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Blasting has been widely used in mining and construction industries for rock breaking. This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media. The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock. The field test aims to provide measurement data to better understand the stress wave propagation in soil/rock and along their interface. Triaxial accelerometers were used for the free field vibration monitoring. The measured results are presented and discussed, and empirical formulae for predicting peak particle velocity (PPV) attenuation along the ground surface and in soil/rock were derived from the measured data. Also, the ground vibration attenuation across the soil-rock interface was carefully examined, and it was found that the PPV of ground vibration was decreased by 37.2% when it travels from rock to soil in the vertical direction. Keywords: Rock blasting, Field tests, Blast wave propagation, Peak particle velocity (PPV), Rock-soil interface

Expansive soils exhibit swell-shrink behaviour in wet-dry periods resulting in distresses on light-weight structures founded on/in them. Therefore, it is essential to investigate the climate-ground interaction when designing structures on expansive soils. Laboratory-based models are preferred to investigate the climatic-ground interaction of expansive soils due to the uncontrollability of the boundary conditions and expenses associated with field monitoring. More flexibility in analysing the climatic-induced hydraulic responses in expansive soils can be achieved by finite element modelling of data from physical model tests. However, these laboratory-based models regularly encounter the effects of boundary flaw, preferential flow paths and entrapped air that needs to be accounted for when numerically simulated. In this study, the authors aim to numerically model the hydraulic responses in an instrumented Vertosol soil column (ISC) under controlled laboratory conditions. The effects of the preferential flow paths and boundary flaws were incorporated into a modified hydraulic conductivity as a practical approach to model the hydraulic responses in ISC. Influence of the entrapped air was rectified by a suitable correction factor. These findings present a practical method for geotechnical practitioners to accurately estimate the suction and volumetric water content profiles in laboratory-based expansive soil model tests., Civil engineering; Earth sciences; Environmental science; Geotechnical engineering; Construction engineering; Soil composition; Soil hydrology; Environmental engineering; Unsaturated soil; Expansive soil; Numerical simulation; Climate-ground interaction; Mechanical properties; Sensors; Wetting

Opening holes in rock including their size and distribution can affect the performance of rock-related structures. A good understanding on this will contribute to, for example, rock cavern design, and construction, tunnelling, and mining engineering. To improve the understanding, a comprehensive investigation of the opening hole effect on the rock mechanical behaviour under biaxial loading condition is carried out by virtue of a hybrid continuum-discrete element method. Laboratory specimens with both single hole and multi-hole of various radii are investigated and compared with the cases subjected to uniaxial compression. It is demonstrated that the confining pressure can increase both the stiffness and strength due to delaying the crack initiation and propagation. The increase due to the confining pressure is more evident for the compressive strength. For single hole specimens with 0.75 mm radius hole, the increase ratio of the compressive strength is a linear increasing function with width and the increase ratio ranges from 2.15 for the specimen with 3.5 mm width to 2.45 for 10 mm width. For the single hole specimen with 10 mm width, the increase ratio starts at 2.13 for the specimen with 0.75 mm radius hole, ascending to the peak of 2.37 for the specimen with 1 mm radius hole, followed by a decline to 2.2 for the specimen with 1.25 mm radius hole. However, for the multi-hole specimens, the increase ratio varies from 1.66 to 3.13. In addition, to verify the influence of confining pressure magnitude on the performance of the rock specimens, totalling 10 confining pressure levels are applied and modelled. The simulation results show that even though there are opening holes in the specimens, the simulated compressive strength generally follows the generalised Hoek-Brown model. Keywords: Rock with opening, Simulation, Biaxial loading, Strength, Stiffness

A series of field tests using controlled blasting was conducted at a location in the North Western part of Singapore to assess the behaviour of pile foundations subjected to ground excitation. The field tests involved three piles with different pile head fixity conditions. The piles were instrumented with strain gauges to evaluate the bending moments and axial force along the piles. For the fixed-head piles, the maximum bending moment occurred at the pile head level. For free-head pile exhibited higher bending moments close to the mid-height of the pile and zero bending moment at the pile head due to the absence of restraints at the top. For all cases, the axial force was maximum at the pile head.

The anisotropic direct tensile behaviour of laminated and transversely isotropic Midgley Grit sandstone (MGS) was investigated in this paper using a particle-based discrete element method (DEM) with consideration of the incipiency of bedding planes. Laboratory experiments were conducted to quantify the direct tensile strength of the incipient bedding planes, and the results were used to calibrate the numerical model. The effects of bedding planes with different relative positions and spacing were discussed. A comparison between the simulated results of this study and the predicted results from failure criteria was completed, and a good agreement was observed.

Rockbolts have been used to minimize the deformation of underground excavations where the surrounding rock masses contain weak planes such as fractures, joints or faults. Rockbolts installed across rock joints are able to resist the opening and shearing movements of rock joints. One of the rockbolt failure modes encountered in the field is caused by the excessive shear loads. A simple analytical model based on the Beam on Elastic Foundation (BEM) method is proposed in this study to predict the shear responses of a bolt installed perpendicularly to rock joint. The shear load-displacement curve of a double shear test can be divided into three stages: the elastic stage, the elasto-plastic stage and the plastic stage. The foundation stiffness for each respective stage are varied with the curvature influencing zone Lc. The pretension effects are taken into account in the proposed analytical model. The model agrees well with the experimental shear tests, suggesting that the analytical model has the capability to predict the shear load-displacement curve of bolts crossing rock joints.

Fracture toughness of anisotropic rocks can vary with many factors such as geological anisotropy, geometrical properties of specimens used in the laboratory (e.g., pre-existing crack properties), and loading conditions. This fact has been widely acknowledged. Yet the variation in fracture toughness remains enigmatic, as there is still lack of a comprehensive study on how those influential factors affect fracture toughness behavior of anisotropic rocks. The present paper shows a broad-spectrum mixed-mode fracture toughness of an anisotropic sandstone from a numerical scheme, which is based on the Discrete Element Method (DEM). In this study, a total of 340 semi-circular bend (SCB) specimens with various geological and geometrical conditions were numerically prepared by systemically varying the orientations of planar anisotropy (i.e. incipient bedding plane), as well as the magnitudes of the ISRM-suggested geometrical parameters of the SCB specimens (i.e. crack length, crack angle, and span length). The numerical model used in the study was calibrated against a series of laboratory experiments to select proper micro-parameters to reproduce the mechanical characteristics of anisotropic Midgley Grit sandstone (MGS). Additionally, four different fracture criteria, which are based on stress and strain analysis, and the analysis of energy density, were used to predict the mixed-mode fracture behaviour of MGS. Numerical findings from this study were compared with experimental observations (qualitatively) and theoretical predictions (quantitatively). A broad agreement was observed in the comparison study.

Blasting has been widely used in mining and construction industries for rock breaking. Ground vibration induced by blasting is an inevitable side effect that may cause damage to nearby structures, if not properly controlled. In this study, response and possible damage of rock-socketed pile near soil-rock interface subjected to ground shock excitations are investigated and quantified with coupled SPH-FEM method. Results indicate that the base of the pile is relatively vulnerable and that the soil properties significantly influence on response of pile subjected to a specific blast load. Furthermore, based on the numerical results, ground vibration attenuation equation is proposed. NRF (Natl Research Foundation, S’pore) Accepted version