|M.Sc Student||Rachel Avraham-Katriel|
|Subject||Measurement of Pressures Acting on and around a Driven|
Model of a Pile in Sand
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Talesnick Mark Lloyd|
|Full Thesis text - in Hebrew|
Axial pile capacity is based on the equilibrium of forces acting on the pile. It takes into account the influence of frictional forces on the shaft. These forces stem from the normal stress acting on the shaft and the friction angle between the pile and the soil.
The friction angle between a pile and soil can be estimated from a laboratory test. Determining the normal stress acting on the pile is not as simple. To date there is no accepted way to measure or determine the normal soil pressure acting on a pile shaft. It is common to estimate the normal stress as the horizontal soil pressure through the coefficient of lateral earth pressure at rest (Ko). The difficulty with this approach is that the installation procedure undoubtedly alters the horizontal pressure from the at-rest state.
In this thesis a new approach to measuring the stresses at the pile interface is presented. Three pile models were tested. Each one was made from aluminum with a square profile of 30 mm?30 mm. Two of the piles were smooth and one was rough. In each test a different combination of soil pressure transducers ("NullGage" type) and shear load transducers, which were developed during the research, were integrated into the pile sides. Tests were performed with sand in both the dense and loose conditions
The results show repeatability and compatibility between the different tests for both the NullGages and the FrictionMeter. From the test data the friction angle between the pile and the sand as well as the stress path at the pile sand interface can be determined.
A second set of tests was conducted in a geotechnical centrifuge at Cambridge University, England. In these experiments a square pile, 20 mm ? 20 mm, was driven into a cell filled with fine dense sand under a gravity field of 50g. Two in soil Nullgages were embedded in the sand at a depth of 80 mm. The in soil gages measured changes in horizontal soil pressure during installation and extraction of the pile in different locations in the cell. The results illustrate the significant changes in horizontal pressure due to the effect of inserting a pile of finite volume in comparison to the pressure change due to translation of the pile through the sand. Significant changes in the normal stress were measured at a distance of more than 10 times the model pile width.