Shear behaviour of rock joints with unsaturated infill

Behaviour of soil-infilled rock joints has significant importance with respect to the strength of fractured rock mass. The presence of even a small amount of fine-grained infill material within a joint can reduce its shear strength considerably, depending on the degree of saturation of infill. Therefore, it is crucial to examine how the infill material can adversely affect the joint shear strength. Previous studies of infilled joints have mainly been focused on idealised regular joint patterns owing to the simplicity and reproducibility in laboratory testing. Current literature on infilled rock joints has also neglected the effect of the degree of saturation of infill on the shear behaviour. In most instances, fully saturated infill has been used or assumed, and the contribution of matric suction on the shear strength of joints having unsaturated infill has not been studied. In this study, a series of triaxial tests on natural joint profiles having joint roughness coefficient (JRC) of 10-12 is carried out at constant moisture content. A semi-empirical model is proposed and validated on the basis of laboratory data

Chalk-steel Interface testing for marine energy foundations

The Energy Technology Partnership (ETP) and Lloyd’s Register EMEA are gratefully acknowledged for the funding of this project. The authors would also like to acknowledge the support of the European Regional Development Fund (ERDF) SMART Centre at the University of Dundee that allowed purchase of the equipment used during this study. The views expressed are those of the authors alone, and do not necessarily represent the views of their respective companies or employing organizations.Peer reviewedPostprin

Evaluation of Mode I Fracture Toughness Assisted by the Numerical Determination of K-Resistance

The fracture toughness of a rock often varies depending on the specimen shape and the loading type used to measure it. To investigate the mode I fracture toughness using semi-circular bend (SCB) specimens, we experimentally studied the fracture toughness using SCB and chevron bend (CB) specimens, the latter being one of the specimens used extensively as an International Society for Rock Mechanics (ISRM) suggested method, for comparison. The mode I fracture toughness measured using SCB specimens is lower than both the level I and level II fracture toughness values measured using CB specimens. A numerical study based on discontinuum mechanics was conducted using a two-dimensional distinct element method (DEM) for evaluating crack propagation in the SCB specimen during loading. The numerical results indicate subcritical crack growth as well as sudden crack propagation when the load reaches the maximum. A K-resistance curve is drawn using the crack extension and the load at the point of evaluation. The fracture toughness evaluated by the K-resistance curve is in agreement with the level II fracture toughness measured using CB specimens. Therefore, the SCB specimen yields an improved value for fracture toughness when the increase of K-resistance with stable crack propagation is considered

Downwearing rates on shore platforms of different calcareous lithotypes

Vertical lowering (downwearing) of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood. The efficacy of mechanical and chemical weathering acting on a given substrate, together with erosional processes, influences downwearing rates. In order to determine the relationship between lithotypes and downwearing rates, data collected from a Transverse Micro-erosion Meter were obtained for shore platforms of three different calcareous lithotypes (biocalcarenite, calcarenite and carbonated siltstone) along the central Algarve coast (Southern Portugal). Downwearing rates ranged between 0.096 mm year−1 and 1.676 mm year−1 in biocalcarenite and weakly cemented calcarenite, respectively. In addition, physical properties of the rocks comprising the platforms were measured, including uniaxial compressive strength (as determined by the Point Load Test), porosity, and calcium carbonate content. The results show that downwearing depends primarily on the intrinsic properties of the substrate. Porosity, in particular, acts in two ways: (i) it tends to weaken the substrate; and, (ii) it controls the downward extent of the water percolation and therefore the depth of the weathering mantle subject to erosion by waves and currents.Portuguese Foundation for Science and Technology (FCT) through Research Projects PTDC/CTEGEX/70448/2006 (BISHOP) and PTDC/CTE-GIX/111230/2009 (EROS)

Physical mechanical consolidation and protection of Miocenic limestone used on Mediterranean historical monuments: the case study of Pietra Cantone (southern Sardinia, Italy)

The present work aims to study the consolidating and protective chemical treatments of the Pietra Cantone, a Miocenic (lower Tortonian) limestone widely used in important monuments and historical buildings of Cagliari (southern Sardinia, Italy). Similar limestones of the same geological period have also been used in several important monuments of Mediterranean area, i.e., Malta and Gozo Islands, Matera (central Basilicata, Italy), Lecce (southern Puglia, Italy) and Balearic Islands (Spain). The Pietra Cantone limestone shows problems of chemical–physical decay, due to their petrophysical and compositional char- acteristics: high porosity (on average 28–36 vol%), low cemented muddy-carbonate matrix, presence of phyllosil- icates and sindepositional sea salts (\3%). So, after placed in the monument, this stone is easily alterable by weath- ering chemical processes (e.g., carbonate dissolution and sulfation) and also by cyclic mechanisms of crystalliza- tion/solubilization of salts and hydration/dehydration of hygroscopic phases of the clay component. To define the mineralogical-petrographic features (composition, texture) of limestone, the clay and salt crystalline phases, the optical microscope in polarized light and diffraction anal- ysis were used. To define the petrophysical characteristics (i.e., shape and size distribution of porosity, surface area(SBET), matrix microstructures, rock composition) and interactions of chemical treatments with rock, SEM–EDS analysis and N2 porosimetry with BET and BJH methods were used. To evaluate the efficacy of Na/K-silicates, ethyl silicate consolidants and protective nano-molecular silane monomer water repellent, the mechanical strengths (uni- axial compressive strength, point load and flexural resis- tance), water/helium open porosity, water absorption and vapour permeability data determined before and after the chemical treatments of the Pietra Cantone samples from monument were compared

Estimation of the strength of Nubian sandstone formation from point load test index and other simple parameters

This study investigates the correlation of the uniaxial compressive strength (UCS) and the point load test (PLT) index Is(50), bulk density, water absorption and the RQD properties of the Sudanese Nubian sandstone formation. The UCS being is the rock property needed in engineering practice but its determination is tedious, time consuming and expensive. Alternatively, the UCS may be indirectly evaluated through establishing relationships with rock parameters which are easier, cheaper and more convenient to determine in the laboratory or in the field. An extensive laboratory testing was executed to determine the above rock properties for many NSF samples taken from Khartoum State and other areas. Statistical analysis was performed on the test data and a reliable linear regression equation has been developed with a UCS to PLT Is(50) conversion factor of 10.18 and may be applied to estimate the strength of the Sudanese sandstone formation. The developed correlation is in good agreement with few of the many methods published for similar rock types which indicates that large errors may result in from applying an inappropriate UCS prediction method. Thus, it is important to establish separate correlations or validate published correlations to check their suitability for a specific rock types and local geologies. Useful correlation relationships of reasonable accuracy were also established for rough estimation of the UCS from the bulk density, water absorption and the RQD properties of the Nubian sandstone formation