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Dynamic loads due to blasting will affect the mechanical properties of rock masses and form an excavation damage zone (EDZ). The rock mass properties within the EDZ are obtained by the geological strength index (GSI) and disturbance factor (D) in the Hoek-Brown criterion. In order to avoid the subjectivity of GSI evaluation, a stochastic-deterministic 3D discrete fracture network (DFN) is constructed to quantify the GSI. The D value is considered to be a value that varies with depth within the EDZ, rather than a fixed value. Quantitative blasting vibration data is used to determine the disturbance factor rather than qualitatively estimated values. When the disturbance factor decreases linearly within the EDZ, the mechanical properties of the rock mass increase linearly to the undamaged value. Numerical simulation is used to analyze the influence of linear decrease of the rock mass properties on the stability evaluation of the tunnel. The results show that different rock mass parameters have a great influence on tunnel convergence and settlement values. The method described in this paper helps to evaluate the stability of surrounding rock more objectively and accurately. [ABSTRACT FROM AUTHOR]

Rock slope failure along road cuts in weathered elevated terrains is a frequent geotechnical issue. The slope stability probability classification (SSPC) system is commonly employed as a reliable, systematic, quick, and probabilistic approach to analyze rock slope failures. The applicability of this technique on weathered metamorphic rock slopes, particularly in high-grade metamorphic terrains like Sri Lanka, has been poorly studied. This study utilized 22 road cuts made in metamorphic rock masses along Kandy-Randenigala and Kandy-Mahiyangana roads in Sri Lanka. The SSPC system was applied to evaluate the stability of cut slopes, and the geotechnical properties of the rock masses were calculated. The slope stability probabilities were validated against the actual stability conditions of the slopes. Rock mass rating (RMR) and Geological Strength Index (GSI) analyses were employed to compare the rock mass properties derived from SSPC. The orientation-dependent analysis of SSPC agreed with the actual stability conditions of the analyzed cut slopes by 91%, except for wedge failures. The rock mass cohesion values and friction angles were derived from SSPC aligned with the literature and were reliable for weathered metamorphic rock masses in Sri Lanka. The current study recommends the SSPC orientation-dependent analysis for conducting a rapid and preliminary assessment of slope stability in structurally controlled weathered metamorphic terrains. [ABSTRACT FROM AUTHOR]

Rock mass integrity is related to rock mass quality and strength. It can be characterized by a single index, or a combination of multiple indices. In this paper, the rock mass integrity classification index and corresponding classification scheme are described. The relationship between intactness index and rock mass structure index in the RMR89 system is examined, and the relationship between Kv and Q′, representing the rock mass structure index in the Q system, was determined. Results of the case study show that there is a good correlation between Kv and the sum of the RQD ratings, joint spacing D, and the joint conditions in the RMR89 system. A better correlation exists between Kv and GSI|2013, a quantitative expression of GSI proposed by Hoek et al. (2013). Based on the above correlations, if a certain rock mass integrity index is unavailable in an engineering project, other indices can be used as alternative to complete the rock mass quality evaluation; however, because the data employed in this paper are from only two projects, the similarity of rock mass conditions should be thoroughly considered. More research is needed to supplement, validate, and revise the results of this study in the future. [ABSTRACT FROM AUTHOR]

This article introduces a new quantitative model for the geological strength index (GSI) based on attribute mathematics theory. This new attribute evaluation index system of GSI consists of the rock mass block index, the joint spacing, the number of joint sets, the absolute weathering index, the large-scale undulation, and the small-scale undulation. Recently, based on attribute mathematics theory, the attribute mathematics evaluation model of GSI was established for identifying and classifying the geological strength index. Finally, based on the confidence criterion and the method of linear interpolation, a quantitative model for the geological strength index is established. To verify the model, an improved numerical method is introduced. Meanwhile, the equivalent transformation method of the Hoek–Brown strength criterion and Mohr–Coulomb strength criterion is cited. The problems in the determination of the reinforcement time to support surrounding rock are solved by the analysis of the construction process mechanics. A new concept called section displacement deviation is proposed for effective comparison of the monitoring data and the simulation predictions. Project applications prove that this quantitative method has strong pertinence and high accuracy and can organically combine geological surveys, experimental data, statistics, and expert opinions, so this evaluation method can decrease the subjectivity of research decisions. The method of the attribute mathematics evaluation of GSI provides a new approach to quantifying the GSI system. [ABSTRACT FROM AUTHOR]

The excavation of rock masses has a crucial importance for the safety and cost of construction of engineering projects. In this study, a flexible excavation assessment (EXCASS) system was developed with two components, the geological strength index (GSI) and the point load strength index (Is50). In order to develop the system, artificial neural network (ANN) analysis were performed using datasets from surface excavations (12 sites in Turkey and 61 sites in Greece reported by Tsiambaos and Saroglou (2010)). The EXCASS system in this study includes two parameters, namely the excavation power index (EPI) and the excavation performance rating (EPR) ranging between the value of 0 and 100. The optimum excavation power index (EPIopt) can be determined theoretically by using ( GSI 2 × Is 50 ) as an input when EPR is equal to 0, for the selection of the optimum excavation method. EPR is a rating which provides relative information on the ease or difficulty of the excavation method. Although the value of EPR varies between 0 and ± 100 in the EXCASS system, the use of the excavation method for "normally classes" is recommended in order to achieve costly and efficient excavation. The EXCASS system, on the other hand, has an ability to respond to possible technological developments by associating the excavation method with the EPI rating. [ABSTRACT FROM AUTHOR]

Engineering geological characteristics of the rapidly growing Auckland urban area are of increasing interest due to ongoing and planned tunnels and excavations. Auckland is mainly underlain by Miocene-age East Coast Bays Formation (ECBF), a highly heterogeneous flysch deposit, and is also affected by lava flows from the Late Quaternary Auckland Volcanic Field (AVF). Therefore, excavations in the region can encounter highly variable rock mass. Here, the geological strength index (GSI) and rock mass rating (RMR) were applied to outcrop in coastal cliff exposures located on Auckland's North Shore, to evaluate the engineering geological properties of the ECBF. Samples were also extracted for laboratory analysis of elastic wave velocities, intact strength parameters and thin section analysis of microtexture. Specific issues identified include lenses of the heavily zeolitized Parnell Volcaniclastic Conglomerate, and marked strength contrasts within the weaker ECBF siltstone and sandstone. The ECBF sandstone, where uncemented, is much weaker and is highly permeable, while the presence of smectite clay may be problematic for tunnelling if it disaggregates, forming a 'sticky spoil'. The presence of larger-scale defects has been problematic for tunnelling, including the presence of low shear strength clay seams along ECBF bedding planes, and bedding planes intersecting tunnel crowns. [ABSTRACT FROM AUTHOR]

The occurrence of rockburst is related to the surrounding rock stress and geological rock mass strength. Rockburst occurs frequently during the construction at a deep tunnel in southwest China (a tunnel with a depth of approximately 2080 m, and a length of 13 km), leading to casualties, damage to construction equipment, and schedule delays. The application of the rockburst criteria based on the stress-strength/strength-stress ratio shows that they are not suitable for the construction stage. This paper suggests a simple and feasible rockburst intensity criterion based on the Geological Strength Index (GSI) for the construction stage. In this criterion, the strength of the rock mass exposed during excavation is estimated by the Hoek-Brown criterion and is used to reflect the geological conditions of the surrounding rock, considering the influences of the joint conditions and engineering disturbance. The maximum principal stress along the tunnel is obtained by the in situ stress inversion. The ratio of the rock mass strength to the maximum principal stress (σcm/σ1) is taken as the evaluation index. The criterion is as follows: σcm/σ1 > 1.2, none rockburst; 0.75 < σcm/σ1 ≤ 1.2, slight rockburst; 0.4 < σcm/σ1 ≤ 0.75, moderate rockburst; and σcm/σ1 ≤ 0.4, intense rockburst. The engineering applications show the reliability of this rockburst intensity criterion. The results of this paper provide a reference for rockburst intensity evaluation during the construction stage of deep tunnels. [ABSTRACT FROM AUTHOR]

The rock mass quality in underground excavations and or tunnelling is a key issue in the design of the most suitable support to ground stability. This work aims to discuss the applicability of the latest version of the geological strength index (GSI|2013) in an anisotropic media during ongoing deep underground excavation by drilling and blasting. The study encompasses a comprehensive geological, geotechnical and geomechanical characterisation and evaluation of the excavation faces in the Marão tunnel (north Portugal). In addition, 305 m (two underground sections) of tunnel were mapped in 74 consecutive face underground excavation advances. Geological, geotechnical and geomechanical data relating to the site investigation were collected and computed in each new face advance. The scanline sampling technique was applied on exposed rock surfaces, a geotechnical analysis of the discontinuities was performed, and the block size of the rock mass was determined. Geotechnical and geomechanical zoning of the studied sections were continuously carried out considering the knowledge of the site rock mass characteristics and behaviour. In addition, a comparison was performed between the version of GSI|2013 and its earlier version (namely, GSI|98) and correlated with rock mass rating. The study will contribute to a better understanding of GSI|2013 and its applicability in geoengineering projects in design or excavation work stages. [ABSTRACT FROM AUTHOR]

A methodology for designing a tunnel support system according to the actual ground conditions and the critical behaviour types is analysed in this paper. The methodology is justified with the principles of the New Austrian Tunnelling Method that incorporates the top heading and bench method. The role of the geological material and its implication in tunnel design, reinforced with advances in site investigation methods, cannot be based solely on the development of the geotechnical classification systems and the consequent quantification of the rock masses. Support requirements for rock masses with equal classification ratings can be different. The procedure presented in this study cannot bypass the geological and/or in situ characteristics dictating or influencing the tunnel behaviour compared with a standardised classification that could miss the specifics and particularities of and around a tunnel section. The step-by-step procedure is applied in a tunnel excavated in tectonically disturbed heterogeneous flysch sediments in Serbia. The complex structure of these materials, resulting from their depositional and tectonic history that includes severe faulting and folding, presents a challenge to geologists and engineers. The possible ground types are evaluated, and then, combined with the factors of the tunnel geometry, the primary stress condition, and the water conditions, several behaviour types are considered. These classified behaviour types, followed by the suitable mechanical properties that are required for effective tunnel engineering design, are the basis for the numerical design of the appropriate primary support measures to achieve stable tunnel conditions. The twin-tube, two-lane highway tunnel was successfully constructed without significant problems. [ABSTRACT FROM AUTHOR]

Flysch deposits are common in Serbia. Approximately 15 % of the 250 km of highways currently under construction will be constructed in flysch. In the most southern part of the E80 project, close to the border crossing with Bulgaria, construction of 3-km long cuts, often over 30 m high, is foreseen by the design. The geology of this part of Serbia is mainly characterized by flysch deposits represented by a sequence of sandstone and siltstone, interchanging in different proportions. After excavation of a majority of the cuts, several slopes suffered from global and structural instabilities. This required re-design of one part of the cuts. For this purpose, a geological strength index (GSI) was estimated and the structural features of rock discontinuities were observed on the faces of the surface excavations. This information and data obtained from laboratory testing enabled the determination of five characteristic rock mass types. For every type, shear strength properties were determined based on three criteria: the Hoek-Brown failure criterion; the Mohr-Coulomb criterion; and an hyperbolic nonlinear envelope. During the process of converting the Hoek-Brown parameters to the parameters of hyperbolic envelope, the Levenberg-Marquardt algorithm (LMA) was utilized to solve for the nonlinear regression problem. Verification of the parameters was performed on several examples. The median angle pressure increases exponentially with the GSI value and ranges between the value characteristic for clays and well-graded gravel. The maximum angle difference is obtained for a GSI value of 30. The average normal effective stress acting on the failed slopes, expressed in the form of the stress level ratio (SLR), is below 0.5. This indicates that the curved part of the shear strength envelope is utilized during the shearing. As such, the linear segment overestimates the shear strength. [ABSTRACT FROM AUTHOR]