Research On Mechanism Of Seep And Deformation Of Accumulative Landslide When Reservoir Impound Early

Reservoir landslide is an important geological disaster which is produced by seepage field, stress field changes due to reservoir water level fluctuation. Reservoir landslide not only threat to the safety of the dam, damage to buildings, but also produces secondary disasters such as reservoir sedimentation. Research carried out in response to the deformation mechanism of landslide in reservoir water effect on the Reservoir landslide prediction and prevention with a strong guiding significance.In this paper, the landslide of Caokedu in Liyuan reservoir area is the the research object. The seepage flow characteristic and laws, stress-strain field, deformation responsible mechanism was studied. Through analysis of the survey, the following main conclusions and results obtained:1、Liyuan power station is located in lijiang, yunnan province,the border between diqing Tibetan autonomous prefecture, yulong county(the right) and shangri-la county, middle reachesof the Yangtze river. The terrain is very high or middle. About ten large-scale fracture zone exsits here. And the lithology is mainly limestone, dolomitic limestone. There are more than ten large deposits in reservoir area, which is mainly ice water deposit.2、Caokedu landslide located the right bank of Liyuan Station which is in the middle Jinsha River. Landslide was " chair-shaped ",the total length 650 m, width 300 m, thickness 15 ~ 70 m, volume greater than four million, which belongs to large deep moraine accumulation of active landslide.Overall the landslide terrain was on " the steep- the slow- down steep " polyline shape. The landslide material primarily consisting of sand, silt stone fragments and fragments of stone clip earth; the surface shape in space is the shape of steep, “Middle and back cliffy, front slow. And middle thick, sides thin”The sliding bed rock is partial-allweatheredBasalt, broken mostly.3、The physical and mechanical, hydrological experiment shows, the gradation of soil is good, the Cu average value is 55, the Ccaverage value is 1.55 and permeability is bad, 1 ~2m/d. The moisture content effect on the shear strength mainly performs to decrease cohesion, decreasefrom 23.33 kpa to 4kPa, and 82% declined. The law is that the strength decrease with moisture content increasing. The more close to saturation, faster the rate decrease.The effect of moisture content to friction angel is small, From 36.33 degrees to 29.69 degrees, 16% declined. The moisture content increase, the friction angel decrease linearly.4、The investigation and monitoring data shows, The landslide has obvious deformation after water storage. Deformation is concentrated in the right and center front edge of the landslide, relative with reservoir level. When the reservoir water level rose from the initial water level to 1570 m, thedeformation ratewere positively correlated with reservoir level raising rate; When itcontinue from 1570 m to rise, the front deformation rate decreases as edge deformation rate decreases; The front deformation rate increase when reservoir level keep stable. When it dropped, the rate increased.5、The seepageresult shows, reservoir water level fluctuation impacting on groundwater levels are mainly concentrated in the range 50 ~ 100 m of landslide. The trailing edge flow and reservoir water effect on groundwater level together. The supply relation of groundwater and reservoir water are changing in diffirent reservoir water level.When the level is lower than 1570 m,the groundwater table is not hysteresis, defined as water synchronous type. When the level is higher than 1570 m, the groundwater table is obvious hysteresis, defined as water hysteresis type.In the process of reservoir, the influence of water level rising rate on the landslide seepage field is very important. When water level rises, if the water level rise rate is less than the permeability coefficient of the landslide, the water infiltration can supply the groundwater immediately; lifting speedof the reservoir water and groundwater are basically same, defined as water synchronous type. if the water level rise rate is more than the permeability coefficient of the landslide, the reservoir water lifting speed is faster than ground water caused by infiltration, the groundwater level will appears concave, show hysteresisphenomenon, defined as water hysteresis type.6、The investigation, monitoring data and numerical analysis shows,CaoKeDu landslide deformation and reservoir level fluctuation has a certain relevance. In the process of early reserving stage, the whole stability of landslide is good, deformation mainly concentrate in the front landslide,The reservoir effecting on front stability is bigger than the whole, the landslide deformation and failure mode is the style of falling back gradually. When reservoir level dropped fast, the landslide is most dangerous. Pore water pressure, softening effect and hydrodynamic pressure is the main factor to affect landslide deformation. The dominant factors are changing in different reservoir level, especially; the hydrodynamic pressure is a key factor to affect the stability of the front shallow landslide.