In the present work, geological, geotechnical, and ground penetration radar studies were carried out along the Mansa Devi hill bypass (MDHB) road Uttarakhand, India in order to assess the slope instability conditions. Seven unstable zones along the entire MDHB road were identified which are prone to landslides. Geologically, the area is composed of mudstone and sandstone with thick overburden constituting sandy soil. The laboratory tests were carried out in order to evaluate the geo-mechanical characterization of soil, sandstone, and mudstone that constitute the slopes. The laboratory tests reveal that the slope is comprised of soil characterized by high permeability and low strength values. The soil is mainly sandy and non-cohesive. The laboratory tests on sandstone reveal that fresh sandstone exhibits exceptionally higher value of unconfined compressive strength (> 100 MPa) than the weathered sandstone (< 35 MPa). The mudstone is non-durable and contains considerable amount of expanded clay minerals which has a tendency to expand in the presence of water. It can weather easily and facilitate instability at shallow depth. A ground penetrating radar survey confirmed that the road is unstable particularly on those spots where the road either lying over mudstone beds or over thick non-cohesive sandy soil. The infiltration rate of water in this sandy soil is generally rapid which allows fast flow of water into the deeper horizons and thus cracks can be seen in road caused by vertical settlement. Similar results are observed in slope stability analysis where the slope covered with sandy soil exhibits factor of safety less than 1.0. However factor of safety is close to 1 where the slopes consist of alternate beds of sandstone and mudstone.

中文翻译：

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印度北阿坎德邦曼萨德维山绕道 (MDHB) 路沿线的地质、岩土工程和 GPR 调查

在目前的工作中，沿印度北阿坎德邦曼萨德维山绕道 (MDHB) 公路进行了地质、岩土工程和地面穿透雷达研究，以评估边坡失稳状况。沿着整个 MDHB 道路确定了七个不稳定区域，这些区域容易发生山体滑坡。地质上，该地区由泥岩和砂岩组成，覆盖层较厚，为砂质土壤。进行实验室测试是为了评估构成斜坡的土壤、砂岩和泥岩的地质力学特征。实验室测试表明，斜坡由具有高渗透性和低强度值的土壤组成。土壤主要是沙质和非粘性的。对砂岩的实验室测试表明，新鲜砂岩的无侧限抗压强度值 (> 100 MPa) 比风化砂岩 (< 35 MPa) 高得多。泥岩是不耐久的，并且含有大量膨胀的粘土矿物，这些矿物在有水的情况下有膨胀的趋势。它很容易风化并促进浅层的不稳定。探地雷达调查证实，道路不稳定，特别是在那些道路位于泥岩床或厚厚的非粘性沙土上的地方。水在这种沙质土壤中的渗透速度通常很快，这使得水可以快速流入更深的地层，因此可以看到由于垂直沉降而导致道路出现裂缝。在边坡稳定性分析中观察到类似的结果，其中沙土覆盖的边坡表现出的安全系数小于 1.0。然而，当斜坡由砂岩和泥岩交替层组成时，安全系数接近 1。