| The rock mass has obvious structure characteristics,which is composed of intact rocks and joint networks.Rock joints,such as bedding planes,faults,cracks and uncomformity interfaces,are affected by the geological forces inside and outside the Earth.Usually,the mechanical properties of rock joints are significantly lower than that of intact rocks;therefore,the mechanical properties of rock joints are key factors controlling the deformation,strength and stability of engineering rock mass.As one of the important mechanical properties for rock joints,the peak shear strength of rock joints is related to rock type,stress state,joint roughness and so on.Among the above factors,the joint roughness has a significant impact on the shear behavior of unfilled rock joints.Therefore,it is of theoretical significance and application value to quantitatively evaluate roughness and peak shear strength of rock j oints,whose results can be applied to evaluate the stability of rock mass in engineering practice.However,the existing roughness quantitative evaluation methods are often based on a single roughness parameter,and it is difficult to fully describe the characteristics of rock joint surface morphology,which leads to the difficulty in fully reflecting the contribution of rock j oint roughness to the rock j oint shear strength.Meanwhile,these methods usually neglect the high-frequency components of rock joint surfaces;thereby causing the deviation of the quantitative evaluation of roughness and peak shear strength of rock joints.Thus,the roughness parameters should be selected from multiple aspects based on the shear behavior of rock joints,and the spectral characteristics of rock joint surfaces should be analyzed to fully consider the high-frequency components contributed to roughness and shear strength of rock joints.Then,the roughness and peak shear strength of rock joints can be quantitatively evaluated,which can be better served to select shear strength parameters of rock joints.Considering the main drawbacks in the current research,detail studies were conducted to quantitatively evaluate roughness and peak shear strength of rock joints.First,rock joint profiles with available joint roughness coefficient(JRC)values were extensively collected from the literature.Then an inclination angle factor and an amplitude height factor were obtained through factor analysis.Subsequently,based on the above main factors,a support vector regression(SVR)model used to predict JRC values was derived.With the consideration that the amplitude height factor and the amplitude height parameters commonly used in the literature are difficult to effectively reflect the high-frequency components in the rock joint surface contributed to the rock joint roughness,an amplitude height index taking both high and low-frequency components into account was proposed through analyzing the spectral characteristics of the rock j oint profiles based on spectral analysis.Then a new roughness parameter combining the amplitude height index and an inclination angle parameter of rock j oints was derived,and the detail application process and validation of the above proposed rock joint roughness quantitative evaluation methods were carried out with the morphology data and laboratory direct shear test results under constant normal stress of natural rock joints.Second,the new roughness parameter based on spectral analysis was expanded to three-dimensional(3D)roughness parameter,and the quantitative calculation method of 3D JRC was consequently proposed.Based on the JRC-JCS shear strength model,a new peak shear strength model considering both the high and low-frequency components contributed to the rock joint shear strength was derived.Finally,taking the rock slope of the left bank abutment in the middle dam site of Rumei Hydropower Station as an example,the roughness of rock j oints in the study area was quantitatively evaluated based on the scanned morphology of laboratory small-sized rock joints and large-sized rock joints located in the field footrill.Consequently,the shear strength parameters of those rock joints were estimated with the proposed new peak shear strength model.The main research results are summarized as follows:(1)The collection of natural rock joint surface morphology data was carried out.The surface topography data of laboratory small-sized rock joints and the large-sized rock joints in the study area were obtained with laboratory and mobile laser scanners,respectively.Then,the denoising and modeling of rock joint morphology data and the alignment of the 3D morphology model were conducted with the Matlab and Geomagic softwares.Note that the laser scanner used for the large-sized rock joints in the field has a lower accuracy than that used in the laboratory;meanwhile,there are more interference factors in the field than that in the laboratory environment.Thus,it also involves filtering the high frequency noise in the process of processing and modeling the morphology data of large-sized rock joints in the field.(2)The quantitative evaluation method for rock joint roughness based on factor analysis and support vector regression(SVR)was proposed.First,eight statistical parameters related to the inclination angle,the amplitude height,and distribution characteristics of those two parameters for asperities along rock joints were selected to quantitively characterize the rock joint roughness with the consideration of the rock joint shear behavior Then,two common factors,named "inclination angle factor" and"amplitude height factor",respectively,were extracted to estimate the JRC value.Consequently,the overlapped information caused by the correlation between the original statistical parameters can be avoided,and thus the effect of overlapped information on the JRC estimation can also be effectively averted.Finally,an SVR model for the JRC prediction was derived with the two common factors and the collected database containing rock joint profiles with available JRC values,and the SVR model was validated through the comparison with JRC back-calculated values and existing methods in the literature.Meanwhile,the JRC prediction results for profiles collected from the natural rock joint in different shear directions indicate that the derived SVR model can also effectively reflect the anisotropic characteristic of the rock joint roughness.(3)The reason for the existing amplitude height parameters cannot effectively reflect the high-frequency components in the rock joint surface was analyzed.The spectral characteristics of 10 standard rock joint profiles proposed by Barton were analyzed by the single-sided power spectral density function(PSD*),and then the distribution of the amplitude height in different frequency components was revealed.The results show that the amplitude height of high-frequency components constituting the rock joint surface is much lower than that of low-frequency components.However,the existing roughness parameters used to reflect the amplitude height of rock joints always neglected the effect of frequency of the components,which leads to the negligence of the contribution of high-frequency components to the rock joint roughness during the calculation process.(4)The quantitative evaluation parameter for rock joint roughness considering both the high and low-frequency components of the rock joint surface was proposed.In order to take the contribution of the high and low-frequency components on the rock joint roughness into account,the frequency of components was considered in the process of calculating the amplitude height parameter First,a new amplitude height index,Pf,was proposed by taking the frequency of components as a weight factor on the average power of the rock j oint profile contributed by the components in each discrete frequency interval.Then,the parameter Z2 was modified to reflect the effect of shear direction on the rock joint roughness,and only the inclination angle facing the shear direction was taken into account when calculating the parameter Z2.Meanwhile,in order to solve the mathematic problem of Z2 when the inclination angle of the asperity equals to 90°,the sine value of the inclination angle is adopted to replace the tangent value in the process of calculating the Z2 parameter Accordingly,a modified statistical parameter Z2*that can effectively reflect the effect of the inclination angle and the shear direction on the rock joint roughness was proposed.Finally,a new roughness parameter,PZ,combining the Pf and the Z2*was derived.The proposed new roughness parameter PZ can simultaneously consider the inclination angle and the amplitude height of rock j oints and the effect of the shear direction on the evaluation results of the rock joint roughness;meanwhile,the new parameter PZ has considered the effect of the rock joint size on the rock joint roughness by the ratio parameter(Pf/Lp),which is the specific value of the Pf to the projected length of the rock joint profile.(5)The quantitative correlations between the JRC and the PZ were obtained with upper,lower and suggested bounds.The comparison with the laboratory direct shear test and the Z2 method show that the estimation error for the peak shear strength of sandstone joints obtained by the average JRC suggested values based on the PZ is less than that obtained by the average JRC values based on the Z2;meanwhile,the peak shear strength estimated by the Z2 is smaller than the direct shear test results.The primary reason for this phenomenon is that the proposed roughness parameter PZ can simultaneously consider the inclination angle and the amplitude height of rock j oints and the effect of the shear direction on the rock joint roughness;while the Z2 only takes the inclination angle of rock joints into account.Meanwhile,the JRC calculation results for profiles collected from the rock joint in different shear directions show that the calculation results based on the new roughness parameters PZ and Z2 are all significantly related to the shear direction;thus,the analysis direction should be consistent with the actual shear direction in the field when analyzing the rock joint roughness quantitatively.In addition,the suggested sampling interval for laboratory rock j oints(100mm)was recommended by analyzing the effect of sampling intervals on the rock joint roughness of laboratory rock joints.(6)The quantitative evaluation peak shear strength model considering both the high and low-frequency components in the rock joint morphology was proposed.In order to reflect the effect of both the high and low-frequency components in the rock joint morphology on the shear strength and comprehensively consider the contribution of the roughness of the 3D morphology to the shear strength of rock joint,the 3D roughness parameter PZ3D expanded from the 2D roughness parameter PZ based on the principle of 2D power spectral density was derived and the 3D JRC calculation method was consequently obtained.Then,the quantitative evaluation peak shear strength model,which can consider both the high and low-frequency components in the rock j oint surface morphology,based on the JRC-JCS shear strength model proposed by Barton was derived Based on the 3D laser scanning morphology data of the collected fresh and well-matched sandstone joints,the peak shear strength of sandstone joints was estimated with the proposed peak shear strength model.The estimation results were compared with results of the laboratory direct shear test and the peak shear strength model proposed by Grasselli in the literature.It is found that the peak shear strength model proposed in this paper can effectively evaluate the peak shear strength of sandstone joints,and relative errors with experimental results are ranging from 0.74%to 22.64%and the average relative error is 7.58%;while the relative error for the Grasselli method are ranging from 20.14%to 74.00%,and the average relative error is 38.62%with larger errors in some samples.(7)The stability analysis of the left abutment slope located in the middle dam site of Rumei Hydropower Station was carried out.?The quantitative evaluation of the rock joint roughness of the left abutment slope was conducted.The results of rock joint roughness evaluation for the small-sized rock joints collected in the study area indicated that the surface morphology of the three dacite rock joint samples all contain high-frequency components obviously.Limited to the quantity and size of the small-sized rock joints,further comprehensive evaluation of the rock joint roughness in the study area was carried out based on the large-sized rock joint morphology data.The scale effect and anisotropy of the large-sized rock joint roughness were analyzed based on the morphology data of three large-sized unweathered dacite joints in the study area,labeled L1,L2 and L3,respectively,which were collected by a laser scanner in the field.On this basis,the roughness of the collected large-sized dacite joints was quantitatively evaluated.The results show that the effective size of the rock joint roughness in the study area is 0.8m,and the roughness of the collected rock joints has obvious anisotropic characteristics;and their JRC values are ranging from 4 to 9—straight and slightly rough hard rock joints,and consistent with the on-site geological survey results.?The shear strength parameters of the dacite joints in the study area were estimated based on the proposed peak shear strength model.The estimation results show that the shear strength parameters based on the three large-sized rock joint samples(L1,L2 and L3)are consistent with the shear strength parameters of hard rock joints obtained by on-site large shear tests in the field,which reflecting the effectiveness of the peak shear strength model proposed in this paper.?The local failure mode of the left abutment slope was analyzed.The spatial distribution characteristics of rock joints in the footrills located along the axis of the left bank dam were firstly investigated.Then,the local failure mode of the left abutment slope near those footrills was analyzed based on the shear strength parameters of the rock j oints obtained in the above-mentioned study results.The results show that the toppling failure,plane failure and wedge failure may exist in the local slope near the footrills below the 2900m elevation of the study slope;however,only toppling failure may exist in the local slope near the footrill PDZ09 and there is no posibility of other failure mode when the elevation of the slope is above 2900m.?The overall stability evaluation of the left abutment slope was conducted based on the discrete element software UDEC.The unfavorable combination of deterministic rock joints such as surface faults and large cracks developed near the slope and small faults revealed in footrills controls the overall stability of the slope.However,the random rock j oints mainly affect the mechanical parameters of the rock mass.Accordingly,taking the section of the left bank dam axis as an example,the overall stability of the left abutment slope was analyzed by the UDEC.The results show that there are mainly two potential sliding areas before the excavation of the abutment slope:the first one,denoted as H1,is the potential sliding area by taking the steep fault fp12 revealed in the footrill PDZ13 or PDZ09 as the trailing edge and C6 as the bottom slip plane;the second one,denote as H2,is the potential sliding area by taking the steep faults revealed in the footrill PDZ07 as the trailing edges and faults fj 70,fj 71,and fj 72 as the bottom slip planes.Due to the cutting effect of the excavation slope,there only exists the potential sliding area H1 after the slope excavation;and,the potential sliding area H2 turns into a stable area after the slope excavation due to the unloading of the slope top.Then,the stability coefficients of the slope under different working conditions were calculated by the strength reduction method.According to the anti-sliding stability coefficient standard of the first-grade slope under different working conditions given by the Design code for engineering slopes in water resources and hydropower projects(SL386-2007),the abutment slope under natural working condition is stable before and after excavation;when it comes to the heavy rain and earthquake working conditions,the slopes are stable before excavation,but its stability coefficients are lower than anti-sliding stability coefficient standard values though in critical stable states after excavation.Thus,further support work is needed for the slope under heavy rain and earthquake working conditions after excavation.Based on the above research results,the main innovations of this paper can be summarized as the following three aspects:(1)The new quantitative evaluation method for rock joint roughness based on factor analysis and support vector regression(SVR)is proposed.This evaluation method adopts representative statistical parameters based on the shear behavior of rock joints,and common factors are extracted from those parameters through the factor analysis.Then,a nonlinear JRC determination method is obtained by training the SVR model for the JRC prediction based on the extracted factors.This method can effectively avoid the deviation of roughness evaluation results caused by the one-sidedness characterization of the rock joint morphology based on a single statistical parameter At the same time,the impact of overlapped information caused by the correlation between original parameters on JRC calulation is effectively reduced by extracting the common factors.Meanwhile,the nonlinear JRC determination method based on training the SVR model can overcome the problem of the inability for traditional regression analysis to be effectively applied due to the computational complexity.(2)The new quantitative evaluation method for rock joint roughness based on the spectral analysis is proposed.This evaluation method proposes an amplitude height index considering both the high and low-frequency components by taking the impact of frequency for the components in rock joint morphology into account based on analyzing the spectral characteristics of the rock joint morphology in detail.Then,a new roughness parameter,PZ,is derived by combining with the inclination angle parameter for rock joints and considering the effect of shear direction.Furthermore,the correlations between JRC and parameter PZ are fitted.This method considers the effect of the amplitude height and inclination angle of rock joint and the shear direction on the roughness,and can overcome the difficulty of the inability for traditional parameters reflecting the amplitude height of rock joints to effectively reflect the contribution of high-frequency components in the rock joint morphology to the roughness.(3)The quantitative evaluation peak shear strength model considering both the high and low-frequency components in the rock joint morphology is proposed.This model is derived based on the three-dimensional expansion of the roughness parameter PZ and the JRC-JCS shear strength model proposed by Barton.This model is easy and simple for engineering application,and can simultaneously consider the contribution of the high and low-frequency components in the rock joint morphology and the roughness of three-dimensional morphology to the shear strength. |
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