Robert Man Ng

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A consistent, systematic approach for predicting settlements above tunnels in soft clay is presented. This predictive scheme provides firstly, a simple method for calculating the maximum surface settlement, and secondly, a detailed method for determining the overall pattern of displacements. In the simple method, the maximum surface settlement is estimated from its relationship with the crown displacement which can be calculated theoretically. The detailed method requires finite element analysis and comprehensive field and laboratory testing. Since the detailed analysis may be used for predicting subsurface as well as surface displacements, it is considered to be very useful for analyzing critical sections of a tunnel. The development of this technique is described and its validity and applicability are examined.;Settlement due to tunnelling is generally attributed to loss of ground and volume change in soil. In this thesis, a gap parameter is used to quantify ground loss and to model approximately the effect of soil reconsolidation in the remoulded area above the crown. The components of the gap parameter are (i) the three-dimensional elasto-plastic deformation at the advancing face of the tunnel, (ii) the physical gap defined by the shield-lining geometry, (iii) the displacement associated with workmanship which includes the effect of grouting. An additional component due to consolidation of remoulded soil above the crown may be included as part of the gap where appropriate. The practicality of using this parameter derives from its simplicity in calculation and only conventional soil parameters are required. Comparison of the calculated gap with available field observations showed reasonable agreement. From a study of thirteen case records, an empirical relationship is established for predicting surface settlement from the gap parameter.;A method of detailed analysis using the finite element method is presented. This analysis which is used in conjunction with the concept of the gap parameter, adopts an anisotropic elastic-perfectly plastic model for soil behaviour. The analysis is also formulated to permit consideration of the construction procedure, soil-liner interaction and variation of soil properties with depth.;An extensive field and laboratory investigation of the Thunder Bay soil is performed. The stratigraphy of the instrumented arrays to be examined is well defined. It is shown that the consideration of the appropriate soil stress path is essential in the selection of soil parameters for use in the analysis. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI



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