|M.Sc Student||Itamar Omer|
|Subject||Development of a Methodology for the Use of a Push-In|
Pressure Cell in Sand, through Investigation of
the Penetration Mechanism of a Pile
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Talesnick Mark Lloyd|
|Full Thesis text|
This research project advances our understanding of the penetration mechanism of a jacked-in pile in sand. The study was originally aimed at developing a fundamental methodology for the use of a push-in pressure cell in granular soil. The push-in pressure cell is intended to measure lateral earth pressures in-situ. An investigation of the penetration mechanism was conducted in order to establish the influence of insertion on the measured lateral earth pressure.
Calibration chamber tests were conducted in order to measure changes in radial stress and radial strain in the vicinity of an advancing pile and to measure the radial stress on the envelope of the push-in pressure cell. Stress measurements were based on the null method which significantly minimizes the error related to soil-sensor interaction due to soil 'arching'. In-soil strains were measured using a newly designed micro strain cell. Measurements of in-soil strains together with measurements of in-soil stresses provided a better understanding of the soil response to insertion of the pile/pressure cell.
In-soil measurements reveal a somewhat different development of the radial stress compared to what is currently found in the literature. It was found that during pile penetration, the radial stresses within the soil mass return to their original values prior to insertion as the pile tip passes far enough beneath the measuring elevation. It was hypothesized that the horizontal pressure acting on the envelope of the push-in cell at a position far enough above the cell tip is equal to the initial lateral earth pressure prior to insertion. However, the measured value of radial stress on the envelope of the push-in pressure cell was substantially lower than the initial lateral pressure. This outcome implies that the stress/pressure on the envelope of an inserted object is governed by a different mechanism than the stress/pressure in the soil further away from the inserted object. In order to complete a methodology for the use of the push-in pressure cell, further investigation of the penetration mechanism is required.
The research improves the understanding of the contribution of skin friction to the overall capacity of jacked-in piles in sand. Furthermore, it may be hypothesized that the horizontal soil pressure acting on a jacked-in pile from the ground surface to a certain point above the pile tip cannot exceed the initial lateral earth pressure prior to insertion of the pile.