Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
This report aims to perform a preliminary design for single steel pipe- drilled shaft socketed in rock. Design is based on limited geotechnical information acquired under preliminary site investigations and performed using closed form solutions as proposed by (Kulhawy and Carter, 1988) During the feasibility and preliminary design stages of a project, limited geotechnical information about the subgrade conditions is available. In these cases, the use of empirical relations for defining the strength and deformation properties of soil and rock can prove useful. These engineering properties are then used, in preliminary design, as input for numerical analysis or closed form solutions. Design can then be used as bases of discussion for foundation method and preliminary cost estimation.
In this report, the strength and deformation properties of soil and rock mass have been established through empirical correlation bounding the strength of the intact rock to the strength of the rock mass. In some cases, strength properties of the rock mass are directly related to the uniaxial compressive strength of the intact rock, whilst in other cases, theproperties of the discontinuities, which together with the intact rock constitute the rock mass, are taken into consideration trough the Geological Strength Index- rock mass classification system proposed by Hoek, (1994).
The methodology of this report has been as: (1) map survey (SGU, 2012) yielding in bedrock constitution for the site in question, (2) study of results from one Ram sounding survey and one soil/ rock probing, (3) relating results to strength properties, (4) design for axial and lateral load using procedures as proposed by (Kulhawy and Carter, 1988), and (5) a finite
element modell in Abaqus for comparison purposes.
Preliminary design based on limited geotechnical information and closed form solutions produced shaft diameter, and shaft socket length necessary to withstand the axial and lateral loads imposed. Suggested dimensions must be compared to allowable deflection and required factor of safety.
As argued by (DiGiogia and Rojas- Gonzalez, 1993), the solutions proposed by Kulhawy et al. (1992) shows reasonable results for laterally loaded shafts for loads within the range of 20-30% capacity of rock mass. It is the author’s opinion that for working loads, this condition is often met in the bedrock of Sweden. Due to the high level of uncertainty surrounding input values, the solution presented in this report is overly conservative. Design optimization is, in this case, a function of experience.