A Study of Toe-excavation Induced Failure Process for a Dip Slope with Rock Anchorage
Date Issued
2012
Date
2012
Author(s)
Huang, Wen-Sung
Abstract
On April 25, 2010, without rainfall and earthquake triggering a massive landslide (200000 m3) covered a 200m stretch of Taiwan’s National Freeway No. 3, killing 4 people, burying three cars and destroying a bridge. The failure mode appears to be a dip-slope type failure occurred on a rock anchorage cut slope. Based on the investigations and the numerical analysis in this study, the toe-excavation at this dip-slope in 1998 was the most crucial factor. Although the excavated area had stabilized soon with rock anchors and backfills. The strength of rock mass had great effect on the stability of dip-slope after backfills.
The strike of Tertiary sedimentary strata is northeast-southwest and dip 12˚ ~15˚ toward southeast. Considering the strength of sliding layer had reduced from peak to residual strength which was caused by the disturbance of excavation, the limit equilibrium method (LEM) analysis was utilized in the back analysis at first. The results showed the stability condition of slope approached the critical state (F.S.≈1). The efficiency reduction of rock anchors and strength reduction of overlying stratum (sandstone) had been considered in following analysis. The results showed the unstable condition (F.S. <1).
This study also utilized the result of laboratory test, geological strength index(GSI) and finite difference method (FDM, FLAC 5.0) to discuss the failure process The analysis indicated that the incremental load of anchors have similar tendency comparing to the monitoring records in toe-excavation stages. This result showed that the strength of the sliding layer was significantly influenced by toe-excavation.
The numerical model which calibrated with monitoring records in toe-excavation stage was used to discuss the failure process after backfilling. The efficiency reduction of rock anchors had less impact on the development of sliding surfaces. But the development of sliding surfaces were significantly influenced by the strength reduction of the rock mass。The sliding surface gradually developed from the toe of the dip-slope to the top of the dip-slope and the stability of the slope became more unstable in the process of rock mass strength reduction .
Subjects
GSI
Dip-slope
Anchor
Limit equilibrium method
back analysis
Type
thesis
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