Abstract
Given that apparent differences exist between physical and mechanical properties of sandstone constituents under natural and saturated states, uniaxial and triaxial tests of sandstone specimens taken from a deep tunnel in Chongqing under the two states were, respectively, conducted in the laboratory. Analysis on the energy conversion of sandstone constituents under natural and saturated states reveals the varying strain energy conversion mechanisms under the two different conditions. It shows that water saturation has significant effects on the strength and deformation characteristics of sandstone constituents. The load bearing capacity and nondeformability decrease once the sandstone constituents are saturated. The strength weakening due to water in saturated specimens mainly takes place after the dilatancy stressσcdand reaches its maximum at the peak stressσf. Strain energies of sandstone constituents under the saturated state are lower than those under the natural state, which indicates that water reduces the strain energy absorption. The strain energy of specimens at the peak stress point under the two states has a good linear positive correlation with the confining pressure. Moreover, the fitting curve of the case under the natural state has a higher slope, which means that the strain energy under such state is more sensitive to the confining pressure than that under the saturated state.
Highlights
Extensive tunnel projects, where issues related to underground water often strike negative impacts on the construction, such as water inrush and water burst [1,2,3], have been built along with the vigorous development of the highspeed railway, high way, and subway in China
Vasarhelyi and Van [6] found that water saturation of 1% could greatly decrease the rock strength and they attempted to propose a method to evaluate the sensitivity of sandstones to water saturation based on the published data
Saturated state II-1 II-2 II-3 138.26 148.53 146.75 111.75 112.89 121.17 26.51 35.64 25.58 (1) The deformation and damage process of sandstone specimens under natural and saturated states can both be divided into five regions: the crack closure region (O-A), elastic region (A-B), stable crack growth region (B-C), crack calescence region (C-D), and postpeak region (D-E) [23, 24], and the specimens under the two states both exhibit brittleness in the postpeak region while the brittle characteristic is more obvious under the saturated state
Summary
Extensive tunnel projects, where issues related to underground water often strike negative impacts on the construction, such as water inrush and water burst [1,2,3], have been built along with the vigorous development of the highspeed railway, high way, and subway in China. Based on the studies mentioned above, it is safe to say the researches focusing on the mechanical characteristic differences existing at each stage of the rock deformation and failure processes between sandstones under natural and saturated states are relatively insufficient. Different changes have happened to the mechanical properties of natural and saturated sandstones involved in the construction, long before geological hazards, such as rock mass instability and water burst, occur in the underground projects, like tunnels. Previous studies on rocks with different water contents mainly focused on the change of physical properties and rarely analyzed the difference in view of energy conversion. The essential reasons behind the differences between physical and mechanical characteristics of rocks with different water contents reflected in the uniaxial and triaxial tests can be revealed based on the principles of energy conversion [19]. The findings of this research are of engineering significance to the stability evaluation and prediction of underground evacuation, such as tunnels, and guidance are offered for the design, construction, and hazard control of the project
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