Failure Mechanism of the Changhe Landslide on September 14, 2019 in Tongwei, Gansu

doi:10.19657/j.geoscience.1000-8527.2020.073

Abstract

Abstract:

A large loess landslide occurred in Xiaozhuang Village (Tongwei, Gansu Province) at around 11:00 am on September 14, 2019. About 800×10⁴ m³ of a historical sliding mass was reactivated by rainfall, and slipped down along a weak interface. The sliding mass destroyed several roads and the Yangpo bridge. Preliminary estimation of 2,975 people in one township and two villages of Tongwei County were affected, causing a direct economic loss of 23.47 million yuan in agriculture, water conservancy, power supply, and infrastructure. Based on site investigation, unmanned aerial vehicle photography and numerical simulation, the deformation and failure characteristics of this landslide are described in detail, and the failure mechanism are preliminarily assessed. The main factor that affected the slope stability is the post-seismic interaction of rainfall and creep, and the failure process comprise five stages: pre-earthquake, earthquake damage, creep weakening, rainfall triggering and final sliding. Sinkholes and underground rivers were well developed in the slope, and represent the key control of the landslide boundary. Strong deformation and failure occurred at the trailing and leading edges of the landslide, but the deformation in the middle was relatively weak. We infer that the landslide was a traction-movement composite one controlled by topography and ground water. Understanding the conditions and mechanism of the Changhe landslide is hugely important for the early identification and risk prevention of similar landslides in the loess region of northwestern China.

Key words: Tongwei, Gansu, loess region, rainfall-induced landslide, revival of seismic landslide, failuremechanism

CLC Number:

P642.22

WANG Haojie, SUN Ping, HAN Shuai, ZHANG Shuai, LI Xiaobin, WANG Tao, XIN Peng, GUO Qiang. Failure Mechanism of the Changhe Landslide on September 14, 2019 in Tongwei, Gansu[J]. Geoscience, 2021, 35(03): 732-743.

Figures/Tables 17

Fig.1 Location map and aerial photos of the landslide

Fig.2 Geomorphologic images and geological map of the study area

Table 1 Physical properties of loess in the study area

土样编号	含水率/%	密度/(g/cm³)	干密度/(g/cm³)	比重G_S	孔隙比e₀	湿陷系数	渗透系数K/(cm/s)	塑性指数
原状土1	8.31	1.60	1.57	2.67	0.57	0.04	8.37×10^-8	7.17
原状土2	9.63	1.72	1.65	2.67	0.39	0.03	9.92×10^-8	10.22
滑带土1	20.48	1.65	1.33	2.67	0.67	0.01	1.34×10^-7	9.13
滑带土2	17.89	1.57	1.33	2.67	0.70	-	1.19×10^-7	8.08

Fig.3 Topographic map showing the distribution of structures in Tongwei area

Fig.4 Image showing the overall characteristics of the landslide

Fig.5 Photos showing deformation characteristics of the landslide (upper part)

Fig.6 Photos showing deformation characteristics of the landslide (middle part)

Fig.7 Photos showing deformation characteristics of the landslide (lower part)

Table 2 Physical and strength properties of rock and soil mass

岩土体	密度/(kg/m³)	弹性模量/MPa	泊松比	黏聚力/kPa		抗拉强度/kPa		内摩擦角/(°)
岩土体	密度/(kg/m³)	弹性模量/MPa	泊松比	天然	饱和	天然	饱和	天然	饱和
黄土堆积体	1 650	50	0.25	35	15	5	2	25.0	21.0
滑体	1 600	45	0.25	20	12	3	1	20.5	18.0
泥岩	2 120	300	0.18	500	500	100	100	35.0	35.0

Fig.8 X-displacement and plastic zone of sliding body under natural conditions and rainfall conditions

Fig.9 Monitoring (M1-M6 location shown in Fig.8 (a)) curves of pore water pressure(a), plastic shear strain (b) andX-displacement (c) of monitor points

Fig.10 Failure process of Changhe landslide

Fig.11 Historical seismic landslide distributions in/around the study area

Fig.12 Rheologic curves of mudstone specimens under different moisture contents (σ3=800 kPa)

Fig.13 Daily and hourly precipitation in the study area

Table 3 Strength properties of natural and water-saturated loess

土体编号	天然状态			饱和状态			天然状态				饱和状态
土体编号	黏聚力 /kPa	内摩擦角 /(°)		黏聚力 /kPa		内摩擦角 /(°)	压缩系数 /MPa^-1	压缩模量 /MPa			压缩系数 /MPa^-1	压缩模量 /MPa
原状土1	35.3	25.0	14.3		20.9		0.08		20.20	0.31		5.10
原状土2	36.6	19.9	18.6		18.0		0.05		29.85	0.94		1.48
滑带土1	19.0	20.5	12.0		17.8		0.17		9.80	0.48		3.48
滑带土2	16.5	19.5	9.8		17.4		0.07		22.73	0.68		2.51

Fig.14 Types of rainfall-induced loess landslides in the loess region of northwestern China

References 16

[1]	吴正军, 丁保艳, 邵东桥. 甘肃省定西市通渭县常河镇滑坡灾害应急调查报告[R]. 兰州: 甘肃地质灾害防治工程勘查设计院, 2019.
[2]	ZHANG M S, LIU J. Controlling factors of loess landslides in western China[J]. Environmental Earth Science, 2009, 59(8): 1671-1680. DOI URL
[3]	TU X B, KWONG A K L, DAI F C, et al. Field monitoring of rainfall infiltration in a loess slope and analysis of failure mechanism of rainfall-induced landslides[J]. Engineering Geology, 2009, 105(1/2): 134-150. DOI URL
[4]	张茂省, 李同录. 黄土滑坡诱发因素及其形成机理研究[J]. 工程地质学报, 2011, 19(4): 530-540.
[5]	SUN P, LI R J, JIANG H, et al. Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province, northwest China[J]. Bulletin of Engineering Geology and the Environment, 2016, 76(4): 1281-1295. DOI URL
[6]	胡向德, 卞伟强. 甘肃省通渭县地质灾害调查与区划报告[R]. 兰州: 甘肃省地质环境监测院, 2009.
[7]	彭达, 杨顺, 李孝波. 甘肃通渭县黄土地震滑坡分布特征及发育机理[J]. 中国地质灾害与防治学报, 2017, 28(3): 31-38.
[8]	BURCHFIEL B C, ZHANG P, WANG Y, et al. Geology of the Haiyuan fault zone, Ningxia-Hui Autonomous Region, China, and its relation to the evolution of the northeastern margin of the Tibetan Plateau[J]. Tectonics, 1991, 10(6): 1091-1110. DOI URL
[9]	CHEN T, ZHANG P Z, LIU J, et al. Quantitative study of tectonic geomorphology along Haiyuan fault based on airborne LiDAR[J]. Chinese Science Bulletin, 2014, 59(20): 2396-2409. DOI URL
[10]	黄润秋, 许强. 中国典型灾难性滑坡[M]. 北京: 科学出版社, 2008:263-268.
[11]	孙萍, 殷跃平, 吴树仁, 等. 高速远程地震黄土滑坡发生机制试验研究[J]. 工程地质学报, 2009, 17(4): 449-454.
[12]	叶帅华, 时轶磊. 降雨入渗条件下多级黄土高边坡稳定性分析[J]. 工程地质学报, 2018, 26(6): 1648-1656.
[13]	冯文凯, 孟睿, 李坤, 等. 贵州省水麻坨滑坡的复杂运动破坏机制探讨[J]. 工程地质学报, 2019, 27(3): 592-600.
[14]	孙萍, 王刚, 李荣建, 等. 降雨条件下黄土边坡现场试验研究[J]. 工程地质学报, 2019, 27(2): 466-476.
[15]	国家地震局兰州地震研究所, 宁夏地震局. 1920年海原大地震[M]. 北京: 地震出版社, 1980:110-118.
[16]	王家鼎, 白铭学, 肖树芳. 强震作用下低角度黄土斜坡滑移的复合机理研究[J]. 岩土工程学报, 2001, 22(4): 445-450.