| In southwestern China,unique high mountains and ravines are developed there.With the development of large hydropower stations in this region,stability problem of high slopes become more serious.Based on well-knit geological investigation and detailed geological data,by means of detailed description and analysis of slope structure,survey of deformation phenomena,estimation of joints'trace,simulation of rock mass discrete network and complex slope model,this paper firstly comprehensively analyses deformation and failure mode and potential dangerous paths of high slope,then calculates discontinuity by combining discrete network and projection of joints in bad with a certain width.Through the above systematic analysis,this paper primarily obtains the following results.(1)From the point of engineering geological characteristics and engineering geological significance,rock mass structures were systematically classified and described in detail and analyzed by mathematical statistics.Finally,we obtained spatial distribution characteristics and engineering geological features of all structures(including deterministic and random discontinuities).The slope structure at the dam site is composed of steep dip faults and amphibolite dykes,and gentle to medium dip joints.(2)Combining slope structure and evolutionary history of river valley,according to the typical intermittent distribution characteristic of gentle to medium dip concentrated joints with gentle to medium dip angles and considering influence of these joints to the slope stability,this paper made a special study of the density characteristic,spatial distribution and composite mode,statistical homogeneity and origin mechanism.?Obtained the spatial distribution and composite mode of gentle to medium dip joints:Most joints are approximately parallel to the slope surface and only develop in surficial slopes with the depth of 150m to 200m;In different elevation,these joints demonstrates a trend as“steep dip in high slope and gentle dip in low”;They are not uniformly distributed along adits and they appear iin the form of concentrated joints belts,sparse belts(or even no joint belts),which is a unique phenomenon of the rock mass in the slope;Distribution of these joints are closely related to dykes and faults(On the one hand,most joints extend to dykes and faults and then disappear and some joints are well developed between dykes.On the other hand,tension fractures along faults and dykes provide material source for the joints filled with clay.)?Deeply analyzed the origin of gentle to medium dip joints by combining geological investigation,scanning electronic microscopy(SEM)and FLAC~3DD simulation the three methods.We believe that these joints are the result of slope unloading,which is responses to intermittent rapid down-cut of the Nujiang river.When the river down cut rapidly,peak stress in the slope is smaller than instantaneous strength of the rock mass and there's insufficient time to develop micro-crack or micro-cracks can't cut through to form macro-fracture.When the river down cut slowly,the hump stress exceeds long-term stress of the rock mass and then generate unloading joints.With the change of down cut speed,unloading joints“jump”from one concentrated joint belt to another.The influence of the existing of weak faults and dykes in hard rock for the distribution of gentle to medium joints mainly performance in two aspects.On the first hand,when there are some neighboring narrow faults or dykes exits in hard rock,tensile and relax centralize along contact boundaries and high shear strain increment zones also develop between these neighboring faults or dykes.On the other hand,a large area of weak faults will let unloading happened in the whole weak zone uniformly and generate less gentle to medium dip joints.(3)According to unloading phenomena investigation in the field in detail,combining the four quantitative indexes of longitudinal wave velocity,integrity coefficient,sum of joint openings and open joint density,this paper describes the unloading characteristics,zonation distribution and composite pattern.?Unloading characteristics and the zonation distribution mainly reflected as“strong unloading only local developed,weak unloading is the primary and deep unlading typically developed”.That's means:strong unloading is not well developed,which is mainly limited in surficial slopes about 15m depth and mainly show wide tension opening.Weak unloading is primary present and boundaries are nearly parallel to landform.Unloading mechanicsm is mainly tension along steep structures at high elevation and turns into shear-tension,shear deformation at lower elevation.Deep unloading is a unique characteristic at the dam site.After a long section of fresh and intact rock in adits,opening along single joint,fault,dyke boundary and concentrated joint belt again could be observed.?As a consequence of the unloading mechanism at the dam site,the unloading model at the dam site present as stairs,which is composed of steep dykes,faults and gentle to medium dip joints(concentrated joint belts).(4)By adopting Laslett,H-H and generalized H-H the method,according to zoning features,joints trace length were evaluated of different zones and the applicability of the three methods are discussed.Because of the limit of evaluation of long trace length of the measurement window,using the fractal theory and considering measurement scale effect,trace length of long joints are revised.Discontinuity of joints also calculated by the Laslett and H-H method.As a consequence of the result of continuity and combining geological deformation phenomena,potential dangerous paths ae preliminary evaluated.The potential dangerous paths in the slope mainly dominate by small scale in surficial slope and the deformation model presents as stairs.(5)In PFC,uniaxial compression and direct shear test are established to calibrate micro-parameters to correspond to macro-scale behavior of rock and structures.This process provides fundamental for the simulation of mechanism of parallel concentrated joint belts and for the stability evaluation of high slopes.(6)Specific to the unique characteristics of intermittent concentrated gentle to medium dip joints,based on field geological survey of rock mass structure and deformation,PFC was employed to simulate the mechanical properties and deformation and failure modes of rock mass with different number,spacing,dip angles,total width of parallel joints under different confining stresses.?Four deformation phenomena of rock mass with concentrated joints are identified:shearing along a single joint,shearing along multiple parallel joints,shearing across joints,and shearing through multiple joints and shaping of joints into stairs.?Peak strength and elastic modulus both decreased with the increase of SJ number.Especially when one joint existed in an intact rock,the peak strength and models declined obviously.But with the increase of joint number,the falling range become smaller.?In the case of fixed spacing,with the increase of joint number,fracture width increases,and the stair-shape phenomenon becomes increasingly obvious.The distance between tensile cracks,which are developed between joints,are have something to do with the joint spacing.Large spacing formed large distance and small spacing formed small distance.When the total width of the jointed belt is constant,the spacing between joints decreases,and the interaction effect between joints becomes obvious as joint number increases.?When dip angle is gentle,with the increase of joints number,peak strength of rock mass has not changed much.But peak strength of rock mass decreased obviously with the increase of joints number.For the rock mass with the same number of joints,with the turning of dip angle from gentle to steep,compared to intact rock,deformation mechanism of turns from has little influence to shear-tension along joints and final turns as tension along steep joints.?With the increase of confining stress,the mechanical property of rock mass with the same joint number but different spacing become similar.(7)Based on density and spatial distribution,slope structure was divided into different zones.The probability statistics models of random joints are calculated.By the DFN in PFC,discrete network of random joints in the whole slope is built and then was coupled with deterministic faults and dykes.Finally,the representative discrete network of the dam site is obtained.By comparing with the measured data in adits,spatial distribution and composite mode,we test the simulation validity.(8)Slope rock material was established by PFC,then the slope material was combined with discrete network and finally obtained the complex slope model.Next,based on gravity increase method,deformation and failure mode and potential dangerous paths are studied.Comparing with geological analysis and 2D discontinuity calculation of gentle to medium dip joints,the deformation model of slope is mainly shown as shear-tension.On the left slope,at high elevation,the potential failure path shapes as long board,which is composed as tension along steep dip large fractures and compression-shear at the slope toe.At low elevation,the potential failure path shapes as stairs,which is composed of tension along steep dip faults and dykes and shear along gentle to medium dip joints.On the right slope,the potential failure model presents as shear-tension.The potential dangerous paths shows as small stairs in surficial slope,which is also composed as steep dip faults and dykes and gentle to medium dip joints.But there is still a large potential dangerous path in deep slope,which could lead the whole slope to fail.(9)The discrete network was export to CAD software,then projection method was used to calculate discontinuity of every whole path and different segments of each path,which could help us to find the lock segment of the dangerous path.The result shows slope deformation and failure model is stairs-shape-based.Deformation model of the whole slope present as“three segment model”.In surficial slope,value of connectivity rate is high.But for the whole failure path,the connectivity rate is low.(10)Based on well-knit geological investigation and detailed geological data,this paper establish the new research idea:based on deformation and failure model analysis,by combining slope discrete structure network and gravitational field,firstly potential dangerous paths are obtained,then based on the discrete network of the whole slope,discontinuity rate was calculated,which is used to evaluate lock segment of potential path.The new research idea improves the reliability of the stability and discontinuity evaluation of high slopes. |
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