2:30 PM - 2:45 PM
[HTT20-04] Case study of P-wave velocity and dynamic elastic modulus in the bore hole according to the RQD of the boring core
Keywords:Rock Quality Designation, Dynamic elastic modulus, PS logging
When the bedrock is crushed, it may not be possible to prepare a specimen for laboratory testing even if the core can be collected by boring survey. On the contrary, even if a specimen can be prepared, the test result may not be appropriate to be treated as a representative value of the ground. Therefore, in this survey, the dynamic elastic modulus at 1m intervals was obtained by PS logging and density logging in the boring hole carried out to confirm the geological properties of the tunnel ground with volcanic rocks. In addition, the dynamic elastic modulus of the bore core specimens was obtained from the ultrasonic propagation velocity test and the density test. Then, RQD(10), which is an index showing the state of cracks in the core and is similar continuous data at 1m intervals, was compared with the values in the range of 0 to 30% and 60 to 100% with the dynamic elastic modulus in the bore hole. Furthermore, the relationship between the P-wave velocity and dynamic elastic modulus in the bore hole and the results of the laboratory test of the core was analyzed.
As a result of the investigation, first, the correlation coefficient between the P wave velocity in the bore hole and the dynamic elastic modulus was 0.91 at 0 to 30% for RQD(10) and 0.95 at 60 to 100% for RQD(10). The average P-wave velocity in the bore hole was 3.7 Km/s for RQD(10) at 0 to 30%, and 4.4 Km/s for RQD(10) at 60 to 100%. The elastic modulus in the bore hole was 23,100 MPa for RQD(10) 0 to 30%, and 38,000 MPa for RQD(10) 60 to 100%. Next, the P wave velocity of the core was 4.8 Km/s on average, the elastic modulus was 44,000 MPa on average, and the uniaxial compressive strength was 52.1 MPa on average. The average P-wave velocity in the bore hole in the 1m section where this core was collected was 4.8 Km/s, and the average dynamic elastic modulus was 45,000 MPa, which was close to the test result of the bore core. The ratio of the P wave velocity in the bore hole of 0 to 30% of 60 to 100% of RQD(10) is 0.83, and the ratio of the dynamic elastic modulus in the bore hole is 0.61. By correcting the strength, it can be used as an index for estimating the value in the section where the core specimen cannot be created and for continuously evaluating the state of shallow ground such as around the tunnel.
As a result of the investigation, first, the correlation coefficient between the P wave velocity in the bore hole and the dynamic elastic modulus was 0.91 at 0 to 30% for RQD(10) and 0.95 at 60 to 100% for RQD(10). The average P-wave velocity in the bore hole was 3.7 Km/s for RQD(10) at 0 to 30%, and 4.4 Km/s for RQD(10) at 60 to 100%. The elastic modulus in the bore hole was 23,100 MPa for RQD(10) 0 to 30%, and 38,000 MPa for RQD(10) 60 to 100%. Next, the P wave velocity of the core was 4.8 Km/s on average, the elastic modulus was 44,000 MPa on average, and the uniaxial compressive strength was 52.1 MPa on average. The average P-wave velocity in the bore hole in the 1m section where this core was collected was 4.8 Km/s, and the average dynamic elastic modulus was 45,000 MPa, which was close to the test result of the bore core. The ratio of the P wave velocity in the bore hole of 0 to 30% of 60 to 100% of RQD(10) is 0.83, and the ratio of the dynamic elastic modulus in the bore hole is 0.61. By correcting the strength, it can be used as an index for estimating the value in the section where the core specimen cannot be created and for continuously evaluating the state of shallow ground such as around the tunnel.