The influence of joints with upward groundwater on dip slope stability
Date Issued
2015
Date
2015
Author(s)
Huang, Shao-Cheng
Abstract
The massive forward slope sliding happened at Taiwan''s National Highway No. 3 3.25k on February 25, 2010, which covers an area about more than 20,000 square meters. After investigating the cause of the disaster that the sliding surface on sandstone/shale interlayer and angle of 14° ,there are three reasons for the occurrence of an event of collapse, Geological disasters dip slope, engineering disturbance- excavation, the time factor- efficiency reduction of rock anchors. However, there is a problem to be resolved, the forward slope slided at National Highway No. 3 occurred in not a torrential rainy day. Based on historical data showing that the groundwater impacts on slope stability. If no heavy rain occured, it might be the groundwater impacts on slope unstable. There are vertical joints and the significant phenomenon of rust stained at partial siliding surface. According to the geophysical survey, the bottom of the sliding surface contains groundwater. Presume presumably the groundwater flow into rock layer by vertical joints ,cause upward water pressure effect slope stability. This study has two parts, physical test and numerical simulation. The physical tests design water flow inclinometer, the specimen material is manufactured of gypsum sand that place on the inclinometer sheets, and give upward water pressure from the specimen bottom. In this study, change inclinometer angle, joint position of specimen, position of seepage, to investigate the effect of upward water on slope stability. In accordance with the physical test, the specimen sliding when the fully open valve is critical state, using this critical state to figure out water pressure formula. And compared with the apply water pressure, the water pressure dissipate to the original 1/15. When the number of joints increase, the upward water pressure reduce. Therefore, compared with the upward water pressure and sample weight, finding out the water pressure required 3.8 times the weight of the block bringing about driving the block. For the numerical simulation, simulating National Highway No. 3 event by FLAC. Top of the model is sandstone, bottom of the model is confined aquifer. The groundwater flow the vertical joints into the sliding surface. In order to understand the impact of cleft water on slope stability, compared with the influence of the efficiency reduction of rock anchors, friction angle decreases, compare to plastic chart and maximum shear strain rate. According to the numerical analysis results, the National Highway No. 3 event has been influenced for a long time by water pressure causing weathered sandstone generate tension cracks on the top of the vertical joints. Due to anchor attenuation influence makes sandstone sliding down, resulted in increasing shear strain in backfill region. When water pressure increases to 114m, the backfilled region will produce large deformation. The friction angle decreases from 19° to 17°, the slope slides along the weak surface easily, and the sliding surface extends to the bottom of the backfill region.
Subjects
dip slope
jointed rock mass
upward groundwater
cleft water
physical model
SDGs
Type
thesis
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