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A full-scale field experiment has been conducted in an instrumented saprolite slope in Hong Kong. Soil moisture probes, tensiometers, piezometers, inclinometers, earth pressure cells, and a rain gauge were installed in the slope before and during excavation of a cut. This paper presents the results from soil moisture probes, tensiometers, and piezometers to reveal the surface infiltration process. The soil moisture and matric suction results show that the maximum "wetting front" during the wet season was limited to the top 3 m of soil, and a transient perched water table could develop in the soil during a very heavy rainstorm. A new method based on the variation of volumetric water content in the soil is proposed to analyze rainfall infiltration. The results indicate the following phenomena: (i) rainfall infiltration was around 70% of the total rainfall, (ii) the infiltrated water mainly increased the soil moisture content of the soil at shallow depths, and (iii) the surface vertical infiltration had a very limited effect on the permanent groundwater table at depth. The wetting-front analysis shows that the unsaturated wetting band theory can be used to assess the movement of the wetting front in the unsaturated saprolite soil.Key words: rainfall infiltration, moisture content, matric suction, wetting front, field instrumentation.

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SUMMARYThis paper proposes a two-dimensional finite element model for the analysis of shield tunnels by taking into account the construction process which is divided into four stages. The soil is assumed to behave as an elasto-plastic medium whereas the shield is simulated by beam-joint discontinuous model in which curved beam elements and joint elements are used to model the segments and joints, respectively. As grout is usually injected to fill the gap between the lining and the soil, the property parameters of the grout are chosen in such a way that they can reflect the state of the grout at each stage. Furthermore, the contact condition between the soil and lining will change with the construction stage, and therefore, different stressreleasing coefficients are used to account for the changes. To assess the accuracy that can be attained by the method in solving practical problems, the shield tunnelling in the No. 7 Subway Line Project in Osaka, Japan, is used as a case history for our study. The numerical results are compared with those measured in the field. The results presented in the paper show that the proposed numerical procedure can be used to effectively estimate the deformation, stresses and moments experienced by the surrounding soils and the concrete lining segments. The analysis and method presented in this paper can be considered to be useful for other subway construction projects involving shield tunnelling in soft soils.