of measuring the resistivity of the uncured soil cement 3 (FIG. 2(a)) using electricity (that is capable of electrical surveying), but in the present embodiment, as shown in FIG. The electrical resistivity of the uncured soil cement 3 is measured.

That is, in the present embodiment, the current electrodes 16 and the voltage electrodes 17 are arranged in one row at a predetermined interval (electrode interval a), and one set of voltage electrodes 17 is arranged inside one set of current electrodes 16 . Then, by applying a current I of a predetermined value to the current electrode 16 while the electrode part 18 is positioned in the soil cement 3, the potential difference (voltage) V is measured by the voltage electrode 17, and the resistance R of the soil cement 3 can be obtained based on the current I and the voltage V. Furthermore, based on the value of the resistance R and the value of the electrode spacing a, the electrical resistivity of the area of the soil cement 3 equal to the electrode spacing a can be determined.

The distance between the current electrode 16 and the voltage electrode 17 in the electrode unit 18 is a, and the voltage V measured at the voltage electrode 17 by passing a predetermined value of current I through the current electrode 16 allows the resistance R to be calculated from the formula: resistance R (Ω) = voltage V (V)/current I (A). Further, based on the resistance R and the electrode spacing a, the electrical resistivity ρ in the region at a distance equal to the electrode spacing a from the current electrode 16 and the voltage electrode 17 is calculated from the formula ρ(Ω·m)=2πaR.

This electrical resistivity ρ is a constant value if the composition of the substances forming the stratum is the same, and changes if the composition of the substances forming the stratum is different. In the present embodiment, this is applied to means for estimating and evaluating the compressive strength of the hardened soil cement 3 filled in the foot protection portion 12 (FIG. 2(c)).

Therefore, as shown in FIG. 2(a), the ground is excavated by the excavator 5 and the root-hardening solution is injected, and as shown in FIG. 2(b), the earth and sand and the root-hardening solution are mixed and stirred to form the soil cement 3. After that, the electrical resistivity ρ is measured by the resistivity measuring means 15 shown in FIG.

The electrical resistivity ρ measured by the resistivity measuring means 15 is sent to the evaluating means 20 . The evaluation means 20 is configured by installing dedicated software in a computer such as a general-purpose PC. The evaluation means 20 may be connected to the resistivity measurement means 15 by wire, or may be wirelessly connected via an infrared signal or a network such as the Internet. The evaluation means 20 preferably has display means such as a display, and input means such as a keyboard or touch panel display for inputting numerical values.

Then, using the evaluation means 20, it is evaluated whether or not the compressive strength of the cured soil cement 3 (FIG. 2(a)) satisfies the required strength.

A method for evaluating this compressive strength will be described.

As an overview, in the present embodiment, as shown in the flowchart of FIG. 4, a plurality of control reference values for the electrical resistivity of the soil cement 3 are set based on the compressive strength required for the hardened soil cement 3 and the effective cement-water ratio calculated based on the characteristic values of the soil in the soil cement-forming portion (setting step, step S0). That is, the correlation between the compressive strength of the soil cement 3, the effective cement water ratio, and the electrical resistivity is obtained.

Next, an excavation hole 8 is excavated by an excavation device 5 to a depth necessary for anchoring the prefabricated concrete pile 2 (excavation step, step S1).

Furthermore, cement milk containing cementitious material and water is injected into the borehole 8, and the earth and sand, which are the soil materials in the borehole 8, and the cement milk are mixed and stirred to construct soil cement (improved soil cement) 3 having an effective cement water ratio in the borehole 8 (construction step, step S2).

After constructing the soil cement 3, the excavator 5 equipped with the resistivity measuring means 15 is advanced into the excavation hole 8 to measure the electric resistivity of the unconsolidated soil cement 3 in the excavation hole 8 (measurement step, step S3). In the present embodiment, as described above, the value of the voltage applied to the voltage electrode 17 is measured by causing a current to flow through the current electrode 16 of the resistivity measuring means 15, and the electrical resistivity is calculated based on the current value, the voltage value, and the electrode spacing a between the current electrode 16 and the voltage electrode 17. The electrical resistivity may be measured at the same time when the soil cement 3 is constructed in step S2.

Thereafter, based on the effective cement water ratio obtained in step S2, the electrical resistivity measured in step S3, and the value corresponding to the required strength of the soil cement 3 in the effective cement water ratio of the soil cement 3 among the plurality of control reference values of the electrical resistivity set in step S0, the values of the effective cement water ratio and the electrical resistivity are checked, and it is evaluated whether the compressive strength of the soil cement 3 after hardening satisfies the required strength, and a pass/fail determination is made (evaluation step, step S4).

Next, the setting of a plurality of control reference values for the electrical resistivity of the soil cement 3 in the above setting step will be described.

First, based on the idea that the compressive strength of concrete is closely related to the progress of the chemical reaction of cement, it is determined by the ratio of the amount of hydrated and crystallized cement in 1 ^m3 of concrete to the amount of water initially used, that is, the cement water ratio.

If the mass ratio obtained by dividing the amount of cement added (mass) by the total amount of effective water (mass) is taken as the effective cement water ratio, there is a good correlation between the effective cement water ratio and the compressive strength, and the compressive strength can be estimated from the amount of cement added and the total amount of effective water.

Here, regarding the total effective amount of water, in the case of soil cement formed in the soil, the amount of water contained in the soil also contributes to the compressive strength, so it is necessary to add this amount of water in the soil to the amount of water added to the water for kneading. Therefore, the total effective water amount W _t is calculated by using W _w0 as natural water amount (mass), W _w1 as excavation water amount (mass), W _w as mass of cement milk mixing water, and W _b as bleeding water generated during hardening (bleeding water amount 24 hours after mixing).
_Wt = _Ww0 + _Ww1 + _Ww - _Wb
Defined by

During construction, the amount of earth and sand entrained in the cement milk liquid from the borehole wall is also thought to affect the compressive strength. Therefore, the specific relationship between the compressive strength and the effective cement water ratio including earth and sand is calculated in advance by using as samples a plurality of foot protection solutions obtained by mixing multiple types of soil cement conditioned soil and multiple types of cement milk at multiple different mixing ratios.

As an example, Kasaoka Clay (registered trademark) and Silica Sand No. 7 preliminarily adjusted to have a saturation degree of about 100% are used as the soil cement conditioned soil, and 11 types are prepared in advance by mixing at a volume ratio (clay:silica sand) of 10:0, 9:1, 8:2, ..., 2:8, 1:9, and 0:10.

Also, cement milk is prepared in advance in three types of water-cement ratios of 60%, 80%, and 100%, which are generally employed.

These soil-cement conditioned soil and cement milk are pre-mixed at volume ratios of 1:1, 1:2, 1:3, and 1:4 to form root hardening solutions. That is, a total of 132 (=11×3×4) kinds of root hardening solutions are prepared.

Then, in these root hardening solutions, the relationship between the compressive strength of the conditioned soil and the effective cement water ratio is confirmed based on the following equation (1).

In the formula, C/W _e is the effective cement water ratio (%), P _cm is the cement milk water-cement ratio (%), ρ _t is the density of the adjusted soil (g/cm ³ ), ω _r is the measured water content ratio (%), q _cm is the proportion of cement milk in the blending volume ratio (1 ≤ q _cm ≤ 4), and ρ _cm is the density of cement milk (g/cm ³ ).

FIG. 5 shows the relationship between the compressive strength of the soil-cement conditioned soil and the effective cement water ratio based on the above samples. In FIG. 5, the numbers in parentheses indicate the water content (%) of the adjusted soil. As shown in FIG. 5, it can be confirmed that the slope of the approximate straight line (regression line) between the compressive strength and the effective cement water ratio of the soil-cement conditioned soil differs depending on the water content, and that the effective cement water ratio converges to about 40% when the compressive strength is 0 N/mm ² .

FIG. 6 shows the relationship between the approximate straight line (regression straight line) gradient θ recalculated from the effective cement water ratio of 40% and the electrical resistivity ρ. In FIG. 6, the numbers in parentheses indicate the water content (%). As shown in FIG. 6, it can be confirmed that the approximate linear gradient θ decreases as the electrical resistivity ρ increases. By linearly approximating the approximation straight line (regression straight line) gradient θ and the electrical resistivity ρ, it can be expressed as a ^linear function.

These results show that there is a very high correlation between compressive strength and electrical resistivity and water content. Therefore, by plotting the data calculated from the above 132 types of root hardening solutions as shown in FIG. 7, a chart (FIG. 8) with a line of electrical resistivity ρ = 0.8 to 3.0 as a control reference value is created. In FIG. 7, the numbers in parentheses indicate the water content (%). This chart may be pre-stored in the evaluation means 20, or may be stored in a cloud server or the like on the network and downloaded at the time of use.

In this way, in the setting step, a plurality of actual samples are used to construct a chart in which a plurality of electrical resistivity values as control reference values are superimposed on the relationship between the compressive strength of the soil cement 3 after hardening and the effective cement water ratio. By using this chart, it becomes possible to correlate the relationship between the compressive strength of the soil cement 3 after hardening, the effective cement water ratio, and the electrical resistivity.

The details of the evaluation steps using this chart will be described.

In the evaluation step, a control reference value for the electrical resistivity is selected from the above chart according to the required strength of the soil cement 3 after hardening at the effective cement-water ratio of the unsolidified soil cement 3. By comparing the selected value with the electrical resistivity measured in the measurement step, it is evaluated whether or not the compressive strength of the soil cement 3 after hardening satisfies the required strength.

Specifically, the line (vertical line) of the effective cement water ratio of the unsettled soil cement 3 in the construction step is superimposed on the chart shown in FIG.

Here, for obtaining the effective cement water ratio (conditions of the soil cement 3 to be molded), the characteristic value of the soil in the soil cement forming part is grasped, the density ρ _cm of the cement milk is grasped, and the proportion q _cm of the cement milk in the mixing volume ratio of the soil cement is grasped, and from these values, the effective cement water ratio of the soil cement 3 is grasped using the above formula (1).

When grasping the characteristic values of the soil in the soil cement forming part, for example, the soil condition described in the ground survey report performed before construction is used, and the soil density ρ _t and the water content ratio ω _r set in soil mechanics etc. are used as characteristic values. Alternatively, the soil density ρ _t and the water content ratio ω _r of the soil are actually measured by performing the tests specified in, for example, JIS A 1202 (soil particle density test method) and JIS A 1203 (soil water content ratio test method). Furthermore, in order to obtain more detailed determination accuracy, it is preferable to sample the earth and sand at the measurement depth and actually measure the state of the earth and sand.

The density ρ _cm of cement milk is calculated from the ratio of water (specific gravity 1.00) mixed with cement milk and cement used (specific gravity 3.16 in the case of general ordinary Portland cement).

Regarding the ratio q _cm of cement milk, since it is generally said that earth and sand do not exceed 30% of cement milk, in that case, the ratio of cement milk is 2.3 when the ratio of soil is 1. Therefore, if the numerical value is rounded in consideration of safety, the minimum value of the cement milk ratio _qcm is 2, and this is set.

As an example, as soil cement 3, as shown in Table 1, one without sediment (cement milk only), one with sediment and estimated soil density ρ _t and water content ω _r based on the soil conditions described in the ground investigation report, and one obtained by sampling soil and sand at the in-situ location and actually measuring soil density ρ _t and water content ω _r by testing are used. From the equation (1), the effective cement water ratio C/We becomes the maximum value when there is no earth and sand, and the effective cement water ratio C/We decreases depending on the water content of the earth and sand when there is earth and sand. In particular, the water content ratio _ωr is higher in the actual measurement, and the effective cement water ratio C/We is the smallest.

These are applied to the chart of FIG. 8, respectively. In FIG. 8, line L1 corresponds to the effective cement water ratio without sediment, line L2 with sediment (density/water content ratio is estimated), and line L3 with sediment (density/water content ratio is actually measured). The compressive strength of the soil cement 3 after hardening can be estimated from the intersections of the lines L1 to L3 and the measured electrical resistivity ρ=2.0.

Therefore, if the required strength of the soil cement 3 is known in advance, it is possible to easily determine whether or not the compressive strength satisfies the required strength only by comparing this value with the actually measured electrical resistivity by selecting a value corresponding to the required strength at the effective cement-water ratio of the unsolidified soil cement 3 to be evaluated from a plurality of management reference values for electrical resistivity as a pass/fail determination threshold value. This determination may be performed automatically by the evaluation means 20, or, for example, by displaying a chart on the display means of the evaluation means 20 and superimposing the electrical resistivity measured in the measurement step on the chart, the judge may visually judge. The electrical resistivity and effective cement water ratio of the soil cement 3 in an unsolidified state may be manually input to the evaluation means 20 by the user using the input means, and the effective cement water ratio may be stored in the evaluation means 20, a cloud server, or the like, or may be calculated by the evaluation means 20 from these data or measured data.

Thus, the correlation between the compressive strength, the effective cement water ratio, and the electrical resistivity of the soil cement 3 is obtained in advance, and the cement milk injected into the borehole 8 and the earth and sand in the borehole 8 are mixed and agitated to construct the soil cement 3 having the effective cement water ratio. More specifically, a plurality of control reference values for the electrical resistivity of the soil cement 3 are set based on the compressive strength and effective cement water ratio of the soil cement 3 after hardening, cement milk is injected into the drilled hole 8 formed, and the earth and sand in the drilled hole 8 are mixed with the cement milk to construct the soil cement 3, and the electrical resistivity of the constructed unconsolidated soil cement 3 is measured. It is evaluated whether or not the soil cement 3 satisfies the required compressive strength after hardening by comparing with the value corresponding to the required strength of the soil cement in . As a result, the compressive strength of the soil cement 3 after hardening can be accurately evaluated in a short time under the condition that the soil cement 3 is in an unsolidified state. In other words, if the effective cement-water ratio of the unhardened soil cement 3 and the required compressive strength of the hardened soil cement 3 are known in advance, the hardened compressive strength of the unhardened soil cement 3 can be evaluated in a short period of time simply by measuring the electrical resistivity of the unhardened soil cement 3 and comparing it with the control standard value. Therefore, even if it is determined that the compressive strength after hardening does not satisfy the required strength as a result of this evaluation, the soil cement 3 is before hardening, so re-construction or the like is easy.

When measuring the electrical resistivity, the resistivity measuring means 15 measures the value of the voltage applied to the plurality of voltage electrodes 17 by causing a current to flow through the plurality of current electrodes 16, and calculates the electrical resistivity based on the current value, the voltage value, and the electrode spacing a between the current electrode 16 and the voltage electrode 17. Therefore, the electrical resistivity can be measured with a simple configuration. Moreover, since the electrode unit 18 having a plurality of current electrodes 16 and a plurality of voltage electrodes 17 can be configured by attaching it to the existing excavator 5 such as an auger, there is no need to manufacture a dedicated excavator, and large-scale modification is not required.

Furthermore, in the evaluation step, a chart in which the compressive strength, the effective cement water ratio, and a plurality of control standard values are entered is used, and the values obtained from the measured electrical resistivity of the unsolidified soil cement 3 and the effective cement water ratio of the soil cement 3 are plotted on the chart to evaluate whether or not the compressive strength of the soil cement 3 after hardening satisfies the required strength.

Moreover, since it can be easily applied to a known concrete pile construction method, it has good versatility and can be easily implemented.

This embodiment will be described below.

In this example, an experiment was conducted on the validity of the evaluation of the compressive strength of the above-described embodiment using the electrical resistivity of the soil cement 3 in an unsolidified state.

Five different types of soil samples (tuffaceous clay, fine sand mixed with gravel, sandy mudstone, sandy soil, and mudstone mixed with sand) collected from the support layer of concrete piles were prepared as soil mixed in the unsolidified soil cement 3 collected from a realization site, and mixed with cement milk at a ratio of 1:2 and 1:3. This state is shown in the chart of FIG.

As shown in FIG. 9, in the effective cement water ratio range of 116.6 to 139.9 [%], the electrical resistivity ρ of the soil cement 3 can be classified with a boundary value of 2.0 [Ω·m]. Therefore, when the required strength of the soil cement 3 is 15 [N/mm ² ] or more, if the electrical resistivity ρ is 2.0 or less, the compressive strength is 15 [N/mm ² ] or less in only 1 of the 9 cases.

REFERENCE SIGNS LIST 1 compressive strength evaluation device 3 soil cement 8 drilling hole 15 resistivity measuring means 16 current electrode 17 voltage electrode 20 evaluation means a electrode interval

Claims (6)

A method for evaluating compressive strength of soil cement for estimating the strength characteristics after hardening of soil cement formed by mixing a cementitious material, a soil material, and water, comprising:
a setting step of determining the correlation between the compressive strength of the soil cement, the effective cement water ratio, and the electrical resistivity;
a building step of building soil cement having an effective cement-to-water ratio by mixing and stirring the cement milk injected into the borehole and the earth and sand in the borehole;
a measuring step of measuring the electrical resistivity of the unconsolidated soil cement in the borehole;
an evaluation step of estimating the strength properties of the soil cement after hardening from the correlation from the effective cement water ratio and the electrical resistivity;
A method for evaluating compressive strength of soil cement, comprising: 2. The method for evaluating compressive strength of soil cement according to claim 1, wherein in the measuring step, a resistivity measuring means having a plurality of current electrodes and a plurality of voltage electrodes is used to measure the value of the voltage applied to the voltage electrodes by passing a current through the current electrodes, and the electrical resistivity is calculated based on the current value, the voltage value, and the electrode spacing between the current electrodes and the voltage electrodes. 3. The method for evaluating compressive strength of soil cement according to claim 1 or 2, wherein in the evaluation step, a chart in which compressive strength, effective cement water ratio, and a plurality of control standard values are entered is used, and values obtained from the measured electrical resistivity of unsettled soil cement and the effective cement water ratio of the soil cement are plotted on the chart to evaluate whether the compressive strength after hardening of the soil cement satisfies the required strength. A soil cement compressive strength evaluation device for estimating the strength characteristics after hardening of soil cement formed by mixing a cementitious material, a soil material, and water,
a resistivity measuring means for measuring electrical resistivity;
an evaluation means for estimating the strength characteristics of the soil cement after hardening based on the correlation between the compressive strength of the soil cement, the effective cement water ratio, and the electrical resistivity, which are obtained in advance from the electrical resistivity of the unsolidified soil cement and the effective cement water ratio of the solidified soil cement measured by the resistivity measuring means;
A soil cement compressive strength evaluation device comprising: The evaluation means compares a value corresponding to the required strength of the soil cement in the effective cement-water ratio of the unsettled soil cement among a plurality of management reference values for the electrical resistivity of the soil cement preset based on the electrical resistivity of the unsettled soil cement measured by the resistivity measuring means, the compressive strength of the cured soil cement, and the effective cement-water ratio of the unsettled soil cement, and determines whether the compressive strength after hardening of the soil cement satisfies the required strength. 5. The apparatus for evaluating compressive strength of soil cement according to claim 4, wherein the compressive strength is evaluated. 6. The apparatus for evaluating compressive strength of soil cement according to claim 4 or 5, wherein the resistivity measuring means has a plurality of current electrodes and a plurality of voltage electrodes, and measures the value of the voltage applied to the voltage electrodes by passing a current through the current electrodes, and calculates the electrical resistivity based on the current value, the voltage value, and the electrode spacing between the current electrodes and the voltage electrodes.

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