垃圾填埋场斑脱土衬里可行性评价

首先对斑脱土衬里(粘土-斑脱土、砂-斑脱土) 进行变水头实验, 得粘土-斑脱土的渗透系数为6.0×10-9~3.0×10-8cm/s, 砂-斑脱土的渗透系数为1.0×10-9~3.0×10-9cm/s.从防渗角度分析, 2种斑脱土混合物均适合作垃圾填埋场的底层衬里.然后对斑脱土衬里进行持水与水迁移实验, 评价斑脱土衬里水的迁移特性.以水迁移实验为基础, 模拟斑脱土衬里与地基5种不同含水量的条件, 对斑脱土衬里进行直接剪切实验, 测定斑脱土衬里的剪切强度及斑脱土衬里与地基接触面的剪切强度.再对斑脱土衬里进行三轴固结不排水实验, 测定其总剪切强度与有效剪切强度.实验结果表明: 地下水具有很大的潜力从地基流向斑脱土衬里, 从而大大提高斑脱土衬里的含水量; 随着含水量的增加, 粘土-斑脱土、砂-斑脱土衬里的抗剪强度逐渐减小.根据实验所获得的抗剪强度参数, 选择日本山谷型垃圾填埋场典型剖面, 对山谷型垃圾填埋场进行稳定性评价.结果表明: 对于角度小于20°的缓倾角山谷型垃圾填埋场, 使用粘土-斑脱土、砂-斑脱土作为底层衬里是稳定的.因此, 2种斑脱土混合物适合作山谷型垃圾填埋场的底层衬里. 

Feasibility Evaluation of Landfill Bentonite-Enhanced Liners

In the first part of this paper, the falling head permeability tests were conducted on bentonite-enhanced liner (BEL) specimens (sand-bentonite and clay-bentonite mixtures) to obtain the hydraulic conductivity. The results show that the hydraulic conductivity of clay-bentonite is about 6.0×10-9—3.0×10-8cm/s, and that of sand-bentonite about 1.0×10-9—3.0×10-9cm/s. Compared with the standard hydraulic conductivity used in Japan (1.0×10-6 cm/s), the hydraulic conductivity of both clay-bentonite and sand-bentonite is much lower. Then, the water retentivity and water migration tests were performed on the two liner specimens to evaluate the water retention and migration properties from saturated/unsaturated base soil. Based on the above tests, direct shear tests were conducted to obtain the internal shear strength of BEL specimens and the interface shear strength between BEL and base soil under five different water control conditions. Triaxial shear tests were also conducted on the two liner specimens to obtain the total and effective shear strength. Test results show that pore water in the underlying base soil has great potential to migrate to the BELs, resulting in a significant increase in water content of BELs, and the shear strength of both BEL internal and BEL/base interface tends to decrease with the increase of water content in BELs. Finally, the slope stability of a typical canyon solid waste landfill related to the two liners under various conditions was analyzed with the obtained shear strength parameters. Landfills at a gentle slope (with the total angle of the slope not greater than 20 degree) do not fail in both cases of sand-bentonite liner and clay-bentonite liner. Therefore, sand-bentonite and clay-bentonite mixtures are suitable for landfill bottom liners.