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Presented here are abstracts of papers in Journal of Rock Mechanics and Tunnelling Technology for five years since its first release in 1995 and has reviewers from India and abroad. It will be our constant endeavour to disseminate technical knowledge of high calibre amongst researchers and practising professionals. Your constant contributions are vital for technological progress.

Hydraulic fracturing stress measurements - theory and practice (Vol 1 No 1, January 1995, pp 1-12)

First hydraulic fracturing insitu stress measurement were conducted in 1968. Since this, theoretical analysis and experimental techniques of hydro-fracturing have enormously been improved. Hydro-fracturing has become a standard technique to measure in situ stresses for most large geotechnical projects. The paper sketches the historical developments, addresses theoretical aspects and describes the wireline technique as an economic practical solution to measure stresses along a borehole profile.

Terzaghi’s (1946) rock load classification developed from tunnels excavated by conventional drill and blast method and supported with steel arches has been evaluated in the light of measured support pressures from 23 tunnel sections with widths varying from 2 to 14 m and 4 sections from 21 to 23 m wide caverns. The study shows that the support pressure in rock tunnels does not increase significantly with the excavation width. This experience has been used to propose another simple classification system for both roof and wall support pressures in tunnels and caverns. The suggested vertical support pressures stand corroborated with field measurements in India. The paper also provides data on extensive tunnel performance studies in poor rock conditions.

The effect of rock properties on the design and results of tunnel blasts (Vol 1 No 1, January 1995, pp 25-39)

Golder Associates Private Limited, 25 Burwood Road, Hawthorn, Melbourne, Victoria 3122 (Australia)

The design and results of tunnel blasts are affected by rock properties more than by any other variable. As the mean spacing between fissures (i.e., natural cracks) decreases, the importance of rock substance strength decreases while that of rock mass strength increases. Because the great majority of new cracks are produced by tension, the dynamic tensile breaking strain (e1) is a very important property of massive rock. In closely fissured rock e1 is less influential than the combined effect of the spacing, orientation, persistence, aperture and infilling of fissures. Explosive charges should be designed such that the peak radial strain at the blast hole wall is equal to the dynamic compressive breaking strain of the rock. Tunnel blasting is affected most by rock strength; it is influenced to a lesser degree by the internal friction, grain size and porosity of the rock.

Landslide hazard zonation mapping of Tehri-Pratapnagar area of Garhwal Himalaya (Vol 1 No 1, January 1995, pp 41-58)

The mountainous terrains such as Himalaya are characterised by steep slopes, high relative relief, weathered, fractured and folded rocks in addition to unfavorable hydrogeological conditions. The planning, design and execution of development schemes in these terrains should take into account the existing instabilities of the area. Moreover the unstable zones facing environmental degradation have to be identified and studied in detail for evolving suitable mitigation measures. For that purpose a quantitative approach based on the numerical rating called landslide hazard evaluation factor (LHEF) rating scheme has been used for preparing the LHZ map of Tehri-Pratapnagar area.

RMi - A system for characterising rock mass strength for use in rock engineering (Vol 1 No 2, July 1995, pp 69-108)

Norwegian Geotechnical Institute, Postbox 3930, Ullevaal Hageby, N-0806 Oslo (Norway)

The RMi (rock mass index) system is based on well defined inherent rock mass parameters. Basically, it combines the compressive strength of intact rock and a jointing parameter composed of 4 jointing characteristics, namely block volume or density of joints, joint roughness, joint alterations, and joint size. From calibration of measured compressive strength of 7 large samples and 1 back analysis, the 4 joint features have been combined to express the effect the jointing parameter has in reducing the strength of intact rock. Generally, the block volume forms the most important input to the RMi. Various methods to determine block volume from different field measurements are described in appendix. RMi can be applied for various purposes in rock mechanics and rock engineering, such as input to Hoek-Brown failure criterion and ground reaction curves, assessment of rock support in tunnels and evaluation of penetration rates of tunnel boring machines.

Finite element analyses of circular, horse-shoe and interacting circular tunnels (Vol 1 No 2, July 1995, pp 109-134)

Excavation of an underground opening in rock at depth causes redistribution of stresses in the rock and is manifested in rock deformations near the excavated surface. Thus, analysis of stress and deformations developed around and underground opening is very important in understanding the stability and support requirement of the excavation. The present study report results of a series of elastic and elasto-plastic finite element analysis of underground openings for plane strain conditions. Hoek-Brown failure criterion has been used for elasto-plastic analysis. For the analysis of single tunnels, two shapes viz, circular and horse-shoe have been selected. In case of interacting tunnels, circular tunnels have been chosen. In each analysis, three in-situ stress conditions viz, K=0.5, 1.0, 1.5 have been considered. In case of interacting tunnels, the pillar width to tunnel diameter (W/D) ratio of 0.3, 0.6 and 1.2 have been adopted for each case. Sequential excavations have been simulated in the analysis. The effect of shape of tunnel, tunnel interaction, sequential excavation and in-situ stress conditions have been brought out.

Landslide blockade on the river Satluj and its removal by underwater blasting (Vol 1 No 2, July 1995, pp 135-146)

Olof Palme Marg, Hauz Khas, New Delhi - 110 016 (India), Fax: (0091-11) 685-3108, Tel No: (0091-11) 663-140 to 43

Blockade of rivers by landslides have been causing a lot of suffering to the human beings from times immemorial. The damage is further aggravated if the blockade is in the vicinity of a River valley project. The Sanjay Vidyut Pariyojana (Bhabha Project) located in Kinnaur District, Himachal Pradesh is one such examples. It is a run of the river scheme located on the right bank of river Satluj utilising the water of Bhabha Khad, a tributary of Satluj river. The landslide blockade near the project caused flooding of the power house and interrupted the power generation in the project. Various factors responsible for the landslide and blockade of river have been studied. A strategic program of surface and underwater blasting was adopted to remove the blockade and restart the power generation. The paper presents the above aspects in brief.

The rock mass index (RMi) applied in rock mechanics and rock engineering (Vol 2 No 1, January 1996, pp 1-40)

Vestfjordgaten 4, N-1300 Sandvika (Norway); Tel: +47 67 57 11 00 Fax: +47 67 54 45 76

The RMi system is based on defined inherent rock mass parameters. Basically, it combines the compressive strength (s_c) of intact rock and a jointing parameter (JP) in the expression RMi = s _c .JP. JP represents the main jointing features, namely block volume (or density of joints), plus roughness, alteration, and size of the joints. This paper shows how RMi can be applied to a) determine the constants s and m in the Hoek-Brown failure criterion for rock masses to asses the shear strength parameters of continuous rock masses; b) work out ground response curves using the same s and m constants; c) quantify the descriptive NATM classification; d) estimate stability and rock support in underground openings. Rock support charts are presented for the three main groups of rock masses: discontinuous (jointed) rock masses, continuous (massive and highly jointed) rock masses, and weakness zones. The applications of RMi in rock engineering probably include a wider range of rock masses than any other numerical characterization or classification system.

Topography induced high in-situ stress under a river valley in Himalayas - a case study (Vol 2 No 1, January 1996, pp 41-58)

Champion Reefs PO, Kolar Gold Fields - 563 117, Tel: (08153) 60263, 61169, Fax: (08153) 60937

The simplifying assumption that the principal stresses are vertical and horizontal with depth breaks down when the ground surface is not horizontal as in the case of valleys and the hills. Knowing the effect of topography on stress distributions is of particular interest I case of construction of superstructure like dam or construction of tunnels in mountainous regions near valley slopes. In this paper we present our experience with in-situ stress measured by hydraulic-fracturing method below a river valley located in Himalayan region. The results show very high horizontal stress below the valley with vertical stress much higher than the overburden. The rotation of maximum compressional stress direction by 90º compared to the regional stress is also another outstanding feature revealed by the test. The site conditions are simulated and analysed by numerical method taking into account two types of loading conditions viz, only gravitational loading and gravitational and tectonic loadings in which case the measured results are incorporated as input parameter. The models show that below the valley, the topography affects both gravitational and tectonic loading as reflected by the localisation and enhancement of stress conditions.

Irrigation Design Organisation, Roorkee - 247 667 (India) Tel: (0091-1332) 73084, Fax: (0091-1332) 72487

Insitu shear strength is difficult to measure. Accurate representation of the real field conditions is difficult because the strength parameters, cohesion (c) and angle of friction (j) are not constant throughout the rock mass but vary from place to place, from project to project. In fact, correct measurement of rock mass strength has always remained a big field problem. Usually failure of a rock mass occurs partially along the joints and partially in solid rock, but in boundary cases, failure may occur entirely along a joint or entirely in solid rock. Thus, the failure of a rock mass lies within the area bounded by the failure envelope for a single joint and the failure envelope for solid rock. This paper discusses the shear strength envelopes developed for various rock mass ratings, degree of saturation and rock types tested in the lesser Himalayas. The recommended failure criteria are based on the results of extensive field tests, judgement and own experience of the author. It has been realised that for highly jointed rock masses shear strength will not be governed by the strength of the rock material. The effect of saturation on the shear strength of poor rocks has been found to be significant. The results of the study have been presented in the form of failure envelops which may be used for estimating the angle of internal friction (j) and shear strength developed at a given normal stress.

The engineering geological and the rock mechanical data must be systematically recorded and properly arranged for presentation purposes. The method presented in this paper requires the recording of key geotechnical parameters in a logging chart containing histograms. Data mapped from different sites at a project can then be manipulated/ interpreted and combined through a PC based spreadsheet to give a condensed description of a larger area or the whole project site. The applications of the geotechnical logging chart Underground Power House of Sardar Sarovar Multipurpose in India and Underground Olympic Stadium in Norway have been presented in this paper.

The approach of Hoek & Bray (1981) to analyse the plane failure analysis is modified to take into account the release joint inclination. Accordingly, the equations to calculate the factor of safety and other parameters have been changed. This modified approach has been subjected to statistical tools and simple equations have been proposed for direct estimation of the factor of safety of plane failure of slopes. These new equations are obtained using the multiple regression analysis. Adequacy of these equations has been tested by applying F Test, Durbin-Watson Test and Heterosedasticity and Homosedasticity Tests.

Numerical modelling is being increasingly used to study rock mechanics problems associated with large excavations in complex geologic formations. This paper concerns the stress analysis of three major hydroelectric projects in India. In one of the projects numerical modelling was used to understand the reasons for the observed of the rock mass and development of several cracks on the cavern walls. In the other two projects, numerical modelling is used to provide base for support design.

Structural Engineering Division, Central Building Research Institute, Roorkee - 247 667 (India)

The application of FEM in the solution of geotechnical engineering problems requires a strong recognition of the proper construction sequence. Efficient numerical strategies are available for this purpose. This paper represents an implementation and solution strategy of one such procedure. The blocky medium is replaced by an assembly of our noded rectangular finite elements for which all the necessary matrices can be derived in a close form. Several examples are solved, both analytically and numerically to examine the performance of the sequential excavation simulation strategy. The outstanding issues are identified.

Influence of geological features on long-term behaviour of underground powerhouse cavities in lower Himalayan region - a case study (Vol 3 No 1, January 1997, pp 23-76)

The reported case history pertains to the first underground powerhouse constructed and instrumented about 27 years ago in soft rocks of the Lower Himalayan region, which is seismo-tectonically active. The analysis and interpretation of data for over ten year period for Chhibro Underground Powerhouse Complex (in dolomite-limestones) has provided useful insight into the long-term behaviour of large powerhouse cavern. The study has proved to be helpful in identifying unknown deficiencies in the existing theories. Methodology for analysis and interpretation of complex instrumentation data has been developed. Seepage caused by charging of the water conductor system is observed to have affected support pressure significantly as has recurring earthquake shocks close to thick shear zones. Time-dependent effect has been observed significantly (in saturated rockmass) where there is seepage problem, i.e., roof of the powerhouse cavity and also near thick shear zone. However, no considerable time-dependent deformations has been noticed where rockmass is dry, i.e., on the roof of the surge tank (located in slates) and the walls of the powerhouse cavity. An empirical support pressure theory has been proposed to account for accumulated strains in rockmass near thick shear zones due to recurring earthquakes in seismic region.

Institute of Geonics, Academy of Sciences of the Czech Republic, Ostrava (Czech Republic)

Results of laboratory study on grouting of polyurethane resin are described. Two types of laboratory equipment are shown - one for study on grouting of fissured rocks, second for study on grouting of rocks with structural porosity. The results of first stage measurements regarding relationship between starting and injecting pressure and stress in fissured rock sample are described. The second stage of tests deals with laboratory process of grouting in pressure box and subsequent testing for the properties of grouted sand and gravel samples, and comparison of the laboratory and in-situ samples of the same materials.

This paper deals with finite element modelling of jointed rock as an equivalent continuum whose properties represent the material properties of the jointed rock. The material properties of the equivalent continuum are represented by a set of empirical relationship which express the properties of the jointed medium as a function of joint factor and the properties of the intact rock. The reliability of the analysis depends upon the joint factor which is a function of the joint orientation, joint frequency and joint strength. So, for a particular jointed medium knowing the intact rock properties and by estimating the joint factor, the properties of the jointed rock can be determined. The results obtained by the above analysis have been compared with the experimental results for three different rock materials for both intact and jointed medium. The results are in good agreement even for single and multiple joints and this can be easily extended to materials with many joints. The accuracy of the results for a discontinuous system depends on how well the joint factor is estimated for that particular case. Attempts are underway to apply it to real discontinuous systems.

AGRA Earth and Environmental Limited, 2227 Douglas Road, Burnaby, BC V5C 5A9 (Canada)

The principal objective in the design of underground support is to help the rock mass support itself. Traditional ground support in tunnelling and mining applications has relied on the techniques such as:

The use of shotcrete together with rock bolting and various types of reinforcement has become a technical and cost-effective alternative to traditional ground support methods in tunnels and mines. When applied to the rock mass, the shotcrete is forced into fissures and open joints and helps to bond the features together. Movement of rock block is prevented by a combination of bond strength and shear strength of the shotcrete in the immediate vicinity of joints. This, together with membrane or arching action of the lining helps the rock mass to support itself. The New Austrian Tunnelling Method (NATM) which traditionally has used mesh reinforcement and the Norwegian Method of Tunnelling (NMT) which is based on Steel Fibre Reinforced Shotcrete (SFRS) has proven valuable in this regard. Benefits of SFRS in tunnelling / mining environments:

This paper details various aspects of SFRS in its historical background; applications; design of shotcrete support; shotcrete materials; shotcrete reinforcement; shotcrete mixture proportioning; batching, mixing and supply; properties of plastic shotcrete; properties of hardened shotcrete; and toughness of SFRS.

A semi-empirical method for the prediction of mine subsidence and associated parameters in Indian coal mines (Vol 4 No 1, March 1998, pp 43-70)

Assistant Professor, Department of Mining Engineering, Indian School of Mines, Dhanbad - 826001 (India)

The empirical methods of subsidence prediction are site specific and are not based upon the rational concepts of Rock mechanics. Purely mechanistic methods on the other hand could not find wide applications because of their limitations in representing the complex behaviour of a rockmass. Moreover, these methods have a main handicap in general availability of accurate rock properties and geological data which are usually difficult and expensive to obtain. In order to overcome disadvantages of these two approaches a hybrid approach of carrying out parametric studies by numerical modelling and using its conceptual results in field database to develop a semi-empirical model has been adopted and discussed here.

The method of prediction of maximum possible subsidence, S_max has been reported elsewhere (Bahuguna et al., 1993). The results obtained from various numerical analysis have been used to identify and correlate the various parameters effecting the shape of the subsidence profile with the known parameters viz the nature of overburden rock mass and the mining geometry. A new Profile Function based on the present work has been recommended for use in the Indian coal fields. The profiles of slope, horizontal displacements and horizontal strains may be obtained from subsidence values along the given line. Results of a few of many cases tested by this method have been discussed and were found to be satisfactory when compared with field values.

On a rational method of analysis and design of tunnel supports based on the finite element technique (Vol 4 No 2, August 1998, pp 97-124)

Department of Civil Engineering, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP (United Kingdom); Tel: (01792) 295517, Fax: (01792) 295676 / 295517, Email: g.n.pande@swansea.ac.uk

The Q-system, also called the Norwegian Geotechnical Institute (NGI) classification system (Barton et al., 1974), plays an important role in the design of supports in tunnels excavated in rock and is frequently used in many pats of the world. One of the major shortcomings of the NGI classification system is that it does not take into account the orientation of rock joints with respect to the exposed surface of the tunnel excavation. This paper proposes a rational methodology in which the NGI classification system is enhanced by taking into consideration the influence of the orientation of joint set(s). Using the finite element method and the multi laminate model for jointed rock masses (Zienkiewicz and Pande, 1977), a set of design charts and tables useful to the practising engineers for circular tunnels are presented. A numerical example is given to illustrate their use.

Influence of saturation on modulus of deformation of Himalayan rock masses (Vol 4 No 2, August 1998, pp 125-137)

The geological nature and deformation characteristics of rocks always play significant and vital role in the selection of site, design, durability, economy and desired performance of dam structures. Results of insitu test obtained from seventy uniaxial jacking tests carried out at natural moisture content and another fifty tests carried out on saturated rock masses show that modulus of deformation is affected significantly by the change in the moisture regime of rocks, particularly for the "poor" and the "fair" category of rock masses. The test involved application of load on rock surface by means of hydraulic jack and measurement of the resulting deformation in dry as well as saturated rock mass. The experimental technique and other conditions during the test performance were maintained the same throughout. This paper identifies the influence of moisture on the deformability of rock mass. When saturated, the reduction in the modulus values can be of the order of 90 per cent for "poor" and 75 per cent for "fair" quality rocks with water sensitive minerals.

Technical note on rock cutting and tunnels on Khandala - Karjat railway line (Vol 4 No 2, August 1998, pp 139-148)

Joint Director (Civil), Indian Railway Centre for Advanced Maintenance Technology, Maharajpur, Gwalior, Madhya Pradesh (India), Tel: (0751) 470869, Fax: (0751) 470841

The 25 km long Khandala - Karjat Rail line in Maharashtra, India is part of 77 km long Bombay - Pune broad gauge railway line. It is a ghat section on 1 in 37 ruling gradient. The total length of the railway line is perched on the most difficult terrain consisting of three lines, i.e., down road, middle road and up road. There are as many as 52 tunnels along the route covering a total track length of 16.853 km inside the tunnels. About 22 percent track is inside the tunnels and about 68.50 percent track is on curves and mostly about 83 percent on steep gradient of 1 in 50 and above. This speaks of how much difficult the Railway Track operation is in Khandala - Karjat section.

Modulus of deformation is recognised as one of the important parameters governing the rock mass behaviour. It is experienced that tunnel section generally take long time to stabilise. These time-dependent deformations effect the tunnel lining along with the modulus of deformation of the rock mass.

The in-situ deformation / closure data from 37 arched tunnel sections through non-squeezing ground conditions have been collected and equations obtained from two models, viz, Burger’s four elements and Polynting’s three elements were used to develop correlation for estimating time-dependent deformation modulus.

The study suggests that time for ninety per cent tunnel closure / deformation is less both for good quality rock and larger span of tunnel. The concept of retarded creep appears to be valid for weak and dry rock masses around a supported tunnel in non-squeezing conditions.

Assistant Professor, Department of Civil Engineering, Indian Institute of Technology, Madras (IIT Madras), Chennai - 600 036 (India) Tel: (044) 2351365 extn 3434/3416, Fax: (044) 2350509, Email: nkumar@civil.iitm.ernet.in

This paper deals with the analysis of rock bolts in bedded strata involving the deep beam concept. It is assumed that there exists a firm competent strata above the rock beds such that the rock bolts may be anchored into this firm strata. Thus the beds which would have otherwise deflected individually and caused separation between beds ultimately resulting in roof falls, are now held together against the firm strata above. This composite member would now behave as a deep beam. As a result, the bending stresses in the beam are reduced and stability of the opening is assured. The deflection in the beam subjects the bolts to tension. It is assumed that no slip takes place between the beds and the transfer of stresses into the bolt due to deflection of the beam is perfect. Since the beam is suspended to the firm strata above it, the transverse loading on it is the self weight of the beam alone and it is assumed that the horizontal insitu stresses along the span direction of the beam are small and do not play a role in the deformation of the beam.

The differential equation for the Timoshenko beam is modified to incorporate the bolt forces. The equations are solved exactly using Laplace Transforms to obtain the bolt forces. A parametric study brings out the effect of the span of the opening, thickness of the beam, number and diameter of bolts on the bolt force, and deflection and bending stresses in the beam. Charts are provided which can be used for the design of openings using rock bolts.

Keywords: Bedded strata, Timoshenko beam, Rock bolts, Laplace transforms, Suspension effect, Bolt forces, Bending stresses, Deflections.

Technical note on ambient stress at the Malanjkhand copper mine project, Madhya Pradesh, India (Vol 5 No 1, June 1999, pp 35-46)

Hydraulic fracturing stress measurements have been carried out in three boreholes (LM-2, LM-17 and LM-21) at the open-pit mine of the Malanjkhand Copper Project. The magnitude and direction of the principal horizontal stresses have been evaluated by inverting shut-in pressure data of each of the three boreholes separately. The results reveal that SHmax is oriented in N70ºE direction at borehole LM-21, which is situated away from the central axis of the mining zone, and is almost the same as that of the ambient stress field evaluated earlier (during 1985-86) at this mine (borehole MDN-4), implying that the ambient stresses prevail at locations about 500 m away from the mining zone. The results further show that the stress field at boreholes LM-2 and LM-17, which are located on the central axis of the mining zone, has rotated anticlockwise such that SHmax is oriented in N25ºE direction and N50ºE direction almost parallel and sub-parallel to the central axis of the mining zone respectively. Interestingly, the rock mass at borehole LM-2 is excessively stressed (compressed) in the direction of the central axis, while it is de-stressed in the direction perpendicular to the mining axis. The mining excavation appears to be responsible for the disturbances of the horizontal stresses at these two boreholes because of their closeness to the mining zone. SHmax orientation at Malanjkhand is significantly different from the mean SHmax orientation of the mid-continent stress province of the Indian subcontinent. This suggests the effect of local geological factors including the nearby ENE trending tectonically action Narmada-Son lineament.

Keywords: In situ stress, orientation, hydraulic fracturing, Malanjkhand, open-pit mine, Narmada-Son lineament, mid-continent stress province, Bengal basin.

Structural Engineering Division, Central Building Research Institute, Roorkee – 247 667 (India)

An existing continuum characterisation model of a jointed medium is implemented in a computer program for non-linear finite element analysis. The implementation is verified by analysing a deep circular opening subject to a hydrostatic initial stress field and different joint orientation with strike parallel to the tunnel axis. This software is then used in the study of the effect of joint orientation on the location and extent of the plastic zone around deep circular opening subject to a non-hydrostatic initial stress field. A shallow circular opening is subjected to an internal pressure and the effect of different joint orientation is also studied. The no-tension zones around a deep powerhouse cavern are also shown to depend upon the joint orientation. The continuum characterisation model offers a simple means to analyse the underground openings more realistically.

Khadakwasla, Pune – 411 024 (India); Tel: (020) 4392511; Fax: (020) 4392004; Emal: root@wapis.nicnet.nic.in

The peak particle velocity and associated frequency of ground motion are considered important parameters for arriving at realistic safety criteria against blast vibrations. These parameters are controlled significantly by the seismic wave velocity through the transmitting medium, in addition to the various blast design parameters. The particle velocity depends on the powder factor which is found to be dependent on seismic wave velocity. The present paper highlights the importance and utility of seismic wave velocity for safe and effective blasting operations.

Keywords: Ground vibration, Particle velocity, Predominant frequency, Attenuation constants, Compressional wave velocity, Powder factor, Blastability

Rock masses near slopes behave as discontinuum due to the presence of discontinuities such as joints, faults, shear zones, bedding planes, etc. The stability depends on the geometry of discontinuities and the slope and orientation of excavated face. The most important factor is the shear strength of potential failure planes. The characterisation of a discontinuity or a shear zone is not possible merely by looking at a specimen or by subjecting to conventional laboratory testing. The genesis of a shear zone, its stress-strain history, the strength-deformation relationship, the degree of particle parallelism and compression texture of shear zone, all combined to modulate its behaviour particularly when it approaches the state of limit equilibrium. Based on extensive experimental results, it was found that the deviator stress which controls the shear failure is a better criterion for evaluating shear strength of joints with thick gouge (t>>a). As such, on the basis of unconsolidated undrained (U-U) triaxial tests, authors suggested a strength criteria for rock masses with gouge filled discontinuities.