Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Estimation of Deformation Modulus of Basaltic Rock Masses in Northeastern and Northwestern Jeju Island

제주도 북동부 및 북서부 현무암반의 변형계수 추정

  • Yang, Soon-Bo (Port and Airport Research Institute, National Institute of Maritime, Port and Aviation Technology) ;
  • Boo, Sang-Pil (Yonung Engineering & Construction)
  • 양순보 (일본 국립연구개발법인 해상.항만.항공기술연구소 항만공항기술연구소) ;
  • 부상필 ((주)연웅 E&C)
  • Received : 2018.10.01
  • Accepted : 2019.01.11
  • Published : 2019.01.31
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Abstract

In this study, the in situ deformation moduli, which were measured by borehole loading tests at basaltic rock masses located in the northeastern onshore and offshore and the northwestern onshore of Jeju Island, were examined in relation to RQD and RMR. The measured deformation moduli were also compared with the estimated deformation moduli from conventional empirical formulas using RQD and RMR. In addition, the measured deformation moduli were analyzed with respect to both the velocity ratio ($V_P/V_S$) and dynamic Poisson's ratio, which were obtained from the elastic wave velocities measured by velocity logging tests. As results, with only RQD, it was inappropriate to evaluate the quality of the Jeju island basaltic rock masses, which are characterized by vesicular structures, to select a measurement method of in situ deformation moduli, and to estimate the deformation moduli. On the other hand, it was desirable to evaluate the quality of the Jeju Island basaltic rock masses, and to estimate the deformation moduli by using RMR. The conventional empirical formulas using RMR overestimated the deformation moduli of the Jeju Island basaltic rock masses. There was qualitative consistency in the relation between velocity ratio and deformation moduli. To estimate appropriately the deformation moduli of the Jeju Island basaltic rock masses, empirical formulas were proposed as the function of RMR and velocity ratio, respectively.

본 연구에서는 제주도 북동부 육 해상 및 북서부 육상에 위치한 현무암반에 대한 공내재하시험으로부터 계측된 변형계수와 RQD 및 RMR의 관계를 각각 살펴보았으며, 기존의 경험식들로부터 추정된 변형계수 값과 비교 분석하였다. 뿐만 아니라, 속도검층시험을 통하여 산정된 탄성파 속도비 및 동적 포아송 비와 변형계수의 관계에 대해서도 각각 살펴보았다. 그 결과, 다공성 구조 및 층상 구조가 특징인 제주도 현무암반의 경우, RQD 값만을 이용한 암반등급의 결정, 변형계수 계측방법의 선정 및 변형계수의 추정은 부적절하며, 최소한 RMR을 통하여 암반등급을 결정하고, 변형계수를 추정하는 것이 바람직하다는 것을 알 수 있었다. RMR을 이용한 기존의 변형계수 추정식은 제주도 현무암반의 변형계수에 비해 큰 값을 예측하는 경향을 보였으며, 탄성파 속도비 및 동적 포아송 비와 변형계수는 서로 정성적인 특성이 일치하는 관계에 있었다. 그리고, 적절한 제주도 현무암반의 변형계수를 추정하기 위한 RMR과 탄성파 속도비를 이용한 변형계수 추정식을 각각 제시하였다.

Keywords

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Fig. 1. Location of the boring areas

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Fig. 2. Depth distributions of elastic wave velocities, velocity ratios and RQD obtained at the borehole JB-01

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Fig. 3. Relation between P-wave velocity (VP) and S-wave velocity (VS) obtained from Down-hole seismic test and Suspension PS logging test at the borehole JB-01

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Fig. 4. Comparison between the velocity ratios (VP/VS) obtained from Down-hole seismic test and Suspension PS logging test at the borehole JB-01

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Fig. 5. Relation between velocity ratio (VP/VS) and RQD at the borehole JB-01

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Fig. 6. Relation between velocity ratio (VP/VS) and RQD

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Fig. 7. Relation between deformation modulus Em and RQD; EM:Elastmeter, GJ: Goodman Jack, PM: Pressuremeter

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Fig. 8. Relation between Em /Ei and RQD; Em : Deformation modulus of rock mass, Ei : Elastic modulus of intact rock, EM:Elastmeter, GJ: Goodman Jack

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Fig. 9. Relation between RMR and deformation modulus Em ; EM:Elastmeter, GJ: Goodman Jack

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Fig. 10. Relation between deformation modulus Em and velocity ratio (VP/VS); EM: Elastmeter, GJ : Goodman Jack

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Fig. 11. Relation between deformation modulus Em and dynamic Poisson's ratio νd; EM: Elastmeter, GJ: Goodman Jack

Table 1. Results of t tests for Y-intercepts and slopes of the linear approximations between velocity ratio (VP/VS) and RQD, which were indicated in Fig. 5

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Table 2. Results of physical and mechanical properties of the basaltic intact rocks, and in situ deformation modulus and RQD of the basaltic rock masses of Jeju Island

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Table 3. Rock mass ratings using the RMR system (Bieniawski, 1989) for the basaltic rock mass in the northeastern onshore of Jeju Island

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Table 4. List of empirical correlations for estimating the rock deformation modulus with RMR

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