JPH04244939A - Method for estimating strength of soil cement - Google Patents

Abstract

PURPOSE:To repair a soil cement body in an yet unsolidified state by rapidly and easily judging the quality of soil cement by collecting a sample from the soil cement body to calculate the moisture content of the sample and estimating the strength of the soil cement body from a regression equation showing the correlation between the preliminarily calculated moisture content and strength of soil cement in the foundation. CONSTITUTION:The earth and sand of a predetermined layer is sampled before execution and mixed with cement milk having a predetermined composition to prepare a sample simulating soil cement to be executed. Moisture content and cement quantity are calculated from the sample and the compression strength of the sample is calculated by a compression test to calculate a regression equation showing the correlation between the moisture content, strength cement quantity and strength. A sample is collected from the soil cement immediately after execution and the moisture thereof is evaporated to calculate reduced moisture content. The strength of the soil cement is estimated from the regression equation related to the preliminarily calculated moisture content and strength and the quality thereof is judged within a short time. Therefore, the presence of the depleted part of the soil cement can be rapidly and easily judged and the repairing of the soil cement in an yet unsolidified state is made possible.

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 the strength of soil cement, and more particularly to a method for estimating the strength of soil cement for quickly determining the quality of soil cement.

0002

[Prior Art] Conventionally, the quality of soil cement created by columnar underground wall construction methods using in-situ soil agitation systems has generally been determined by collecting specimens on-site, and after 7 days and 2
A method is used in which a uniaxial compressive strength test is conducted after 8 days, and it is determined based on the strength whether a predetermined quality has been obtained. However, with this method, it takes at least a week to judge the quality, so follow-up management is required after the soil cement has hardened, and defective parts of the soil cement can be discovered by checking the quality quickly after construction, and if the soil cement is still hardening. It is not possible to carry out repairs unless the

On the other hand, a method for determining the quality of soil cement that has not hardened immediately after construction has been proposed in the ``Guidelines for Early Judgment of Concrete Quality''. There is a hydrochloric acid solution heat method that uses the difference to determine the amount of cement and controls the quality from the water-cement ratio.

0004

[Problems to be Solved by the Invention] However, in the hydrochloric acid dissolution heat method, it is time-consuming to dilute the sample to form a predetermined mortar solution, and it also requires a considerable amount of time to add hydrochloric acid and finish generating heat. It takes about 25 minutes to judge the quality of soil cement. On the other hand, in the above-mentioned in-situ soil stirring system column type underground wall construction method, reinforcing materials such as H-beams and steel pipes are added to the soil pile as a soil cement body created with soil cement at an early stage before the soil cement hardens. Therefore, it is necessary to quickly determine the quality of the soil cement, especially the quality of the soil cement located deep, and if necessary, repair the defective part by re-installation before inserting the reinforcing material. In addition, in order to shorten the construction period by reducing the waiting time of the machine to judge the quality of soil cement, it is desirable to judge the quality in a short time, for example, about 15 minutes after applying soil cement. However, the above-mentioned hydrochloric acid dissolution heat method has a problem in that it cannot fully meet such demands.

[0005] Therefore, the present invention was made to solve the above problems, and its purpose is to more quickly and easily determine the quality of soil cement, and to repair a soil cement body before it hardens. The present invention aims to provide a method for estimating the strength of soil cement.

[0006]

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned problems, and its gist is to quickly determine the quality of unhardened soil cement immediately after construction. This is an estimation method in which a sample is taken from a predetermined location of a soil cement body, the moisture content of the sample is calculated, and based on the moisture content, the moisture content of soil cement in the ground where soil cement is to be constructed is calculated in advance. The method of estimating the strength of soil cement includes estimating the strength from a regression equation showing the correlation between the strength and the strength.

Another gist of the present invention is a method for estimating the strength of soil cement for quickly determining the quality of unhardened soil cement immediately after construction, comprising:
A sample was taken from a predetermined location of the soil cement body, the water content of the sample was calculated, the cement content of the sample was dissolved and dried to calculate the soil amount, and the calculated amount was subtracted from the sample weight. The method of estimating the strength of soil cement includes estimating the strength based on the amount of cement from a previously prepared regression equation showing the correlation between the amount of soil cement and the strength in the ground where the soil cement is to be applied.

The present invention will be explained in more detail below.

[0009] In the present invention, soil cement is stabilized soil consisting of cement, earth and sand, and pore water, which is obtained by adding cement to local materials and further adding supplementary materials as necessary. Columnar bodies are created underground by rotating the rod while excavating the ground with a machine such as a machine, injecting a hardening material such as cement milk or bentonite at high pressure, and then mixing and stirring it with the soil in situ using a stirring blade, etc. It is.

[0010] Furthermore, the strength of soil cement estimated by the present invention does not necessarily have to be an accurate value that should be compared with the design strength. It is sufficient as long as it is sufficient.

[0011] In the strength estimation method of the present invention, prior to soil cement construction, regression equations showing the correlation between moisture content and strength and the correlation between cement content and strength are determined for the ground at the construction site. To obtain these regression equations, first, earth and sand are collected from a predetermined layer of the ground by, for example, boring. Next, a predetermined blend of cement milk or the like is added to the collected soil and mixed to prepare a sample that imitates the soil cement to be constructed. Furthermore, the water content and cement content of the sample are determined by a method similar to the method described later, while a specimen for compression test is created from the sample and the compressive strength is determined,
Calculate each regression equation from these.

[0012] In order to judge the quality of soil cement immediately after construction according to the present invention, first, a sample is taken from a predetermined location of the planned soil cement body whose quality is to be judged. As a method for collecting a sample, for example, there is a method in which an H-shaped steel provided with a sample collecting means at a predetermined location is built into a soil cement body, and then the steel is pulled out again to collect a sample. Next, after measuring the weight of the collected sample, the moisture in the sample is evaporated and the remaining amount of evaporation is measured. From these measured values, the moisture content is calculated as the evaporation loss, and the above moisture content and strength determined in advance are calculated. The strength of soil cement is estimated from the regression equation showing the correlation and its quality is determined. Here, examples of methods for evaporating water include heating a frying pan containing a sample, and methods for measuring the weight of a sample include methods using various weight measuring devices. Preferably, if an infrared moisture meter is used, the weight of the sample can be measured by directly evaporating moisture, so that rapid and highly accurate measurement results can be obtained. The infrared moisture meter is
An infrared lamp is installed on the sample pan of a precision balance. Water is evaporated using infrared rays, the amount remaining after evaporation is measured, and the amount of water is measured from the difference in weight before and after evaporation. Note that when the water content of the sample is large, the evaporation time can be shortened by washing the sample with a low boiling point solvent such as ethyl alcohol and replacing it with water.

According to another method of the invention, the quality of soil cement is determined from the amount of cement in a sample. That is,
For example, calculate the moisture content of the sample using the same method as above, measure the soil content, subtract these amounts from the sample weight to calculate the cement content, and calculate the correlation between the previously determined cement content and strength. The strength of the soil cement is estimated from the regression equation that indicates the quality of the soil cement. To measure the amount of soil, for example, acid is added to the sample to dissolve the acid-soluble cement component, which is then washed and removed, the dissolved residue is filtered, and the water is evaporated to calculate the evaporated remaining amount of the sample. Find this and use it as the soil amount. Here, examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, and the like. In addition, examples of methods for dissolving and removing cement include adding acid to a container containing a sample and stirring it, but preferably,
For example, the dissolution of cement can be further promoted by using a method such as immersing a container containing a sample and an acid in an ultrasonic cleaner and allowing the acid to act on the container. Furthermore,
Examples of the method for filtering the dissolved residue include a method using filter paper and a funnel, but preferably,
For example, if pressure filtration is performed using a pressure filter, the filtration work can be performed quickly. The filtered residue is preferably washed with water or ethyl alcohol, and the amount of evaporated residue, that is, the amount of soil, is measured in the same manner as described above, for example by heating with a frying pan or using an infrared moisture meter. .

[0014]

[Examples] The present invention will be explained in detail with reference to Examples below, but the present invention is not limited thereto.

[0015] Materials were collected by boring from the sand layer existing below the groundwater level at the soil cement construction site, cement milk was added, bentonite was further added to suppress the permeability coefficient, and the mixture was mixed for 3 minutes and then allowed to stand for 2 minutes. Breathing water was removed to create a sample simulating soil cement underground. In addition, the fresh density and air amount of the sample were measured using a mortar air meter in order to make corrections to comply with the conditions of soil cement located below the groundwater level. In addition, as shown in FIG. 1, 12 types of cement milk formulations were prepared to prepare samples. The symbols in the figure indicate sample numbers.

[0016] From the prepared samples, 100.0 g of each sample was taken, heated in a frying pan, the dry weight was measured, and the amount of water contained in the sample was calculated.

[0017] Also, about three times the amount of concentrated hydrochloric acid was added to the sample, and after dissolving the cement by applying ultrasonic waves for 3 minutes, the dissolution residue was washed and this was used as No. The mixture was filtered using 2-ring paper and a Buchner funnel, and the residue was dried by heating in a frying pan to measure the amount of soil. Then, the amount of cement was calculated by subtracting the amount of water and the amount of soil from 100.0 g. Note that the time required for measurement and calculation for each sample was about 10 minutes.

On the other hand, each of the above-mentioned samples was poured into a simple mold of 5 x 10 cm to form a strength specimen, and in order to comply with the conditions of soil cement located below the groundwater level, 3 kg was poured for 1 hour after casting.
It was cured in a tank at /cm2 pressure. Furthermore, after curing the specimen for a predetermined period of time in a constant temperature water bath at 15° C., the strength was measured by a compressive strength test.

FIG. 2 shows the relationship between the moisture content of the sample and the strength of the specimen obtained through experiments. Here, the horizontal axis of the figure represents the water/(cement+sand) ratio, ie, W/(S+C), and the vertical axis represents the strength. The correlation coefficient for each sample is 0
．． 915, the regression equation is strength = -15.46 + 59.42
×W/(S+C).

Furthermore, as shown in FIG. 3, these measured values are within the confidence value of 95% for 10 samples and within 90% of the confidence value for all samples, so the moisture content of the samples is It can be seen that the quality of soil cement can be determined sufficiently by measuring the .

FIG. 4 shows the relationship between the amount of cement and the strength of the specimen obtained through experiments. Here, the horizontal axis of the figure represents the cement/sand ratio, that is, C/S, and the vertical axis represents the strength. The correlation coefficient for each sample was 0.768, and the regression equation was intensity=-5.31+78.31×C/S.

Furthermore, as shown in FIG. 5, these measured values are within the 95% confidence value for 8 samples and 90% confidence value for all the samples, so the amount of cement in the samples is It can be seen that the quality of soil cement can be determined sufficiently by measuring the .

Note that the symbols shown in FIGS. 2 to 5 are sample numbers, which correspond to the sample numbers in FIG. 1.

[0024] Then, a sample was taken from a predetermined location of the soil cement body immediately after construction, and the quality of the soil cement was determined by estimating the strength from the water content or cement content of the sample using the above regression formula. The time required to judge the quality was within 10 minutes.

[0025]

[Effects of the Invention] As described above, according to the present invention, a sample is taken from soil cement immediately after construction, and the moisture content or cement content of the sample is calculated in a short time using a simple method. The quality is determined by estimating the strength from a regression equation showing the correlation between the moisture content and strength of soil cement or the correlation between the cement content and strength. therefore,
Since it is possible to quickly and easily determine the presence or absence of defects in the soil cement, it is possible to repair the soil cement by re-applying the soil cement before it hardens.

[Brief explanation of the drawing]

FIG. 1 is a table showing the formulation of cement milk mixed with samples used in examples of the present invention.

FIG. 2 is a chart showing the relationship between moisture content and strength of samples used in Examples of the present invention.

FIG. 3 is a chart showing reliability values of the relationship between moisture content and strength of samples used in Examples of the present invention.

FIG. 4 is a chart showing the relationship between cement amount and strength of samples used in Examples of the present invention.

FIG. 5 is a chart showing reliability values of the relationship between cement amount and strength of samples used in Examples of the present invention.

Claims (2)

[Claims] Claim 1: A soil cement strength estimation method for quickly determining the quality of unhardened soil cement immediately after construction, comprising: collecting a sample from a predetermined location of a soil cement body; and calculating the moisture content of the sample. A method for estimating the strength of soil cement, in which the strength is estimated from a regression equation showing the correlation between the moisture content and strength of soil cement in the ground where the soil cement is to be constructed, calculated in advance based on the moisture content. Claim 2: A soil cement strength estimation method for quickly determining the quality of unhardened soil cement immediately after construction, in which a sample is taken from a predetermined location of a soil cement body, and the water content of the sample is determined. In addition to calculating the amount of cement, the cement content of the sample is dissolved and dried to calculate the amount of soil, and based on the amount of cement calculated by subtracting these calculated amounts from the sample weight, a pre-prepared soil cement is applied. A soil cement strength estimation method that estimates strength from a regression equation that shows the correlation between the amount of soil cement in the ground and its strength.