| Rock mass,existing in a certain geological environment,is a special geological body with certain rock component and structure,and in the long geological history it has experienced repeated geological activities,frequent deformations and failures.Rock mass structure cybernetics proposes that rock mass structure not only reflects the tectonic evolution history, also controls its deformation-failure character.Based on the viewpoints mentioned above,the thesis makes a systematic research on rock mass structure of shoreline slope in New Badong Country,three Gorges reservoir.Due to its poor geological condition,there exist plenty of ancient landslides in the new Badong county,i.e.Huangtupo landslide,Zhaoshuling landslide etc.Although almost landslides have been controlled by geological disasters and its engineering treatment for three times,while with water storage level up to 175cm,still some environmental geology and engineering geology problems bothering residents in the New Badong Country needed to be solved,such as " whether fan-shaped slope is formed by deep sliding?" "if Vojoint landslide is formed by the weak and soft zones developed in shoreline slope slide?" Regarding to above-mentioned questions,the thesis analyzes structure of shoreline slope in New Badong Country based on both observation data of monitoring profile(300m deep)and others' achievement;indicates the formation and evolution process of shoreline slope slide and internal and external geological enviroment during its development;sets up a spatial model of rock mass structure via systemetic research of its deep structure which provide a reliable basis for deep stability forecast of shoreline slope after water storage;explains the formation mechanism of complicated landslides existing in terms of rock mass structures of slopes;studys the main influence factors of different landslides to provide reference for evaluation of similar structural slopes' stability.To conclude,this thesis illustrates evolution process and stability of the shoreline slope in New Badong County and has theoretial and pratical significance for analysis, reduction and prevention of geological disaster.Phased achievements included are as follows.(1)Based on Gu Dezhen's classification of 5 grades on rock mass discontinuity,the thesis summarizes and perfects the acquisition and description method of discontinuity;proposes the acquisition approach ofⅢ,Ⅳdiscontinuity,combining field measurement,digital photography and rock core analysis together.The method has three innovations,firstly correcting distortion coefficient of digital camera by field scale.Secondly the strike-dip of discontinuous is interpreted by comparing the discrete degree with field measurement data.Finally the integrity degree of deep rock mass structure is represented by the RQD,quality coefficient and fractal dimension value of rock core.According to the ultrasonic detection data,the fifth degree discontinuity is described by the nonlinear relation of density,density increment from drying to saturation,compressive strength,compaction coefficient and longitudinal wave velocity of rock block.(2)Fuzzy cluster method(FCM)is applied to eliminat subjective uncertainty when dividing discontinuity group.The author improves precision of discontinuity's mean trace length by empirical adjusting the intersected number of discontinuity and sample window.The contour map of spatial RQD of rock mass is drawn by simulating three-dimensional network of discontinuity.(3)By combining deep borehole with field investigation data,the bottom contour map of third Member of Triassic Badong Formation(T2b3)is drawn,the character of disputed faults is defined.Two stripes of normal faults cut through the bottom of T2b3 on the front of slope from Daping to Baitupo.The faults are thrust fault on both sides of Zhaoshuling landslide.The Maogouliangzi faults belong to shallow fault which haven't long distantness vertical lifting or horizontal offset in the stratum of T2b2.(4)Reservoir shoreline slope in New Badong county was in the complex littoral facies environment in sedimentation time.T2b3 sedimentation undergoes a repetitious marine transgression and regression process,which includes evaporate platform(supra-tidal belt), restricted platform(inte-rtidal belt),open platform(shelf lagoon),platform edge shoal,open platform(shelf lagoon),restricted platform(inter-tidal belt),open platform(shelf lagoon)as well as platform edge shoal;weak intercalation,which is mainly distributed in open platform (shelf lagoon)and restricted platform(inter-tidal belt),was formed in the period of relatively dynamic sedimentary environment.New Badong county undergoes a complex past of tectonic stress.For different areas,action strength and stress concentration are different.Especially Yangtze River valleys in front of Xirangpo Slope,Zhaoshuling Slope,Baitupo Slope as well as front of Huangtu Slope hold a concentrated tectonic stress.In this region,joint,cleavage and interlayer sliding belts develop widespreadly,which provides tectonic conditions of complex deformation of slope.Affected by super-genic transformation of external dynamic force,tension stress areas in the reservoir shoreline of New Badong county,formed in the process of Yangtze River cutting, focused on steep slope section near riverbed,fault zones in the end of the slope,contact zones of soft and hard rock as well as changing zones of terrain.Underground water plays an important role in the super-genie transformation of rock mass structure for two characteristics,i.e. dissolution of limestone and weathering of mudstone of mud-limestone,transformation action of underground water irstly occurs along structure plane,while its result is controlled by original structure plane property and scale.The geological evolution process of reservoir shoreline slope in New Badong county is reflected by that of rock mass structure,which explains whether obvious sliding plane exists in the interface between T2b2 and T2b3.Yhe result shows that the interface between T2b2 and T2b3 is continues transition without no sliding conditions,and the sliding mainly occurs in the interface of soft strata at the certain range of the interface between T2b2 and T2b3.(5)The classification method of deep rock mass structural integrity is adopted to make the systemetic division of Baitupo Slope and Xirang Slope into five ranks,i.e.excellent,very good, good,poor and very poor.Controlled by reservoir shoreline litho-logy and structure features in these two slopes,the integrity degree of rock mass in Baitupo Slope is poorer than Xirangpo Slope,and the integrity of rock mass of upper block is poorer than footwall rock mass in the front of Baitupo Slope.(6)Rock block strength is analyzed by energy consumption in rock test,using the work of peak external load and the energy dissipation of rock block rupture to characterize soft and hard degree of rock block,use the fracture energy ratio between the Pre- and Post-peak and the dissipation rate of fracture energy to characterize the brittle and viscous degree of rock block. The results show that the soft and hard degree of rock block is uneven distribution in vertical direction,it is closely related to the sedimentary environment and mineral composition of the rock and the strength of the rock whose gray matter is higher in mineral composition is greater than the rock whose clayish fine is higher.According to the integrity degree of the rock and the distribution of weak and soft zone,the author carries on intensity zoning in the reservoir shoreline of Baitupo and Xirangpo,estimates strength parameter of rock mass via geological strength index(GSI)and divides it into four strength grades.(7)In terms of tectonic structure,distribution,genesis,strength etc.,the author carries on system research for reservoir shoreline deep weak and soft zone in New Badong City.13 strips transfixion weak and soft zone which develops in the T2b3 strata can be divided into weak intercalation being rich in clayish fine,cataclasite weak and soft zone,corrosion transformation weak and soft zone and soft rock weak and soft zone according to the substance in weak and soft zone and structural characteristics.The genesis of weak and soft zone is most controlled by the deposition and tectonism of original rock.After the formation of fracture zone,and then, fracture zone is subjected to the supergene transformation of groundwater,gray matter composition is corroded,so the content of clayish fine is relative increasing,river continues down-cutting and recementing to form present weak and soft zone structure.With electron microscope scanning(SEM),the author obtains the microstructure of weak and soft zone,and find that weak and soft zone widespread develop scratch and the minerals show directional alignment,all of that reflect the characteristics that weak and soft zone exists deep creep. Analysising the comprehensive shear strength of weak and soft zone from geological evolution and scale effect,the author thinks it experiences groundwater change transformation caused by river down-cutting after the formation of the weak and soft zone.Its development direction can be divided into two species,one hand is corrosion softening,which happens when the groundwater cycle becomes strong,strength recycled after repeat consolidation,which happens in the environment of groundwater retention or no groundwater.The strength of weak and soft zone which contains crushed stone is similar to rock mass strength which contains microfissure, and it has obvious scale effect.According to the test data and the strength data of landslide slip belt soil in Badong new urban,the author thinks it is more reasonable that the angle of shearing resistance in weak and soft zone takes 25-30°.(8)Based on the properties,density of structural plane and its intersected relations with slope,the rock mass structure of slope is divided into four classes,twelve subclasses.The statistical results of rock mass structure and landslides from head of the Three Gorges reservoir to Badong shoreline indicate that the variational inclination co-rotating shoreline slope is a kind of the most developmental rock structure.This kind of structure develops in the concentrated part of tectonism,the slip surface is chair-shape or wavy.Considering the resistance effect of the lateral boundary of slope,combing rock bridge failure theory of the direct shear test,represented with T2b2 and T2b3,the solving process of upper limit value of angle between strata's inclination and aspect of co-rotating slope is derived.It holds that the upper value of angle is relative with the degree of soft and hard,the hard rock's upper value of angle is lower than the soft rock's.(9)considering the scale effect of rock structure,the evaluation system of rock stability of shore slope is proposed which is three levels including region-urban-single slope.Using new city zone of Badong as the example of regional,urban rock stability evaluation of slope,the spatial rock structure evaluation method based on rock structure fuzzy recognition and information model is proposed.The index weight of fuzzy recognition is obtained from rough set,and the rock structure is recognized by fuzzy theory.Basing on the classification of rock structure,applying information model to evaluate spatial stability of slope,the comparison between evaluation results and present hazard is done,which verifies the rationality of the method.Using the main slope rock structure developed in shoreline of new city zone of Badong,the stability evaluation method of single slope which has different rock structure is discussed.Firstly, the consequent layer co-rotating slope whose slip surface has two kinds of structures and strength constitutive relations,that is main slip segment of consequent layer has the characteristics of strain softening,and resistance segment of incision layer is elastic brittle.Cusp catastrophe theory is used to discuss the occurrence condition of consequent layer slope.The stability of consequent layer slope is relative with stiffness ratio of the two material and slope shape,combing test and experience data,it holds that stiffness ratio is related with normal stress and times of shear of slip surface.When the front unloads or the back edge loads,the stiffness ratio will decrease,it is easy to induce slide.Periodical lifting of water level and rainfall annual is equivalent to repeated shear on slip surface,it leads to the change of stiffness ratio,that's why the slide is always associated with many times displacement acceleration.Secondly,for incision layer or wedge slide,slip surface is always formed by transfixion of structural plane,proliferates connected rate is proposed,probability distribution model of minimum unit area shear strength is obtained.Finally,based on the deep rock structure and intensity zoning of Baitupo slope, using numerical analysis to simulate the change of seepage and stress field after the operation of reservoir.Based on strength reduction of FLAC,the deep stability under deferent condition are calculated,it holds that the shoreline is overall stabile during the operation of the reservoir, under limit state of strength reduction,the slip surface is shear transfixion along zone of weaknessThis thesis pays its priority on 300-meter core in New Badong county,the research data of rock core is very valuable,not only reveals the geological evolution history and deep structure information of T2b3,the main easy-sliding stratum,but aslo it is significant to interpret the formation cause of main slides.And meanwhile a set of systematic evaluation models and methods are established via rock structure research in New Badong county.Dynamic evolution of rock structure and multi-scale evaluation model proposed in this thesis has theoretical significance for similar slope evaluation.The research results have important practical significance for engineering construction in New Badong county and stability prediction of shoreline slope after water storage.
|
PDF Full Text Request