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| 1 | Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions显示文摘Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb(MC) has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown(H-B) standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion 'c then σn tan φ' should replace 'c plus σn tan φ' for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected. | Nick Barton | 2013 | Journal of Rock Mechanics and Geotechnical Engineering2013，5，4： | 41 |
| 2 | An approximate nonlinear modified Mohr-Coulomb shear strength criterion with critical state for intact rocks显示文摘In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now,leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD,and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comprehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions. | Baotang Shen Jingyu Shi Nick Barton | 2018 | Journal of Rock Mechanics and Geotechnical Engineering2018，10，4： | 6 |
| 3 | Understanding the need for pre-injection from permeability measurements: What is the connection?显示文摘Pre-grouting ahead of tunnels has three main functions:to control water inflow into the tunnel,to limit groundwater drawdown above the tunnel,and to make tunnelling progress more predictable since rock mass quality is effectively improved.It helps to avoid settlement damage caused by consolidation of clay deposits beneath built-up areas,since towns tend to be built where terrain is more flat,due to the clay deposits.There are so many instances of settlement damage that the profession needs to take note of the need for high-pressure pre-grouting,to use micro-cements and micro-silica additives.The use of highpressure injection may cause joint jacking,but this is local in extent when the rapid pressure decay away from an injection hole is understood.This effect is variable and depends on the geometrical parameters of the joints.This pressure-decay advantage must not be violated by maintaining high pressure when grout flow from the injection hole has ceased.The latter can cause damage to the grouting already achieved.Simplified methods of estimating mean hydraulic apertures(e)from Lugeon testing are described,and from more sophisticated three-dimensional(3D)permeability measurement.The estimation of the larger mean physical joint apertures(E)is based on the joint roughness coefficient(JRC).Comparison is then made with the empirical aperture-particle size criterion E>4d95,where d95 represents almost the largest cement particle size.Depending on joint set orientations and on the available micro-cements,the decision must be made of which range of pre-injection pressure should be aimed for,using successive reductions of the water-cement ratio w/c.More simple estimation of permeability,also with depth dependence,can be made with the empirical link between a modified rock mass quality Q and permeability,which is termed QH2O.The value of this parameter can be based on core-logging or intunnel face logging.The 3D before-and-after-grouting permeability measurements have been used to justify the quantification of rock mass quality Q-parameter improvement,and the consequent increases in expected P-wave velocity and deformation modulus,for application in dam foundation treatment and its monitoring. | Nick Barton Eda Quadros | 2019 | Journal of Rock Mechanics and Geotechnical Engineering2019，11，3： | 5 |
| 4 | Risk of shear failure and extensional failure around over-stressed excavations in brittle rock显示文摘The authors investigate the failure modes surrounding over-stressed tunnels in rock.Three lines of investigation are employed:failure in over-stressed three-dimensional(3D) models of tunnels bored under 3D stress,failure modes in two-dimensional(2D) numerical simulations of 1000 m and 2000 m deep tunnels using FRACOD,both in intact rock and in rock masses with one or two joint sets,and finally,observations in TBM(tunnel boring machine) tunnels in hard and medium hard massive rocks.The reason for 'stress-induced' failure to initiate,when the assumed maximum tangential stress is approximately(0.4-0.5)σ_c(UCS,uniaxial compressive strength) in massive rock,is now known to be due to exceedance of a critical extensional strain which is generated by a Poisson's ratio effect.However,because similar 'stress/strength' failure limits are found in mining,nuclear waste research excavations,and deep road tunnels in Norway,one is easily misled into thinking of compressive stress induced failure.Because of this,the empirical SRF(stress reduction factor in the Q-system) is set to accelerate as the estimated ratio σ_(θmax)/σ_c >> 0.4.In mining,similar 'stress/strength' ratios are used to suggest depth of break-out.The reality behind the fracture initiation stress/strength ratio of '0.4' is actually because of combinations of familiar tensile and compressive strength ratios(such as 10) with Poisson's ratio(say0.25).We exceed the extensional strain limits and start to see acoustic emission(AE) when tangential stress σθ≈ 0.4σc,due to simple arithmetic.The combination of 2D theoretical FRACOD models and actual tunnelling suggests frequent initiation of failure by 'stable' extensional strain fracturing,but propagation in 'unstable' and therefore dynamic shearing.In the case of very deep tunnels(and 3D physical simulations),compressive stresses may be too high for extensional strain fracturing,and shearing will dominate,both ahead of the face and following the face.When shallower,the concept of 'extensional strain initiation but propagation' in shear is suggested.The various failure modes are richly illustrated,and the inability of conventional continuum modelling is emphasized,unless cohesion weakening and friction mobilization at different strain levels are used to reach a pseudo state of yield,but still considering a continuum. | Nick Barton Baotang Shen | 2017 | Journal of Rock Mechanics and Geotechnical Engineering2017，9，2： | 5 |
| 5 | Nonlinear shear behavior of rock joints using a linearized implementation of the Barton-Bandis model显示文摘Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing,inducing dilation and resulting in nonlinear joint shear strength and shear stress vs.shear displacement behaviors.The Barton-Bandis(B-B) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints.The B-B model accounts for asperity roughness and strength through the joint roughness coefficient(JRC) and joint wall compressive strength(JCS) parameters.Nevertheless,many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr-Coulomb(M-C) model,which is only appropriate for smooth and non-dilatant joints.This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior.To bridge the B-B and the M C models,this paper aims to provide a linearized implementation of the B-B model using a tangential technique to obtain the equivalent M-C parameters that can satisfy the nonlinear shear behavior of rock joints.These equivalent parameters,namely the equivalent peak cohesion,friction angle,and dilation angle,are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing.The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre-and post-peak regions of shear displacement,respectively.Likewise,the pre-and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established.Verifications of the linearized implementation of the B-B model show that the shear stress-shear displacement curves,the dilation behavior,and the shear strength envelopes of rock joints are consistent with available experimental and numerical results. | Simon Heru Prassetyo Marte Gutierrez Nick Barton | 2017 | Journal of Rock Mechanics and Geotechnical Engineering2017，9，4： | 4 |
| 6 | Reducing risk in long deep tunnels by using TBM and drill-and-blast methods in the same project-the hybrid solution显示文摘There are many examples of TBM tunnels through mountains,or in mountainous terrain,which have suffered the ultimate fate of abandonment,due to insufficient pre-investigation.Depth-of-drilling limitations are inevitable when depths approach or even exceed 1 or 2 km.Uncertainties about the geology,hydro-geology,rock stresses and rock strengths go hand-in-hand with deep or ultra-deep tunnels.Unfortunately,unexpected conditions tend to have a much bigger impact on TBM projects than on drill-and-blast projects.There are two obvious reasons.Firstly the circular excavation maximizes the tangential stress,making the relation to rock strength a higher source of potential risk.Secondly,the TBM may have been progressing fast enough to make probe-drilling seem to be unnecessary.If the stress-to-strength ratio becomes too high,or if faulted rock with high water pressure is unexpectedly encountered,the 'unexpected events' may have a remarkable delaying effect on TBM.A simple equation explains this phenomenon,via the adverse local Q-value that links directly to utilization.One may witness dramatic reductions in utilization,meaning ultra-steep deceleration-of-the-TBM gradients in a log-log plot of advance rate versus time.Some delays can be avoided or reduced with new TBM designs,where belief in the need for probe-drilling and sometimes also pre-injection,have been fully appreciated.Drill-and-blast tunneling,inevitably involving numerous 'probe-holes' prior to each advance,should be used instead,if investigations have been too limited.TBM should be used where there is lower cover and where more is known about the rock and structural conditions.The advantages of the superior speed of TBM may then be fully realized.Choosing TBM because a tunnel is very long increases risk due to the law of deceleration with increased length,especially if there is limited pre-investigation because of tunnel depth. | Nick Barton | 2012 | Journal of Rock Mechanics and Geotechnical Engineering2012，4，2： | 2 |
| 7 | Shear Strength of Rockfill显示文摘 | NICK Barton BJORN Kjaernsli | 1981 | Journal of the Geotechnical Engineering Division1981，107，7： | 1 |
| 8 | Norwegian tunnelling methods显示文摘 | Skjeggedal Thor Bollingmo Per Barton Nick | 1995 | Tunnels & Tunnelling1995，27，6： | 1 |
| 9 | Shear strength of rock-fill 显示文摘 | Barton Nick Kjernsli Bjorn | 1981 | Journal of the Geoteehnical Engineering Division ASCE1981，107，7： | 1 |
| 10 | Norwegian tunneling methods显示文摘 | THOR SKJEGGEDAL PER BOLLINGMO NICK BARTON | 1995 | Tunnels & Tunnelling1995，12，6： | 1 |
| 11 | Engineering geological characterization of low strength anisotropic rocks in the Himalayan region for assessment of tunnel support显示文摘 | Rajinder Bhasin Nick Barton Eystein Grimstad Panayotis Chryssanthakis | 1996 | Engineering Geology1996，，3： | 1 |
| 12 | Shear strength of rockfill 显示文摘 | Nick Barton Bjom Kjaernsli | 1981 | Journal of the Geotechnical Engineering Division1981，107，7： | 1 |
| 13 | Advances in joint roughness coefficient (JRC) and its engineering applications显示文摘The joint roughness coefficient (JRC), introduced in Barton (1973) represented a new method in rock mechanics and rock engineering to deal with problems related to joint roughness and shear strength estimation. It has the advantages of its simple form, easy estimation, and explicit consideration of scale effects, which make it the most widely accepted parameter for roughness quantification since it was proposed. As a result, JRC has attracted the attention of many scholars who have developed JRC-related methods in many areas, such as geological engineering, multidisciplinary geosciences, mining mineral processing, civil engineering, environmental engineering, and water resources. Because of such a developing trend, an overview of JRC is presented here to provide a clear perspective on the concepts, methods, applications, and trends related to its extensions. This review mainly introduces the origin and connotation of JRC, JRC-related roughness measurement, JRC estimation methods, JRC-based roughness characteristics investigation, JRC-based rock joint property description, JRC's influence on rock mass properties, and JRC-based rock engineering applications. Moreover, the representativeness of the joint samples and the determination of the sampling interval for rock joint roughness measurements are discussed. In the future, the existing JRC-related methods will likely be further improved and extended in rock engineering. | Nick Barton Changshuo Wang Rui Yong | 2023 | Journal of Rock Mechanics and Geotechnical Engineering2023，15，12： | 0 |
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