模拟人工冻结凿井状态下冻土强度特性研究

Study on the Strength Characteristics of Frozen Soil in Artificial Freezing Sinking

通过模拟人工冻结凿井中冻土冻结、受力的实际过程 ,对已冻结试样进行不同温度、不同初始围压状态下的减载试验研究 .结果表明 :温度和土层深度是影响深部冻土破坏强度和破坏应变的主要因素 ,当温度不变时 ,破坏强度和破坏应变随初始围压呈线性关系变化 .破坏强度受温度的影响取决于初始围压 ,在低初始围压状态下 ,冻土的破坏强度受温度变化影响不明显 ,但随着初始围压增大即土层深度加深 ,破坏强度受温度的影响也逐渐明显 .破坏应变随温度的降低而逐渐减小 ,且呈双曲线形变化 ,但当温度低于 - 7℃时 。

With the developing of civil engineering in permafrost regions, frozen soil mechanics have been made great progress in solving general problems in foundation engineering. However, the availability of these theories is still inappropriate to solve the problems in the artificial freezing shaft, because the forming process of artificial frozen soils is different from that of natural frozen soils. The natural frozen soil is formed under frigid climate without pressure, while the artificial frozen soil is formed by artificial refrigerating method with higher loading. In order to simulate the actual freezing and loading process of frozen soil in artificial freezing shaft, experiments on loess were carried out under an artificial controlling condition in laboratory. First, a series of standard soil samples were taken into a pressure chamber to conduct the \%K\%\-0 consolidation test, then let the temperature drop down to a certain degree, and hold it for 20 h, at last, kept the axial pressure constant and unloaded the confining pressure. The following conclusions can be drawn. The subfreezing temperature and soil depth are the main factors which strongly affect the failure strength and the failure strain of the frozen soil in artificial freezing shaft. The failure strength and the failure strain increase monotonically with the increasing initial confining pressure. Their relations can be described by formulas: \%(σ\-1-σ\-3)\%\-f=\%k\-1σ\-3+c\-1\% and \%ε\%\-\{1f\}=\%k\-2σ\-3+c\-2\%, where \%k 1 ?c 1 ? k 2 \%and\% c\% 2 are empirical parameters. The relationship between failure strength and temperature is determined by initial confining pressure. The failure strength is not responsible to the subfreezing temperature at the lower initial confining pressure, but it obviously responds to the subfreezing temperature when it becomes higher. Failure strain depends on temperature fluctuation at any confining pressure. The failure strain in the test decreases with temperature decreasing and presents hyperbola-shaped tendency. At different initial confining pressure, the influence of temperature fluctuation on failure strain is less at the temperature below-7 ℃,and the quadratic equation \%(ε\-\{1f\}=Aθ\+2+Bθ+C\% ) can be used to describe the relationship between failure strain and temperatures fluctuation, where θ is temperature in ℃, \%A, B\%and \%C\%depend upon initial confining pressure.