الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 144 |  |  |
| | | from | 144 | | |
Abstract
Collapsible soils are special types of unsaturated soils that undergo a sudden volumetric change due to wetting with or without extra loading. These soils show high apparent strength in natural state; while collapse takes place due to wetting as the bonds between particles break down. While the literature on collapsible soils is quite extensive, there are significant issues still need to be addressed. An area that appears require to further work pertains to the evaluation and control of collapsible soils. Therefore, experimental test program was performed on natural collapsible soil comparing its behavior with improved soils by mixing collapsible soil with well graded sand. Two mixing ratios were considered by replacing 33 % and 50 % of collapsible soil by well graded sand. Time-settlement relationships under different levels of loading for natural soils and the two improved soils are developed. The initial and final modulus of deformation is presented at both natural and inundated states. A proposed coefficient of collapse (Ccv) is developed and the effect of improvement is discussed. Also, time-degree of collapse relationships for natural collapsible soil under different levels of loading are presented comparing its behavior with the response of improved soil. The thesis concludes that the collapsible potential is highly affected by the stress level and the added sand ratio. Collapse potential increased substantially with increasing percentage of clay in collapsible soils. The results indicate some proposed equations to relate the collapse potential with the applied stress. Moreover, the study deduces the relationships between the factors of the proposed equations and the percentage of the added sand. The results showed that upon inundation, initial deformation modulus dropped to 18.91 % from its value for natural collapsible soil, whereas final deformation modulus risen sharply to 200 % from its value for the same soil. The study illustrated that the behavior of collapsible soils through the value of the coefficient (Ccv) is similar to the behavior of cohesive soils after inundation. Degree of collapse (Uc) is not affected by increased stresses either collapsible soils or improved soils Approximately 90 to 95 % of the degree of collapse is observed to occur through 60 minutes after inundation. In addition, the study presents relationships between the factors of the proposed equations and the applied stresses at initial, intermediate and final stages for degree of collapse (Uc).This study has led to the collection of high quality data on the improvement of collapsible soils.