Observation of Ground Subsidence Caused by Shield Tunnel Construction in Sand

Tunnel excavation in soft grounds may lead to surrounding soil displacements. Prediction of these movements is necessary for estimating potential risks to preexisting structures Considering soil complex behavior, especially granular soils which are commonly encountered in Tabriz city, empirical methods are of particular position. In this paper we present a setup of physical modeling, which allows to directly observe the soil displacements. By this experimental setup, the settelemt has been measured during tunnel coustruction in sandy soil at civil engineering laboratory of Sahand university of technology. Volume loss at tunnel depth has been used to model tunneling effect on surrounding soil. The front wall of the model is transparent and soil layers movements have been recorded by digital camera. The movment of the sand has been measured by image processing technic. The taken frames have been extracted and processed by means of GeoPIV code. Then, the calculated surface and sub-surface settlement curves have been compared with peck curve. Obtained results show that surface and subsurface settlement curves in dry sand sample follow Gaussian curve with acceptable accuracy but putting figure in its parameters must be done carefully. During excavation in drained condition such as sand, ground loss at depth may not be the same as that at the surface, therefore the use of tunnel volume loss may lead to inaccurate prediction of surface settlement.

Keywords:

Settlement , Mechanized Tunneling , Sand , Physical Modeling , Image Processing