Time-dependent response of rock around tunnels

PROPERTIES:TIME DEPENDANCE 943117 Rock mechanics in the 1990s: hydraulic fracturing for enhanced rocovery ed B. C. Haimson, International Journal of Rock Mechanics and Mining Sciences, 30(7), 1993, pp 1231-1279. These p.apers were originally presented at the 34th US Symposmm on Rock Mechanics, June 1993.9 papers are presented on the following topics: modelling o f propagation and closure of mierohydranlic fractures: crack reopening behaviour for hydrofrac stress measurements; inelastic rocks behaviour in hydraulic fracturing; performance improvement of open hole stress tools; effects of solution chemistry during rock fracture; rock dilatancy near the tip of a propagating hydraulic fracture; 3 D hydraulic fracture numerical simulation using Newtonian and power-law fluids; and shallow hydraulic fracture incremental growth from inversion of elevation changes. -R.Gower 943118 Rock mechanics in the 1990s: stochastic methods in rock engineering ed B. C. Haimson, International Journal of Rock Mechanics and Mining Sciences, 30(7), 1993, pp 1605-1637. These papers were originally presented at the 34th US symposium on Rock Mechanics, June 1993.5 papers cover the following topics: modelling transient flow m hard fractured rocks with discrete failure network; fracture size estimation through simulated s .amjpling; zeroth order statistical modelling of fracture in rock m compression; probabilistic slope analysis for structural failure; and spatial simulation of rock strength properties using a Markov-Bayes method. -R.Gower 943119 Rock mechanics in the 1990s: acoustic emission and failure prediction ed B. C. Haimson, International Journal of Rock Mechanics and Mining Sciences, 30(7), 1993, pp 883-950. These papers were originally presented at the 34th US symposium on Rock Mechanics, June 1993. 10 papers form this section, with the first exploring the role of acoustic emission in rock fracture. Others papers examine: microcrack damage assessment; hydraulic fracturing mechanisms; precursory pressure anomalies prior to coal mine failures; microseismic activity prior to a mountain bump; rock fracture development from microfracturing; the Kaiser effect; anisotopic crack damage and stress-memory effects under triaxial loading; rock damage assessment using the Kaiser effect; and a theoretical examination of b-value attenuation in acoustic emissions. -R.Gower 943120 SEM study of fracture development in a compressed marble specimen and implications for earthquake precursors Zhao Yong-Hong, Huang Jie-Fan & Wang Ren, Acta Geophysica Sinica, 36(4), 1993, pp 453-462. Uniaixal compression tests of marble plates each containing a slot were conducted under direct SEM observation. The initiation, propagation, plan distribution and coalescence of cracks on the speennen surface were monitored through the whole test process. From the microphotographs taken at different stages of loading, the opening and closure of microcracks in the frontier area of a propagating fracture were studied, and the variations of fracture width with the loading level and with the position of measuring point were analysed. The concept o f using a scalar as the damage parameter in rock damage mechanics was put forward and the possible significance of the test results for understanding various earhquake precursors, such as crustal deformation and groundwater anomalies, etc., was investigated. -from English summary 943121 F r a c t a l dimension of main fractures of marble under different experimental conditions Li Biao, Ma Shengli & Zhang Liu, Seismology & Geology, 15(2), 1993, pp 157-163. Marble s a~nl?les were deformed in triaxial compression under confining pressures from I0 to 60 MPa. The fractal dimension of mare fractures is calculated and analysed. D value does not change with sample size when the environment and material conditions are the same. As confining pressure increases, D value decreases below 35 MPa and

137A

increases above 35MPa, suggesting that when fractal geometry of fault traces is analysed in field, the environmental conditions in which the fault is formed and the possible change with depth should be considered. -from English summary

Time dependent behaviour 943122 Mechanisms a n d consequences of creep in crystalline rock R. Pusch, in: Comprehensive rock engineering. Vol. 1, ed LA. Hudson, (Pergamon), 1993, pp 227-241. This chapter reviews the general character of creep in rock. It then considers creep as a stochastic process, looking at temperature effects, creep mechanisms and their associated empirical laws, and rate process theory. Creep measurement is detailed for laboratory and field settings, and finally the practical significance of creep is analysed in terms of failure potential. -R.Gower 943123 Rock rheology N . D . Cristescu, in: Comprehensive rock engineering. VoL 1, ed J.A. Hudson, (Pergamon), 1993, pp 523-544. Rheological properties in this chapter are considered as time dependent properties and study the slow deformation of rocks subjected to various loadings. Volumetric deformation, elastic/viscoplastic constitutive equations and linear viscoelasticity are detailed. Rock creep around horizontal tunnels and tunnel support analysis are given for underground excavation and safety. -R.Gower 943124

Time-dependent response of rock a r o u n d tun-

nels

B. Ladanyi, in: Comprehensive rock engineering. Vol. 2, ed J.A. Hudson, (Pergamon), 1993, pp 77-112. This chapter deals only with the tire dependence of the tunnel lining pressure caused by the time-dependent response of the surrounding ground. Its main purpose is to show the present state of knowledge on the rheological behavior of rocks and rock masses and its effects on the design of tunnel linings by analytical and numerical methods. As the pertinent literature on such methods is extremely extensive, only some typical analytical solutions and numerically solved tunneling problems, based on various theological models, will be shown in this chapter. -from Author 943125 The creep of potash salt rocks from Saskatchewan E. J. S. Duncan & E. Z. Lajtai, Geotechnical & Geological Engineering, 11(3), 1993, pp 159-184. The results of creep tests on the Esterhazy- and the Patience-Lake-types of potash salt rocks from Saskatchewan, Canada are presented. Since the yield stress of both types of potash lies between 9 and 11 MPa, there is very little creep below 11 MPa. Between 11 and 13 MPa, creep strain production increases sharply through plastic deformation. Above about 13 MPa, however, plastic creep is dominated by brittle creep caused by microcracking. As a result, the lateral and volume creep strain curves may then display the transient and the steady-state, or all three stages of creep, while the axial strain, which is not affected by microcracking, usually attenuates for the whole duration. Two different interpretations of the results are offered. -from Authors 943126 Analysis of delayed failure in sloping excavations D. ¥. Griffiths & C. O. Li, Journal of Geotechnical Engineering- ASCE, 119(9), 1993, pp 1360-1378. The paper describes a finite element technique that takes account of transient effects through a Blot analysis, enabling coupling of pore pressure variations to a nonlinear soil stress-strain law. The technique is applied to the transient stability of excavated soft slopes. Long-term instability is modeled by allowing the pore suctions, initially generated by the excavation process, to dissipate. For the slope under analysis, the coefficient K o is seen to have a significant influence on the undrained (short-term) factor of