Received 20 July 2009; accepted 17 October 2009 *Corresponding author. Tel: 86 13775972665 E-mail address: gaoyanan_23@126.com doi: 10.1016/S1674-5264(09)60181-2 Visco-elastic-plastic model of deep underground rock affected by temperature and humidity GAO Yanan 1,2,3,* , GAO Feng 1,2 , ZHANG Zhizhen 1,2 , ZHANG Tao 1,2 1 School of Sciences, China University of Mining & Technology, Xuzhou 221008, China 2 State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221008, China 3 College of Engineering, California State Polytechnic University, Pomoa CA 91768, USA Abstract: As the depth of exploitation increases, studies on constitutive models of rock affected by temperature and humidity be- come very important. Based on the Nishihara model, a visco-elastic-plastic rock model was established by using the coefficients of thermal and humidity expansion, thermal viscosity attenuation, humid viscosity attenuation and acceleration rheology components. We used the definition of a controlled heat circle to explain the model. The results show that the behavior of rock, affected by tem- perature and humidity, is stable as a function of time when the stress is lower than the first yield stress σ S1 ; the creep rate will in- crease due to the effect of temperature and humidity when the stress is greater than or equal to σ S1 ; the creep rate will accelerate at an increasing rate when the stress is greater than or equal to the second yield stress σ S2 , which results in a failure of the roadway. The model derived in this study can completely describe visco-elastic-plastic characteristics and reflects the three stages of rock creep. Keywords: temperature; humidity; creep; controlled heat circle 1 Introduction During the process of deep underground mining, deformation of rock is significantly affected by high temperature and humidity, caused by cooling water. In deep underground engineering, the behavior of rocks under the effect of temperature and humidity has been the focus of research by both domestic and foreign scientists, who carried out a number of stud- ies on the subject. An experimental study on the me- chanical properties of granite concerning temperature and time was carried out by Liu et al., who formu- lated a mechanical model of the uniaxial stress-strain relationship of granite and derived an empirical for- mula of cohesion changing over time and with tem- perature [1] . A stable creep constitutive equation of bedded rock salt was derived by Xi et al. by fitting experimental data [2] . Wei et al. used a component that can describe the acceleration creep to investigate the visco-elastic behavior of rock under pore pressure [3] . Based on a seepage field and coupled stress field case in engineering rock mass, a study by Zhang et al. led to the formation of a similarly coupled solid-liquid material to model water seepage in a fractured rock mass and obtained rules of rock failure under seep- age [4] . Their results were consistent with those ob- tained from in-situ tests. Coupled Thermo-Hydro- Mechanical (THM) issues relating to the design and performance of nuclear waste repository were re- viewed and discussed by Hudson et al [5] . Zhang made a 2D numerical analysis of unsaturated media under a THM coupled process [6-8] . Neaupane et al. studied the THM model under freezing condition and an elastic range based on a Liquefied Natural Gas (LNG) prob- lem [9] . This model was also used for an application in numerical simulation concerned with the phase change of void water. Consolidated undrained tri- axial tests on specimens of diatomaceous soft rock were carried out by Liao et al. under different pres- sures and loading rates, stress and strain con- trolled [10] . Their test results show that the diatoma- ceous soft rock has an obvious strain rate effect. Gao et al. established and studied a model using compre- hensive consideration of visco-elastic and damage characteristics [11] . But all of these studies either con- cerned the TM/HM coupled process without creep behavior, especially the acceleration of creep, or were only concerned with creep behavior. In this study, we considered the effects of temperature and humidity in Mining Science and Technology 20 (2010) 0183–0187 MINING SCIENCE AND TECHNOLOGY www.elsevier.com/locate/jcumt