An example of estimating rock mass deformation around an underground opening using numerical modeling

Abstract

In rock engineering, rock strength is regarded as an important rock mass parameter and it is widely estimated using the uniaxial compressive strength ( UCS) test. A UCS test in laboratory requires sampling and preparation of core samples, which necessitates time consuming and expensive studies. Furthermore, preparation of cores is almost impossible for a weak rock material taken from foliated, laminated or thinly bedded rock masses of low Rock Quality Designation (RQD) values (0–20%). In this case, determination of UCS by laboratory test may be impossible in compliance with ISRM or ASTM standards. To overcome this difficulty, indirect tests, such as Point Load Index ( PLI), Schmidt Hammer ( SH) Rebound Number tests are often employed to predict the UCS. However, indirect tests are likely to yield UCS values with large standard deviations depending on the geological origin of the rock mass. The Block Punch Index ( BPI) has recently been developed to overcome the drawbacks of UCS and indirect tests and to minimize the errors arisen from the structural deficiencies and large standard deviations. In this study, determination of rock mass behavior in laminated–foliated Bornova Melange (yellowish-brown flysch and grayish-black flysch) and well-jointed Yamanlar Volcanics–Altindag Formation, where the second phase of the Izmir Metro tunnels was excavated is aimed. The BPI ratings were directly used in RMR calculations and indirectly used to estimate the UCS values of rock materials. Then, the obtained results were input into numerical models along with the rock mass strength ( UCS RM ) and deformation modulus of rock mass ( E RM ). The results obtained from the numerical models agreed with that obtained results from inner tunnel convergence and ground settlement measurements.