The aim of this thesis was simplified design of diaphragm wall affected by excavation from both sides. This wall is a part of temporary shaft that serves for exchange of tunnel boring machines and at the same time it is a permanent structure of an adjacent metro station. Part of the thesis deals with description of construction sequence of diaphragm walls, excavation of the shaft, excavation of the adjacent metro station and following construction of metro tubes and backfilling of the shaft. Inseparable part of the thesis is assessment of geological conditions and geotechnical parameters. Furthermore, a study on temperature loads on struts was carried out and the results of the study were used for design of the struts. To fulfil the requirements of the assignment several models of the shaft structure and adjacent metro station were built in program Plaxis and one model of the diaphragm wall of the shaft was created in program Geo5. The model outputs were subsequently compared to each other. Furthermore a model of lateral support frame was created in program Scia Engineer. Outputs from programs Plaxis and Scia Engineer were used as a basis for design checks of the structure. The design checks were done according to Eurocodes. The diaphragm wall and the lateral support frame were designed to support the loads considered in this thesis. In order to simplify the calculation variable loads from construction machines were not considered and the only variable load considered was the temperature load on struts. Lateral support frame was also designed to accidental load – loss of a strut.

Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / Doubly symmetric I-section columns are often utilised in portal frame construction. The sheeting (or cladding) is carried by sheeting rails connected to the outer flange of these columns. Although it is common practice to include the sheeting rails in the longitudinal bracing system, by connecting the sheeting rail to the cross-bracing, designers must be wary because the connection between column and sheeting rail will not prevent twisting of the columns cross-section. It has been shown ([11], [12], [17]), that by including this eccentric restraint into the bracing of the column, that a torsional-flexural buckling mode of failure can occur when the column is subjected to axial load only. It was seen that this phenomenon is provided for in BS 5950 [18], but is not present in many other design codes of practice, in spite of this phenomenon being relatively well known. In some cases the compression resistance of a column can be significantly reduced when compared to that of a flexural buckled configuration. Previous work performed by Helwig and Yura [15] proposed specific column to sheeting rail connections which would allow for the sheeting rails to be used as elastic torsional braces and effectively rigid lateral braces. However, it is the objective of this investigation to determine if it is possible to include the eccentric sheeting rails into the bracing system, even when using a relatively simple cleat connection with only two bolts onto the sheeting rail. The objective of the research was investigated by conducting experimental tests coupled with a series of detailed finite element analyses. The purpose of the experimental set-up was to investigate the behaviour of a column laterally supported on one flange by a continuous sheeting rail and to compare it to the behaviour of a column laterally supported on both flanges by means of fly-braces (“kneebraces”). The behaviour of the columns, as determined by the experimental tests, was validated by the finite element analyses. The evident conclusion that can be drawn is that, for the case of a continuous sheeting rail, connected to column simply by two bolts and a cleat, that sufficient torsional restraint is provided to the column to prevent torsional-flexural buckling from being critical. This result is helpful, as it means that the buckling capacity of a column can be increased four-fold by enforcing the second flexural buckling mode instead of the first mode through utilising a continuous sheeting rail connected to a cross-bracing system as longitudinal bracing on the columns. This can be achieved without the need to provide any specific detailing to the column to sheeting rail connection. It is however, recommended that further experimental work be conducted on varying lengths of column in order to further validate the results of this work.