Impact of pile foundations adjacent to tunnels in sandy stratum

In recent years, with rapid urbanization and construction of underground pipeline facilities for the transmission of electricity, supply of water, sewage disposal or provision of facilities like telephone lines, gas pipe lines, etc., it is highly probable to encounter an existing pipeline system in the vicinity of a proposed foundation of a structure. Hence, design and construction of new foundation structure near the existing subsurface pipeline system is imperative and should be addressed for keeping either a minimum safe clearance between tunnel/buried pipe and pile without compromising the capacity of pile or estimating the reduced capacity due to existing nearby pipeline or tunnel, which is an important aspect in the analysis and design of pile foundation. Present study demonstrates a model and numerical study of the behaviour of a single pile in the vicinity of existing tunnel/buried pipe in a cohesionless soil. During experimental work, a small scale pile model was tested for its load–settlement behaviour without and with the existence of buried PVC pipe modelled as a tunnel in the vicinity near the shaft. The complete experimental set-up consisted of a steel box filled with sand at two different relative density values and vertical concentric load was applied on the model pile through a hydraulic jack and reaction frame arrangement connected with a proving ring. Results of pile loading test have been provided, which demonstrate the tunnel–pile interaction problem effect on the pile capacity, and it was also numerically verified using commercially available finite-element tool. With due verification, parametric study is performed, through finite-element analysis, by varying the range of input parameters such as unit weight, internal friction angle, diameter of pile and elastic modulus of pile material to the soil modulus ratio. Based on the results of numerical analysis in terms of load–settlement curves, it is noted that there is 15–20% reduction in the pile capacity of a single pile to be installed in cohesionless soil in the vicinity of the existing buried pipe or tunnel, which depends on the geometries of the pile and tunnel construction, properties of the in situ soil and zones of influence due to relative stiffness of soil and pipe materials.