Study On Multi-buckling Failure Of The Bedded Rock Masses On The Consequent Slopes

Layered rock mass, widely distributing in the nature, is one of the rock mass structure which is inclined to give rise to geological hazards. As is known to all, it is a little more difficult for consequent bedding rock slope to topple and fall than other rock structures, so buckling failure becomes the most prevalent failure mode of consequent bedding rock slope. As a matter of fact, bedding rock slopes with variable height ranging from tens of meters to hundreds of metes are likely to buckle as long as they meet the buckling criteria, which will result in a threat to the construction and operation of railway, highway and hydropower, as well as residents’ lives and property. Buckling failure of rock stratum has been studied systematically and significant results have been achieved. However, what has been focused to research over years is just based on single buckling, while more than one buckling was surveyed in practical bedding rock slope simultaneously in engineering investigation, such as Ci’ha Gorge hydropower station. Few of multi-buckling has been studied and the mechanism of deformation and failure within it has not been uncovered yet. Taking buckling characteristics of consequent bedding rock slope at right bank in Ci’ha Gorge hydropower station as an example, this paper obtained complete multi-buckling categories on the basis of field investigation and promulgated research results. Moreover, the mechanism of each failure mode is analyzed tentatively by numerical simulation.The main achievements are as follow:(1) According to established research results, formula of calculating critical slope length and critical load of buckling failure are summarized and the major factors inducing buckling failure are concluded. Then, buckling failure mode is presented consisting of single-buckling and multi-buckling, including one-layer collapse, slipping collapse and retaining wall collapse.(2) Respectively, taking multi-buckling failure at left bank and at No.3 slope and No.1 slope downstream in Ci’ha Gorge hydropower station as the research object, the main mechanism of multi-buckling, obtained by means of field investigation and numerical simulation, are as follow:(a) Multi-bucklingin the same layer:Rivers incises- buckle – river incises again- buckle again.(b) Slipping multi-buckling:Hard rock layer at leading edge buckle-slide with large displacement-hard rock layer exposed at trailing edge buckle.(c) Retaining wall multi-buckling:Rivers incises-hard rock layer exposed at trailing edge buckle-riverincises again-hard rock layer at leading edge buckle.(3) The buckling mode varies with the combination of stratum and the way of river incision. For homogeneous rock stratum, multi-buckling in the same layer will take place eventuallyregardless of hard or soft rock as the river incises. For rock stratum overlapped by hard and soft rock, as river incises by the hard stratum leading edge, the slipping displacement of hard stratum is long enough as a result of its critical buckling length is longer and empty face is higher when the buckling failure takes place, which makes the soft rock exposed at trailing edge buckle easily. As a whole, it behaves as slipping multi-buckling. If river incises hard stratum first, both top and bottom of hard stratum will buckle, which acts as retaining wall multi-buckling.