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Results
Performance of Rock Slopes during the 2010/11 Canterbury Earthquakes (New Zealand)
Massey, C. (GNS Science) | Richards, L. (Rock Engineering Consultant) | Pasqua, F. Della (GNS Science) | McSaveney, M. (GNS Science) | Holden, C. (GNS Science) | Kaiser, A. (GNS Science) | Archibald, G. (GNS Science) | Wartman, J. (University of Washington) | Yetton, M. (Geotech Consulting (NZ) Ltd.)
Abstract The 2010/11 Canterbury earthquakes triggered many mass movements in the Port Hills including rockfalls, rock and debris avalanches, slides and slumps and associated cliff-top cracking. The most abundant mass movements with the highest risk to people and buildings were rockfalls and rock/debris avalanches. Over 100 residential homes were impacted by landslides, leading to the evacuation of several hundred residents. Volumes of rock leaving several of the larger cliffs during the earthquake sequence were determined from terrestrial laser scan change models. There were no seismically instrumented cliff sites and there was some distance between the cliffs and nearest strong-motion sites. Therefore, we synthesised free-field rock-outcrop seismograms by employing a stochastic approach controlled by source models and regional parameters derived using spectral inversion of the extensive strong motion data set. Relationships between volumes leaving cliffs during the earthquakes and site peak ground acceleration (PGA), peak ground velocity (PGV) and Arias intensity were compared for different sites. Multiple linear regression was used to analyse the variables that best predict the volumes of debris that fell from the slopes during the main earthquakes. The best correlation between the volume of debris falling per square metre of slope face and the seismic forcing parameters was for vertical PGV. The results from the multiple linear regression incorporating slope height, inclination, PGV horizontal and PGV vertical, improved the statistical relationship. Field data and results from the 2D seismic site response assessment indicate that the following factors affect dynamic performance of the modelled cliffs:cliff geology—mainly material modulus, shear strength and shear wave velocity; slope geometry—ridge-scale versus site-scale effects; and the temporal aspects of the earthquake shaking (i.e., single acceleration peaks of large amplitude versus multiple peaks of smaller amplitude). Model results show that amplification of shaking does not increase linearly with increasing height, but instead reflects changes in the cliff geology where material strength, modulus and shear-wave velocity contrasts lead to acceleration contrasts. These factors show that the use of well documented case histories provide the basis for more certainty in seismic landslide assessments compared to those that are only empirically based.
- Oceania > New Zealand (0.55)
- North America > United States > Kansas > Butler County (0.25)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- North America > Canada > Alberta > Hill Field > Aecog (W) Et Al Clearwatr 9-5-86-11 Well (0.98)
- North America > Canada > Alberta > Richmond Field > Cve Richmond 10-19-69-19 Well (0.94)
ABSTRACT: A detailed understanding of geological conditions is required to define realistic failure mechanisms and derive the required inputs for dam stability assessments. This paper initially outlines the rock material and rock mass properties at five New Zealand dam sites and then summarises approaches to the selection of design input parameters and analytical stability methods. The dams are founded on rock mass types that include closely-jointed greywacke, foliated schist and jointed sintered to moderately welded ignimbrite. Rock mass characterisation and laboratory strength testing provide inputs for classification systems such as the Geological Strength Index and failure criteria such as that of Hoek-Brown, but even where these are well defined, care is needed in the recognition of appropriate failure modes in the foundation geological model. The case histories include examples of the use of the Hoek-Brown failure criterion for estimating global rock mass strength, the Barton empirical equation for discontinuity shear strength and the empirical estimation of rock mass deformability. Analytical methods include both limit equilibrium and finite element methods and use of Strength Reduction Factor for sliding stability. A critical prior requirement for analyses is to assess whether they are for global rock mass strengths or structurally-defined kinematic mechanisms. The discussion section considersinfluences on input parameter values such as the Hoek Brown material constant mi. 1. INTRODUCTION Stability assessments are required for both the design of new dams and performance evaluations of existing dams. Apart from small dams with low hazard ratings, their design should be based on comprehensive, site-specific investigations and geotechnical properties, rather than precedent or empirical charts. Most dams have individual or unique characteristics, and there is a real challenge in selecting investigation techniques most suitable for the nature of the site and applying appropriate methodologies in the design process. This paper outlines experiences in obtaining design parameters for the foundations of five existing dams in New Zealand, and the analytical approaches used for stability assessments. Initially there is an overview of foundation intact rock material properties obtained from laboratory testing and rock mass properties obtained from rock mass characterization. Then, derived input parameters are used in limit equilibrium and finite element analyses of dam stability, using either global rock mass strength and deformability or shear strength along structurally controlled defects. The paper finishes with some discussion of the factors that influence the design parameters outlined in the paper. 2. ROCK CHARACTERISATION Figure 1 shows a map of New Zealand with locations of large dams [1], many of which are part of hydroelectric schemes. The dams are founded on a range of lithologies that include Upper Palaeozoic to Mesozoic-age greywacke and schist, Tertiary-age sedimentary rocks and Quaternary-age ignimbrites. The five case history dams, (four gravity and one arch), are founded on greywacke, schist and ignimbrite. 2.1. Rock material properties Unconfined testing (unconfined compressive strength - UCS or qu, Brazilian tensile strength - st and Youngs modulus - Ei) has been performed on cores obtained from block samples and/or triple tube drilling at most of the sites.
- Oceania > New Zealand (1.00)
- North America > United States (1.00)
- North America > Canada > Ontario > Toronto (0.28)
- Phanerozoic > Paleozoic (0.54)
- Phanerozoic > Cenozoic (0.54)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.68)
- Management > Professionalism, Training, and Education > Communities of practice (0.56)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (0.56)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)
ABSTRACT Upper Paleozoic to Mesozoic-age greywackes are widespread throughout New Zealand. This paper describes the characteristics of the greywacke rocks based on field mapping, laboratory testing and rock mass classification from sites around the country. The rocks comprise hard sandstones, interbedded sandstones and mudstones, and mudstones. Where unweathered, intact rock materials have unconfined compressive strengths generally above 100MPa and moderate to high modulus ratios. The rock masses, which are typically closely-jointed and commonly tectonically disturbed, have an unusual combination of very high intact strength and joints with low persistence. The effect of these properties on rock mass deformability and strength is illustrated by estimation of dam foundation deformability from tiltmeter measurements and assessment of critical foundation failure mechanisms from estimates of defect and global rock mass strengths. 1 INTRODUCTION In New Zealand, the term ‘greywacke’ is applied to the very well indurated to slightly metamorphosed, interbedded mudstones and muddy sandstones belonging to the Torlesse Supergroup. These Upper Paleozoic to Mesozoic-age basement rocks are widespread throughout New Zealand (Fig. 1) where they are the bedrock of many of the country's engineering projects and also an important source of roading and concrete aggregate. Greywacke rocks are commonly closely-jointed as a result of their complex geological history. This paper is part of a long-term New Zealand research project into the engineering properties of unweathered greywacke. Studies at three sites (Aviemore Dam, Belmont Quarry, Taotaoroa Quarry – Fig. 1) have involved engineering geological mapping, laboratory testing of intact rock and assessment of rock mass properties (Read et al. 1999, 2003, Richards & Read 2006, Read & Richards 2007). Postgraduate studies involving mapping, laboratory testing and analysis of earlier in situ testing (e.g. Cook 2001) also form part of the project. This paper summarises geotechnical characteristics of greywacke rock masses and discusses influences of defect characteristics on their strength and deformation properties. 2 GREYWACKE PROPERTIES 2.1 Rock material Greywacke sequences (Begg & Mazengarb 1996) consist of interbeds of:Sandstone – coarse to medium grained, and medium to dark grey. Individual grains are poorly sorted angular quartz and feldspar, plus fragments of metamorphic and igneous rocks. The intergranular filling is clay minerals formed during induration or slight metamorphism. Mudstone – layers of clay, silt or mud, generally dark grey to black, sometimes red from iron minerals. Proportions of mudstone to sandstone vary between localities. For example, at Waitaki near Aviemore, mudstone is the dominant lithology, while elsewhere (e.g. Karapiro near Taotaoroa) sandstone dominates. More massive beds of both lithologies may be up to tens of metres thick, although more cyclic deposition can result in interbedding with discrete beds < 0.5m thick. Figure 2 summarises intact compressive strength and deformation parameters for greywackes from a number of sites. Sandstones, which have moderate modulus ratios, have strengths > 100MPa with stronger rocks being coarser grained. Mudstones, with moderate to high modulus ratios, are generally weaker than the sandstones and strong to very strong.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (1.00)
ABSTRACT ABSTRACT: Greywacke rocks, which are widespread throughout New Zealand, are composed of strong to extremely strong, sandstones, interbedded sandstones and mudstones, and mudstones. The rock masses are closely-jointed and often tectonically disturbed as a consequence of their complex geological history. Local experience indicates that the combination of high intact strength and low defect persistence in a closely jointed rock mass is not well-suited to multi-parameter rock mass classification systems such as Rock Mass Rating (RMR) and Tunnelling Quality Index (Q). A preferred approach is a comprehensive engineering geological description to characterise the greywackes for input to a specifically developed descriptive classification system. This step provides a direct linkage to classifications like RMR or the simpler Geological Strength Index (GSI) classification system, which is based on defect spacing and quality only, as a required input for the Hoek- Brown failure criterion. 1 INTRODUCTION In New Zealand, the term ‘greywacke’ is applied to the very well indurated to slightly metamorphosed, interbedded mudstones and muddy sandstones belonging to the Torlesse Supergroup. These Upper Paleozoic to Mesozoic-age basement rocks are widespread throughout New Zealand (Fig. 1). Many of the country’s engineering projects are sited in these rocks and they are also an important source of roading and concrete aggregate. Greywacke rocks are commonly closely-jointed as a result of their complex tectonic and geological history. This paper is part of a long-term New Zealand research project into the engineering properties of unweathered greywacke. Three dam or quarry study sites (Aviemore, Belmont, Taotaoroa – Fig. 1) have been engineering-geologically mapped, laboratory testing carried out to determine the properties of the intact rock and rock mass properties assessed (Read et al. 1999, 2003, Richards & Read 2006).
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.70)
ABSTRACT: Derivation of the Hoek-Brown intact rock parameters (constant mi and uniaxial compressive strength óci) is more problematic for weak rock than for high-strength materials. This paper applies the results of laboratory strength testing of some New Zealand weak (i.e. qu<25 MPa) Tertiary-age sandstone and Quaternary-age ignimbrite in unconfined and triaxial compression and indirect tension to the determination of mi and óci. Multi-stage undrained triaxial testing gave an underestimate of sandstone strength, and drained triaxial testing of ignimbrite at slow rates of loading reduced mi values by up to 30%. The ISRM and ASTM rock triaxial test methods are not well suited to weak rocks and some modifications would be appropriate, in particular allowing specimen drainage and reducing rates of loading. The addition of indirect tensile testing to the suite of testing to determine mi and óci is recommended. The paper also endorses the guidelines that the parameters should be determined, where possible, by laboratory testing with triaxial confining pressures ranging from zero to one half the unconfined compressive strength. INTRODUCTION The Hoek-Brown failure criterion is a practical and widely accepted method for assessing the strength of jointed rock masses. The generalized failure criterion [1, 2] is defined by: [Equation available in full paper] (1) Where ¿1 &¿3 are the maximum and minimum effective stresses at failure respectively, mb is the Hoek-Brown constant m for the rock mass, s and a are constants which depend on the characteristics of the rock mass, and ¿ci is the uniaxial compressive strength of the intact rock material. In order to use the criterion, the following three properties need to be determined [1]: 1 the uniaxial compressive strength ¿ci of intact rock material, 2. the value of mi, the Hoek-Brown constant for intact rock material, and 3. the value of the Geological Strength Index GSI [3] of the rock mass. This paper firstly describes the results of several laboratory testing programs to determine the intact rock properties, ¿ci and mi, for weak rocks (i.e. unconfined intact strength<25 MPa according to the ISRM guidelines [4]). The rocks tested are New Zealand Tertiary-age sandstone from a coal mine and Quaternary-age ignimbrite from a hydroelectric power station. The particular problems of establishing mi values are then discussed, together with comparisons with values for other similar rocks and observations on the approach for obtaining more confident values.
- North America > United States (0.68)
- Oceania > New Zealand (0.55)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.69)
- Energy > Oil & Gas > Upstream (0.69)
- Energy > Power Industry (0.54)
- North America > Canada > Alberta > Mountain Field > Amoco Chiefco A-1 Sterco 16-25-47-21 Well (0.98)
- North America > United States > Kansas > Beaumont Field (0.89)
- North America > Canada > Alberta > Morley Field > Canlin Morley 9-4-26-7 Well (0.89)
Abstract. This paper provides understanding of Canada's northern frontier resource potential with emphasis on the Beaufort-Mackenzie Basin. To a lesser extent it outlines the regulatory regime in place to meet the challenges posed by the disposition of resources in an arctic environment that lacks existing infrastructure. Growing concern about North American conventional natural gas supply and the increasing demand for environmental reasons is giving rise to renewed interest. The National Energy Board, as regulator of northern exploration and development, reveals that; a probabilistic resource estimate, discovered and undiscovered potential of 12 billion barrels and 168 Tcf, along with vast quantities of non-conventional gas hydrates remain for exploitation. Resources in the Beaufort-Mackenzie Basin, are in Tertiary, deltaic sandstones, trapped by extensional faulting along a rifted continental margin. The discussion centres on the probabilistic estimate of these discovered resources supported by exploration background and selected field examples. The challenge is to develop this resource in a remote pristine environment that requires preservation of the unique existence of complex, shallow permafrost in the eastern Beaufort Sea and Mackenzie Delta. Encouragement for a natural gas and liquids pipeline infrastructure reaching the Mackenzie Delta is discussed with reference to recent world-class gas discoveries in the southern Northwest Territories. INTRODUCTION A comprehensive statistical analysis of all Mackenzie Delta and Beaufort Sea oil and gas fields, by pay zone in the reservoir, was undertaken by the National Energy Board (Board) using publically released seismic and well information1. The probability distribution of these discovered resources is presented in context with six depositional environments. A section on natural gas hydrates is included because of the challenge they pose to safe drilling and development as resource potential. l The Mackenzie Delta - Beaufort Sea, located between 69 degrees to 71 degrees north latitude is part of the Beaufort Basin. The delta is 575 kilometres east of Alaska's North Slope and 1150 kilometres north of the recent Fort Liard gas discoveries in the southern Northwest Territories, figure 1. The 242 exploration wells drilled within the basin, since 1970, have resulted in 53 discoveries; 20 gas, 13 oil, and 20 oil and gas, making this a highly prospective resource area, figure 2. For regulatory purposes this region is part of "frontier lands" under Federal legislation. Figure 1 - Existing pipelines, permafrost regions. 68 Challenging Hydrocarbon Potential in Canada's Northern Frontier Basins l Figu Figure 2 - Discovered resources, outline of Tertiary depositional sequences. 1
- Geology > Structural Geology > Tectonics (1.00)
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.51)