| The alpine deep canyon region of the southeastern margin of Qinghai-Tibet Plateau provides favorable terrain conditions for a large number of slope deformations including toppling.In the internal and external conditions which conduce to deformation.A series of the toppling deformation-rupture signs in the anti-dip slope make the slope structure very complex.In particular,Breaking Face or Breaking Belt that a band-like region is a position where shear mechanical properties of the rock mass and soil are significantly reduced.So this region is seen as one of a potential shear slip interface.It may eventually lead to shallow or deep slip.It can be seen that the shear mechanical properties of Breaking Belt Rock Mass(BBRM)are critical.In view of this,on the basis of summarizing the existing research results,through the investigating of two toppling cases,this paper puts forward four meanings of toppling deformation-rupture signs for anti-dip slope.That is,the evidence of the toppling of anti-dip slope,the basis for dividing the range of toppling extent,the factor of rock mass quality evaluation and the potential shear slip interface in slope.Then the writer analyzes the mechanical causal mechanism and distribution of deformation-rupture signs which are caused by toppling,and the distribution feature of the toppling degree is summarized.The possible distribution of Breaking Belt in the anti-dip slope is discussed from two aspects of engineering geological survey and numerical calculation.Furthermore,the type of BBRM is classified according to the lithology,causal mechanism and cataclastic structure.And the quality of rock mass is evaluated.For BBRM whose type is brittle broken,quantitative characterization of the degree of fragmentation is carried out by using the survey method based on image acquisition and processing and by using fractal analysis theory.Finally,the shear strength model for brittle broken BBRM is discussed.The research results have some theoretical significance and application value.The main contents and research results of this paper are as follows:(1)Study on the distribution of Breaking Belt in the toppling deformation slope.The study on the distribution of Breaking Belt in the slope is carried out from aspects of engineering geological survey and calculation.The distribution of toppling deformation-rupture signs on the surface and in the internal of the slope are the special contents in engineering geological survey for toppling deformation slope.Inside the slope,there are six forms of deformation-rupture signs caused by toppling.And the distribution of signs as the main basis for summing up the range of toppling extent.The potential instability interfaces develop in the positions where the toppling deformation-rupture signs are very developed,where lithology and rock structure changes greatly before and after in some staggered area,where unfavorable fault,faulty face and weak interlayer are developed.The separatrixes of the range of toppling extent also tend to be determined at these positions.In the joint finite element numerical calculation,strain yield elements develop in the upper side of rock plate located in the middle-upper sides of the slope.It is shown that the strain stress is easy to control the failure of the rock plate at the initial stage of the toppling.And the linear regression of strain yield unit coordinates is conducted.There is a good correspondence between the dip of the straight line and the dip of the rock plate which is located in anti-dip slope.(2)Study on structural characteristics and rock mass quality evaluation of BBRM.Rock plate which lithology is different has different toppling results,according to this,the types of BBRM are divided into brittle broken,flexible bended,and mixed.The main characteristic of the brittle broken type is that the lithology is a hard rock with elastic or elastic-plastic,such as limestone,dolomite,sandstone and so on.There is a significant change in the dip angle of the rock plate which caused by rock plate broken.Tension-shearing rupture planes develop in rock mass,and these planes accompany by a certain open.Or the rock mass tends to be fragmental block.The whole rock mass is broken and loose.The main characteristic of the flexible bended type is that lithology is a soft rock with plastic-elastic-plastic or elastic-plastic creep property,such as slate,phyllite,mudstone and so on.The dip of the rock plate is gradually changing from steep to slow.Or the "S" type of crumpled bending develops.The inner rock mass in the bent zone has a certain mylonite structure.The rock mass is weak on the whole.The mixed type has some brittle broken feature and some flexible bended feature.Tension-shearing rupture planes develop but close.It is presumed that after the pre-broken the rock mass re-compacted under the overburden pressure,at the same time the rupture planes closed again and re-cemented.The toppling angle of the rock plate is large but has a better integrity than the first two types.The results of rock mass evaluation show that BBRM belongs to class ? which means poor rock mass.And the Hoek-Brown method is used to evaluate shear parameters.(3)Quantitative analysis method study for the fragmentation degree of BBRM.Aiming at PD02 137~142m brittle broken BBRM of Xingguang three group anti-dip slope,Xiluodu.Using high-digit digital camera to acquire the image of broken rock mass.The distribution of structural planes and fragments is obtained through vectorizing.It is found that BBRM has different characteristics of different degree of fragmentation.That is,structural planes cutting,fragmented,not completely out of the matrix rock.Statistical analysis results of fragments are acquired: Maximum Observed Dimension(MOD)of the fragment corresponds to lognormal distribution,the mathematical expectation is 4.66 cm,the standard deviation is 1.62.Short Axis Observed Dimension(SAOD)of the fragment corresponds to poisson distribution,the mathematical expectation is 2.89 cm,the standard deviation is 1.70.The ratio of MOD to SAOD corresponds to index distribution,the mathematical expectation is 2.03,the standard deviation is 0.82.From two kinds of fractal analysis of blocks distribution and structural planes distribution.The former has a fractal dimension of region(c)is 2.5073,and the latter has an average fractal dimension is 1.85.(4)Study on shear strength model of brittle broken BBRM.The region(c)of PD02 137~142m brittle broken BBRM of Xingguang three group anti-dip slope tends to be Fragmented.It is the region where mechanical property is lowest.The zonal region(c)extends to outside of slope with gently dip angle.It is harmful to slope stability.In the process of deformation evolution of slope,the most probable failure of this region is shear slip to outside.Shear mechanic parameters are equivalently transformed form Barton model: internal friction angle is 24°,cohesion is 0.77 MPa,and transformed form Hoek-Brown model: internal friction angle is 26°,cohesion is 2.1MPa. |
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