Rock Mass Strength Research Articles

The Mechanism of Rockbolts in Jointed Rock under Uniaxial Tension

In this research, the rockbolt mechanism of a jointed rock mass under uniaxial tension was systematically revealed with a laboratory test and a numerical simulation. It was found that the rockbolt rock mass experienced five stages under uniaxial tension, the densification stage, elastic stage, plastic deformation stage, progressive debonding stage, and complete debonding stage. The stress-strain curve and ultimate tensile strength of a rockbolt rock mass were analyzed by taking the rockbolt spacing and rockbolt angle as variables. It was found that the improvement effect of the reduction of the rockbolt spacing on the ultimate tensile strength was limited. When the rockbolt spacing was reduced to a certain limit, the stress concentration area between adjacent rockbolts was connected and destroyed, resulting in the increase of the rockbolt rock strength becoming smaller, and even having a downward trend. The increase of the rockbolt angle led to the change of the stress mode and failure mode of the whole structure, and the ultimate tensile strength first increased and then decreased. The optimal rockbolt angle was between 60° and 70°. It is worth noting that there was an obvious mechanical occlusion between the thread on the rockbolt surface and the rock mass, resulting in the multi-stage step-down characteristic of the stress-strain curve in the complete debonding stage. The results of this study can provide a reference for the design and construction of similar projects.

Considerations Related to Active Stress Management in Deep Mining

The objective of mining is to supply society with mineral and therefore to extract mineral deposits safely and economically, and as completely as possible. As shallow deposits are becoming more and more depleted and as the mineral demand is rising, mining has to advance to greater depths or more challenging mining environments. Operational and technical challenges arise consequently. The different challenges are discussed briefly, and it is shown that in particular the importance of rock mechanics increases because the resulting stress and energy changes can cause rock pressure phenomena and rock pressure problems. The intensity of rock pressure phenomena and rock pressure problems is a function of several parameters, of which the prevailing stress magnitudes and the rock mass strength are central. Whilst rock pressure phenomena are manageable and do not endanger the objectives of mineral extraction, rock pressure problems threaten the objective of mineral extraction and may in extreme cases prevent the continuation of an operation. As the stress magnitudes rise with depths, but the rock mass strength does generally not increase with depths, the importance of rock pressure control increases with depth. To control the rock pressure, two different strategies, a passive and an active strategy, can be distinguished. The two strategies are discussed. Despite the advantages offered by the active strategy, the passive strategy is still dominantly applied. Reasons for this dominance are identified and discussed. To facilitate the application of the active strategy, a stress management concept is proposed. Finally, the requirements for a wider implementation of an active stress management strategy are briefly discussed.

Effect of intermittent joint distribution on the mechanical and acoustic behavior of rock masses

The mechanical characteristics and acoustic behavior of rock masses are greatly influenced by stochastic joints. In this study, numerical models of rock masses incorporating intermittent joints with different numbers and dip angles were produced using the finite element method (FEM) with the intrinsic cohesive zone model (ICZM). Then, the uniaxial compressive and wave propagation simulations were performed. The results indicate that the joint number and dip angle can affect the mechanical and acoustic properties of the models. The uniaxial compressive strength (UCS) and wave velocity of rock masses decrease monotonically as the joint number increases. However, the wave velocity grows monotonically as the joint dip angle increases. When the joint dip angle is 45°–60°, the UCS of the rock mass is lower than that of other dip angles. The wave velocity parallel to the joints is greater than that perpendicular to the joints. When the dip angle of joints remains unchanged, the UCS and wave velocity are positively related. When the joint dip angle increases, the variation amplitude of the UCS regarding the wave velocity increases. To reveal the effect of the joint distribution on the velocity, a theoretical model was also proposed. According to the theoretical wave velocity, the change in wave velocity of models with various joint numbers and dip angles was consistent with the simulation results. Furthermore, a theoretical indicator (i.e. fabric tensor) was adopted to analyze the variation of the wave velocity and UCS.

Multi-source monitoring data helps revealing and quantifying the excavation-induced deterioration of rock mass

There exist many high-steep rock slopes in Southwest China due to the construction of large-scale hydropower projects. The study on excavation-induced damage of high rock slopes is vital for disaster prevention and mitigation. Due to the complexity of high-steep rock slopes, assessing the excavation-induced deterioration of rock mass is often challenging. This study used the space-borne Interferometric synthetic aperture radar (InSAR) and multipoint displacement meters to monitor the slope displacements before and after the excavation. Based on the multi-source monitoring data and the parameter estimation method, we evaluated the changes in rock mass properties due to slope excavation. We employed an improved particle swarm optimization algorithm with dynamic topology and adaptive parameter adjustment and a neural network-based surrogate model in the parameter estimation. The degradation of rock mass strength and stiffness coincides with the increased sensitivity of slope deformation to rainfall infiltration. An in-depth analysis indicates that the absence of vegetation protection and excavation-induced deterioration of rock masses are responsible for the noticeable slope deformation during the rainy season. As slope excavation profoundly influences slope stability and deformation, we should pay closer attention to the excavation way and support style. This study also demonstrates the benefits of using multi-source monitoring data in slope deformation analysis. The findings can aid in comprehending the deformation evolution and instability mechanisms of rock slopes excavated at the hydropower sites, thereby contributing to the prevention and mitigation of landslide disasters.

Integrated D-InSAR and Ground-based Radar for Open Pit Slope Stability Monitoring and Implications for Rock Mass Young’s Modulus Reduction

Excavation and material stockpiling activities in the mining process cause a change in the distribution of forces and stresses in the material. As a result, the material will seek a new equilibrium by releasing the load through a landslide. As part of mitigation, it is necessary to monitor displacements occurring on slopes using high-accuracy devices. Ground-based radar is a technique considered to have good ability to detect displacements in real-time. However, ground-based radar has a weakness in that it cannot detect vertical displacement. One of the emerging technologies that is used for monitoring vertical displacements as LoS displacements is D-InSAR analysis. With the integration of both methods, displacements that occur horizontally and vertically on a slope can be detected properly. In addition, the decrease in rock mass strength due to displacement can be predicted based on numerical analysis using the finite element method. Monitoring was carried out from December 10th, 2021 to April 9th, 2022. The monitoring results from the beginning to the end of the period showed that the horizontal and vertical displacements that occurred in the low wall area were 1247.34 mm and 292.5 mm, respectively. Correlated with these conditions, the Young’s modulus value of the rock mass decreased between 3% and 35%.

Influences of true 3D twin flaws on principal stress status and crack occurrence of brittle rock-like samples under uniaxial compression: Insights from experimental and DEM studies

Fracture structures commonly have negative impacts on the strength and safety of rock mass, and various combinations of 2D and 3D flaws make the destruction procedure becomes more complicated. Therefore, laboratory tests based on three types of flawed rocks (symmetric twin flaws with different 2D-3D occurrences) are finished to detect the mechanical, optical and acoustic characteristics of fractured rocks during the uniaxial compression test; PFC3D simulations are conducted for analyzing the deformation features, principal stress distributions, and detailed failure mechanism of the fractured rocks. The main results are as follows: 1) Different combinations of 2D & 3D preset flaws directly influence the results of deformation, stress distribution, and failure developments. 2) Rotation of the intermediate stress axes only appear near the flaw inclination boundary (when the monitoring position moves outwards), while the directions of intermediate principal stress axes remain stable near the flaw strike boundary. 3) Separating cracks by various occurrences helps to construct local failures along different directions, and make some local failures visible and clear; the traditional cracks (short line or thin oval shape) are induced by the uneven deformation in x-o-z planes, and the separated cracks (wide oval or standard disc shape) result from the uneven deformation in y-o-z planes. 4) Surrounding rocks at different positions suffer various modes of failures, the non-ignorable thickness of preset flaw leads to simultaneous Mode I and Mode II failure at the flaw tip, and the mixed Mode II&III failure only occurs in the rocks adjacent to the flaw strike boundary.

Triaxial Compression Strength Prediction of Fissured Rocks in Deep-Buried Coal Mines Based on an Improved Back Propagation Neural Network Model

In deep coal mine strata, characterized by high ground stress and extensive fracturing, predicting the strength of fractured rock masses is crucial for stability analysis of the surrounding rock in coal mine strata. In this study, rock samples were obtained from construction sites in deep coal mine strata and intact, as well as fissured, rock specimens were prepared and subjected to triaxial compression tests. A numerical model based on the discrete element method was then established and the micro-parameters were calibrated. A total of 288 triaxial compression tests on the rock specimens under different conditions of confining pressure, loading rate, fissure dip angle, and fissure length, were conducted to obtain the triaxial compressive strength of the fractured rock specimens under different conditions. To address the limitations of traditional back propagation (BP) neural networks in solving stochastic problems, a modified BP neural network model was developed using a random factor and an interlayer mean square error corrected network model evaluation function. The traditional and modified BP neural network models were then employed to predict the triaxial compressive strength of the fractured rock specimens. Through comparative analysis, it was found that the modified BP neural network prediction model exhibited smaller errors and significantly reduced overfitting, making it an effective tool for predicting the strength of fractured rocks in deep coal mine strata.

Fast perception of rock mass strength and integrity in TBM tunnelling using in-situ penetration test

Tunnel boring machine (TBM) is the preferred method in the construction of long-distance and deep-buried tunnel due to its advantages in safety and high efficiency. However, the TBM method is very sensitive to the condition of the surrounding rock. The strength and integrity characteristics of rock mass have great influence on the safe and efficient tunnelling. To provide a fast perception method for these characteristics during the TBM tunnelling process, an in-situ penetration testing system is proposed in the present study. The development and testing procedure of the system are elaborated. The system is applied to a TBM-excavated water conveyance tunnel to continuously perceive the strength and integrity characteristics of the surrounding rock. Firstly, the force-penetration (F-P) responses of the surrounding rock under penetration are qualitatively studied. Then, series of penetration indices are summarized to quantify the characteristics of the F-P responses. Finally, the quantitative relationships between the rock strength and the penetration indices are studied. The results indicate that the in-situ penetration testing system can perceive the rock mass strength and integrity characteristics qualitatively and quantitatively. On the qualitative aspect, the F-P responses can be categorized into four types (Type I to Type IV), which correspond to the level of rock mass strength and integrity. On the quantitative aspect, a single penetration index cannot represent the complete information of the F-P response. The descriptive classification of the rock mass strength (class I to III) is established through multiple penetration indices. The in-situ penetration testing system can be used as a method to quickly perceive the strength and integrity characteristics of the surrounding rock in TBM tunnelling.

Slope Stability Analysis of Alterated Dasit Rock on Ponorogo Pacitan Road Using Hoek-Brown Failure Criteria

To mitigate landslide on rock slopes the information on adequate safety factors is needed. The strength of rock and soil is one of the important parameters on a slope stability analysis. This paper discussed the stability of the altered and dissected dacite rock. To make it easier to determine the Hoek-Brown failure criteria, the GSI rock mass classification is used. By using the Hoek-Brown failure criterion and supporting by the Rocsience software the analysis of safety factor of rockslide has been conducted. From field and laboratory observations of the rock masses that make up the slopes at the study site, a Geological Strength Index value of 25 was obtained. Base on GSI and some field condition can be obtained the Hoek-Brown parameter are γ = 2.6 t/m3, mi = 25, Disturbance Factor (D) = 1.0, mb = 0.118, s = 3.73e-6, 𝑎 = 0.531. The rock mass strength of the sample was brittle so that it can easily collapse. The purpose of this analysis is to do further study to overcome the problems that occur in most rocks, especially those related to transportation routes next to the slope.

Elasto-plastic and post-yield weakening jointed rockmass response in a comparison of equivalent-continuum and explicit structural models

The strength and stiffness of a composite rockmass (intact material, defects, joints, bedding, etc.) are primary inputs for the engineering analysis of rock slopes and underground excavations. The Geological Strength Index (GSI) has served rock engineering for three decades as a rockmass assessment system based on the blockiness of the rockmass and discontinuity condition. GSI is used to factor the Hoek–Brown strength envelope for intact rock to represent jointed rockmasses in conventional equivalent-continuum numerical modelling. Modern numerical tools can represent networks of discrete (explicit) structure with assigned discontinuity properties. This provides an opportunity to compare explicit structural modelling with the conventional implicit equivalent-continuum approach. In this paper, explicit structural models are developed using elasto-plastic (constant-strength) constitutive models for intact rock and realistic parametric ranges for explicit structure properties. Explicit model results are compared to equivalent-continuum results, validating the classical implicit approach while also identifying key limitations. Explicit models with post-yield weakening of the intact and structural elements are then developed and compared to post-yield weakening implicit models that use post-yield dilation and empirical relationships between peak and residual GSI. The results provide guidance for practical modelling in strain-weakening rockmasses, including recommendations for post-yield dilation in the traditional implicit approach.

Evaluation of the Bekhme Dam Site – NE Iraq using the Proposed Reduction System of the Rock Mass Strength

Evaluation of the Bekhme Dam Site – NE Iraq using the Proposed Reduction System of the Rock Mass Strength

An Experimental Investigation on Mechanical Properties and Failure Characteristics of Layered Rock Mass

Layered rock mass is a common rock mass structure with diverse forms and complex mechanical properties. Three types of composite layered rock mass prepared using sandstone and shale can be divided into sandwiched type, interbedded type and superimposed type. The total height of the combined rock mass is 50 mm, which is a cylinder composed of sandstone and shale with a diameter of 25 mm and different thickness. Uniaxial compression tests on sandstone, shale and combined rock mass were performed. The results show that, with the increase in the content of soft components, the compressive strength and elastic modulus of the combined rock mass tend to decrease. The mechanical properties of the superimposed rock mass will be between the two components and close to the soft component in numerical value. The mechanical properties of sandwiched rock mass are obviously affected by the properties of the sandwiched rock. When the content of the components is consistent, interbedded rock mass often shows higher strength and elastic modulus. Compared with other rock mass, interbedded rock mass has more stable mechanical properties. The stress–strain curve can be divided into the compaction stage, elastic stage, plastic development stage and post-fracture stage. The composition content of the rock mass plays a decisive role in the compaction stage. The failure modes are mainly shear failure and tensile failure. With the increase in soft rock content, the failure degree of soft rock is gradually weakened, and the failure modes show a trend from tensile failure to shear failure. The experimental results provide theorical guidance for underground engineering construction.

Real-time estimating method on rock strength via MWD of roofbolter and its application to in-situ grouting quality evaluation

Grouting reinforcement is an effective method for controlling fractured rock in the deeply buried roadways of coal mines. However, quantitatively evaluating the strength of grouted rock masses remains a challenge. The design of grouting reinforcement is primarily based on empirical knowledge. Consequently, this study proposes a real-time in-situ method for evaluating grouting quality using measure while drilling (MWD) based on a roofbolter. Initially, we validated the method through a numerical study using the discrete element method. Several 3D rock samples with varying crack densities were established and drilled numerically, demonstrating that the strength of fractured rock masses can be better estimated using the rock drillability index rather than drilling specific energy. Therefore, a model, known as the Pd–Rc model, was established to estimate rock strength based on the rock drillability index. Subsequently, an in-situ validation was conducted using a self-developed MWD testing system to assess the grouting quality in fractured rock masses. The results show that the strength of the rock mass increases by 38%, 56.0%, and 49.7%, respectively, after grouting, as observed in three boreholes. This method allows for quantitative estimation of grouting quality.

Substantiation of the optimal mining sequence of an ore deposit under conditions of high stress and low rock mass strength

Introduction. When choosing the mining sequences of an ore deposit, technological and organizational factors are mostly taken into account. However, when using systems with caving which involve considerable mined-out spaces, the geomechanical factor, which determines stability of mine workings, plays a determining role. The research objective is to reveal the dependence between the stability of the development and face-entry headings within the mined-out space influence zone and the excavation sequence of the isolated ore block under conditions of high stress and low ore and rock mass strength. Methods of research. Numerical modeling of the enclosing ore and rock mass secondary stressstrain state formation was carried out by the finite element method in the Rocscience RS3 program together with the original FEM software package. Modeling was performed for two variants of block excavation – from the center to the flanks and from one flank to the other along the strike. For the analysis, we proposed a coefficient representing the product of compressive stress concentration zones length by their existence duration. Results. Based on the analysis of the maximum stress concentration areas distribution in the marginal rock mass, as well as the time of their influence, the optimal sequence of actual mining was substantiated according to the factor of influence on bottom workings stress-strain state – from flank to flank along the strike. Conclusions. The obtained result confirms the model representations about the mechanism of rock mass stressed redistribution in the process of lens-shaped deposit excavation. The representations suggest that during mined-out space development along the strike, compressive stresses concentrate at its ends. However, the intensity of end sections expansion in the flank to flank variant is two times as high as in the center to flank variant. The duration of the stress concentration zones impact on the bottom workings is therefore less, which is indicated by the proposed coefficient.

Failure characteristics and the law of the energy evolution of granite with different pre-crack inclination angles under uniaxial compression loading

Cracks affect the strength of rock masses and eventually threaten their stability in engineering. In order to study the fracture characteristics and mechanical properties of cracked rocks, uniaxial compression tests of pre-cracked granite samples with a central circular through hole were carried out by using MTS816 rock mechanics testing system. The inclination angles of different pre-cracks are 0°, 15°, 30°, 45°, 60°, 75°, and 90° respectively, and the influence of the crack stop hole near the crack tip on the failure behavior of pre-cracked samples is also considered. The results indicate that, compared with the intact sample, the peak strength of pre-cracked samples decreases significantly and is related to the pre-crack inclination angle. The failure mode of the sample varies with the pre-crack inclination angle, and the crack stop hole near the crack tip also has a certain influence on the crack growth to a certain extent. However, in terms of failure mode and its transformation law, the influence of central circular through hole and crack stop hole can be ignored. Generally speaking, the larger the inclination angle of the pre-crack, the more the total energy required for failure of the sample, and the more the stored elastic strain energy. Before the peak strength, the elastic strain energy of the sample is greater than the dissipated energy, after the peak strength, the dissipated energy gradually exceeds the elastic strain energy due to energy conversion. It is found that the pre-crack reduces the energy storage capacity of the sample, and the total energy is ultimately dominated by sample integrity. The dissipated energy rate increases first, then decreases, and finally increases again, the inflection points are the end of micro-crack closure and the peak strength, respectively. The crack stop hole changes the law of energy evolution to a certain extent, which can improve the ability of rocks to accumulate energy when designed at an appropriate position, so as to improve its load-bearing capacity in a certain range. The results display the mechanical properties of pre-cracked granite samples under uniaxial compression and are conducive to its application in engineering.

Back-Analysis of Rock Mass Strength at a Radioactive Waste Disposal Site Using Acoustic Emission Monitoring Data and 3D Numerical Modelling

In this study, a new method was examined that used acoustic emission (AE) monitoring data, in combination with a primary Boundary Element stress analysis, to back-calculate rock mass strength. The presented AE data came from the National Radioactive Waste Repository (NRWR) for low- and intermediate-level waste (LLW/ILW). AE monitoring is able to detect the pre-peak, peak, and post-peak stress changes in rock mass. The presented method used AE monitoring data to back-calculate parameters, such as uniaxial compressive strength and the rock mass deformation modulus. The AE initiation threshold was used to develop an objective function that considered the stress in the rock mass and the rock mass strength. The findings of this research propose that most AE events can be related to the crack initiation threshold, and in space, most of them are located at points away from the excavated walls. In the vicinity of the excavation damage zones around the cavities, the stress conditions beyond the crack damage boundary of the rock mass occur in many areas, leading to significant irreversible deformations. This novel method was demonstrated to aid in the prediction of rock mass strength and is a valuable, non-invasive method for improving the spatial prediction of rock mass parameters, which will lead to safer underground storage facilities.

Prediction of Grade Classification of Rock Burst Based on PCA-SSA-PNN Architecture

The uncertainty and complexity of rock burst brings great difficulties to the prediction of rock burst grades. In order to estimate the risk grades of rock burst, an integrated method combining principal component analysis (PCA) and sparrow search algorithm (SSA) with probabilistic neural network (PNN) was proposed. Considering that the in situ stress of rock mass, the strength of rock, and the strength of rock mass are the key influencing factors of rock bursts, the maximum in situ stress σ max , maximum tangential stress σ θ , rock strength σ ci , rock mass strength σ cm , and three rock burst evaluation indexes ( σ θ / σ ci , σ ci / σ max , and σ cm / σ max ) were selected to constitute the rock burst grade evaluation index system. Forty-three groups of rock burst engineering data were gathered. After preprocessing the rock burst data using PCA, four of the new linearly independent indexes PCA1, PCA2, PCA3, and PCA4 were obtained for estimating rock burst grades. The SSA was utilized to optimize the smoothing factor in the PNN. Using PCA-SSA-PNN-based architecture, a new multi-index rock burst grade prediction method was proposed. The results from the new multi-index rock burst grade prediction method were compared with those from single- and multi-index prediction methods. It shows that the predictions from the multi-index rock burst prediction methods are closer to the actual rock burst grades than that from the single-index rock burst prediction methods; compared with other multi-index rock burst prediction methods, the prediction accuracy of PCA-SSA-PNN is greater (up to 90%) and more available in the prediction of rock burst grades. The results presented herein may provide reference for the rock burst warning.

The effect of valley confluence and bedrock geology upon the location and depth of glacial overdeepenings

ABSTRACT Overdeepenings are erosional landforms, cut by glaciers into bedrock in basins and valleys. Overdeepening is the glaciological and geomorphological process that produces these landforms. The overdeepening process is important because it has the potential to influence the response of ice masses to climatic changes. In this paper, we analyze topographic and bathymetric digital elevation models to examine several hundred glacial overdeepenings in Labrador, Canada. We investigate controls upon the location and depth of overdeepenings. Our analyses show that the location of overdeepenings correlate strongly with confluences of glacial valleys and, importantly, that the correlation is strongest where confluence geometry requires the speed-up of ice-flow due to change in valley cross-sectional area. Further, we find that the magnitude of ice-flow speed-up correlates with depth of overdeepenings only for confluences situated in or near major geological fault-zones. Our findings therefore support the hypothesis that overdeepening can be initiated by an increase in ice velocity. Further, we conclude that overdeepening is most efficacious where fractured bedrock enables efficient quarrying. In summary, we find that the primary control upon the location of overdeepenings arises from confluences of glacial valleys due to ice speeding up at these locations, and that the depth of overdeepenings are controlled by rock mass strength. These findings are relevant for landscape evolution modelling and may be used in model testing.

A Rock Mass Strength Prediction Method Integrating Wave Velocity and Operational Parameters Based on the Bayesian Optimization Catboost Algorithm

Tunnel Boring Machines (TBMs) have been the main equipment for tunneling and underground construction due to their high safety performance and tunneling efficiency. However, the unknown and changing geological conditions during construction pose a challenge to TBM construction. As one of the essential parameters of rock properties, accurate acquisition of uniaxial compressive strength (UCS) is crucial for TBMs to adapt to changing ground conditions in a timely manner. Therefore, this study proposes a Catboost intelligent model based on Bayesian Optimization to predict UCS. Rock mass are velocity information and key TBM operational parameters are used as model input variables. The Gaussian data augmentation method is used to compensate for the difficulty of obtaining field data in large quantities. The Zhujiang Delta Water Resources Allocation Engineering field data are used in the model, and the obtained evaluation indicators MAPE, RMSE, VAF and a20-index are obtained as 9.91%, 499.38 MPa, 90.7% and 0.95, respectively. In addition, another project is selected to verify the applicability of the model. The validation results also confirm that the model is valid and reliable when applied to practical engineering.

Design bond stress parameters for rock anchors in Brisbane

Little published information is available on bond stress parameters at the grout-ground interface for the design of ground anchors within Brisbane rocks. In the absence of data, a designer will typically fall back to ‘universal’ correlations with measurable parameters such as Uniaxial Compressive Strength (UCS) or descriptions of rock type to nominate design bond stress values. In doing so, there is often little understanding of the limitations of such correlations or how applicable those correlations are for the rocks encountered within the local region. A study of Proof Test data from testing of sacrificial ground anchors constructed within materials from the Brisbane Tuff and Neranleigh Fernvale Beds Stratigraphic Units for an infrastructure project in Brisbane has been carried out to consider bond stress values at the grout-ground interface. Materials within the bond zone of ground anchors constructed in Brisbane Tuff and Neranleigh Fernvale Beds units have been classified into different rock units based on rock substance strength and Geological Strength Index. Details of anchor construction and testing procedures are presented, together with the adopted approach to test interpretation. Data from Proof Testing of ground anchors bonded into these materials is then interpreted and evaluated for each unit, with relationships developed for each rock type for ultimate and yield bond stress values at the grout-ground interface as a function of rock substance strength (UCS) and rock mass strength (based on Hoek and Brown,2018). For both rock types, grout-ground interface bond stresses increase with rock strength and quality, with better correlations evident based on rock mass strength than for UCS data. Comparisons of the interpreted bond stress relationships based on UCS are made for both rock types to published information for ground anchors and shaft adhesion parameters for cast-in-situ piles. Suggestions are made for amendments to the Proof Anchor test method to reduce the potential for premature termination of the test and consequent underestimation of the bond stress, and to obtain consistency between Proof and Production test methods.