Abstract
In this study, a test technique that enables continuous control of the sample stress state from freezing to testing is proposed to investigate the influence of freezing pressure on the mechanical properties of ice under uniaxial compression. In this method, the water is frozen into the standard cylindrical ice specimen under high hydraulic pressure in a triaxial pressure chamber, and then, the temperature field and stress field of the ice specimens are adjusted to the initial state of the test; finally, an in situ mechanical test is conducted in the triaxial chamber. The uniaxial compression test of ice specimens with temperature of −20°C and freezing pressure of 0.5–30 MPa is performed in the strain rate range of 5 × 10−5−1.5 × 10−6 s−1. The results show that, as the freezing pressure increases, the ductile-to-brittle transition zone of the ice specimen during failure moves to the low strain rate range, and the failure mode of the specimen changes from shear failure to splitting failure. Further, the brittleness index of the ice specimen first increases, then decreases, and then again increases with the increase in freezing pressure. The brittleness index reaches the maximum (minimum) when the freezing pressure is 30 MPa (20 MPa). The peak stress of the ice specimen also increases first, then decreases, and then increases with the increase in freezing pressure. The maximum value is also at the freezing pressure of 30 MPa, but the minimum value is obtained at the freezing pressure of 0.5 MPa. The failure strain of the ice specimen first decreases and then increases with the increase in freezing pressure, and the maximum (minimum) value is achieved at the freezing pressure of 0.5 MPa (10 MPa). When the ice specimen exhibits brittle failure, the relationships between the residual stress and the freezing pressure and between the peak stress and freezing pressure are the same, but when the ice specimen exhibits ductile failure, there is no obvious relationship between the residual stress and the freezing pressure.
Highlights
Artificial ground freezing method is the most important construction method to stabilize the ground and prevent groundwater ingress during excavation
Results and Discussion e stress-strain curves for all the 32 groups of tests are classified and summarized according to the freezing pressure in Figure 7. e test conditions and characteristic results corresponding to each curve are shown in Table 1. e curves with the same test conditions are represented in the same color, and the two repetitions are distinguished by different markers
(2) e failure modes of ice specimens changed from shear failure to splitting failure with the increase in the freezing pressure. e influence of freezing pressure on the failure characteristics of ice specimens was similar to that of low temperature, and the ductile-brittle transition zone moved to a slow strain rate range
Summary
Artificial ground freezing method is the most important construction method to stabilize the ground and prevent groundwater ingress during excavation It allows the penetration of deep, unstable, and water-bearing strata containing sands, silts, and clays. Due to the influence of high pressure in the deep environment, there are still many difficulties in drilling and coring in deep permafrost layer [6]. To solve these problems, the mechanical properties of deep frozen soil [7,8,9] and frozen rock [10, 11] have been experimentally investigated, but the research on the coupling problems of ice-soil and ice-rock, which are based on the mechanical properties of deep-environment ice, is not Advances in Civil Engineering mature. Compared with the shallow layer conditions, the deep formation pressure increases significantly [12,13,14], and the freezing pressure of the deep groundwater can exceed 10 MPa due to the high pressure and the limit on the formation of frost heaving. erefore, it is of great significance to examine the influence of freezing pressure on the mechanical properties of ice
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