Shear strength model for overconsolidated clay-infilled idealised rock joints

Saturated infilled joints can contribute to the instability of rock masses during undrained shearing. This paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour. A revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material. Tests were conducted under consolidated undrained conditions in a high-pressure triaxial apparatus on joints having a dip angle of 60°. Pore pressure development in the infill materials was monitored. The results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio (t/a), whereas the shear behaviour is controlled by the infill alone beyond this critical value. The proposed model for predicting the shear strength of rough infilled joints describes how the OCR influences the shear strength, pore water pressure development, and critical t/a ratio

Revised Shear Strength Model for Infilled Rock Joints Considering Overconsolidation Effect

An infilled rock joint is likely to be the weakest plane in a rock mass. The most pronounced effect of the presence of infill material is to reduce the friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill the smaller the shear strength of the rock joint, and once the infill reaches a critical thickness, the infill material governs the overall shear strength and joint walls (rock) play no significant role. However, some infilled joints may gain strength over time due to consolidation mechanisms, but may be weakened upon subsequent joint movements. Several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), i.e. t/a ratio. CNS models provide a much better accuracy of the infilled joint behaviour in the field but none of these models have focused on the overconsolidation effect of the infilling material. This paper presents a critical review on the existing models and a series of laboratory investigations carried out on idealised saw-toothed rock joints at the University of Wollongong in order to verify the effect of overconsolidation. The tests show how the overconsolidation ratio (OCR) influences the shear strength. The critical thickness, i.e., t/acrit, decreases with increasing OCR. A revised model for predicting the peak shear strength of rough infilled joints considering the effect of OCR is presented on the basis of the laboratory tests performe

Shear strength model for overconsolidated clay-infilled idealised rock joints

Saturated infilled joints can contribute to the instability of rock masses during undrained shearing. This paper reports an experimental investigation into the effect of the overconsolidation of infilled rough joints on undrained shear behaviour. A revised model is presented for predicting the shear strength of rough infilled joints on the basis of experimental tests carried out on idealised sawtoothed joints with natural silty clay as the infill material. Tests were conducted under consolidated undrained conditions in a high-pressure triaxial apparatus on joints having a dip angle of 608. Pore pressure development in the infill materials was monitored. The results show that the effect of asperities on shear strength is significant up to a critical asperity height to infill thickness ratio (t/a), whereas the shear behaviour is controlled by the infill alone beyond this critical value. The proposed model for predicting the shear strength of rough infilled joints describes how the OCR influences the shear strength, pore water pressure development, and critical t/a ratio

MSEC2008-72202 DESIGN AND FABRICATION OF A ROLLER IMPRINTING DEVICE FOR MICROFLUIDIC DEVICE MANUFACTURING

ABSTRACT Microfluidic devices are gaining popularity in a variety of applications, ranging from molecular biology to bio-defense. However, the widespread adoption of this technology is constrained by the lack of efficient and cost-effective manufacturing processes. This paper focuses on the roller imprinting process, which is being developed to rapidly and inexpensively fabricate micro-fluidic devices. In this process, a cylindrical roll with raised features on its surface creates imprints by rolling over a fixed workpiece substrate and mechanically deforming it. Roller imprinting aims to replace processes that were developed for laboratory scale prototyping which tend to not be scalable and have high equipment requirements and overheads. We discuss the limitations of PDMS soft lithography in large-scale manufacture of microfluidic devices. We also discuss the design, fabrication, and testing of a simple roller imprinting device. This imprinter has been developed based on the principles of precision machine design and is implemented using a three-axis machine tool for actuation and position measurement. A framework for the micromachining of precision imprint rolls is also presented