Abstract
Drilled shafts socketed in crystalline rock salt are a common type of foundations used in the Dead Sea region to support high vertical and lateral loads. The existing subsurface condition consists of soft clay followed by crystalline salt. Due to the difference in nature and geological features, the performance of such foundations type under vertical loading in the crystalline rock salt is different from their known behavior in common rock types. This paper is an attempt to understand the real behavior of socketed drilled shafts in crystalline salt through a finite element modeling of a field pile load test carried out in this formation. The studied case is of a steel tubular pile provided with a reinforced concrete socket in the crystalline salt formation. The prevailing salt layers in the pile test area are highly fractured crystalline rock salts of variable strength ranging from weak to moderately weak. Full details of the pile load test, description of the subsurface conditions and salt strength tests are presented in this paper along with the finite element analysis details and results. The developed shear resistance along the socket length of the pile is verified and compared to the commonly used correlations for rock formations. The performed analyses and comparison with the field pile load test results provided a better understanding and good information about the drilled shafts performance under vertical loading condition in such formation. The analyses carried out in this paper deal with the short term behavior of the Dead Sea rock salt as the creep effect directly impact the long term performance.
1. INTRODUCTION
Behavior of concrete piles socketed in rock depends on many factors such as the rock strength, rock quality, concrete strength, drilling fluids effect and roughness of the interface surface. Rock characteristics are highly affected by the weathering and environmental conditions. Finite element analysis (F.E.) has proven a good ability to simulate the soil and rock behaviors in wide range of civil engineering applications. For the study of the performance of piles socketed in the Dead Sea crystalline rock salt using the F.E. approach, choosing the reasonable constitutive model is an essential factor. Accordingly, in this paper three different constitutive models that are the Linear Elastic (LE), Mohr-Coulmob (MC) and the Hardening Soil (HS) have been investigated. The geotechnical parameters of the rock salt needed for the different models were estimated based on several sources that are the laboratory tests, in-situ tests and the back analysis of the field pile load test results. More emphasis in choosing the geotechnical parameters was given to the in-situ tests results and the back analysis outcome to eliminate the scale effect playing an important role in the laboratory tests results.
