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Abstract
This paper addresses the physical modelling of a tunnel for saturated and unsaturated sand as well as tests in dry condition. A series of tests were conducted for a 50 mm diameter tunnel buried 25 mm into a poorly graded fine sand under different normal stresses: 0.78, 1.56, 2.34 and 3.31 kPa. Suction was controlled by means of the hanging column technique (HCT). Particle image velocimetry (PIV) was also utilised to obtain the vector displacement and compared with the results of the physical modelling. The results of the fully saturated sample showed that the sample experienced a sudden spatial collapse above and around the tunnel's crown. In addition, large displacement on top of the tunnel's crown was also observed for the fully dry case. However, the unsaturated sample did not experience any sudden collapse. This was attributed to the effect of the suction contribution on strength.
Highlights
Comprehensive research can be found in the literature characterising the behaviour of buried pipes under external loading conditions, [1,2,3]
This paper reports a series of 1g tests of a tunnel buried 25 mm into a fine sand at various saturation conditions: dry, saturated and unsaturated
A fine sand classified as poorly graded sand (SP) according to the Unified Soil Classification System (USCS) was used in this study
Summary
Comprehensive research can be found in the literature characterising the behaviour of buried pipes under external loading conditions, [1,2,3]. Many constitutive material models based on the finite element method have been used to conduct studies on various saturation conditions [1, 6, 7]. These models predominantly require a cumbersome list of parameters which in turn needs advanced soil testing, good selection and understanding of the parameters. Wetting and drying cycles have a significant influence on the stability of tunnel induced ground surface stability (surface settlement). Many catastrophic accidents such as tunnel induced sinkholes, plastic collapse, and swelling can be bracketed and attributed to the effect of drying and wetting cycles on strength. The experimental results of the surface settlement and the particle size velocimetry (PIV) results are presented
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