This paper describes studies done by various researchers on one form of problematic soils that are not suitable to be used as foundation subsoil. Methods to identify these soils are provided, and various methods suggested for the design of proper foundations to combat their detrimental effects. These types of soils are commonly termed ‘collapsible’. Collapsible soils are moisture sensitive in that an increase in moisture content is the primary triggering mechanism for their volume reduction (compression). These weak soils usually have low dry densities and can be identified with various types of laboratory and field tests. Because of their very low bearing capacity (when wetted) they are not considered for any types of foundations or pavements in their original or natural conditions. Their load-bearing capacity can be improved by various measures, such as the use of sufficiently strong footings that will remain undamaged in spite of possible differential settlements, or by transmitting the structural loads to a deeper and stronger soil layer by means of various types of piles. Also, whenever feasible, the weak soil should be treated with cementing agents such as Portland cement, or preloading techniques should be used to strengthen the collapsing soils and carry the actual loads further.
Stabilising soft, wet and unconsolidated peat soil by using cement as binders and silica fume as additive is often cost-effective compared with other ground improvement methods. This study was carried out by adding 5-50% (by weight) cement to peat soil, and silica fume was added at the rate of 5-10% (by weight) of cement. An air-curing technique was used to cure the samples, as it was found that the water content of the untreated peat soil was very high. The air-cured peat samples were tested for unconfined compressive strength (UCS) and California bearing ratio (CBR) for two conditions: soaked and unsoaked. For the soaked condition the samples were submerged in water for a period of 96 h; the samples after 90 days of air curing were considered as being in the unsoaked condition. From the test results, it was observed that the UCS and CBR increased by a factor as high as 11 and 25 respectively as compared with untreated peat soil. The optimum dose of cement and silica fume was also evaluated. It was observed that the upper layer of in situ peat soil can be stabilised with cement and silica fume to increase the strength of sub-base for the pavement.
Peat layers are weak; much weaker and more compressible than inorganic soils, and thus do not provide suitable support for most engineering structures. The usual methods have been either to remove peat and replace it with suitable soil or to pass piles through it to the stronger soil layers below. On the other hand, research has been carried out to discover ways to strengthen peat deposits by deep stabilization. Peat was reinforced with precast columns stabilized with cement and silica fume. Unconfined compressive strength, Rowe cell consolidation test and plate load test were carried out to evaluate the increase in strength. The compression index (C c) of peat samples, upon use of stabilized precast columns, was found to reduce by 36 % using only 5 % cement. Further, when 10 % silica fume was added along with cement, the C c decreased by 42 %. Plate load test results indicated that the bearing capacity of peat can be improved significantly by over 84.6 % when 15 % cement is used, and also the use of silica fume with cement further increased it to 107.7 % compared with untreated peat. The precast stabilized columns (stabilized with cement and silica fume) can be used successfully to improve the engineering behaviour of soft peat deposits and as a result improve its strength and bearing capacity. Finite element analysis was carried out to understand the distribution of stresses in peat as well as in the stabilized column.
Abstract. Clay soils are commonly stiff in dry state but lose their stiffness when saturated with water. Soft clays are characterized by low bearing capacity and high compressibility. In this research, waste stone sludge obtained from slab stone processing, from stone washing plants were recycled for Stabilization of clayey soil with lime. Thus, the effectiveness of using waste stone powder and lime in stabilizing fine-grained clayey soil (CL) was investigated in the laboratory. The soil samples in natural state and when mixed with varying percentages of lime and waste stone powder were used for the laboratory tests that included atterberg limits tests, grain size analysis, standard Proctor compaction tests, unconfined compression tests and California bearing ratio tests. The results show significant reduction in plasticity and changed the optimum moisture content and maximum dry density of clayey soil with increasing percentage content of waste stone powder and lime. The results of the unconfined compressive strength (UCS) and California bearing ratio (CBR) tests show that at the different curing times, the addition of waste stone powder and lime caused an increase in the value of UCS up to 6% waste stone powder content and 7% lime content, and increase in the value of CBR to 6% waste stone powder content and 9% lime content, thereafter, the values of UCS and CBR decreased.
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