Flat TDR을 이용한 현장 지반의 물리적 특성 및 전단파속도 예측

Abstract

Recently, some studies using non-destructive testing, a fast and economical method to complement traditional quality control testing of compaction in the design using Time Domain Reflectometry (TDR) have been performed as a method to minimize ground disturbance. And it has been developed jointly the Flat TDR, an equipment, using a flat probe has been developed to measure quickly the natural water content and dry unit weight of the ground through the ground surface without disturbing the ground. In addition, to improve the performance of the existing TDR equipment, which has been limited only to measurement of dry unit weight and natural water content, a study on ground stiffness measurement through shear wave signal analysis using the shear seismic wave measuring device mounted in the equipment was also conducted. The sample ground was a total of six sites: one in Hampyeong, one in Damyang, one in Boseong, two in Naju, and one in Haenam. The Flat TDR results of eight sample sites previously performed in the laboratory were compared and analyzed with those of this study. The laboratory tests such as TDR compaction test and water content measurement, and field tests such as TDR field measurement test, field density test, and dynamic cone penetration test were performed. The results of laboratory tests showed the error range of 0.3-1.0% for water content and 0.1-2.1% for dry unit weight, suggesting that water content and dry unit weight measured through TDR measurement management are reliable. The results of field tests showed the error of 0.8% for water content and 2.5% for dry unit weight between real value measured through field density test and those measured by TDR system, suggesting that Flat TDR system may be used very usefully in managing the compaction management. The results of the field density test and the dynamic cone penetration test show that a higher degree of compaction correlates with the higher values of shear modulus measured in the higher Nd and TDR systems in the dynamic cone penetration test, indicating that the shear modulus measured by the TDR system is a satisfactory index to evaluate the stiffness of the ground. In addition, the shear modulus analysis result according to the arrival time of the shear elastic wave showed that the shortest arrival time (0.2914 msec) at the Naju#1 site was measured in the case with the highest shear wave velocity (171.59 m/s) and shear modulus (46.87 MPa) and that the longest arrival time (0.3814 msec) at the Hampyeong site was measured in the case with the lowest shear wave velocity (131.10 m/s) and shear modulus (26.60 MPa), indicating that the arrival time and shear wave velocity, shear modulus have negative relationship and that the shear wave velocity measurement of the TDR measuring equipment is sufficient to confirm the shear modulus. In addition, the shear modulus tendency according to the water content of in six sites was compared and analyzed with the compaction curve. The results showed that the shear modulus according to the water content showed a similar pattern to that of the compaction curve, indicating that the higher degree of ground compaction is correlated with higher elastic modulus.