Study on Physical and Mechanical Characteristics and Stability Analysis of Ancient Landslide Deposit in East Tibet

doi:10.19657/j.geoscience.1000-8527.2019.003

Abstract

Abstract:

The proposed Sichuan-Tibet Railway is the most complicated railway in nature and geological environment. The geological disaster, as a key control node of local and even the whole line, is related to the success or failure of Sichuan-Tibet Railway construction. Field investigation shows that the Denongnongba ancient landslide is located on the first order land of the right bank in Zangqu River, and has attracted much attention in the process of railway line selection or construction in Sichuan and Tibet, and its stability is a necessary condition for railway selection line. Based on field investigation, this paper systematically calculated and analyzed the physical and mechanical parameters and stability of the ancient landslide deposit. The results show that under natural conditions, the dry density of gravel is above 1.75 g/cm³, and the water content is less than 4%, and the cohesion and internal friction angle of the deposit are significantly correlated with water content, which decreases with the increase of water content. Based on FLAC^3D numerical simulation and GEO-SLOPE stability result, it is shown that the landslide deposit is stable under natural and rainstorm conditions, but the stability of toe and the posterior edge of slope is poor under heavy rainfall condition, and the stability coefficient of toe is only 0.761. Under the action of rainstorm, earthquake and human activity, the deposit is likely to be local instability, which affects the safety of railway construction and the residents on the slope, and it is necessary to take comprehensive management and stability monitoring to the landslide.

Key words: Sichuan-Tibet Railway, ancient landslide, physical and mechanical parameter, numerical simulation

CLC Number:

P642.2

ZHAN Meiqiang, GE Yonggang, JIA Lirong, YAN Hua. Study on Physical and Mechanical Characteristics and Stability Analysis of Ancient Landslide Deposit in East Tibet[J]. Geoscience, 2019, 33(05): 1118-1127.

Figures/Tables 15

Fig.1 Stratigraphic distribution in the Zangqu River area

Fig.2 Plane map of the Denongnongba ancient landslide

Fig.3 Engineering and geological profile of the Denongnongba ancient landslide

Table 1 Basic physical parameters of the Denongnongba ancient landslide deposit

采样点编号	天然密度/(g/cm³)	含水率/%	干密度/(g/cm³)	饱和度/%	孔隙比	渗透系数/(cm/s)	液限/%	塑限/%
A	1.80	3.0	1.75	0.82	0.51	6.5×10^-3	23.7	15.2
B	1.89	3.6	1.82	1.02	0.44	5.2×10^-3	20.5	13.8
C	2.03	2.8	1.97	0.83	0.34	3.5×10^-3	20.2	14.5
D	1.96	3.2	1.89	0.93	0.36	3.3×10^-3	20.3	10.2
E	2.15	2.7	2.09	0.84	0.26	1.0×10^-3	20.9	13.9
F	2.04	3.4	1.97	1.01	0.31	1.8×10^-3	22.7	12.3

Fig.4 Relationship between fine particle content and dry density of samples from the Denongnongba ancient landslide deposit

Fig.5 Relationship between void ratio and permeability coefficient of samples from the Denongnongba ancient landslide deposit

Table 2 Mineral compositions of samples from the Denong-nongba ancient landslide deposit(%)

样品编号	石英	云母	高岭石	方解石	长石
A-1	41.2	29.6	16.8	10.1	2.3
B-1	39.6	33.5	12.8	11.0	3.1
C-1	36.8	30.7	10.1	19.5	2.9
D-1	10.6	47.9	3.8	10.7	27.0
E-1	6.2	59.2	3.1	10.0	21.5
F-1	8.5	53.1	3.4	11.1	23.9

Fig.6 Curves of shear strength in plastic limit state for samples from the Denongnongba ancient landslide deposit

Fig.7 Curves of shear strength in liquid limit state for samples from the Denongnongba ancient landslide deposit

Table 3 Shear strength parameters in liquid-plastic limit state for samples from the Denongnongba ancient landslide deposit

采样点编号	液、塑限状态	抗剪强度参数
采样点编号	液、塑限状态	黏聚力c/kPa	内摩擦角 $φ$ /(°)
A	塑限	32.8	38.6
A	液限	13.4	30.7
B	塑限	44.3	42.6
B	液限	17.8	37.2
C	塑限	38.1	36.7
C	液限	20.9	25.4
D	塑限	19.8	32.7
D	液限	6.3	28.2
E	塑限	14.5	42.4
E	液限	3.5	37.4
F	塑限	20.9	28.7
F	液限	6.5	24.4

Table 3 Shear strength parameters in liquid-plastic limit state for samples from the Denongnongba ancient landslide deposit

采样点编号	液、塑限状态	抗剪强度参数
采样点编号	液、塑限状态	黏聚力c/kPa	内摩擦角 $φ$ /(°)
A	塑限	32.8	38.6
A	液限	13.4	30.7
B	塑限	44.3	42.6
B	液限	17.8	37.2
C	塑限	38.1	36.7
C	液限	20.9	25.4
D	塑限	19.8	32.7
D	液限	6.3	28.2
E	塑限	14.5	42.4
E	液限	3.5	37.4
F	塑限	20.9	28.7
F	液限	6.5	24.4

Fig.8 Three-dimensional geological model of the Denongnongba ancient landslide

Table 4 Value of computation parameters of the FLAC3D computational model

地层	工况	泊松比	密度/(kg/m³)	黏聚力/kPa	内摩擦角/(°)	弹性模量/MPa	切变模量/MPa	体积模量/MPa
残坡积物	天然	0.26	1 831	23	33	65	25.6	47.1
残坡积物	暴雨	0.26	1 893	21	26	65	25.6	47.1
滑坡堆积体	天然	0.24	2 030	54	41	140	59.3	72.9
滑坡堆积体	暴雨	0.24	2 115	47	32	140	59.3	72.9
基岩	天然	0.27	2 200	140	46	56 000	22 580	35 897
基岩	暴雨	0.27	2 040	150	43	56 000	22 580	35 897

Fig.9 Results of numerical calculation by FLAC3D for the Denongnongba ancient landslide

Table 5 Safety factors of the Denongnongba ancient landslide calculated by GEO-SLOPE

工程条件	安全系数
工程条件	Morgenstern-Price	Janbu	Bishop	Ordinary
天然暴雨	古滑坡堆积体整体稳定性
	2.693	2.586	2.678	2.564
	1.928	1.866	1.933	1.850
天然暴雨	坡脚稳定性
	1.056	1.056	1.057	1.056
	0.761	0.761	0.761	0.761
天然暴雨	古滑坡堆积体后缘稳定性
	1.370	1.369	1.370	1.369
	1.031	1.030	1.031	1.030

Fig.10 Typical photos of the Denongnongba ancient landslide

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