Erodibility is an important factor in studies of geomorphology. Along with other factors such as climate, time, and tectonics, it contributes to the shape and evolution of landscapes. Several methods exist to quantify erodibility that examine rock mass properties such as fracture characteristics and strength of intact rock. These systems can be used to predict such varied properties as the slope of a rock mass, the geometry of bedrock channels, and the likelihood and type of potential slope failures. Yet, these systems are limited by shortcomings such as subjectivity, limited calibration, and failing to produce reasonable predictions of slope when rocks are mechanically or chemically weak. To address these and additional issues, original and modified versions of three erodibility rating indices are applied in a variety of lithologic, climatic, and erosional environments. Ratings are compared to topography for calibration purposes and to examine whether erodibility and topography will correlate in all environments studied. Several of the techniques tested are successful at improving ratings' correlation to topography in slowly eroding landscapes, while other landscapes do not correlate to ratings. A new adjustment factor for chemically weak rocks further improves this correlation in certain environments. Finally, suggestions are made for the future use of erodibility indices that incorporate specific techniques and alterations from the study as well as general impressions from use. / Master of Science

The evolution of mountain landscapes is controlled by complex interactions between large-scale tectonic, surficial and climate conditions. Dominant processes are attributed to creating characteristic features of the landscape, but topographic features are the cumulative result of coupled surficial processes, each locally effective in a different climate or elevation regime. The focus of erosion by glacial, fluvial, or mass wasting processes is highly sensitive to small changes in boundary conditions, therefore spatial and temporal variability can be high when observed over short time scales. This work evaluated methods for dissecting the history of complex alpine landscapes to understand the role of individual processes influenced by changing climate and underlying bedrock. It also investigated how individual and combined mechanisms of surficial processes influenced the evolution of topography in the Teton Range in Wyoming. Detrital apatite (U-Th)/He thermochronology and cosmogenic radionuclide erosion rates were applied to determine spatial and temporal variability of erosion in the central catchments of the range. Spatial variability existed between the glacial and fluvial systems, indicating that sediment erosion and deposition by these processes was controlled by short-term variability in climate conditions. Effective glacial incision also controlled other processes, specifically enhancing rock fall activity and inhibiting fluvial incision. Short-term erosion rates were highly variable and were controlled by stochastic processes, particularly hillslope failures in response to slope oversteepening due to glacial incision and orientation and spacing of bedrock fractures. Erosion rates averaged over 10 ky time scales were comparable to long-term exhumation rates measured in the Teton Range. The similarity of spatial erosion patterns to predicted uniform erosion and the balance between intermediate and long-term erosion rates suggests the landscape of the Teton Range is approaching steady-state, but frequent stochastic processes, short-term erosional variability and coupled processes maintain rugged topographic relief. / Ph. D.

The geological disposal of nuclear waste, in underground openings and the long-term performance of these openings demand a detailed understanding of fundamental rock mechanics. A full scale field experiment: Äspö Pillar Stability Experiment was conducted at a depth of 450 m in sparsely fractured granitic rock to examine the rock mass response between two deposition holes. An oval shaped tunnel was excavated parallel to the σ3 direction to provide access to the experiment and also provide elevated stress magnitudes in the floor. In the tunnel floor two 1.75-m diameter 6-m deep boreholes were excavated so that a 1-m thick pillar was created between them. In one of the holes a confinement pressure of 700 kPa was applied and in the other displacement transducers were installed. The pillar volume was monitored by an Acoustic Emission System. Spatially distributed thermocouples were used to monitor the temperature development as the pillar was heated by electrical heaters. The excavation-induced stress together with the thermal-induced stress was sufficient to cause the wall of the open borehole to yield. The temperature-induced stress was increased slowly to enable detailed studies of the rock mass yielding process. Once the rock mass loading response was observed, the rock mass was unloaded using a de-stress slotting technique. This thesis focuses on the in-situ study of the rock mass response to coupled mechanical thermal loading and thermal-mechanical unloading. The experiment, its design, monitoring and observations are thoroughly described. An estimate of the yielding strength of the rock mass is presented and compared with laboratory test and results from other rock mass conditions reported elsewhere in the open literature. General conclusions about the effect of the confining pressure and the observations from the unloading of the pillar are also presented. Important findings are that the yielding strength of the rock mass has been successfully determined, low confinement pressures significantly affects the onset of yielding, the primary mode of fracture initiation and propagation is extensional, no significant time dependency of the yielding process was observed. The unloading studies also indicated that what appeared to be shear bands likely was a propagating zone of extensile failure that weakened the rock so that displacements in the shear direction could occur. / <p>QC 20100622</p>

In this thesis, suggestion of appropriate excavation and support systems and selection of rock mass strength parameters for the determination of these systems were carried out for the &Ccedil / ubukbeli Tunnel in Antalya. &Ccedil / ubukbeli Tunnel is a twin tube flute shaped tunnel with 1985 m length, 12 m width, 10 m height and maximum overburden thickness of 130 m. The tunnel area consists of limestone, clayey limestone, claystone, marl and siltsone. Rock mass classification systems are used for evaluation of rock mass characteristics and estimation of strength parameters. Selection of appropriate numerical method and software tool, namely Phase2, is accomplished after an extensive literature survey. The rock mass was divided into sections according to the RMR, Q, NATM and GSI classification systems along the tunnel and excavation and support systems were determined empirically along these sections. Thereafter, geomechanical parameters (i.e. modulus of deformation Em, Hoek-Brown material constants m and s etc.) were selected based on these classification systems. Finite element analysis was carried out as the final step of the design in order to investigate deformations and stress concentrations around the tunnel, analyze interaction of support systems with excavated rock masses and verify and check the validity of empirically determined excavation and support systems. As the result of design studies accomplished along tunnel route, B1, B2, B3 and C2 type rock classes are assumed to be faced during construction of &Ccedil / ubukbeli Tunnel and appropriate excavation and support systems are proposed for these rock classes.

Closely jointed greywacke rock masses are widespread throughout both the North and South Islands of New Zealand and much of New Zealand's infrastructure is constructed upon greywacke rock masses. This thesis deals with determining the rock mass strength of unweathered closely jointed New Zealand greywacke rock masses. Currently, the estimation of rock mass strength and deformability is reasonably well predicted through the use of such empirical failure criteria as the Hoek-Brown failure criterion and empirical expressions to predict deformability. However, previous studies upon predicting the strength and deformability of unweathered closely jointed New Zealand greywacke rock masses has shown that existing empirical methods of determining strength and deformability are unsatisfactory. The problem with predicting rock mass strength and deformability moduli of New Zealand greywacke and the lack of adequate data to calibrate a failure criterion was the starting point for this work. The objective of this thesis was to increase the knowledge of intact and defect properties of closely jointed greywacke, develop reliable rock mass data with which to calibrate a failure criterion and improve the ability to estimate the rock mass strength of greywacke rock masses. A review of existing failure criteria for rock masses was conducted and of these criteria, the Hoek-Brown rock mass failure criteria was selected to calibrate to both the intact rock and rock mass failure data, because of its broad acceptance in the rock mechanics community. A database of greywacke properties was developed based on previous studies upon unweathered greywacke around New Zealand and is attached to the thesis as an Appendix. The database included descriptions of greywacke defect properties and mechanical properties of the intact rock and joints. From this database, inputs could be justified for numerical modelling and later analyses of failure criteria. Records from the construction archives of the Benmore and Aviemore hydroelectric power projects in the South Island of New Zealand were reviewed to obtain information and results from a series of shear tests carried out on unweathered closely jointed greywacke in the 1960s. Data on rock mass strength at failure and rock mass deformability were extracted from these records to assess the predictability of the failure criterion and deformability expressions. Problems experienced during the shear tests at the Aviemore dam site created doubt as to the actual rock mass strengths achieved at failure. The behaviour of these tests was studied using the finite difference code FLAC. The work was aimed at investigating the potential for transfer of shear force between the two concrete blocks sheared in each test and the impact shear force transfer had upon the likely normal stresses beneath each block at failure. The numerical modelling results indicated that a combination of preferential failure occurring in one direction, and doubt in the actual normal load applied to the concrete blocks during testing lead to premature failure in the blocks sheared upstream. The blocks sheared in the opposite direction failed at normal stresses that are reflective of the strength of an unweathered greywacke rock mass, but these results could be explained by failure occurring along defects therefore not satisfying the assumptions of homogeneity typically required of a rock mass failure criterion. The Hoek-Brown failure criterion for intact rock was investigated by fitting it to the largest intact greywacke datasets. For a full set of test data (i.e. including tensile data), the Mostyn & Douglas (2000) variant of the Hoek-Brown failure criterion gave the best fit for a full set of rock mass data. A multiple regression method was developed which improved the fitted curve to intact data in the tensile region and gave the best estimate of tensile strength if no existing lab results for tensile strength were available. These results suggest that the Hoek-Brown failure criterion is significantly limited in its applicability to intact NZ greywacke rock. Hoek-Brown input parameters different to those suggested by Hoek et al (2002) are recommended for using the Hoek-Brown failure criterion for intact NZ greywacke. For closely jointed NZ greywacke rock masses, the results from the shear tests at Aviemore and Benmore were separated into different GSI classes and Hoek-Brown envelopes fitted to the datasets by multiple regression. Revised expressions were proposed for each Hoek-Brown input parameter (mb, s, ab) as a function of the GSI. The resulting revised Hoek-Brown failure envelopes for NZ greywacke offer a significant improvement on the existing criterion used to predict the strength of NZ greywacke intact rock and rock masses. The differences in the behaviour of the reaction blocks that failed before the test blocks and the reduction in rock strength due to sliding along defects from that predicted could be reasoned from recorded observations and the behaviour of the concrete blocks during the shear tests. This study has clearly illustrated the need for continued research in this area. This includes (1) a means of assessing the role of defects upon the shear strength of closely jointed greywacke rock mass into a failure criterion, (2) further modelling of the in-situ shear tests by a discrete element procedure to expressly determine the role of the defect on failure, (3) more testing on rock masses to obtain more data to calibrate a rock mass failure criterion, and (4) more studies on predicting the strength of extremely disturbed rock masses.

Two new three-dimensional rock mass strength criteria are developed in this dissertation by extending an existing rock mass strength criterion. These criteria incorporate the effects of the intermediate principal stress, minimum principal stress and the anisotropy resulting from these stresses acting on the fracture system. In addition, these criteria have the capability of capturing the anisotropic and scale dependent behavior of the jointed rock mass strength by incorporating the effect of fracture geometry through the fracture tensor components. Another significant feature of the new rock mass strength criterion which has the exponential functions (equation 6.7) is having only four empirical coefficients compared to the existing strength criterion which has five empirical coefficients; if the joint sets have the same isotropic mechanical behavior, the number of the empirical coefficients reduces to two in this new strength criterion (equation 6.10). The new criteria were proposed after analyzing 452 numerical modeling results of the triaxial, polyaxial and biaxial compression tests conducted on the jointed rock blocks having one or two joint sets by the PFC3D software version 5. In this research to have several samples with the same properties a synthetic rock material that is made out of a mixture of gypsum, sand and water was used. In total, 20 joint systems were chosen and joint sets have different dip angles varying from 15 to 60 at an interval of 15 with dip directions of 30 and 75 for the two joint sets. Each joint set also has 3 persistent joints with the joint spacing of 42 mm in a cubic sample of size 160 mm and the joints have the same isotropic mechanical behavior. The confining stress combination values were chosen based on the uniaxial compressive strength (UCS) value of the modeled intact synthetic rock. The minimum principal stress values were chosen as 0, 20, 40 and 60 percent of the UCS. For each minimum principal stress value, the intermediate principal stress value varies starting at the minimum principal stress value and increasing at an interval of 20 percent of the UCS until it is lower than the strength of the sample under the biaxial loading condition with the same minimum principal stress value. The new rock mass failure criteria were developed from the PFC3D modeling data. However, since the joint sets having the dip angle of 60 intersect the top and bottom boundaries of the sample simultaneously, the joint systems with at least one of the joint sets having the dip angle of 60 were removed from the database. Thus, 284 data points from 12 joint systems were used to find the best values of the empirical coefficients for the new rock mass strength criteria. λ, p and q were found to be 0.675, 3.16 and 0.6, respectively, through a conducted grid analysis with a high R2 (coefficient of determination) value of 0.94 for the new criterion given by equation 6.9 and a and b were found to be 0.404 and 0.972, respectively, through a conducted grid analysis with a high R2 value of 0.92 for the new criterion given by equation 6.10. The research results clearly illustrate how increase of the minimum and intermediate principal stresses and decrease of the joint dip angle, increase the jointed rock block strength. This dissertation also illustrates how different confining stress combinations and joint set dip angles result in different jointed rock mass failure modes such as sliding on the joints, failure through the intact rock and a combination of the intact rock and joint failures. To express the new rock mass strength failure criteria, it was necessary to determine the intact rock strengths under the same confining stress combinations mentioned earlier. Therefore, the intact rock was also modeled for all three compression tests and the intact rock strengths were found for 33 different confining stress combinations. Suitability of six major intact rock failure criteria: Mohr-Coulomb, Hoek-Brown, Modified Lade, Modified Wiebols and Cook, Mogi and Drucker-Prager in representing the intact rock strength was examined through fitting them using the aforementioned 33 PFC3D data points. Among these criteria, Modified Lade, Modified Mogi with power function and Modified Wiebols and Cook were found to be the best failure criteria producing lower Root Mean Square Error (RMSE) values of 0.272, 0.301 and 0.307, respectively. Thus, these three failure criteria are recommended for the prediction of the intact rock strength under the polyaxial stress condition. In PFC unlike the other methods, macro mechanical parameters are not directly used in the model and micro mechanical parameter values applicable between the particles should be calibrated using the macro mechanical properties. Accurate calibration is a difficult or challenging task. This dissertation emphasized the importance of studying the effects of all micro parameter values on the macro mechanical properties before one goes through calibration of the micro parameters in PFC modeling. Important effects of two micro parameters, which have received very little attention, the particle size distribution and the cov of the normal and shear strengths, on the macro properties are clearly illustrated before conducting the said calibration. The intact rock macro mechanical parameter values for the Young’s modulus, uniaxial compression strength (UCS), internal friction angle, cohesion and Poisson's ratio were found by performing 3 uniaxial tests, 3 triaxial tests and 5 Brazilian tests on a synthetic material made out of a mixture of gypsum, sand and water and the joint macro mechanical parameter values were found by conducting 4 uniaxial compression tests and 4 direct shear tests on jointed synthetic rocks with a horizontal joint. Then the micro mechanical properties of the Linear Parallel Bond Model (LPMB) and Modified Smooth Joint Contact Model (MSJCM) were calibrated to represent the intact rock and joints respectively, through the specific procedures explained in this research. The similar results obtained between the 2 polyaxial experiments tests of the intact rock and 11 polyaxial experimental tests of the jointed rock blocks having one joint set and the numerical modeling verified the calibrated micro mechanical properties and further modification of these properties was not necessary. This dissertation also proposes a modification to the Smooth Joint Contact Model (SJCM) to overcome the shortcoming of the SJCM to capture the non-linear behavior of the joint closure varying with the joint normal stress. Modified Smooth Joint Contact Model (MSJCM) uses a linear relation between the joint normal stiffness and the normal contact stress to model the non-linear relation between the joint normal deformation and the joint normal stress observed in the compression joint normal stiffness test. A good agreement obtained between the results from the experimental tests and the numerical modeling of the compression joint normal test shows the accuracy of this new model. Moreover, another shortcoming associated with the SJCM application known as the interlocking problem was solved through this research by proposing a new joint contact implementation algorithm called joint sides checking (JSC) approach. The interlocking problem occurs due to a shortcoming of the updating procedure in the PFC software related to the contact conditions of the particles that lie around the intended joint plane during high shear displacements. This problem increases the joint strength and dilation angle and creates unwanted fractures around the intended joint plane.