Jointed Sandstone Research Articles

Rock Slope Stability Analysis along NH-44 in Sonapur Area, Jaintia Hills District, Meghalaya

Abstract: Occurrences of landslide are most common and critical issue in North-East India. The various types of slope failures have been affected most part of slopes and road section between Malidor to Sonapur area (approx 30 Km) along NH-44 within Jaintia hills district, Meghalaya, India. These slope failures causes considerable loss of life and property along with many inconveniences such as disruption of traffic along highways. The unscientific excavations of rock slopes for road widening or construction purposes may weaken the stability of the slopes. The rocks exposed in the area are highly jointed sandstone and shale of Barail Group of Oligocene age. The Sonapur landslide is most dangerous and destructive rock fall-cum debris flow. The present study includes the kinematic analysis of the slope to assess the potential failure directions as the rocks are highly jointed in some parts of road cut sections. The continuous slope mass rating (CSMR) technique has been applied for slope stability analysis at five vulnerable locations. Kinematic analysis indicates mainly wedge type of failure along with few toppling and planar failures. These failure required immediate treatment to prevent the slide and long term stability of the slope.

Numerical Modeling of Jointed Rock Under Compressive Loading Using X-ray Computerized Tomography

As jointed rocks consist of joints embedded within intact rock blocks, the presence and geometrical fabric of joints have a great influence on the mechanical behavior of rock. With consideration of the actual spatial shape of joints, a numerical model is proposed to investigate the fracture evolution mechanism of jointed rocks. In the proposed model, computerized tomography (CT) scanning is first used to capture the microstructure of a jointed sandstone specimen, which is artificially fabricated by loading the intact sample until the residual strength, and then digital image processing (DIP) techniques are applied to characterize the geometrical fabric of joints from the CT images. A simple vectorization method is used to convert the microstructure based on a cross-sectional image into a layer of 3-D vectorized microstructure and the overall 3-D model of the jointed sandstone including the real spatial shape of the joints is established by stacking the layers in a specific sequence. The 3-D model is then integrated into a well-established code [three-dimensional Rock Failure Process Analysis, (RFPA3D)]. Using the proposed model, a uniaxial compression test of the jointed sandstone is simulated. The results show that the presence of joints can produce tensile stress zones surrounding them, which result in the fracture of jointed rocks under a relatively small external load. In addition, the spatial shape of the joints has a great influence on the fracture process of jointed rocks.

Practical strength criterion for coal mine roof support design in laminated soft rocks

The stone roofs of coal mine roadways typically comprise low strength, thinly bedded and closely jointed mudstones, siltstones and sandstones. A practical strength criterion for use in currently available numerical codes should include consideration of the pronounced transverse isotropy introduced by the bedding and the tensile strength should be set to zero. The compressive strength is then the greater of either the damage/brittle criterion implemented as cohesion = UCS/6 and a friction angle of 0° or a purely frictional component with a friction angle of 33°. This criterion can be used to estimate the maximum height of a roof fall in bedded sedimentary rocks similar to coal measures.

Self‐potential signals induced by periodic pumping tests

We measured the variations of the self‐potential (SP) during periodic pumping tests performed at a test site located near a freshwater reservoir (Kemnader See, Bochum, Germany). Successions of injection and production intervals were applied in a borehole penetrating a jointed sandstone aquifer. We report the SP observations for tests with periods ranging between 10 and 60 min and flow rates between 10 and 25 L min−1. The SP responses at the surface exhibit the imposed period but are not truly harmonic contrary to the hydraulic pressure and SP measured in monitoring wells. In the grassy zone around the injection well, the amplitude of the SP signals decreases with distance from the injection well (around one order of magnitude at 10 m) in rough agreement with predictions for radial flow in a homogeneous medium around an infinite source. The shape of the SP responses also evolves with distance. Fourier spectral analysis reveals that the surface signals generally contain two main components at the main period and at half the period with the relative weight of the subperiodic components increasing with distance. Furthermore, the characteristics of the SP responses depend on whether the boreholes are left open or closed by packers. The comparison between surface and borehole measurements suggests that nonlinear phenomena are acting, probably related to the saturation and desaturation processes occurring in the vadose zone.

The importance of site-specific characters in prediction models for blast-induced ground vibrations

The aim of this study is to show the effect of geological factors in predicting the level of blast-induced ground vibrations. The site-specific character of ground must be involved in the prediction models especially if the ground conditions have a variable character like in this case. But in a blasting environment, this is only possible by using an empirical way. Towards this aim, an in-situ experimental study in a highly jointed sandstone quarry was carried out to incorporate the variable conditions into the prediction models. Therefore, 60 shots were organized and their ground vibrations monitored in two different directions to compare the results. These shots were normal production shots involving the true technological properties as well as geological properties into the prediction model. Based on these, the empirical relations between particle velocity, the amount of explosive and distance have been developed. The results show that the performances of these estimations depend on the site-specific character of these empirical relations. The best prediction was obtained with only 2.08% error level provided that the true technological and geological properties are involved.

Periodic pumping tests

SUMMARY We performed pumping tests with a periodic succession of injection and production intervals in a field of three shallow boreholes penetrating a jointed sandstone formation. Tests were conducted at periods ranging from 10 to 5400 s and pumping rates between 5 and 20 l min−1. Two types of analysis for the periodic pumping tests are presented. Injectivity analysis rests on the determination of the amplitude ratio and phase shift between the periodic flow rate and pressure records from the pumping well. Interference analysis is based on an evaluation of attenuation and phase shift between the periodic pressure signals at the pumping and monitoring wells. A periodic excitation permits to employ standard signal processing tools, such as fast Fourier transformation, facilitating the evaluation of weak signals. The observed amplitude ratio and phase shift values are compared to analytical predictions of 1-D and radial flow models. Results of interference tests are particularly diagnostic for the applicability of a subsurface model. Our test results do not fully agree with any of the considered analytical models suggesting a heterogeneous subsurface. We suppose that the two analysis methods yield averaged hydraulic properties of different volumes of a heterogeneous subsurface. Periodic injectivity tests screen the subsurface to increasing penetration depth if pumping period is systematically increased, while the subsurface volume between pumping and monitoring well dominates the outcome of an interference test at all periods. Periodic pumping provides several operational advantages compared to conventional testing, such as drawdown, pulse or shut-in tests. Periodic testing can be superposed on a long-term operation reducing operational conflicts and permitting continuous monitoring of changes in subsurface properties. Processing of periodic signals provides results even in a field with strong transient changes in fluid pressure related, for example, to operations in nearby wells. Periodic pumping can be performed in a closed loop minimizing the total fluid volume involved.

Economic coalbed methane production in the Canadian Foothills: Solving the puzzle

The producibility of methane at economic rates from thick and very gassy coals in the Canadian Foothills and Mountains remains a major challenge. These structurally deformed, and often sheared, coals are generally characterized by low permeabilities, which is the main limiting factor restricting the flow of gas through natural fractures. A preliminary evaluation of the cleating in the coals and of the jointing in the interburden clastics was carried out in the Elkview mine of SE British Columbia. Field observations were supplemented by microscopic evidence on coal microtextures produced by shearing and their impact on coal permeability. Permeability of the coals tested at simulated in situ stress conditions and parallel to bedding surfaces was highly variable, ranging from 2.09 md in Seam 3, Greenhills mine, to less than 0.001 md in the sheared Seam 10, Elkview mine. This variation may be rationalized based on variations in maceral composition, stress history, degree of shearing, and the mode of deformation of the coal seams in these tectonically complex regions. Shearing gave rise to a variety of complex textures in coal, such as slickensides, shear cones and striated features, small-scale thrusts in the hangingwall, and brittle and ductile microtextures. Furthermore, the coal seams act as aquitards to the flow of water, most likely because of low permeability. Water flow occurs at the contact between coal and interbedded coarser clastics and within the highly fractured and jointed sandstone units. The cone of effective depressurization required for coal gas drainage to occur in the study area is influenced by: (a) the development of a joint system in the more competent clastic beds that would provide the high permeability pathways for water and gas, and (b) the ability of the rocks above the coals to re-pressurize as a result of either surface recharge or water flow both laterally and vertically within the succession. Therefore, multidisciplinary studies of hydrology, coalification history, and structure would help increase our understanding of the mechanisms and timing of cleat development, effect of shearing on coal permeability, and presence of systematic fractures in the non-coaly lithologies.

Rock mass characterization for the underground cavern design of Khiritharn pumped storage scheme

A general approach to rock engineering designing aspects adopted at the Khiritharn Pumped Storage Scheme is described. The scheme involves excavation of three large caverns and tunnels in jointed sandstone within a suture zone in Southeast Thailand. Geological condition and engineering properties of the sandstone were investigated. Strength and modulus properties of the intact rock were determined from laboratory tests and properties of rock mass were empirically estimated for the design analysis in the de.nite study stage on the basis of three rock mass classi.cation systems namely the Rock Mass Rating (RMR), Geological Strength Index (GSI) and a Japanese system (EPDC). While the GSI gives strength and modulus of deformation values slightly higher than the RMR classi.cation, the EPDC gives a lower value of modulus of deformation but comparable rock mass strength value for the level of con.ning pressures at the depth of the cavern excavation. The results of stress analysis and loosening wedge analysis for the cavern excavations suggest favorable excavation condition.

The Effects of Fire on Rock Art: Microscopic Evidence Reveals the Importance of Weathering Rinds

This paper presents results of the first study of pre-fire and post-fire samples collected from rock engravings and adjacent sandstone joint faces. A 2001 wildfire at Whoopup Canyon, Wyoming, stimulated a comparison of 1991 and 2003 samples. Optical microscopy of ultra-thin sections, backscattered electron microscopy, x-ray (energy dispersive and wavelength dispersive) analysis of cross sections, and high-resolution transmission electron microscopy reveal that fires create some thermal fractures that enhance panel erosion, but most of the fire-induced erosion occurs along weathering rinds that form long before petroglyph manufacturing. In addition, rock varnish on top of petroglyphs experiences spalling, and fire ash with a clear potassium spike strongly adheres to rock varnish on petroglyphs and spalled sandstone. In the past, site managers assumed minimal damage away from massive spalls and other macrodamage on fire affected petroglyphs, an assumption no longer tenable. Since it is difficult to protect rock art after a fire starts, mitigation efforts can include identification of areas of intense weathering-rind development as locales most susceptible to erosion, and clearing trees and shrubs near rock art by hand.

Origin of minerals in joint and cleat systems of the Pottsville Formation, Black Warrior basin, Alabama: Implications for coalbed methane generation and production

Coalbed methane is produced from naturally fractured strata in the lower Pennsylvanian Pottsville Formation in the eastern part of the Black Warrior basin, Alabama. Major fracture systems include orthogonal fractures, which consist of systematic joints in siliciclastic strata and face cleats in coal that strike northeast throughout the basin. Calcite and minor amounts of pyrite commonly fill joints in sandstone and shale and, less commonly, cleats in coal. Joint-fill calcite postdates most pyrite and is a weakly ferroan, coarse-crystalline variety that formed during a period of uplift and erosion late in the burial history. Pyrite forms fine to coarse euhedral crystals that line joint walls or are complexly intergrown with calcite.Stable-isotope data reveal large variations in the carbon isotope composition of joint- and cleat-fill calcite (10.3 to +24.3 Peedee belemnite [PDB]) but only a relatively narrow range in the oxygen-isotope composition of this calcite (16.2 to 4.1 PDB). Negative carbon values can be attributed to 13C-depleted CO2 derived from the oxidation of organic matter, and moderately to highly positive carbon values can be attributed to bacterial methanogenesis. Assuming crystallization temperatures of 2050C, most joint- and cleat-fill calcite precipitated from fluids with 18O ratios ranging from about 11 to +2 standard mean ocean water (SMOW). Uplift and unroofing since the Mesozoic led to meteoric recharge of Pottsville strata and development of freshwater plumes that were fed by meteoric recharge along the structurally upturned, southeastern margin of the basin. Influxes of fresh water into the basin via faults and coalbeds facilitated late-stage bacterial methanogenesis, which accounts for the high gas content in coal and the carbonate cementation of joints and cleats.Diagenetic and epigenetic minerals can affect the transmissivity and storage capacity of joints and cleats, and they appear to contribute significantly to interwell heterogeneity in the Pottsville Formation. In highly productive coalbed methane fields, joint- and cleat-fill calcite have strongly positive 13C values, whereas calcite fill has lower 13C values in fields that are shut in or abandoned. Petrographic analysis and stable-isotope geochemistry of joint- and cleat-fill cements provide insight into coalbed methane reservoir quality and the nature and extent of reservoir compartmentalization, which are important factors governing methane production.

Clast fabric in relict periglacial colluvium, salamanca re‐entrant, southwestern new york, usa

Samples of macrofabric data obtained from colluvial deposits near the late‐Wisconsinan glacial margin display widely divergent characteristics. Those from highly weathered and jointed sandstone plot as girdle distributions. Samples from red colluvium of early‐Wisconsinan age form moderately strong clusters. Fabrics from shallow depth in medium‐textured brown colluvium of late‐Wisconsinan age generally have modes aligned with the local slope but are weak, and appear to have been modified by frost heaving. Clasts in the basal layers of an overlying loess unit were emplaced by frost heaving from the brown colluvium and have very weak or uniform fabrics. Particle shape exerts an influence on fabric strength in the brown colluvium, with samples composed of more elongated clasts displaying stronger fabrics. Fabrics from near‐surface deposits show generally weaker shape and strength characteristics and higher inclinations than those at depth. Calculated seasonal frost penetration is consistent with the depth to which weaker, more steeply inclined fabrics are found. Sampling in relict periglacial deposits should be performed only below the level of disturbance by seasonal frost.

Scaling of fracture connectivity in geological formations

A new method to quantify fracture network connectivity is developed and applied to analyze two classical examples of fault and joint networks in natural geological formations. The connectivity measure accounts for the scaling properties of fracture networks, which are controlled by the power law length distribution exponent a, the fractal dimension D and the fracture density. The connectivity behavior of fracture patterns depends on the scale of measurement, for a < D + 1, but is independent of scale for a > D + 1. Analysis of the San Andreas fault system shows that a < D+1 and that the connectivity threshold is reached only at a critical length scale. In contrast, for a typical sandstone joint pattern, a ≈ D + 1, which is on the cusp where the connectivity threshold is highly sensitive to the minimum fracture length in the system.

Assessment of rock slope stability along the proposed Ankara-Pozant? autoroad in Turkey

The main objective of this study is the determination of the slope stability and excavatability category of discontinuous rock exposed between 53+000 and 58+000 km of the proposed Ankara–Pozanti autoroad in Turkey to provide secure access. The study area is mostly in the outcrops of highly jointed sandstone with minor layers of marl. This Maastrichtian–Eocene Group also contains conglomerate and limestone bands of flysch character called the Pas˙ada* Group. Quaternary alluvial deposits occur throughout the site. The area was divided into four design sectors based on cut slope locations. Rock slope stability was assessed kinematically as well as through utilizing limit equilibrium analyses. The excavation category was determined to range from hard to extremely hard ripping. Remedial measures for unstable rock slopes are discussed.

Laboratory studies on shear behaviour and strength prediction of grout jointed sandstone : Shrivastava, R K; Jalota, A V; Amir, A A A; Rao, K S Proc 1st International Workshop on Scale Effects in Rock Masses, Loen, 7–8 June 1990P149–154. Publ Rotterdam: A A Balkema, 1990

Laboratory studies on shear behaviour and strength prediction of grout jointed sandstone : Shrivastava, R K; Jalota, A V; Amir, A A A; Rao, K S Proc 1st International Workshop on Scale Effects in Rock Masses, Loen, 7–8 June 1990P149–154. Publ Rotterdam: A A Balkema, 1990

Hydrogeological investigation of a proposed waste disposal site at Nant Y Gwyddon, South Wales

ABSTRACT The paper describes an investigation into the feasibility of siting a large landfill site on an extensive hilltop plateau, in an area receiving annual rainfall in excess of 2000 mm. The underlying rocks mainly comprise jointed sandstones. Water resources are located on and adjacent to the area and are fed by streams rising within it. The method of site operation required (i.e. containment or dispersal) could be determined only be means of detailed investigation capable of quantifying pollution risks. A groundwater tracing test was performed in conjunction with a surface water survey. These are described and the results and interpretation presented. The proposed method of site development is summarised.

Columnar jointed sandstone in Beacon Supergroup, Britannia Range, Antarctica

Abstract A columnar jointed structure occurs in Hatherton Sandstone (Devonian) where it is intruded by Ferrar Dolerite (Early Jurassic) in the Britannia Range, Antarctica. Although Ferrar Dolerite sills and dikes intrude sedimentary rocks of the Beacon Supergroup over much of the Transantarctic Mountains, this is the first report of columnar jointed sandstone. Petrography of the jointed rock shows it to be a medium to fine grained, moderately well sorted quartzarenite composed of moderately well to well rounded grains of quartz and very minor amounts of potassium feldspar and quartzose rock fragments. A series of measurements of microjoints showed nearly random orientations.

Deformability of joints and its relation to rock foundation settlements

This study explores several aspects of the 'discontinuous' approach to prediction of settlements of foundations on jointed rock. The first part presents the results of experiments with numerical and analytical solutions. It is shown that solutions of continuum elasticity cannot be used without introducing errors due to method alone, which could be serious for sensitive structures.The second part of the study describes measurements of joint stiffness on samples of natural joints in limestone and sandstone. Normal and shear stiffness coefficients were measured. It was found that the unit shear stiffness coefficient varies greatly with displacement, and an empirical relationship was derived that might be useful in analysing other rocks.

A study of relations between rock fabric and joints in sandstone : Reik, GA Univ. Karlsruhe, D Currie, JB Univ. Toronto, Ontario, CDN 14F, 2T, 23R Canad. J. Earth Sci. V11, N9, Sept. 1974, P1253–1268

A study of relations between rock fabric and joints in sandstone : Reik, GA Univ. Karlsruhe, D Currie, JB Univ. Toronto, Ontario, CDN 14F, 2T, 23R Canad. J. Earth Sci. V11, N9, Sept. 1974, P1253–1268

Erratum: A Study of Relations between Rock Fabric and Joints in Sandstone

The ground magnetometer traverses across the Avalon lineament were made by Memorial University students S. 07Brien, D. Hughes, B. Ryan, and A. Harris as part of a Geophysics field project under the direction of J. Hodych; their assistance is gratefully acknowledged. We also wish to thank D. F. Strong of Memorial University for critically reading the manuscript and R. K. Stevens for valuable discussion. BURKE, K. B. S . , HAMILTON, J. B., and GUPTA, V. 1973. The Caraquet Dike: Its tectonic significance. Can. J . Earth Sci., 10, pp. 1760-1768. STRONG, D. F. and WILLIAMS, H. 1972. Early Paleozoic flood basalts on northwestern Newfoundland: their petrology and tectonic significance. Proc. Geol. Ass. Can., 24, pp. 43-54. STRONG, D. F. 1974. Plateau lavas and diabase d i e s of northwestern Newfoundland. Geol. Mag. 111, (in press). WILSON, J. T. 1%6. Did the Atlantic close and then reopen? Nature, 211, pp. 676-681.

Deformation behaviour, strength and interaction of joints in sandstone : Wawersik, WR Johnson, RS Abstract. Eos. Trans. Amer. Geophys. Union, V54, N4, 1973, P466

Deformation behaviour, strength and interaction of joints in sandstone : Wawersik, WR Johnson, RS Abstract. Eos. Trans. Amer. Geophys. Union, V54, N4, 1973, P466