JP6384954B2 - Method for estimating compressive strength of soil cement and soil cement storage - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for estimating the compressive strength of soil cement and a soil cement storage device that are applied to a rooted portion at the lower end of a pile when the pile is installed in an embedded pile embedding method.

  In the prefabricated pile embedding method, cement milk, which is the root-setting liquid, is injected into the lower end of the pile hole, and the in-situ soil and root-setting liquid located at the lower end of the pile are replaced or mixed and stirred, so It is formed.

  Here, since the root consolidation part is a kneaded product of in-situ soil and cement milk, the strength test of the injected cement milk alone is not reliable as a strength confirmation method for the root consolidation part.

  Therefore, conventionally, the strength of the root solidified part has been confirmed by collecting the core of the root solidified part that has been bored and hardened to the root solidified part, and performing a compression test of the collected core for four weeks of age. It was.

  In addition, as a method of confirming this type of strength, when constructing a pile, soil cement, which is a kneaded mixture of in-situ soil and rooting liquid, is collected from the bottom of the pile hole, and a specimen is created from this sample. A method for measuring the compressive strength is known (for example, see Patent Document 1).

  Furthermore, a method for determining the strength by measuring the specific gravity of the soil cement and comparing the specific gravity of the soil cement with the specific gravity of the injected cement milk is also known.

  In addition, a method is also known in which a correspondence table between the specific gravity and compressive strength of soil cement is prepared for each soil quality of the construction site, and the strength is determined by comparing the specific gravity of the collected soil cement with the correspondence table (for example, patent document). 2).

  Furthermore, the specific gravity and temperature of the injected cement milk are measured, the specific gravity and temperature of the excavation residue as in situ soil (muddy water) are measured, and the specific gravity and temperature of the cement milk mixture as the collected soil cement are measured. The cement milk replacement rate is estimated based on these measurement results, and the compressive strength is confirmed by comparing the cement milk replacement rate with corresponding data of the cement milk replacement rate and the compressive strength prepared in advance. It is known (for example, refer to Patent Document 3).

  Moreover, the compressive strength of concrete or mortar can be accurately estimated based on the cement water ratio, which is the ratio of cement to water in the concrete or mortar. That is, as indicated by the formula of cement water ratio (c / w) = cement mass (c) / water mass (w), the compressive strength of concrete increases as the cement water ratio increases and the proportion of cement increases. As a method for estimating the cement water ratio of unsolidified concrete or mortar, a method using a washing test, a method using a hydrometer, and a method using heat of acid dissolution are known.

JP 2009-102817 A JP2013-122166A JP 2012-127057 A

  However, as in the above-mentioned Patent Document 1, in the method of producing a specimen of soil cement, it takes 4 weeks to obtain the result, so it is practically difficult to reflect the test result in the construction of the pile. It is.

  In the method of comparing the specific gravity of the above-mentioned soil cement and the specific gravity of the cement milk to be injected, since there is contamination of in situ soil and groundwater in the actual root consolidation part, the accuracy is low as a strength confirmation method of the root consolidation part, Not practical.

  In the method of determining strength based on the correspondence table between the specific gravity and compressive strength of soil cement prepared in advance as in Patent Document 2 described above, it is not only necessary to prepare a correspondence table for each soil type, but also the actual roots. Since the hardened portion is contaminated with in-situ soil and groundwater, the strength estimation based only on the specific gravity is not practical as a strength confirmation method for the root hardened portion.

  As in the above-mentioned Patent Document 3, the method of estimating the cement milk replacement rate by measuring the specific gravity and temperature of cement milk, in-situ soil, and soil cement has a problem that cannot be applied when the in-situ specific gravity is different. is there.

  In order to estimate the compressive strength of soil cement, which is originally a mixture of water, cement, and in-situ soil, it is necessary to grasp the amount of water and the amount of cement in the soil cement, and it is difficult to estimate the compressive strength from the specific gravity. The accuracy is low and not practical.

  The method for estimating the cement water ratio by the washing test described above is defined in JIS A 1112, but the test is complicated and time consuming, and it is very difficult to separate the clay and cement components. Not practical.

  The method for estimating the cement water ratio using the above-mentioned hydrometer is to add water to the mortar and dilute it, measure the specific gravity of the liquid in which the aggregate is precipitated, estimate the amount of cement, and heat the mortar. Although it is absolutely dry and measures the amount of water to calculate the cement water ratio, there is a problem that cannot be applied when the soil in situ contains a lot of clay.

  The above-described method for estimating the cement water ratio by the heat of dissolution of the acid can estimate the cement water ratio with a relatively high accuracy in a short time. However, in principle, it cannot be applied when blast furnace cement or limestone is included, and since it is necessary to ensure safety because hydrochloric acid is used as a powerful drug, it is not suitable for construction sites. is there.

  Therefore, there has been a demand for a practical estimation method that can accurately estimate the compressive strength of soil cement in a relatively short time with high accuracy regardless of the specific gravity of the in situ soil.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above points. A method for estimating the compressive strength of a soil cement that can be easily implemented in a relatively short time and has good accuracy, and a soil cement used in the method for estimating the compressive strength of a soil cement. The purpose is to provide storage.

  The method for estimating the compressive strength of a soil cement according to claim 1 is a method for estimating the compressive strength of a soil cement that constitutes a root-solidified portion in a pile embedding method, wherein an unsolidified soil cement is removed from the root-solidified portion. The temperature of the collected soil cement is kept warm, the temperature change associated with the hardening of the soil cement is measured, and the maximum temperature at the time of hardening of the soil cement is measured using the maximum temperature of the soil cement. And the cement water ratio of the soil cement based on the relational expression showing the correlation between the cement water ratio of the soil cement and the cement water ratio of the soil cement using the calculated cement water ratio. Based on the relational expression showing the correlation with the compressive strength of the soil cement, the compressive strength of the soil cement in the solidified state of the root solidified part is calculated. They are intended.

  The method for estimating the compressive strength of a soil cement according to claim 2 is the method for estimating the compressive strength of a soil cement according to claim 1, wherein the correlation between the maximum temperature at the time of hardening of the soil cement and the cement water ratio of the soil cement is provided. The relational expression indicates that the unsolidified soil cement or cement paste with different cement water ratios is kept warm, the maximum temperature at the time of hardening of the soil cement or cement paste of each cement water ratio is measured, It is derived from each measured maximum temperature.

  The soil cement storage device according to claim 3 is a soil cement storage device used in the method for estimating the compressive strength of soil cement according to claim 1 or 2, wherein the soil of the rooting portion collected when the pile is installed A container body capable of containing cement, a heat retaining means for retaining the soil cement in the container body, and a temperature measuring means for measuring a temperature change of the soil cement that hardens while being kept warm are provided.

  According to the present invention, the cement water ratio is estimated based on the heat generation characteristics when the soil cement is hardened, and the compressive strength of the solid soil cement is estimated based on the cement water ratio. It can be easily implemented with good accuracy.

It is sectional drawing which shows the structure of the soil cement storage device which concerns on one embodiment of this invention. It is a graph which shows the temperature change of the soil cement for every cement water ratio. It is a graph which shows the relationship between the maximum temperature in the case of hardening, and a cement water ratio. It is a graph which shows the relationship between cement water ratio and compressive strength.

  Hereinafter, the configuration of an embodiment of the present invention will be described in detail.

  In the embedding method of piles such as ready-made concrete piles, first, the auger screw is inserted into the hollow part of the cylindrical pile, and the pile is submerged while forming the pile hole for excavating the ground and installing the pile with this auger screw Let In addition, when installing a pile in a pile hole, after excavating a ground previously with an auger screw and forming a pile hole, the method of inserting and installing a pile in this pile hole may be used.

  In this state where the pile is arranged in the pile hole, cement milk as a root hardening liquid is injected from the hollow portion of the pile to the tip which is the lower end of the pile hole and the pile.

  Further, the in situ soil in which the lower end of the pile is located in the pile hole and the cement milk are agitated and mixed, and the soil cement, which is a kneaded product of the in situ soil and the cement milk, is hardened to form a solidified portion. In addition, when excavating the ground beforehand and forming a pile hole, after pouring root hardening liquid into the front-end | tip of a pile hole, a pile is inserted in this pile hole.

  In the pile embedding method described above, the compressive strength of the soil cement constituting the root consolidation portion is confirmed in order to secure the bearing strength of the root consolidation portion and to prevent a construction failure such as insufficient pile support capability.

  When checking the compressive strength of the soil cement, after injecting the cement milk, use the hollow part of the pile to collect the unsolidified soil cement from the rooted part and keep the collected soil cement at a certain temperature. Keep warm.

  Here, since soil cement is a kneaded product of in-situ soil and root-setting liquid, heat is generated due to a hydration reaction when the cement and water react and harden.

  Then, when the cement water ratio (c / w), which is the ratio between the mass of cement and the mass of water in the soil cement or cement paste, was changed and the temperature change during the curing of each soil cement or cement paste was measured, It was found that the temperature characteristics based on the heat generation at the time differ depending on the cement water ratio. That is, the degree of heat generation due to the hydration reaction changes due to the difference in the cement water ratio, resulting in a difference in the maximum temperature during curing.

  Further, soil cements having different temperature characteristics were cured under certain conditions, and the compressive strength was measured after curing. As a result, it was found that there was a correlation between the maximum temperature during curing and the compressive strength of the soil cement after curing.

  Therefore, based on each of these measurement results, a relational expression showing the correlation between the maximum temperature at the time of hardening of the soil cement and the cement water ratio of the soil cement, and after the hardening of the soil cement and the cement water ratio of the soil cement It is possible to derive a relational expression showing a correlation with the compressive strength of.

  Therefore, the temperature change at the time of hardening of the soil cement in a state where it is collected at the time of pile construction and kept at a constant temperature is measured.

  In addition, using the maximum temperature of the soil cement measured for this temperature change, the cement of the soil cement is based on the relational expression showing the correlation between the maximum temperature at the time of hardening the soil cement and the cement water ratio of the soil cement. Calculate the water ratio.

  Furthermore, using this calculated cement water ratio, the compressive strength of the solid cement is calculated based on the relational expression showing the correlation between the cement water ratio of the soil cement and the compressive strength after hardening of the soil cement. Estimate the compressive strength of soil cement.

  In addition, in the actual construction of piles, the roots are formed several meters to several tens of meters below the ground. Although the temperature of such a place varies depending on the region, it is almost constant regardless of the season. It is about 10 ° C in Hokkaido, about 17 ° C in metropolitan areas such as Tokyo and Osaka, and about 20 ° C in southern Kyushu.

  That is, the actual solidified part is kept warm in the ground, and when measuring the temperature change when the collected soil cement is cured, it is as close as possible to the underground temperature condition, so that the collected unsolidified It is important to measure the temperature change while keeping the soil cement warm. As described above, since the ambient temperature of the actual solidified portion is almost constant, it is preferable to measure the temperature change while storing the collected soil cement at a predetermined ambient temperature while keeping the temperature.

  Therefore, when measuring the temperature change of the collected soil cement, it is preferable to store the soil cement in the soil cement storage device 1 shown in FIG.

  The soil cement storage device 1 includes a mold 2 as a container that can store the soil cement of the root-solidified portion collected when the pile is installed, and a heat insulation that keeps the soil cement in the mold 2 at a constant temperature. The heat insulating material 3 as a means and the temperature measuring means 4 which measures the temperature change of the soil cement which hardens | cures in the state kept warm are provided.

  The mold 2 has a bottomed cylindrical shape that is open on one side in the axial direction. For example, it is convenient to use a tin-made disposable concrete specimen molding mold (trade name: sono mold, summit mold, plastic mold, etc.). is there.

  The heat insulating material 3 covers the periphery of the mold 2 in a state in which the soil cement is accommodated without a gap. Then, by covering the periphery of the mold 2 with the heat insulating material 3, the soil cement in the mold 2 is kept at a constant temperature.

  Thus, the mold 2 that contains the soil cement and is covered with the heat insulating material 3 is accommodated in the plastic outer container 5.

  The outer container 5 includes a bottomed cylindrical container body 6 that is open on one side in the axial direction, and a lid body 7 that can close the opening of the container body 6.

  In addition, a through hole 8 is provided in the heat insulating material 3 and the lid body 7 located on the opening side of the outer container 5.

  The temperature measuring means 4 has a temperature sensor 9 for measuring the temperature of the soil cement. The temperature sensor 9 can be inserted into the through-hole 8 and can measure the temperature of the soil cement in the mold 2 while being inserted into the through-hole 8.

  In addition, a data logger 10 for recording the measured temperature is connected to the temperature sensor 9, and the measured temperature is recorded by the data logger 10 while measuring the temperature of the soil cement by the temperature sensor 9. . Note that the temperature measuring unit 4 may be configured such that the data logger 10 is not provided, as long as the temperature measured by the temperature sensor 9 can be read.

  Next, the operation and effect of the one embodiment will be described.

  According to the method for estimating the compressive strength of soil cement, the cement water ratio is estimated based on the heat generation characteristics when the soil cement hardens, paying attention to the heat of hydration when the soil cement hardens. Therefore, the compressive strength after hardening of the soil cement can be estimated regardless of the specific gravity of the in situ soil. Further, since it is sufficient that the maximum temperature can be grasped from the temperature change accompanying the curing, for example, the maximum temperature during the curing can be measured for about one day, and it takes relatively no time to obtain the result. Furthermore, as with the method of discharging excavated soil generated when excavating a pile hole, unsolidified soil cement can be collected, so it is possible to collect soil cement easily without special equipment, etc. Can be implemented on the ground. Therefore, the estimation of the compressive strength of the soil cement can be easily performed in a relatively short time, and the accuracy thereof is good.

  The relational expression showing the correlation between the maximum temperature during curing of the soil cement and the cement water ratio of the soil cement is the relationship between the maximum temperature during curing with the soil cement or cement paste having different cement water ratios kept warm. By measuring, since it derives from each cement water ratio and each measured maximum temperature, it can derive | lead-out easily beforehand at the time of construction of a pile.

  In addition, since the relational expression showing the correlation between the maximum temperature at the time of hardening of the soil cement and the cement water ratio of the soil cement can be obtained corresponding to the ambient temperature of the actual construction site, the accuracy of estimation can be improved. It can be improved.

  Here, when estimating the compressive strength, since it is important to correspond to the temperature conditions of the place where the construction is actually performed, by using the soil cement storage device 1, it is possible to measure the temperature change while keeping the temperature, The accuracy of estimation can be improved.

  Moreover, since the soil cement storage device 1 has a simple configuration and good transportability and handling properties, it is easy to use at a construction site. Therefore, the method for estimating the compressive strength of the soil cement can be easily implemented.

  Furthermore, since the soil cement storage device 1 can be stored in a predetermined ambient temperature by using the soil cement storage device 1 in an environment where the ambient temperature can be easily managed, for example, indoors, the estimation accuracy can be further improved.

  The exothermic phenomenon due to the hydration reaction between cement and water described above has been used so far to prevent the occurrence of temperature cracks in mass (large section) concrete and high strength, high cement water ratio concrete. there were.

  However, soil cement, which is a kneaded mixture of in-situ soil and cement milk used for the construction of piles, and cement milk, which is a root-setting liquid, have a low cement water ratio that does not require concern about temperature cracking. In the construction of this pile, attention was not paid to the exothermic phenomenon due to the hydration reaction as described above, and the temperature change was not measured during the curing.

  Examples will be described below.

  First, the temperature characteristic by the difference in cement water ratio was confirmed.

  Cement milk having different cement water ratios and soil cement having different cement milk mud water replacement rates were prepared as test materials.

  In addition, the cement water ratio (c / w) of each test material was 1.67, 1.25, 1.00, and 0.83, respectively.

  Each specimen was stored in a soil cement storage container and kept warm. Moreover, the temperature change at the time of hardening of a test material was measured in the state stored while keeping heat in this way.

  In the soil cement storage device, the test material is accommodated in a disposable mold (dimensions: diameter 15 cm, height 30 cm, product surface: sonomold) in which a temperature sensor is installed.

  Further, a heat insulating material is provided so as to cover the periphery of the disposable mold in a state in which the test material is accommodated without a gap.

  Furthermore, the disposable formwork in a state in which the heat insulating material is wound is accommodated in a plastic outer container (dimensions: diameter 20 cm, height 40 cm).

  And the temperature at the time of hardening of the test material in a disposable mold is measured with the temperature sensor installed in the disposable mold, and this measured temperature is recorded with a data logger.

  FIG. 2 shows the relationship between the cement water ratio of each test material and the temperature change.

  As shown in FIG. 2, the temperature at the time of hardening of each specimen reached the maximum temperature within 24 hours after the start of storage in the soil cement storage device. In other words, when actually constructing the pile, cement milk is injected, the in-situ soil and cement milk are stirred and mixed, and then the maximum temperature can be grasped in about 24 hours, and the compressive strength is determined based on this maximum temperature. It can be calculated.

  The maximum temperature of the specimen was higher as the cement water ratio was higher.

  Next, the relationship between the cement water ratio and the maximum temperature during curing was confirmed.

  Prepare soil cement and cement milk with different cement water ratios as test materials, and cure each test material while curing each of these test materials under a certain condition (atmosphere temperature 10 ° C or 20 ° C). The maximum temperature in the temperature change of was measured.

FIG. 3 shows the relationship between the cement water ratio and the maximum temperature at the time of curing when stored at the ambient temperature of 10 ° C. and when stored at the ambient temperature of 20 ° C.

  As shown in FIG. 3, there is a correlation between the cement water ratio and the maximum temperature at the time of hardening of the specimen, both when stored at an ambient temperature of 10 ° C and when stored at an ambient temperature of 20 ° C. Was.

  In addition, from this result, when stored at an atmospheric temperature of 10 ° C., the relational expression (1) showing the correlation between the maximum temperature at the time of curing and the cement water ratio is the maximum temperature X, and the cement water ratio is If Y, Y = 0.020X + 0.23.

  In addition, when stored at an ambient temperature of 20 ° C., the relational expression (2) indicating the correlation between the cement water ratio and the maximum temperature at the time of curing is as follows. When the maximum temperature is X and the cement water ratio is Y, Y = 0.018X + 0.13.

  Furthermore, the compressive strength of the test material of each cement water ratio at the age of 28 days was measured. FIG. 4 shows the relationship between the actual cement water ratio and compressive strength of each test material. In addition, the mass of water with an actual cement water ratio is the sum of the mass of water contained in cement milk, the moisture content of the in situ soil, and the amount of drilling water.

  As shown in FIG. 4, a correlation was established between the cement water ratio of the test material and the compressive strength of the test material at the age of 28 days.

  Further, from this result, the relational expression (3) showing the correlation between the cement water ratio and the compressive strength indicates that if the cement water ratio is X and the compressive strength on Example 28 is Y, Y = 31.30X− It is shown at 18.35.

  For example, when the compressive strength is actually estimated at the construction site, the collected soil cement is kept warm, and the temperature change accompanying the hardening of the soil cement in the kept state is measured.

  And when the atmospheric temperature which stored the soil cement of the heat-retaining state is 10 degreeC, the maximum temperature of the measured temperature changes was substituted into Formula (1), the cement water ratio was calculated, and it heat-retained. When the ambient temperature at which the soil cement in the state is stored is 20 ° C., the maximum water temperature among the measured temperature changes is substituted into Equation (2) to calculate the cement water ratio.

  By substituting the cement water ratio calculated in this way into Equation (3) and calculating the compressive strength, the compressive strength of the soil cement in the root-solidified portion can be estimated.

  In addition, when the atmospheric temperature stored differs from the said Example, the relational expression which shows the correlation with the cement water ratio of the soil cement and the maximum temperature in the atmospheric temperature is calculated | required, and it applies. Further, when the ambient temperature is 10 ° C. or higher and 20 ° C. or lower, the cement water ratio may be obtained by interpolating Equation (1) and Equation (2).

DESCRIPTION OF SYMBOLS 1 Soil cement storage device 2 Form as container 3 Thermal insulation as heat retention means 4 Temperature measurement means

Claims (3)

A method for estimating the compressive strength of soil cement that constitutes the root of the pile embedding method,
Collect unsolidified soil cement from the root solidified part,
Keep the collected soil cement warm,
Measure the temperature change accompanying the hardening of the soil cement in the state of keeping the heat,
Using the maximum temperature of the soil cement from which this temperature change was measured, based on the relational expression showing the correlation between the maximum temperature at the time of hardening of the soil cement and the cement water ratio of the soil cement, Calculate the cement water ratio,
Using the calculated cement water ratio, the compressive strength of the soil cement in the solidified state of the root-solidified portion is calculated based on the relational expression showing the correlation between the cement water ratio of the soil cement and the compressive strength of the soil cement. A method for estimating the compressive strength of soil cement. The relational expression showing the correlation between the maximum temperature during hardening of the soil cement and the cement water ratio of the soil cement is
Keep the unsolidified soil cement or cement paste in different cement water ratios, respectively,
Measure the maximum temperature when curing soil cement or cement paste for each cement water ratio,
The method for estimating the compressive strength of soil cement according to claim 1, wherein the method is derived from each cement water ratio and each measured maximum temperature. A soil cement storage device for use in the method for estimating compressive strength of soil cement according to claim 1 or 2,
A container body that can store soil cement of the root solidified part collected when the pile is installed,
Insulation means for keeping the soil cement in the container warm,
A soil cement storage device comprising temperature measuring means for measuring a temperature change of the soil cement that hardens while being kept warm.

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