Rainfall infiltration depth and formation mechanism of slow-inclination soil landslides in Nanjiang
ZHANG Qun1, XU Qiang2, YI Jing-song3, XU Liang1, MA Zhi-gang1
1. Sichuan Province Geological Environmental Monitoring Station, Chengdu 610081, China; 2. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China; 3. Institute of Mineral Exploration Technology, Chinese Academy of Geological Sciences, Chengdu 611734, China
Abstract：Lots of slow-inclination soil landslides were triggered by the rainfall on September 16th in 2011 in Nanjiang. The typical landslides have sliding bodies with thickness concentrated in 1~5 m, and they always slide along the bedrock cover interface which is a smooth surface. By designing rainfall infiltration tests, establishing G-A infiltration model and calculating atmosphere influence depth considering the effect of atmosphere on the slope, the rainfall infiltration depth of landslides is analyzed, and the distribution causes of sliding thickness are investigated. The slope stability is analyzed based on the unsaturated soil strength theory when the infiltration peak is located in the soil layer and the base cover interface under the natural and rainfall conditions. The results show that the permeability of red clay in Nanjiang is extremely low, the rain infiltration depth is very limited in short and heavy rainfall, and it is generally only about 50 cm. The atmosphere influence depth is 5.37 m in the study area. In this range the rain easily infiltrates. However, with the increase of depth, the weathering degree of the soil is gradually weakened, the pore ratio and permeability gradually decrease, and infiltration is gradually difficult until the bedrock. The rainfall infiltration depth is the main cause of the typical landslides with shallow slide. Under rainfalls, when the depth of infiltration peak is less than the thickness of soil layer and the potential sliding surface is in the infiltration peak surface, the slope is stable. When the depth of
infiltration peak is equal to the thickness of soil layer and the potential slip surface is located on the base cover interface, stagnant water at the interface is generated, the water level rises, the pore pressure increases, and the interface produces softening and lubrication. The interface effect is the main cause for the slow-inclination soil slide along the bedrock cover interface which is a smooth surface.
成因机理研究. 南江红层地区缓倾角浅层土质滑坡降雨入渗深度与[J]. 岩土工程学报, 2016, 38(8): 1447-1455.
ZHANG Qun， XU Qiang， YI Jing-song， XU Liang， MA Zhi-gang. Rainfall infiltration depth and formation mechanism of slow-inclination soil landslides in Nanjiang. Chinese J. Geot. Eng., 2016, 38(8): 1447-1455.
[1] MONTGOMERY D R. Hydrologic response of a steep unchanneled valley to natural and applied rainfell[J]. Water Resources Research, 1997, 33(1): 91-109. [2] LEE C F, DAI F C. Analysis of rainstorm-induced slide-debris flows on natural terrain of Lantau Island, Hong Kong[J]. Engineering Geology, 1999, 51(4): 279-290. [3] 黄润秋, 戚国庆. 非饱和渗流基质吸力对边坡稳定性的影响[J]. 工程地质学报, 2002(4): 343-348. (HUANG Run-qiu, QI Guo-qing. The effect of unsaturated soil suction on slope stability[J]. Journal of Engineering Geology, 2002(4): 343-348. (in Chinese)) [4] 黄润秋, 戚国庆. 滑坡基质吸力观测研究[J]. 岩土工程学报, 2004, 26(2): 217-219. (HUANG Run-qiu, QI Guo-qing. Observation of suction in a landslide[J]. Chinese Journal of Geotechnical Engineering, 2004, 26(2): 217-219. (in Chinese)) [5] 张永安, 李 峰, 陈 军. 红层泥岩水岩作用特征研究[J].工程地质学报, 2008(1): 22-26. (ZHANG Yong-an, LI Feng, CHEGN Jun. Analysis of the interaction between mudstone and water[J]. Journal of Engineering Geology, 2008(1): 22-26. (in Chinese)) [6] 王运生, 吴俊峰, 魏 鹏, 等.四川盆地红层水岩作用岩石弱化时效性研究[J]. 岩石力学与工程学报, 2009(增刊1): 3102-3108. (WANG Yun-sheng, WU Jun-feng, WU Peng. Reserarch on time effect of rock weakening by water-rock interaction of redbeds in SiChuan basin[J]. Journal of Engineering Geology, 2009(S1): 3102-3108. (in Chinese)) [7] 刘龙武, 郑健龙, 缪 伟. 广西宁明膨胀土胀缩活动带特征及滑坡破坏模式研究[J]. 岩土工程学报, 2008(1): 29-33. (LIU Long-wu, ZHEGN Jian-long, LIAO Wei. Researches on characteristics of swell and shrinking active zone of expansive soil and failure mechanism of landslides[J]. Chinese Journal of Geotechnical Engineering, 2008(1): 29-33. (in Chinese)) [8] 胡泽铭. 四川红层地区缓倾角滑坡成因机理研究[D]. 成都:成都理工大学, 2013. (HU Ze-ming. Study on formation mechanism of the slow-inclination landslide in red stratum Region, Sichuan[D]. Chengdu: Chengdu University of Technology, 2013. (in Chinese)) [9] 张 群, 许 强, 甯 娜. 降雨条件下低缓浅层土质滑坡稳定性影响因素及耦合研究[J]. 水文地质工程地质, 2014(5): 90-94. (ZHANG Qun, XU Qiang, NING Na. A study of the stability influence factors and coupling for inclined-shallow soil landslides under the condition of rainfall[J]. Hydrogeology & Engineering Geology, 2014(5): 90-94. (in Chinese)) [10] 李 江, 许 强, 胡泽铭, 等. 红层缓倾角土质滑坡发育环境、分布规律及影响因素研究[J]. 科学技术与工程, 2014(12): 88-93. (LI Jiang, XU Qiang, HU Ze-ming. Study on factors of development environment distribution characteristics and soil landslides on low-angled rock formation of red bed[J]. Science Technology and Engineering, 2014(12): 88-93. (in Chinese)) [11] 李 宁, 许建聪, 钦亚洲. 降雨诱发浅层滑坡稳定性的计算模型研究[J]. 岩土力学, 2012, 33(5): 1485-1490. (LI Ning, XU Jian-cong, QIN Ya-zhou. Research on calculation model for stability evaluation of rainfall-induced shallow landslides[J]. Rock and Soil Mechanics, 2012, 33(5): 1485-1490. (in Chinese)) [12] 余 飞, 陈善雄, 许锡昌, 等. 合肥地区膨胀土路基处置深度问题探讨[J]. 岩土力学, 2006(11): 1963-1966. (YU Fei, CHEN Shan-xiong, XU Xi-chang. Study on determination of treatment depth for expansive soil subgrade in Hefei[J]. Rock and Soil Mechanics, 2006(11): 1963-1966. (in Chinese)) [13] FREDLUND D G, RAHARDJO H. Soil mechanics for unsaturated soils[M]. New York: Wiley, 1993: 20-50.
