JP7518865B2 - Method and device for evaluating compressive strength of soil cement - Google Patents

Description

The present invention relates to a method and device for evaluating the compressive strength of soil cement after it has hardened.

Conventionally, for example, when burying precast concrete piles, a base protection section is constructed at the deepest part of the pile in order to transmit the load of the superstructure through the pile to a wide area of the supporting layer. The excavation hole for the base protection section is excavated slightly larger than the outer diameter of the pile in order to ensure greater bearing capacity, and the gap between the pile and the excavation hole is filled with soil cement. The soil cement is formed by mixing and stirring the soil in the excavation hole with cement milk injected into the ground from above ground.

To determine whether the base reinforcement portion meets the required strength, there are several methods, including measuring the strength of a specimen made by directly collecting cement milk from a mixing plant during pile construction, checking the strength by collecting unconsolidated samples (soil cement) during pile construction (see, for example, Patent Document 1), and directly collecting specimens using a boring machine after the soil cement has hardened.

JP 2009-102817 A

However, with these methods, the check is carried out some time after construction, so if any defects are found as a result of the check, it will be difficult to re-install the piles.

In addition, when measuring the strength of specimens made by directly collecting cement milk from a mixing plant, this method only measures the consolidated strength of the base protection section used during pile construction, and does not confirm the strength of the soil cement, which is a mixture of in-situ soil and cement milk, and therefore lacks reliability as a method for confirming the strength of the base protection section.

When checking strength by collecting unconsolidated samples (soil cement), after drilling pile holes, cement milk is injected and mixed with the soil inside. The soil cement is then collected with a special sampler from a special hole created separately from the pile hole where construction will actually take place, and after a certain age period (3-28 days) a compression test is carried out to check the quality. Because this is a localized evaluation in which samples are taken from a part of the foot protection area, it is difficult to say that it is an overall evaluation.

In the case of a core boring survey, in which specimens are taken using a boring machine after the soil cement has hardened, cement milk is injected after drilling a pile hole, mixed and stirred with the soil inside, and the pile is then inserted. After the soil cement has hardened (2-4 weeks later), specimens are taken using a boring machine and a compression test is carried out to check the strength and quality. This is costly as boreholes must be drilled to install the sampling equipment. Also, as this is a localized evaluation in which samples are taken from a part of the foot protection area, it is difficult to say that an overall evaluation is being carried out.

The present invention has been made in consideration of these points, and aims to provide a method and device for evaluating the compressive strength of soil cement that can accurately evaluate the compressive strength of soil cement after it has hardened in an unconsolidated state in a short period of time.

The method for evaluating the compressive strength of soil cement according to claim 1 is a method for evaluating the compressive strength of soil cement, which estimates the strength characteristics of soil cement after hardening, which is formed by mixing a cement-based material, an earthen material, and water. The method includes a setting step for determining a correlation between the compressive strength of the soil cement, an effective cement-water ratio, and an electrical resistivity, a construction step for constructing a soil cement having an effective cement-water ratio by mixing and stirring the cement milk injected into the borehole with the soil and sand in the borehole, a measurement step for measuring the electrical resistivity of the unconsolidated soil cement in the borehole, and an evaluation step for estimating the strength characteristics of the soil cement after hardening from the correlation based on the effective cement-water ratio and the electrical resistivity. In the evaluation step, a chart on which the 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 the unconsolidated soil cement and the effective cement-water ratio of the soil cement is plotted on the chart to evaluate whether the compressive strength of the soil cement after hardening satisfies the required strength .

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

The soil cement compressive strength evaluation device according to claim 3 is a soil cement compressive strength evaluation device for estimating the post-hardening strength characteristics of soil cement formed by mixing a cement-based material, an earthen material, and water, comprising: a resistivity measuring means for measuring electrical resistivity; and an effective cement-water ratio of the unconsolidated soil cement measured by the resistivity measuring means, and the strength characteristics of the soil cement after hardening are estimated based on a correlation between the compressive strength of the soil cement, the effective cement-water ratio, and the electrical resistivity, which is previously determined, using the electrical resistivity of the unconsolidated soil cement measured by the resistivity measuring means and the effective cement-water ratio of the unconsolidated soil cement. and an evaluation means for evaluating whether or not the compressive strength of the soil cement after hardening satisfies the required strength by comparing the electrical resistivity of the unconsolidated soil cement measured by the resistivity measuring means, the compressive strength of the soil cement after hardening, and the effective cement-water ratio of the unconsolidated soil cement with a value corresponding to the required strength of the soil cement at the effective cement-water ratio of the unconsolidated soil cement among a plurality of control standard values of the electrical resistivity of the soil cement that are preset based on the electrical resistivity of the unconsolidated soil cement measured by the resistivity measuring means, the compressive strength of the soil cement after hardening, and the effective cement-water ratio of the unconsolidated soil cement .

The soil cement compressive strength evaluation device according to claim 4 is the soil cement compressive strength evaluation device according to claim 3 , in which the resistivity measuring means has a plurality of current electrodes and a plurality of voltage electrodes, 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 value of the current, the value of the voltage, and the electrode spacing between the current electrodes and the voltage electrodes.

According to the present invention, the compressive strength of soil cement after hardening can be evaluated accurately in a short time while it is in an unconsolidated state.

1 is a block diagram showing a compressive strength evaluation device according to an embodiment of the present invention; FIG. 1A is a schematic diagram showing the drilling equipment drilling underground, FIG. 1B is a schematic diagram showing the drilling equipment being pulled out of the borehole, and FIG. 1C is a schematic diagram showing a precast concrete pile being buried in the borehole. FIG. 2 is a schematic diagram showing a resistivity measuring means (electrode arrangement) of the compressive strength evaluation device. 4 is a flowchart showing a method for evaluating the compressive strength of the above soil cement after hardening. 1 is a chart showing the relationship between the compressive strength of soil-cement adjusted soil and the effective cement-water ratio. 1 is a chart showing the relationship between the gradient of an approximate straight line recalculated using an effective cement-water ratio of 40% as a base point and electrical resistivity. 1 is a chart showing the relationship between compressive strength, effective cement-water ratio, and electrical resistivity using a number of samples of root consolidation fluids mixed at different mixing ratios. This is a chart containing control standard values for evaluating the compressive strength of hardened soil cement using the above-mentioned compressive strength evaluation device. 1 is a chart showing the relationship between compressive strength, effective cement-water ratio, and electrical resistivity in this embodiment.

One 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 an unconsolidated (unhardened) state of soil cement 3 supporting a prefabricated concrete pile 2, which is a prefabricated pile. The compressive strength evaluation device 1 may be applied to any device that can reach the soil cement 3 underground, but in this embodiment, it is applied to an excavation device 5 such as an auger that can inject a root strengthening liquid such as cement milk while excavating the ground to the supporting layer.

As shown in FIG. 2(a), the drilling device 5 has a drilling head 6 as a drilling body that drills into the ground in the direction of travel, and a drilling wing 7 that can drill into the ground together with the drilling head 6.

The drilling wing 7 is provided so that its tip can move toward and away from the drilling head 6. In other words, the drilling wing 7 is pivotally supported at its base end to the drilling head 6, and the tip can rotate around the pivoted portion.

The drilling device 5 can excavate the ground in either a normal state in which the drilling wing 7 is close to the drilling head 6, or an expanded state in which the drilling wing 7 is separated outward from the drilling head 6. That is, the drilling device 5 forms an upper excavation section 10 in the drilling hole 8 by excavating the ground to a predetermined depth (supporting layer) with the drilling head 6 and drilling wing 7 in the normal state. In addition, after reaching the supporting layer, the drilling device 5 excavates in an expanded state to form an expanded excavation section 11 in the drilling hole 8. A root fixing section 12 (FIG. 2(c)) is formed at the position of the expanded excavation section 11.

As shown in FIG. 1, the compressive strength evaluation device 1 has a resistivity measurement means (electrical resistance measurement device) 15 that measures the electrical resistivity of the unhardened soil cement 3. The resistivity measurement means 15 may be placed at any position in the drilling device 5, but is, for example, placed in the drilling head 6 shown in FIG. 2(a), or in a screw, stirring rod, or connecting rod connected to the top of the drilling head 6.

The resistivity measuring means 15 shown in FIG. 1 may be of any configuration capable of measuring the electrical resistivity of the unhardened soil cement 3 (FIG. 2(a)) using electricity (capable of electrical exploration), but in this embodiment, as shown in FIG. 3, it has an electrode unit 18 equipped with a set (two) of current electrodes 16 that pass current and a set (two) of voltage electrodes 17 that measure voltage, and this electrode unit 18 measures the electrical resistivity of the unhardened soil cement 3 using Wenner's four-electrode method.

That is, in this embodiment, the current electrodes 16 and the voltage electrodes 17 are each arranged in a row at equal intervals (electrode spacing a), with one set of voltage electrodes 17 arranged inside one set of current electrodes 16. Then, by passing a predetermined value of current I through the current electrodes 16 with the electrode portions 18 positioned in the soil cement 3, the potential difference (voltage) V is measured by the voltage electrodes 17, and the resistance R of the soil cement 3 can be calculated based on the current I and voltage V. Furthermore, the electrical resistivity of a region in the soil cement 3 that is in a range equal to the electrode spacing a can be calculated based on the value of resistance R and the value of the electrode spacing a.

The electrode spacing between the current electrode 16 and the voltage electrode 17 in the electrode section 18 is a, and a predetermined value of current I is passed through the current electrode 16, and the voltage V measured at the voltage electrode 17 is used to calculate the resistance R from the formula: resistance R (Ω) = voltage V (V) / current I (A). Based on the resistance R and the electrode spacing a, the electrical resistivity ρ in a 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 materials that make up the stratum is the same, but it changes if the composition of the materials that make up the stratum is different. In this embodiment, this is applied as a means for estimating and evaluating the compressive strength after hardening of the soil cement 3 that is filled in the foot protection section 12 (Figure 2 (c)).

Therefore, as shown in FIG. 2(a), the ground is excavated using an excavation device 5, the foot-solidification liquid is injected, and as shown in FIG. 2(b), the soil and the foot-solidification liquid are mixed and stirred to form soil cement 3, and then the electrical resistivity ρ is measured using the resistivity measuring means 15 shown in FIG. 1.

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

Then, the evaluation means 20 is used to evaluate whether the compressive strength of the hardened soil cement 3 (Figure 2(a)) satisfies the required strength.

We will explain how to evaluate this compressive strength.

In summary, in this embodiment, as shown in the flowchart of FIG. 4, multiple 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 formation area (setting step, step S0). In other words, the correlation between the compressive strength, effective cement-water ratio, and electrical resistivity of the soil cement 3 is obtained.

Next, the drilling device 5 excavates the borehole 8 to the depth required to anchor the precast concrete pile 2 (drilling step, step S1).

Furthermore, cement milk containing cementitious material and water is injected into the borehole 8, and the soil material in the borehole 8, which is the soil and sand, is mixed and stirred with the cement milk to construct a soil cement (soil cement improved body) 3 in the borehole 8 that has an effective cement-water ratio (construction step, step S2).

After the soil cement 3 is constructed, the drilling device 5 equipped with the resistivity measuring means 15 is advanced into the borehole 8 to measure the electrical resistivity of the unconsolidated soil cement 3 in the borehole 8 (measurement step, step S3). In this embodiment, as described above, a current is passed through the current electrode 16 of the resistivity measuring means 15 to measure the voltage value applied to the voltage electrode 17, 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. Note that the measurement of electrical resistivity may be performed simultaneously with the construction of the soil cement 3 in step S2.

After this, 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 soil cement 3 at the effective cement-water ratio of soil cement 3 among the multiple control standard values of electrical resistivity set in step S0, the effective cement-water ratio and electrical resistivity values are compared to evaluate whether the compressive strength of soil cement 3 after hardening satisfies the required strength, and a pass/fail judgment is made (evaluation step, step S4).

Next, we will explain how to set multiple control reference values for the electrical resistivity of soil cement 3 in the above setting step.

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

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

Regarding the total available water volume, 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 this amount of water in the soil must be added to the amount of mixing water to be added, and since a certain amount of bleeding water is generated during molding and does not contribute to the compressive strength of the soil cement, this bleeding water is excluded from the amount of water to be added. Therefore, the total available water volume _Wt is calculated by taking the amount of natural water (mass) as _Ww0 , the amount of excavation water (mass) as _Ww1 , the mass of mixing water for cement milk _{as Ww} , and the bleeding water generated during hardening (the amount of bleeding water 24 hours after mixing) as _Wb ,
W _t =W _w0 +W _w1 +W _w -W _b
It is defined by:

During construction, the amount of soil and sand drawn into the cement milk liquid from the borehole wall is also thought to affect the compressive strength, so the specific relationship between the compressive strength and the effective cement-water ratio including soil and sand is calculated in advance by using as samples multiple foot protection liquids made by mixing multiple types of soil-cement adjusted soil and multiple types of cement milk in multiple different mixing ratios.

As an example, Kasaoka clay (registered trademark) and silica sand No. 7, which have been adjusted to a degree of saturation of nearly 100%, are used for the soil cement adjusted soil, and 11 types are prepared in advance, mixed in volume ratios (clay:silica sand) of 10:0, 9:1, 8:2, ..., 2:8, 1:9, and 0:10.

In addition, three types of cement milk with commonly used water-cement ratios of 60%, 80%, and 100% are prepared in advance.

The soil-cement adjusted soil and cement milk are mixed in advance in volume ratios of 1:1, 1:2, 1:3, and 1:4 to make the root fixing liquid. In other words, a total of 132 (=11 x 3 x 4) types of root fixing liquid are prepared.

Then, for these foot consolidation liquids, the relationship between the compressive strength of the adjusted soil and the effective cement-water ratio is confirmed based on the following formula 1.

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

The relationship between the compressive strength and effective cement-water ratio of the soil-cement adjusted soil based on the above samples is shown in Figure 5. In Figure 5, the numbers in parentheses indicate the moisture content (%) of the adjusted soil. As shown in Figure 5, the gradient of the approximation line (regression line) between the compressive strength and effective cement-water ratio of the soil-cement adjusted soil varies depending on the moisture content, and it can be confirmed that the effective cement-water ratio converges to about 40% when the compressive strength is 0 N/ ^mm2 .

Therefore, the relationship between the gradient θ of the approximation line (regression line) recalculated using an effective cement-water ratio of 40% as the base point and the electrical resistivity ρ is shown in Figure 6. In Figure 6, the numbers in parentheses indicate the water content (%). As Figure 6 shows, it can be confirmed that the gradient θ of the approximation line decreases as the electrical resistivity ρ increases. By linearly approximating the gradient θ of the approximation line (regression line) and the electrical resistivity ρ, they can be expressed as a linear function; in the example shown, θ = -12.275ρ + 39.229 and the coefficient of determination R ² = 0.84.

These results show that there is an extremely high correlation between compressive strength, electrical resistivity, and water content. Therefore, by plotting the data calculated from the above 132 types of root consolidation liquid as shown in Figure 7, a chart (Figure 8) is created in which, for example, a line of electrical resistivity ρ = 0.8 to 3.0 is drawn as a control standard value. In Figure 7, the numbers in parentheses indicate the water content (%). This chart may be stored in advance in the evaluation means 20, or may be stored in a cloud server on the network and downloaded when used.

In this way, in the setting step, a chart is constructed using multiple actual samples, superimposing electrical resistivity as multiple control standard values on the relationship between the compressive strength after hardening of the soil cement 3 and the effective cement-water ratio. By using this chart, it becomes possible to correlate the relationships between the compressive strength after hardening of the soil cement 3, the effective cement-water ratio, and the electrical resistivity.

The evaluation steps using this chart are explained in detail below.

In the evaluation step, a control standard value for electrical resistivity corresponding to the required strength of the hardened soil cement 3 at the effective cement-water ratio of the unconsolidated soil cement 3 is selected from the chart above, and the selected value is compared with the electrical resistivity measured in the measurement step to evaluate whether the compressive strength of the hardened soil cement 3 satisfies the required strength.

Specifically, a line (vertical line) representing the effective cement-water ratio of the unconsolidated soil cement 3 in the construction step is superimposed on the chart shown in Figure 8, and from among the multiple control standard values, the one that passes through the point where that line intersects with the required strength (horizontal line) or is closest to that point is selected. If the electrical resistivity measured in the measurement step is located above or overlaps the selected control standard value, it is judged as passing, and if it is located below, it is judged as failing.

Here, to obtain the effective cement-water ratio (conditions for the formed soil cement 3), the characteristic values of the soil in the soil cement forming area are determined, the density ρ _cm of the cement milk is determined, and the proportion q _cm of the cement milk in the soil cement mix volume ratio is determined, and the effective cement-water ratio of the soil cement 3 is determined from these values using the above formula 1.

When grasping the characteristic values of the soil in the soil cement formation portion, for example, the soil condition described in the ground investigation report carried out before construction is used, and the soil density _ρt and water content _ωr set in soil mechanics or the like are used as the characteristic values. Alternatively, soil is sampled from the original location, and the soil density _ρt and water content _ωr are measured by carrying out tests specified in, for example, JIS A 1202 (test method for soil particle density) and JIS A 1203 (test method for soil water content). Furthermore, in order to obtain more precise judgment accuracy, it is preferable to sample soil at the measurement depth and measure the state of the soil.

The density ρ _cm of the cement milk is calculated from the ratio of the water (specific gravity 1.00) in the cement milk mixing mix to the cement used (specific gravity 3.16 in the case of ordinary Portland cement).

Regarding the proportion of cement milk, q _cm , it is generally considered that the amount of soil and sand relative to the amount of cement milk should not exceed 30%, so in this case, if the amount of soil is 1, the proportion of cement milk will be 2.3. Therefore, if the value is rounded off in consideration of safety, the minimum value of the proportion of cement milk, q _cm , will be 2, and this value will be set.

As an example, as soil cement 3, as shown in Table 1, one without soil (cement milk only), one with soil and whose soil density _ρt and water content _ωr are estimated based on the soil condition described in the ground investigation report, and one in which soil is sampled from the original site and the soil density _ρt and water content _ωr are actually measured by testing are used. From the formula 1, when there is no soil, the effective cement-water ratio C/We is at its maximum value, and when there is soil, the effective cement-water ratio C/We decreases depending on the water content of the soil. In particular, the actual measurement of the water content _ωr is higher, and the effective cement-water ratio C/We is at its smallest.

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

Therefore, if the required strength of the soil cement 3 is known in advance, a value corresponding to the required strength at the effective cement-water ratio of the unconsolidated soil cement 3 to be evaluated from a plurality of control reference values of electrical resistivity is selected as a threshold value for pass/fail judgment, and it is possible to easily judge whether the compressive strength meets the required strength simply by comparing this value with the measured electrical resistivity. This judgment may be performed automatically by the evaluation means 20, or, for example, a chart may be displayed on the display means of the evaluation means 20, and the electrical resistivity measured in the measurement step may be superimposed on the chart, so that the evaluator can visually judge. The electrical resistivity and effective cement-water ratio of the unconsolidated soil cement 3 may be manually input to the evaluation means 20 by the user using the input means, and the effective cement-water ratio may be data stored in the evaluation means 20 or a cloud server, or may be calculated by the evaluation means 20 from the data or the measured data.

In this way, the correlation between the compressive strength, effective cement-water ratio, and electrical resistivity of the soil cement 3 is determined in advance, and the cement milk injected into the borehole 8 is mixed and stirred with the soil and sand in the borehole 8 to create soil cement 3 with an effective cement-water ratio. The electrical resistivity of the unconsolidated soil cement 3 in the borehole 8 is measured, and the strength characteristics of the soil cement 3 after hardening are estimated from the correlation between the effective cement-water ratio and electrical resistivity. 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 formed borehole 8 to mix the soil and sand in the borehole 8 with the cement milk to construct the soil cement 3, the electrical resistivity of the constructed unconsolidated soil cement 3 is measured, and the measured electrical resistivity is compared with a value among the control reference values that corresponds to the required strength of the soil cement at the effective cement-water ratio of the soil cement 3 to evaluate whether the required compressive strength of the soil cement 3 after hardening is satisfied. This allows the compressive strength of the soil cement 3 after hardening to be accurately evaluated in a short time while the soil cement 3 is in an unconsolidated state. In other words, if the effective cement-water ratio of the unconsolidated soil cement 3 and the compressive strength required for the soil cement 3 after hardening are known in advance, the compressive strength of the soil cement 3 after hardening can be evaluated in a short time while the soil cement 3 is still unconsolidated, simply by measuring the electrical resistivity of the unconsolidated soil cement 3 and comparing it with the control standard value. Therefore, even if the result of this evaluation indicates that the compressive strength after hardening does not satisfy the required strength, it is easy to reapply the soil cement 3 before it hardens.

When measuring the electrical resistivity, the resistivity measuring means 15 passes a current through the multiple current electrodes 16 to measure the voltage value applied to the multiple voltage electrodes 17, and calculates the electrical resistivity based on the current value, voltage value, and the electrode spacing a between the current electrodes 16 and the voltage electrodes 17, making it possible to measure the electrical resistivity with a simple configuration. Moreover, since it can be configured by attaching the electrode unit 18 having the multiple current electrodes 16 and multiple voltage electrodes 17 to an existing drilling device 5 such as an auger, there is no need to manufacture a dedicated drilling device, and no large-scale modifications are required.

Furthermore, in the evaluation step, a chart on which compressive strength, effective cement-water ratio, and multiple control standard values are entered is used, and values calculated from the measured electrical resistivity of soil cement 3 in an unconsolidated state and the effective cement-water ratio of soil cement 3 are plotted on the chart to evaluate whether the compressive strength of soil cement 3 after hardening satisfies the required strength, making it easy to evaluate by visual inspection, etc.

In addition, it can be easily applied to known concrete pile construction methods, making it versatile and easy to implement.

This example is explained below.

In this example, an experiment was conducted to examine the validity of the evaluation of compressive strength in the above embodiment using the electrical resistivity of unconsolidated soil cement 3.

Five different types of soil samples (tuffaceous clay, fine sand mixed with gravel, sandy mudstone, sandy soil, and mudstone mixed with sand) were prepared from the supporting layer of concrete piles as soil to be mixed into the unconsolidated soil cement 3 taken from the actual site, and cement milk was mixed and stirred in ratios of 1:2 and 1:3 for Examples 1 to 10 in Table 2. The compressive strength and electrical resistivity were measured and plotted on a chart. The results are shown in the chart in Figure 9.

As shown in Figure 9, in the range of effective cement-water ratio of 116.6 to 139.9%, the electrical resistivity ρ of soil cement 3 can be classified with a boundary value of 2.0 Ω·m. Therefore, when the required strength of soil cement 3 is 15 N/mm ² or more, if the electrical resistivity ρ is 2.0 or less, there is only one example in nine in which the compressive strength is 15 N/mm ² or less, confirming that the electrical resistivity ρ is an effective indicator for determining compressive strength.

REFERENCE SIGNS LIST 1 Compressive strength evaluation device 3 Soil cement 8 Borehole 15 Resistivity measuring means 16 Current electrode 17 Voltage electrode 20 Evaluation means a Electrode spacing

Claims (4)

A method for evaluating compressive strength of soil cement, which estimates strength characteristics of soil cement after hardening, the soil cement being formed by mixing a cement-based material, a soil material, and water, comprising:
A setting step of determining a correlation between the compressive strength of the soil cement, the effective cement-water ratio, and the electrical resistivity;
A construction step of constructing a soil cement having an effective cement-water ratio by mixing and stirring the cement milk injected into the borehole with the soil and sand in the borehole;
A measuring step of measuring the electrical resistivity of unconsolidated soil cement in the borehole;
An evaluation step of estimating strength characteristics of the soil cement after hardening from the correlation between the effective cement-water ratio and the electrical resistivity,
In the evaluation step, a chart on which compressive strength, effective cement-water ratio, and a number of control standard values are entered is used, and values calculated from the measured electrical resistivity of the soil cement in the unconsolidated state and the effective cement-water ratio of the soil cement are plotted on the chart to evaluate whether the compressive strength of the soil cement after hardening satisfies the required strength.
A method for evaluating the compressive strength of soil cement. The method for evaluating compressive strength of soil cement according to claim 1, characterized in that in the measurement step, a resistivity measuring means having a plurality of current electrodes and a plurality of voltage electrodes is used, a current is passed through the current electrodes to measure a voltage value applied to the voltage electrodes, and an electrical resistivity is calculated based on the current value, the voltage value, and the electrode spacing between the current electrodes and the voltage electrodes . A soil cement compressive strength evaluation device that estimates the strength characteristics of soil cement after hardening, the soil cement being formed by mixing a cement-based material, a soil material, and water,
A resistivity measuring means for measuring electrical resistivity;
and an evaluation means for estimating strength characteristics of the soil cement after hardening based on a correlation between the compressive strength of the soil cement, the effective cement-water ratio, and the electrical resistivity, which is determined in advance using the electrical resistivity of the unconsolidated soil cement measured by the resistivity measuring means and the effective cement-water ratio of the unconsolidated soil cement ,
The evaluation means evaluates whether or not the compressive strength of the soil cement after hardening satisfies the required strength by comparing the electrical resistivity of the soil cement in the unconsolidated state measured by the resistivity measuring means, the compressive strength of the soil cement after hardening, and the effective cement-water ratio of the unconsolidated soil cement with a value corresponding to the required strength of the soil cement at the effective cement-water ratio of the unconsolidated soil cement among a plurality of control standard values of the electrical resistivity of the soil cement that are preset based on the effective cement-water ratio of the unconsolidated soil cement.
A soil cement compressive strength evaluation device characterized by the above . The soil cement compressive strength evaluation device according to claim 3, characterized in that the resistivity measuring means has a plurality of current electrodes and a plurality of voltage electrodes, 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 value of the current, the value of the voltage, and the electrode spacing between the current electrodes and the voltage electrodes.

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