鄂尔多斯红色砒砂岩干湿循环作用下力学性能试验研究

为了分析鄂尔多斯市准格尔旗不同粒径砒砂岩的力学性能,进行不同干湿循环次数试验,得到了砒砂岩收缩变形和强度特性的变化规律.结果表明:<2.00 mm(原状砒砂岩)试样在3次干湿循环后收缩变化最大;0.50~1.00 mm试样一直缓慢收缩沉积;0.25~0.50 mm和<0.25 mm试样在第3次循环后土体的密实度达到最强.在此基础上,利用直剪仪测定其抗剪强度.在相同的垂直荷载下,发现<2.00 mm试样随着循环次数的增大,1~3次循环的过程中抗剪强度增加最大,之后小幅度增加;0.50~1.00 mm试样随循环次数的增加呈现出缓慢增长的趋势;0.25~0.50 mm和<0.25 mm试样随着循环次数的增加而先略有降低,之后稍有增加并逐渐保持稳定.砒砂岩内摩擦角变化,<2.00 mm和0.50~1.00 mm粒径随干湿循环次数增加而递增;而0.25~0.50 mm和<0.25 mm粒径内摩擦角几乎不变化.黏聚力变化,<2.00 mm 和0.50~1.00 mm试样呈现出先增大逐渐平缓的趋势;0.25~0.50 mm和<0.25 mm试样呈现先减小随后小幅度增大的趋势.

Experimental study on mechanical properties of red Pisha-sandstone under wet-dry cycles in Ordos

In order to analyse the mechanical properties of red Pisha-sandstone, the Pisha-sandstones with different particle sizes(<2 mm, 0.50-1.00 mm, 0.25-0.50 mm, and < 0.25 mm)in Jungar Banner, Ordos City, were tested with various dry-wet cycles(1, 3, 5, 7, 9), and the shrinkage deformation and strength characteristics of sandstone were obtained. Results show that the biggest shrinkage is reached after 3 dry-wet cycles for the Pisha-sandstone with < 2 mm particle size(original sandstone), for the sandstone with 0.50-1.00 mm particle size, however, its samples keep a slow contracting deposition. Interestingly, for the sandstone with < 0.25 mm particle size, the soil compactness achieves the maximum value at the 3rd cycle. On this basis, a direct shear device is applied to determine the shear strength of Pisha-sandstones. Under the same vertical load, the shear strength of the stone sample with <2 mm particle size increases with increasing number of cycles, but the maximum increment in the strength is exhibited in 1-3 cycles, and then the strength get large slightly. The shear strength of the sample with 0.50-1.00 mm particle size rises slowly and steadily with increasing number of cycles. The shear strength of the samples 0.25-0.50 mm and <0.25 mm particle sizes decreases a little initially then increases a bit and finally becomes saturated.. For the samples with <2 mm and 0.50-1.00 mm particle sizes, their internal friction angle increases with increasing number of cycles; for the samples with 0.25-0.50 mm and <0.25 mm particle sizes, however, the angle hardly changes with the number. For the samples with <2 mm and 0.50-1.00 mm particle sizes, the cohesion force increases firstly and keep flat basically; the samples with 0.25-~0.50 mm and <0.25 mm particle sizes, the force decreases initially then shows a small increase.