Presented in this paper is a study of the effect of compactive effort (CE) and long-term soaking on the strength characteristics of a clayey gypsiferous subgrade soil. The tested soil is A-6 (6) soil according to American Association of State Highway and Transportation Officials (AASHTO) soil classification system. To study the effect of CE and long term soaking on the properties of the tested soil, various California bearing ratio soil samples were prepared and compacted at optimum moisture content of the modified AASHTO compaction, but using four different chosen CEs of 12, 25, 56 and 70 blows/layer and then soaked for 0, 4, 7, 15, 30 and 120 days. The California bearing ratio (CBR) tests indicate that the CBR increases significantly in a nonlinear manner with increasing CE for all soaking periods, indicating improvement in soil strength with increased compaction. The rate of increase dies out with increasing CE. The CBR tests reveal also that there is a serious drop in the CBR due to soaking for all CEs.

A study of the strength characteristics of a fine-grained gypsiferous soil intended for use as a construction material for forming highway and airport embankments in desert areas is reported herein. The tested soil was a sandy lean clay (CL) according to the Unified Soil Classification System and an A-6 (6) soil according to American Association of State Highway and Transportation Officials (AASHTO) soil classification system, containing about 35% total soluble salts (TSS) of which 33% was gypsum. To study the properties of the tested soil, various California bearing ratio (CBR) soil samples were prepared at the dry optimum moisture content of 2% and soaked for 0, 4, 7, 15 and 30 days. The CBR tests revealed that there was a serious drop in the CBR due to soaking, which is in full agreement with the drop in c and φ with soaking period, indicating that if gypsiferous soils are used as fill material they should be protected from ingress of water. To study the deformation properties of the tested soil, vertical swelling/settlement measurements were carried out on each CBR sample during soaking using a 0·002 mm dial gauge. The effect of soaking period on the distribution of moisture, TSS and gypsum content was also studied. It was observed that there was an increase in moisture content and a decrease in TSS and hence gypsum with increasing soaking for CBR samples compacted at the dry optimum moisture content.

The piled raft is a geotechnical composite construction consisting of three elements: piles,raft and soil. It is suitable as a foundation for large buildings. This paper presents an analysis of piled raft foundation, included material nonlinearity and soil structure interaction. An efficient computer program in FORTRAN 9Ois developed for this analysis. A 20 node disoparametric brick element has been used to model pile, raft, soil and interface materials. Thin layer interface element has been used to model the contact zone between the pile and soil, and between raft and soil. The behavior of the piled raft material is simulated by using a linear elastic model. However, the behavior of soil and interface materials is simulated by an elasto-plastic model by the use of Mohr Coulomb failure criterion. Some of the variables of piled-raft system, related to settlement and differential settlement in sandy soil, have been studied, where the length of piles and distance between piles an effective role in reducing both settlement and differential settlement of foundation system. Also increasing the thickness of raft foundation reduces the effectiveness of additional piles for the purpose of reducing differential settlement.