|M.Sc Student||Nadav Bar-Ya'akov|
|Subject||Pressure Distribution on a Buried Structure under Static|
Pressure at Ground Level
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Talesnick Mark Lloyd|
|Professor Dancygier Avraham|
|Full Thesis text - in Hebrew|
In order to design buried structures economically on one hand, and safely on the other, an accurate estimation of the contact pressures acting on the structures is necessary. One of the most important observations derived from studies on this subject is the substantial influence of arching on the contact pressures acting on the structures.
For experimental studies on this subject, the challenge lies in the reliability of the measurement of soil contact pressure. Most of the commercial pressure gages rely on the deflection of a membrane in the measurement process which induces a significant error in the measured pressure. In order to overcome this difficulty, a new pressure gage was developed at the Technion. The new gage, "Null Gage", maintains deflection close to zero by compressing air into the gage, and by doing so the membrane does not deflect during the measurement process.
In the current work, experiments were performed on a model structure, buried in sand, in an axi- symmetric geometry. Four "Null Gages" were integrated into the model walls, roof and floor, in order to measure the contact pressures which developed on the structure model. Null Gages placed at different locations on the model roof allowed for the estimation of a rudimentary distribution of soil contact pressure on the roof of the structure.
Over 60 experiments were conducted in the project, 38 of them considered to give valid data. The data was processed and analyzed by comparing the results from the experiments with different roof flexibility, different burial depth and different number of loading cycles. The resulting analysis shows a substantial increase in the force acting on the roof in comparison to the free field stress. This increase was independent of roof flexibility, and is a function of the relatively high overall stiffness of the model in comparison to the stiffness of the medium around it.
As part of the analysis an attempt was made to differentiate between two arching phenomena that occur simultaneously on a structure with flexible roof, each having an opposite effect on the development of contact pressure. Despite the non linear nature of the arching effect, the use of superposition produced reasonable results.
Contact pressure measured on the model side wall indicate that the coefficient of lateral earth pressure is independent of the relative burial depth. The measurements resulted in a coefficient of lateral earth pressure 15-20% lower than that commonly used in practice.