Design Methodologies and Contemporary Challenges in the Rock Socketing of Bored Piles within the Indian Context: A Case Study

Rock socketing for bored pile foundation is a point of interest for the construction team, contractor, and the client; determining the optimum socket length in the rocks is critical in determining the project's time and economy. In recent times, large infrastructure projects requiring high loads on the foundation system, such as bridges, have required piles with diameters ranging from 1,000 to 2,000 mm, posing a significant challenge when the drilled shaft requires socketing in rocks. The current consensus is that a pile's load carrying capacity is determined by the properties of the rock in which it is embedded/socketed. Axial load from a pile is typically transmitted to the rock via adhesion at the pile-rock interface and end bearing at the pile tip. The strength, degree of fracturing, modulus of deformation of the rock mass, the condition of the walls and base of the socket, and the geometry of the socket are the most important factors that influence the design procedure. According to the Indian standard code for bored pile design, depending on the type of rock, any of the following methods may be used to compute compression capacity: based on the rock's uniaxial compressive strength, based on the rock's limit pressure, and based on the rock's shear strength and pile structural strength. The length of a socket in rock is 1−2 D for sound relatively homogeneous rock such as granite and gneiss, 2−3 D for moderately weathered closely jointed rock such as schist and slate. Soft rocks and sedimentary rocks, including hard shale, sandstones, siltstone, and mudstone, are 3−4 D in diameter, where D is the pile diameter, although it should be estimated based on the static computations and preferably verified by load test. The rivers in northeast states of India flow across a vast landscape with high scour potential; a number of projects have been proposed and are currently being implemented across it to improve connectivity and facilities; this river basin is primarily composed of granite, gneiss, and quartzite as rock bed. According to available laboratory and field data, the strength of the rock is high even for very low to nil RQD, which has increased the time required to drill in rock to the required depth. An attempt has been made in this paper to investigate current practices in determining rocket socket length, termination criteria, and the major challenges and difficulties encountered in drilling in rocks for bored shafts in order to arrive at the termination level.