南宁地铁区域饱和圆砾土大型动三轴试验研究

Large-scale dynamic triaxial tests on saturated gravel soil in Nanning metro area

以南宁地铁区域圆砾层土质为研究对象,对饱和状态下的圆砾土开展了一系列大型排水动三轴试验,分析了相对密实度、动应力幅值和振动次数对饱和圆砾土累积应变、应力–应变滞回圈和孔压的影响。研究表明,饱和圆砾土累积轴向应变?–振动次数N曲线在动应力幅值较小时为稳定型曲线,呈双曲线增长规律,其参数?与初始相对密实度Dr呈线性关系;动应力幅值较大时为破坏型曲线,呈幂函数增长规律。饱和圆砾土应力应变滞回圈形状呈双直线型,其面积在动应力幅值较小时随着振动次数的增加先增大后减小,其割线模量随着振动次数的增加先减小后增大。饱和圆砾土的孔压在动应力幅值较小时随着振动次数的增加先增大再减小,且循环加载后期Dr=0.5试样的孔压大于Dr=0.3和Dr=0.7试样的孔压,这与不同初始相对密实度条件下粗粒土的破碎特性有关。

The gravel soil in Nanning metro area is taken as the research object, and a series of large-scale drained dynamic triaxial tests are conducted on saturated gravel. The effects of the relative density, dynamic stress amplitude and number of loading cycles on the accumulation strain, stress-strain hysteresis loops and pore pressure of saturated round gravel are analyzed. The experimental results show that when the dynamic stress amplitudes are small, the curves of accumulated axial strain with number of loading cycles are stable with the increasing rule of hyperbolic function. A linear relation between the parameter α in the hyperbolic function and the relative density Dr is found. However, the curves exhibit failure type and the increasing rule conforms to power function under a large dynamic stress amplitude. The stress-strain hysteresis loops of saturated round gravel exhibit double-lined type. When the dynamic stress amplitude is small, with the increasing number of loading cycles, the area of hysteresis loops firstly increases and then decreases, the secant modulus firstly decreases and then increases, and the pore pressure firstly increases and then decreases. In the later period of cyclic loading, the pore pressure is high when Dr=0.5 in comparison to the situation Dr=0.3 or 0.7, and this result relates to the gravel breaking characteristics at different initial relative densities.