A non-destructive method of determining rock strength,
Robert J. Allison, University of Durham, Department of Geography

Rock material strength is an important componet of many geomorphological studies. Current methods for determining this parameter result in sample destruction, preventing further analysis. A new non-destructive technique is described for indirectly determining material strength, by measuring Dynamic Young’s Modulus. Tests have been conducted on Jurassic Portland Limestone and Upper Cretacious Chalk to assess the apparatus. Young’s Modulus is becoming an increasingly important rock material property.

Die Eis- und Salzkristallisation im Porenraum von Sandsteinen und ihre Auswirkungen auf das Gefüge unter besonderer Berücksichtigung gesteinsspezifischer Parameter,
Günther Weiss, Münchner Geowissenschaftliche Abhandlungen

In der vorliegenden Arbeit werden die Folgen der Frost- und Salzeinwirkung aus das Gefüge von fünf aus unterschiedlichen erdgeschichtlichen Epochen stammenden Sandsteinen aus der Bundesrepublik Deutschland diskutiert, wobei dem dynamischen Prozeß der Salz- und Eiskristallisation im Porenraum besonderes Augenmerk geschenkt wird.
An diesen Gesteinen wurde eine Vielzahl von Kennwerten und Merkmalen erfaßt, z. B. mineralogische und Gefügeigenschaften, porenraumbezogene Merkmale, Festigkeits- und Verformungseigenschaften. Damit sind die gesteinsspezifischen Randbedingungen für die anschließende Verwitterungssimulation bekannt. 

Non-destructive determination of Young's modulus and its relationship with compressive strength, porosity and density,
R.J. Allison, University of Durham, Department of Geography

The Grindosonic apparatus, new equipment capable of indirectly determining rock compressive strength, is discussed. This utilizes the principle that elasticity theory can be applied to rock masses (Attewell & Farmer 1976; Selby 1982) and directly measures the fundamental vibration frequency of a rock sample of regular dimensions following shock excitation. Dynamic Young’s modulus and a variety of other parameters can be established.
Samples of Upper Cretaceous Chalk en Upper Jurassic Portlend Limestone are used to demonstrate the apparatus and ist application. Test specimens were prepared and analysis conducted on material extracted at a number of locations throughout the Isle of Purbeck in Dorset, UK. Samples suitable for deformation in traxial compression were also prepared and correlations drawn between compressive strength, dynamic Young’s modulus, porosoty and density.

The Relations between Modulus of Elasticity and Temperature in the Context of the experimental Simulation of Rock Weathering by Fire,
A.S. Goudie, R.J. Allison, S.J. McLaren

Fires occur frequently in many biomes and generate high temperatures on the ground surface. There are many field examples of fire causing rock disintegration. The simulation of fire in the laboratory (using a furnace) and the monitoring of changes in rock modulus of elasticity (with a Grindosonic apparatus), reveal that different rocks respond differently to heating. Significant decreases in elasticity occur at temperatures as low as 200°C and granites display particularly marked reductions. Extended periods of heating are not required for significant reductions to occur. It is postulated that the degree of change in elasticity as a result of simulated fire is such that rock outcrops subjected to real fires are likely to be sufficiently modified as to increase their susceptibility to erosion and weathering processes.

Geotechnical Properties of Rock Masses : their Control on Slope Form and Mechanisms of Change along the Napier Range, Western Australia,
R.J. Allison, A.S. Goudie, N.J. Cox

Slope form and the mechanism of change which slope profiles exhibit are frequently subject to scrutiny by geomorphologists. However, the majority of studies do not consider fundamental material properties and rock mass geotechnical characteristics. The results presented highlight the importance of synthesising standard geomorphological site investigation techniques with quantifiable rock geotechnical parameters, in order to understand slope form and development. Field research has been undertaken along the Napier Range of the Kimberley Region, Western Australia. The Napiers are an extensive, upraised, Devonian limestone reef, alon which a number of characteristic slope profiles can be identified. Laboratory studies of yield strength, stress-strain characteristics, elastic properties and discontinuity parameters have been conducted on material sampled at sites representative of each slope profile type. The results suggest that highly concave slopes have formed in limestone which exhibits little deformation before yield, has a high modulus of elasticity and few irregular fractures. Convexo-concave slopes, on the other hand, are characteristic of material which displays a greater ability to strain below yield, a relatively low modulus of elasticity and a pronounced discontinuity pattern. It is the combination of the field investigations and laboratory study which most successfully explains variations in slope form.

The Form of Rock Slopes in Tropical Limestone and their Association with Rock Mass Strength,
R.J. Allison, A.S. Goudie

The form of rock slopes has been studied in a tropical limestone environment. Investigations have concentrated on the Napier Range, an upper Devonian fringing and barrier reef complex, in the Kimberley region of Western Australia. Seven different characteristic slope forms occur along the Range. A minimum of three profiles have been analysed for each type of slope, using a high-length integral. A rock mass classification has been completed on each surveyed transect. The rock mass classification technique has not been previously applied to tropical limestone slopes. Results indicate that by aggregating data for individual slope units along a profile, associations can be drawn between profile shape and the geometrical characteristics of the rock mass as determined by its mass strength. A continuum of slope profile types has been defined for the Napeir Range and within the continuum, the importance of specific rock mass properties in determining spatial variations in slope form have been identified.

Critical degree of saturation as a threshold moisture level in frost weathering of limestones
Angélique Prick, Université de Liège

The moisture content has a deciding impact on the behaviour of a rock undergoing frost action. A particular critical degree of saturation Scr characterizes each material; only when the moisture content exceeds Scr will the material be damaged by frost. This parameter was defined for ten French limestones by measuring their dynamic Young’s modulus. Scr values depend on porosimetric characteristics of the rocks, especially their trapped porosity. The critical degree of saturation accounts for the various rock dilatometrical behaviours during freeze-thaw cycle.

La désagrégation mécanique des roches par le gel et l’haloclastie. Application de la méthode dilatométrique et mise en relation avec le comportement hydrique et les caractéristiques physiques des échantillons.
Angélique Prick, Université de Liège

Ce travail constitue une contribution à l’étude de l’altération par l’action de l’eau, des sels et du gel de calcaires tendres français d’âge secondaire. L’altération est évaluée par la méthode dilatométrique et des mesures du module d’élasticité dynamique. Le comportement dilatométrique d’échantillons soumis à 30 cycles d’humidification/séchange montre la mise en place d’un équilibre hydrique dans le milieu poreux, ce qui s’accompagne de migrations d’eau dont les caractéristiques dépendent des conditions thermiques et hydriques dans les diverses parties de la carotte. Ceci induit une contraction anisotrope de certains échantillons.
Les échantillons soumis à la cristallisation du sulfate de calcium ont montré une prise de longueur résiduelle significativement supérieure à la réponse dilatométrique d’échantillons du même lithologie soumis à des cycles en eau distillée. Le gypse forme des croûtes superficielles sur les calcaires, ce qui induit une impermébilisation de leur surface et limite les prises d’eau el les dilatations hydrauliques postérieures. L’hydratation des cristaux de sulfate de sodium formés existants ne cause pas de prise de longueur résiduelle significative: une partie des cristaux de sulfate de sodium formés dans le milieu poreux sont dissous par les humidifications postérieures en eau distillée. On peut corréler certaines caractéristiques porosimétriques à la réponse à l’haloclastie.
Les processus altérants intervenant lors du gel d’un échantillon humide sont non seulement la dilatation volumique accompagnant la transformation de l’eau en glace mais également la cryosuccion, qui a été à l’origine de contractions importantes des échantillons liés à la migration d’eau non gelée vers les cristaux de glace existants. Les facteurs influençant la réponse dilatométrique au gel sont le degré de saturation de la roche (supérieur ou inférieur à un degré de saturation critique), la lithologie (les migrations sont les mieux développées chez les roche à porosité multimodiale) et la vitesse du refroidissement.