The change of a vehicle’s velocity due to an impact, DeltaV (v) is often calculated and used in the scientific investigation of road traffic collisions. Two types of model are in common use to achieve this purpose, those based on the conservation of linear and angular momentum and the CRASH model which also considers the conservation of energy. It is shown that CRASH and major implementations of the momentum models are equivalent provided certain conditions are satisfied. Explicit conversions between the main variants of the models are presented. A method is also presented which describes a new formula for determining the total work performed in causing crush to a particular vehicle. This has the advantage of incorporating restitution effects and yields identical results to the momentum only models. Although the CRASH model has received adverse criticism due to perceived inaccuracies in the results, little work has been performed to determine the theoretical limitations on accuracy. This thesis rectifies that shortcoming. A Monte Carlo simulation and analytical model are developed here to provide two independent methods for determining the overall accuracy of the CRASH method. The principal direction of force was found to be the most likely to introduce error based on the CRASH assessment. It is shown how this and other sources of error in the CRASH model can be quantified for a particular collision suggesting priorities for minimising the overall uncertainty. The data from a series of well known crash tests are used with each of the models to provide comparison and validation data. It is recognised that without additional data velocity change is of limited use for forensic investigation. However DeltaV can be used as a proxy for acceleration and is particularly useful in studies involving injury causation. A method is also presented here which uses the change in velocity sustained by a vehicle in a planar collision to estimate the velocities of a vehicle before and after a collision. This method relies solely on conservation laws and is also applicable to situations where the coefficient of restitution is non-zero. An extension to the method is also described which allows an initial estimate to be modified to generate more realistic directions of force. This extension has the desirable effect of reducing uncertainty in the estimation of the direction of force which significantly improves the overall accuracy.

Seismic tomography is a promising tool to help understand and evaluate the stability of a rock mass in mining excavations. Lab measurements give evidence that velocities of seismic wave propagations increase in high stress areas of rock samples. It is well known that closing effects of cracks under compressive pressures tend to increase the effective elastic moduli of rocks. Tomography can map stress transfer and redistribution and further forecast rock burst potential and other seismic hazards, which are influenced by mining. Recorded by seismic networks in multiple underground mines, arrival time of seismic waves and locations of seismic events are used as sources of tomographic imaging survey. An initial velocity model is established according to properties of a rock mass, then velocity structure is reconstructed by velocity inversion to reflect the anomalies of the rock mass. Mining-induced seismicity and double-difference tomographic images of rock mass in mining areas are coupled to show how stress changes with microseismic activities. Especially, comparisons between velocity structures of different periods (before and after rock burst) are performed to analyze effects of rock burst on stress distribution. Tomographic results show that high velocity anomalies form in the vicinity of rock burst before the occurrence, and velocity subsequently experiences a significant drop after the occurrence of rock burst. In addition, regression analysis of travel time and distance indicates that the average velocity of all the monitored region appears to increase before rock burst and reduce after them. A reasonable explanation is that rock bursts tend to be triggered in highly stressed rock masses. After the energy release of rock bursts, stress relief is expected to exhibit within rock mass. Average velocity significantly decreases because of lower stresses and as a result of fractures in the rock mass that are generated by shaking-induced damage from nearby rock burst zones. Mining-induced microseismic rate is positively correlated with stress level. The fact that highly concentrated seismicity is more likely to be located in margins between high-velocity and low-velocity regions manifests that high seismic rates appear to be along with high stress in rock masses. Statistical analyses were performed on the aftershock sequence in order to generate an aftershock decay model to detect potential hazards and evaluate stability of aftershock activities. / Ph. D.