عنوان مقاله [English]
In this paper, a physical model has been used to investigate the settlement of twin tunnels in sand with two different relative densities. This physical model is built in Sahand University of Technology, which includes a setup to model the tunneling process and a sand pluviator to preparation of uniform samples with different relative densities. The soil displacements were obtained using image processing technique. The results show that the Gaussian distribution curve provides an adequate approximation to the shape of the measured settlement data for each tunnel in dense sand. However, in loose sand due to the narrow shape of the settlement trough, this method does not provide a good description of the displacements. In order to obtain a better fit to the observed soil settlement, a new equation is suggested in this paper.
Many researchers have investigated the settlement of twin tunnels and most of them reported an increase in volume loss in the second tunnel and an asymmetric settlement for twin tunnels. However, most of these reports include case studies and numerical modeling. Therefore, there is a lake of laboratory results especially in sands. In addition, pervious researches on single tunnel show that the relative density of sand has a significant influence on the magnitude and the shape of the settlement too. Therefore investigating this subject is important for twin tunnels.
Methodology and Approaches
In this research in order to assess the ground loss around the tunnel, the pipes system has been used. This system consists of two pipes with different diameters. The small internal pipe is placed inside a larger external pipe. The gap between two pipes controls the magnitude of the volume loss. A strongbox was made of steel with a plexiglass front to allow measuring the surface and the subsurface displacements by using a digital camera. The tunnel model placed in strongbox and the sand was poured using a traveling sand pluviator. The image processing technique has been used for analyzing the displacement of the soil particles.
Results and Conclusions
The following main conclusion can be drawn from this study:
-The new suggested equation provides a good approximation to the measured settlements data for the single and twin tunnels in sandy soil.
- For both loose and dense sands, the volume loss increases around the second tunnel but this increase is more significant for the loose sandy soil.
- In loose sandy soil due to the narrow shape of the settlement trough, there are two distinct peaks in surface settlement. However, in dense sand a single settlement trough is obtained near the surface.