# Triaxial Loading and Unloading Tests on Dry and Saturated Sandstone Specimens  
[PERSON]  
1 School of Resources and Safety Engineering, Central South University, Changsha 410083, China; [EMAIL_ADDRESS] (D.L. ); [EMAIL_ADDRESS] (Z.S. ); [EMAIL_ADDRESS] (Q.Z.) [PERSON]  
1 School of Resources and Safety Engineering, Central South University, Changsha 410083, China; [EMAIL_ADDRESS] (D.L. ); [EMAIL_ADDRESS] (Z.S. ); [EMAIL_ADDRESS] (Q.Z.) [PERSON]  
1 School of Resources and Safety Engineering, Central South University, Changsha 410083, China; [EMAIL_ADDRESS] (D.L. ); [EMAIL_ADDRESS] (Z.S. ); [EMAIL_ADDRESS] (Q.Z.) [PERSON]  
2 State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China 23 College of Resources and Environmental Science, Chongqing University, Chongqing 400044, China 35 Correspondence: [EMAIL_ADDRESS]; Tel. : +86-159-7426-9965 23334  
was found a negative exponential relationship between rock strength and moisture content [10]. Meanwhile, [PERSON] et al., [11] conducted the triaxial compression tests and found that the internal friction angle decreases while the cohesion increases when the meta-sedimentary rocks was saturated by water. Most of previous related studies were focused on the influence of water on the uniaxial or conventional triaxial strength of rocks [5; 6; 7; 10]. However, few experimental and numerical studies are reported to discuss the effect of water content on the strength and deformability of the rocks under triaxial stress conditions [12; 13; 14]. In the practical engineering, the existence of groundwater not only affects the mechanical properties of rock, but also influences the damage degree and even the failure mode of the rock [15]. [PERSON] et al. [16] investigated the effects of water and joints on the properties of rock masses using the data from the Shirengou iron mine. Their numerical simulation results indicated that water is the critical factor for rock damage pattern. Several scholars also conducted experiments on deep rock and successfully showed a layered failure for saturated rock in tensile tests [17]. Spalling behaviors were studied in pure-triaxial unloading conditions and scanning electron microscope (SEM) observations revealed the distribution of microcracks in the fragments [18]. Besides, there are many studies related to rock uniaxial compression and tensile failure affected by water [19; 20; 21; 22]. The deformation and failure of rock are energy-driven processes which include energy absorption, evolution, dissipation, and release [23; 24; 25; 26]. Based on uniaxial and triaxial compression tests, [PERSON] and [PERSON] [27] studied the characteristics of rock energy evolution during unloading failure and concluded that the strain energy stored in rock material is sufficiently large to cause failure when it is released. Furthermore, water injection to reduce rockburst occurrences has also been discussed mainly on numerical simulation [28; 29; 30], and partially for experiments [2; 31]. The numerical modeling showed that the peak stress can be reduced as water injection, which causes a significant reduction of internal energy stored within the rock, and the possibility of a rockburst occurrence may be reduced [28]. Moreover, the effects of water on rock energy evolution have also been studied [32; 33; 34; 35; 36; 37], though it mainly concerns on uniaxial compression [34; 35] and axial loading-unloading experiments [32; 33; 36; 37]. Undoubtedly, the above study enriches our knowledge of the effect of water on rock failure and energy evolution. However, there are a few studies concern on the effect of water on rocks under triaxial tests, especially for the influence of unloading high confining pressure conditions, which represents a more realistic site environment.