| Anti-dip slope is a type of inclination of which the surface conforms approximately to the strike of the rock strata, and the surface dip is opposite to the dip of rock strata. It is generally acknowledged as a slope of high stability and less likely to appear losing stability; therefore, at present, there are only a few studies focus on its deformation characteristics and stability. With the quacking pace and extension of human engineering activities, issues in regard to the stability of this type of slope begin to appear extensively in mines, water conservancy and hydropower, highway and railroad slopes. During engineering practices, owing to the insufficient recognition of its deformation characteristics and evolution mechanism, man are often unable to determine its deformation tendency, resulting in making false judgement on its stability. Based on this, the author of this dissertation believes that a systematical research on the characteristics and evolution mechanism of anti-dip slope deformation is conducive to the advancement of theoretical research on prevention and reduction of anti-dip slope; therefore, is of significant engineering application value.Research concerning anti-dip slope requires researchers to identify its deformation characteristics, including surface deformation and deep deformation. Surface deformation is controlled by deep deformation and is a representation of the latter. It presents varied spatial deformation and failure characteristics as a result of its different spatial position and rock mass structure. Deep deformation mainly includes toppling deformation depth and changing patterns of strata dip within the range of deformation depth. Hence, only a systematical and comprehensive analysis of both surface deformation and deep deformation can accurately uncover the characteristics of toppling deformation.At present, only a few studies take evolutionary characteristics of anti-dip slope deformation as their research content. Most of them, however, are based on descriptive analysis of deformation characteristics of single engineering project in a certain particular stage and fail to regard it as a dynamic evolutionary system. To anti-dip slope, its toppling deformation tends take on different changing characteristics over time; therefore, different evolutionary stage of toppling deformation naturally corresponds to different deformation characteristics. This implies that toppling deformation needs to be seen as a dynamic evolution process for deformation characteristics in a certain stage is inadequate to reflecting the overall development state of deformation. Given the circumstances, the author of the present research applied multi-field evolution information to get access to comprehensive analysis so as to mark out evolutionary stages for toppling deformation and to establish corresponding relations between each stage and deformation characteristics. In this way, correct prediction of deformation development tendency is assured.Taking anti-dip slope as research subject and engineering geology and rock mechanics as the theoretical guidance, this dissertation carried out the present study from the following four aspects, with the employment of such technical methods as geological survey, indoor and outdoor test, three-dimensional laser scanner, ArcGIS and numerical simulation.1. Sensitivity of Influencing Factors of Toppling Deformation and Geometric Model of Prone-Toppling(1) Maximum horizontal displacement, deformation area and total displacement are selected as evaluation indexes. The calculation results with regard to the sensitivity of influencing factors of toppling deformation are obtained from the three evaluation indexes and are later compared and analyzed. The analysis shows that result based on total displacement is able to offset the deficiencies of the other two and perfectly meets the actual situation as well.(2) The calculation result of toppling deformation sensitivity indicates that among the first grade influencing factors, factor of geometrical characteristic has the maximum influence on toppling deformation; in the secondary grade, slope angle, strata thickness and density as well as Poisson’s ratio are high sensitivity factors; strata dip angle, internal friction angle of rock mass and stratification are secondary sensitivity factors; whereas, elasticity modulus, cohesion of rock mass, tensile strength, stiffness ratio of stratification and stratification cohesion are low sensitivity factors.(3) Under the action of geometric characteristic factor, response regularity result shows toppling deformation becomes more significant with the increase of slope gradient and strata dip angle; the total displacement of toppling deformation increases firstly and then decreases as the strata thickens, and reaches maximum deformation at 0.2m.(4) Support vector machine is applied to establish the prediction model for total displacement of toppling deformation. It stimulates a geometric model for anti-dip slope prone-toppling, which is a quarter spheroid with slope gradient 80°, dip angle of strata 80°, and strata thickness 0.19m as thecenter. The long equatorial radius of the spheroid is 31° (the axial direction of strata dip angle); the short equatorial radius is 21° (the axial direction of slope gradient), and the polar radius is 0.075m (the axial direction of strata thickness). The long equatorial radius of the spheroid:the short equatorial radius:the polar radius is 2.48:1.68:1.2. Analysis of Toppling Deformation Failure and Temporal and Spatial Evolution Characteristics(1) Xiaodongcao to Zhengjiadagou bank slope is essentially a bending and toppling deformation body. According to its special distribution features, the surface deformation of the bank slope can be divided into seven deformation areas. Areas of distinct surface deformation are found at the front and rear of the bank slope, with its macro manifestation displays surface tensile fracture, colluvial deposits slippage and strata bending and breaking.(2) The analysis results of geophysical prospecting, wave velocity, footrill and test pit show that the influencing depth of toppling deformation is 50m to 110m, with relatively shallow deformation depth at the front of the bank slope and deeper in the rear.(3) The analysis results of three-dimensional laser scanning of the front section of the bank slope and imaging interpretation of the rear reveal that the strata dip angle of the front presents no obvious change, and the rock mass of the bank slope mainly takes on shear deformation; the strata dip angle of the rear gradually steepens with the variation in depth. When the depth is within 0 to 40m, the strata dip angle is mainly an approximate 20° low-angle dip with gently variation; when it is in the range of 40m to 85m, the strata dip angle gradually steepens and tends to normal. Toppling deformation frequently appears when the depth is in the range of 40m to 85m.(4) Surface displacement monitoring results show that the front area of the bank slope is mainly a horizontal-based deformation and the rear a vertical-based. Deep displacement monitoring results show that bank slope of its elevation above 900m exhibits toppling deformation failure model, with relatively slow deformation rate and weak deformation strength; whereas, bank slope of its elevation below 900m displays shear failure model, with fast deformation rate and strong deformation strength.(5) The evolution cycle of bank slope toppling deformation is twelve months long. In the beginning four months, the middle area of the bank slope presents distinct deformation advantage, and the deformation extends linearly from the right side to the left; in the follow-up eight months, it gradually loses deformation advantage, and the deformation fades away from the left to the right in scattered spots. The belt-like deformation area in the middle of the bank slope determines the evolution law of the total bank slope deformation; the global deformation of the bank slope falls behind its deformation in central area. Moreover, the increase in the displacement of central belt-like deformation area tends to induce the increase in the total displacement of the rear. The belt-like area is inferred as clavicular section of the toppling deformation.(6) The largest areas with severe horizontal deformation are areas of medium slope gradient, low elevation and north slope exposure, accounting for 19.4% of total area; the largest areas with severe vertical deformation are areas of low slope gradient, high elevation and the north-west slope exposure, accounting for 87.9% of total area. Bank slope toppling deformation is a horizontal-based deformation with vertical deformation as the supplementary.3. Stability of Toppling Deformation and Its Evolution Mechanism(1) Simple shear test requires no presupposition of shear failure surface; it requires small shearing strength, large shearing strain, and is therefore a thorough test for specimen shear failure. The specimen failure crack presents 45° linear distribution along the diagonal, and the specimen crack loads side diagonal. Direct shear test crack approximately presents straight line hole-through shear failure surface, and develops into a near 45° flocculent secondary crack. Results of numerical simulation tests show that the ratio of simple shear to direct shear test cohesion is 1.0:1.66; the ratio of their friction angles is 1.0:1.08; mechanical parameters difference is mainly reflected in cohesion, and the difference existed between simple shear and direct shear test is mainly caused by the distinct variation in the ratio of strain energy to frictional energy transited by server work during the tests.(2) Stability coefficient computational methods of Srama, WGB and Limited Rigid Body Equilibrium are applied to calculate the bank slope stability, and the results show consistency in variation trend of stability. As WGB method takes connectivity of sliding surface and shear stress of strip and block flank into consideration, the calculated result of stability coefficient is relatively high; because Limited Rigid Body Equilibrium leaves out the connectivity of sliding surface and the shear stress of slice flank, the stability coefficient result worked out by this method is relatively low; Srama method takes the shear stress of strip and block flank into account, yet leaves out the connectivity of sliding surface, so the result of the stability coefficient worked out by this way is mediate. Layered anti-dip rock slope deformation as is controlled by the structural plane of rock mass presents shear deformation along the layer of the rock mass. Therefore, in view of the advantages of WGB and Srama in the calculation of the shear stress of strip and block flank over Limited Rigid Body Equilibrium, the former two are more suitable for anti-dip slope. Besides, both WGB and Srama divide strip and block on the basis of actual rock formation, and hence can better reflect the authentic deformation of layered anti-dip rock slope than vertical division of strip and block by the method of Limited Rigid Body Equilibrium.(3) Before the action of reservoir water, bank slope with elevation below 700m belongs to stability area where the rock mass of the bank slope is prone to develop shear deformation under the effect of sliding force resulting from top toppling deformation and provide anti-sliding force. Bank slope with elevation in the range of 700m to 900m belongs to relatively stable area, a mixing zone of bank slope slippage and toppling failure, with the strata strip and block presents two different deformation models. Bank slope with elevation above 900m belongs to basically stable area and the rock mass in this area develops toppling deformation and provides sliding force. After reservoir water takes effect, area with elevation less than 700m displays weakening in rock mass and decreasing in strength, resulting in local shearing deformation failure, and transforming from stable area to unstable area with the slope surface deformation takes on horizontal sliding. Bank slope with elevation between 700m and 900m transforms from a relatively stable area to a less stable area under the traction of bottom sliding deformation and the push and press of top toppling deformation. Bank slope with elevation above 900m is less affected by reservoir water; changes in its stability can be faintly detected due to the effect of traction from the middle and forepart deformation. Therefore, it still belongs to basically stable area with vertical toppling deformation takes the main model.(4) Bank slope toppling deformation and interface elevation of shear deformation are proportional to bedding mechanics parameters. The higher the bedding mechanics parameters, the smaller the bank slope toppling performance area. Under the effect of the internal friction angle of bedding, interface elevation is higher than cohesion. When cohesion is less than 50kPa and internal friction angle is small than 30°, most of the slope bank area develops toppling deformation, with shear deformation area only distributed in area of 53m to 56m elevation. When internal friction angle is larger than 35°, most area of the slope bank takes on shear-based deformation, with toppling deformation only distributed in area of elevation above 1000m.(5) The early stage of bank slope deformation displays the increase in toppling deformation strips and blocks. The angle of deflection of bank slope is relatively small with the deflection range within 8°, which is consistent with the occurrence interpretation results of imaging. The follow-up toppling deformation of bank slope presents toppling deformation strips and blocks as well as the sharp increase in toppling deformation angle. In the absence of external factors, bank slope inclines to evolve in 140 toppling strips and blocks and around area of toppling angle 30°.(6) Under the action of reservoir water, the stability of bank slope reduces significantly. Compared to the original evolution path, the new one drifts slightly to the coordinate axis of toppling strips and blocks, reflecting that the reservoir water has no significant impact on the evolution path of bank slope deformation. By reducing the rock-soil body mechanical parameter of the slope toe, reservoir water weakens the shearing resistance strength at the front of the bank slope, and thus brings down the total stability coefficient of the bank slope.4. Multi-field Evolution Characteristics of Toppling Deformation and Its Evolution Mechanism(1) Based on the examination of micro-parameters of bank slope rock, the present study ascertained the mechanics strength parameters of bank slope rock mass by applying Hoek-Brown criterion and numerical test; it stimulated the evolution process of bank slope toppling deformation by employing PFC software, and obtained multi-field evolution characteristics of stress field, displacement field and energy field during the process of bank slope deformation. It shows that the front area of the bank slope takes on shear deformation under the effect of horizontal stress; the middle and the rear area presents toppling deformation as a result of the action of vertical stress.(2) The analysis results of evolution characteristics of the stress field demonstrates that the bank slope displays high stress state at the slope toe gully; the shallow stress field of the bank slope is vertical stress-based and horizontal stress, vertical stress and shear stress increase gradually with depth. During the evolution process, stress fields vary significantly according to areas and evolution periods.(3) The analysis results of evolution characteristics of the displacement field reveals that the surface is a horizontal-based deformation; the displacement values and speed reach to the largest when the horizontal displacement elevation is in the range of 900m to 1050m, and centered on this range the displacement values and speed gradually decrease towards the direction of slope toe and crest, with the horizontal displacement value at the slope crest larger than that of the slope toe. Surface vertical displacement along with regularities of the spatial distribution of bank slope parallels to horizontal displacement. The fore area of the bank slope exhibits uplift as a result of shear deformation. The deep displacement of the mid-area of the bank slope increases with depth, presenting typical toppling deformation features.(4) The analysis results of evolution characteristics of the energy field shows that in the process of toppling deformation evolution strain energy is the biggest energy, with friction energy follows up and kinetic energy the smallest, and each energy increases along with time step and the energy zoom interval is between 100,000 and 300,000 time steps. Based on evolution characteristics curve of energy field, the evolution process of bank slope toppling deformation is divided into shear deformation stage, stage of main toppling fracture surface hole-through, stage of secondary toppling and fracture surface development.(5) During the shear deformation stage, deep horizontal stress of the bank slope toe rises sharply and its value tends to get larger when the deformation is closer to the valley bottom. High horizontal stress causes the shear crack of the bank slope to form cut-through which gradually stretches from the valley bottom of slope toe to the deep area of slope body, developing shear fracture surface. Influenced by horizontal deformation traction at the forepart of the bank slope, the middle part of the bank slope experiences increase in vertical stress under its own weight, causing deflection in strata dip angle along the deep and the occurrence of topping fracture. The toppling fracture surface then stretches from the middle part of the bank slope to the slope crest and cuts through, shaping major fracture surface. During the stage of secondary fracture surface development, bank slope body deformation is controlled by vertical stress, with its major fluctuation occurs in the middle, secondary at the front, and stable fluctuation at the rear end. The secondary fracture surface at the forepart approximately parallels to the major fracture surface, displaying dispersed distribution in the shear deformation area of the bank slope, with no deflection in strata dip angle. The secondary fracture surface in the middle of the bank slope conforms to the major facture surface in arc shape and produces outer slope development. Besides, the closer it gets to the slope surface, the steeper the dip angle of secondary fracture surface tends to be and the smoother the strata dip angle becomes. The secondary fracture surface at the rear edge of the bank slope shows small-scale development, parallels to major fracture surface, and has small deflection in strata dip angle.The innovation of the present research includes:(1) Based on the evaluation indexes of maximum horizontal displacement, deformation area and total displacement, it compared and analyzed the results of the sensitivity of influencing factors of toppling deformation, determined their sensitivity values, and concluded the prone-toppling geometric model for toppling deformation by probing into the response regularity of toppling deformation under the action high sensitivity factors.(2) By applying such measuring techniques as three-dimensional laser scanner and borehole camera, it comprehensively analyzed the characteristics for toppling deformation in spatial variation; by using ArcGIS, it analyzed the space-time evolution characteristics of toppling deformation, and determined the distribution areas of shear deformation and toppling deformation.(3) By synthesizing the evolutionary characteristics of displacement field, stress field and energy field, it divided the evolution of toppling deformation into different stages and illuminated the evolution mechanism for toppling deformation. |
PDF Full Text Request