흙의 지반공학적 특성 평가를 위한 비파괴 측정 시스템 개발

Abstract

Soil compaction is very important in construction site of the road and railroad. Field compaction control is to check whether or not the geomaterials meet the minimum acceptable dry density, water content, and elastic modulus. Because of this, dry density, water content, and elastic modulus are important factors affecting the degree of soil compaction. Conventional method such as the sand cone test and the plate load test are used to measure those properties. However, this method may cause some errors depending on the operator, and was the destructive testing method at surface of the soil. In order to solve this problem, the TDR(Time Domain Reflectometry) system was developed in abroad and has been studied continuously by foreign researchers. However, it requires driving the rod probes into the ground, and is still a destructive testing method. This study aims to develop a non-destructive TDR system that can measure the dry density, water content, and elastic modulus without disturbing and destruction the surface of the soil. Therefore, in this study, a new TDR system equipped with a flat type probe has been developed to improve the currently used TDR system that measures the dry density and water content. In order to verify the developed TDR system, TDR tests were conducted on Jumunjin sand and three typical sandy soils. Also, additional tests, to seek relational equation between electrical conductivity and long term voltage level, were performed to measure the correction value of the developed probe. Using the TDR signals, dielectric constant, electrical conductivity, and soil constants were derived. Therefore, the dry density and water content of the soils were determined through the TDR tests. Also, in this study, the Piezoelectric stack, which is an instrument for measuring the elastic modulus of soil, has been added to the TDR system with a flat type probe. And then, elastic modulus variation of reinforced soil with time was determined by using the TDR system. The applicability of the TDR system was examined by comparison of the measured values by TDR and the real values. The values of dry density and water content were found to have about 2% and 0.5% error, respectively. Also, the values of compression and shear modulus increased from 198.65MPa to 541.80MPa and from 125.55MPa to 302.02MPa with time, respectively. Based on the test results, it has been confirmed that the new TDR system can be used as an alternative to the previous TDR system as it can measure the dry density, the water content, and the elastic modulus with reasonable accuracy, leading to significant time and cost savings. Consequently, it appears that the developed TDR system will be very useful to advance the current practice of compaction control.