The safety of pipelines distributed in the infrastructure of many industries has become very important since the industrial revolution. The guided ultrasonic wave technique can provide the possibility for rapid screening in long pipelines with corrosion. Especially the torsional mode T(0,1) of guided waves has been used in the cases of the pipe in the hidden region substantially. The ability of evaluating the inaccessible areas of the pipe makes the guided ultrasonic wave technique sit high on the roster of non-destructive testing tool for pipe inspection. However, the problem arises when attempting to detect the corrosions at the welded support bracket or under the bitumen coating on the pipe. The signal reflected from the corrosion will be covered by a large signal induced by the welded support or attenuated by the bitumen coating seriously. Therefore, the effects of welded support and bitumen coating on the T(0,1) mode are investigated by the experimental and the simulative methods. The continuous wavelet transform analysis is the signal processing method to extract the hidden signal of corrosion in this dissertation. There are five test pipes in the experiments. The response of the normal welded support is studied on the #1 test pipe. The #2 test pipe is used for attenuation investigation. The reflected signals of the features on the #3, #4, and #5 test pipes are measured and processed by continuous wavelet transform during defect detection process. In addition, the linear hexahedron elements are used to build the finite element models of the 6-inch steel pipe with support bracket and the pipe with bitumen coating. It is found that the effects of support bracket on the reflection comprise mode conversion, delayed appearance, trailing echoes, and frequency dependent behavior. When the T(0,1) mode impinges on to the support bracket, it will convert into the A0 mode inside the support due to the circumferential disturbance on the pipe surface. The reflection of the support bracket is identified as three parts formed by the direct echo, delayed echo and the trailing echo. The constructive interference of the A0 mode reflecting from the boundaries inside the support causes that the reflection spectrum shows two maxima peak at around 20-22 kHz (frequency regime of 0.0) and 32-34 kHz (frequency regime of 4.0) from both the experimental and simulated results. For the bitumen coating, the data collected from the welds and defects under the bitumen coating on the #2 test pipe show the attenuation effect on guided wave propagation and the difficulty of minor corrosion detection. In the finite element model of coated pipe, the results of predicted attenuation curves of T(0,1) mode indicate that the attenuation effect on guided wave propagation is aggravated with the increased value of the thickness, density or damping factor of the coated layer. Especially, in the case of 5-mm, the predicted attenuation curve shows a maximum point. Before this point, the attenuation increases with the operating frequency. For long range pipe inspection, it is the best way to avoid choosing the operating frequency around the corresponding frequency of the point. The measured data of corrosion affected by the welded support or the coated bitumen layer was processed by continuous wavelet transform to form a time-frequency analysis. The corrosion signals were identified in the contour map of the wavelet coefficient successfully. The understanding of the guided wave propagation on the pipe welded with support or pipe coated with bitumen is helpful to interpret the reflected signals. The use of continuous wavelet transform on signal processing techniques can improve the ability of defect detection on pipe with complex geometries.

Within the confines of this study, numerical simulations of time dependent variation of downdrag forces on the diaphragm walls are analyzed for a generic soil site, where consolidation is not completed. As part of the first generic scenario, consolidation of a clayey site due to the application of the embankment is assessed. Then two sets of diaphragm walls, with and without bitumen coating, are analyzed. For comparison purposes, conventional analytical calculation methods (i.e., rigid-plastic and elastic-plastic soil models) are also used, the results of which, establish a good basis of comparison with finite-element based simulation results. Additionaly, the same generic cases are also analyzed during the stages of excavation, when diaphragm walls are laterally loaded. As the concluding remark, on the basis of time dependent stress and displacement responses of bitumen coated and uncoated diaphragm walls, it was observed that negative skin friction is a rather complex time-dependent soil-structure and loading interaction problem. This problem needs to be assessed through methods capable of modeling the complex nature of the interaction. Current analytical methods may significantly over-estimate the amount of negative skin friction applied on the system, hence they are judged to be over-conservative. However, if negative skin friction is accompanied by partial unloading as expected in diaphragm walls or piles used for deep excavations, then they may be subject to adverse combinations of axial load and moment, which may produce critical combinations expressed in interaction diagrams. Neglecting the axial force and moment interaction may produce unconservative results.