AbstractCollapsible soils covers naturally over 10% of the earth’s surface. This makes it a global problem and it is essential that engineers identify and control collapsibility prior to construction. Hence in this thesis, a study on identification, evaluation and control of soil collapsibility is undertaken.
Four geologically different soils have been tested at five compactive variables from optimum moisture content (OMC). The soils tested include: Brown inorganic silty clay of low plasticity (A); White inorganic silt with slight plasticity (B); Red inorganic clay of intermediate plasticity (C); and Brown sand-clay mixtures with inorganic clay of low plasticity (D). The soils were each compacted at moisture variations 60% - 80%, 80% - 95%, 95% - 105%, 110% - 125% and 125% - 150% respectively representing ‘Low Dry OMC’, ‘High Dry OMC’, ‘At OMC’, ‘Low Wet OMC’ and ‘High Wet OMC’.
The major causes of collapsibility of soil and the geomorphological processes that gives the pedogenesis of collapsible soils, is highlighted and great emphasis is placed on the adverse effect of collapsible soils.
The experimental results from particle size distribution, Atterberg, compaction, triaxial and double oedometer tests showed that the soil’s percentage fine with the fines material (silt or clay), coefficient of uniformity, optimum moisture content, Atterberg limits, and stress-strain properties affect the metastability of the soils and they can be compared to the soil’s collapse potential when pressures and moisture content are applied on the soils. Results obtained showed that the soil’s collapse potential is directly proportional to 1) percentage fines, 2) the difference between the silt and clay percentage, 3) the Atterberg limits (liquid limit, plastic limit and plasticity index), and 4) internal friction angle; and inversely proportional to 1) coefficient of uniformity, 2) initial moisture content, 3) cohesion and finally 4) peak deviator stress. Each soil’s geological property proved to have an adverse effect on the metastability of the soils especially the dry of optimum moisture content.
The most interesting results were obtained from the oedometer test. Results of the critical pressure varied with each soil and their compactive variable; Most of the soils at their ‘dry OMC’ had the highest collapse potential. In general, the lower the critical pressure the higher the collapse potential of the soil.
The experimental data obtained herein were checked with the past research collapse indexes and found the results agreeing with just two research work out of eighteen examinations.
Finally models for identifying soil collapsibility are generated with relationship between parameters from sieve, Atterberg, proctor compaction and triaxial. Laboratory data and data from twelve research work were used to verify the models and they show that the models work. After the verification of these formulas with past research data collected, the best models were three compactive variable models. The models give a collapsibility index in terms of percentage fines, initial moisture content, initial degree of saturation and initial dry density.
|Date of Award||2015|
|Supervisor||Samson Ngambi (Supervisor), Essie Ganjian (Supervisor) & Ian Jefferson (Supervisor)|
- soil collapsibility