兰州盆地第三系砂岩工程地质特性评价研究

EVALUTION OF THE ENGINEERING GEOLOGICAL CONDITION OF N-SANDSTONE IN LANZHOU BASIN

兰州盆地广泛分布的第三系砂岩沉积厚度大,多同泥岩互层分布,砂岩受水影响易发生软化,容易导致工程结构特别是地下隧道工程围岩出现失稳问题。为评价研究兰州盆地第三系砂岩工程地质特性,首先收集兰州至重庆铁路、兰州至中川铁路砂岩段勘察试验资料,统计分析得到了砂岩的物理力学性质;然后对代表性砂岩进行电镜扫描试验研究其在不同含水率下的微结构变化特征;最后确定了影响砂岩工程特性的主要影响因素为:含水率、黏粒含量、地下水阴离子浓度、孔隙比。通过采用突变理论建立了第三系砂岩工程地质特性定量评价模型,砂岩工程地质特性可以划分为5级:恶劣(S≤0.64)、较差(0.64<S≤0.71)、一般(0.71<S≤0.79)、较好(0.79<S≤0.87)、良好(S≥0.87)。应用模型对兰渝铁路桃树坪隧道砂岩进行评价,该区域砂岩评价结果介于0.57～0.77之间,工程地质特性处于一般到恶劣状态,评价结果与现场实际结果一致。

The N-sandstone, of which with the characters of poor diagenetic grade, liable to weathering and disintegration, is the extremely soft rock. The N-sandstone is widely distributed in Lanzhou Basin, Gansu Province, China. The structure of the huge thickness N-sandstone will be easily disturbed under the effect of ground water and then softening. That would lead to the instability happened in the engineering basement, especially in the tunnel structure. For studying the engineering geological condition of N-sandstone, the investigation and test data of the Lanzhou to Chongqing Railway and Lanzhou to Zhongehuan Railway was studied and then obtained the physieo- mechanical properties of the sandstone. Additionally, through applying scanning electron microscope technology the microstructure change character under the effect of different water content was studied also. Finally, the main effect factors of the engineering geological condition were determined and as follows： water content, clay content, anion concentration of groundwater and porosity. The catastrophe progression method was adopted to establish the engineering geological condition quantitative evaluation model of sandstone. The engineering geological condition of N-sandstone can be divided into five grades： severe（S≤0.64） ,bad（0. 64〈S≤0. 71） ,general（0. 71〈S≤0. 79）, well（0. 79〈S ≤ 0. 87） and peffeet（S≥0.87）. The evaluation result about the Taoshuping Tunnel of Lanzhou-Chongqing Railway was between 0. 57 to 0. 77. The engineering geological condition was sever and general. The evaluation result was in keeping with the actual situation.