ICE - Institution of Civil Engineers - Virtual Library

This paper introduces new soil stabilisers for reducing the swelling potential of expansive soils. In this study three different polymers (furan, poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVA)) were utilised as soil stabilisers. For evaluating the effect of these polymers on swelling potential and microfabric of expansive soils, three soil samples of high plasticity index were selected. First the engineering, chemical and mineralogical characteristics of the untreated soils were determined, and three different pairs of dry density and water content (dry of optimum, optimum and wet of optimum) were chosen, from standard Proctor compaction curve. Treated soil specimens were prepared at 3%, 5% and 10% of furan content and 1%, 3% and 5% of polymethyl methacrylate and polyvinyl acetate content. The addition of polymethyl methacrylate and polyvinyl acetate can also diminish the swelling potential of soil specimens, but to a lesser degree. The addition of additives produced aggregations and clay-granular matrices within the fabric, which reduced the swelling potential of the soil samples.

Land reclamation often involves the placement of loose granular soil by means of hydraulic filling. Sand fill formed by hydraulic filling generally does not allow densification by surface compaction methods because of their limited depth of influence. Loose granular soil is susceptible to liquefaction upon the impact of dynamic forces. Even under static conditions, loose granular soil may be subjected to bearing capacity failure and large settlements, because of its low shearing resistance and high compressibility. Various densification methods are used for improving such soils to increase the friction angle and elastic modulus. Several methods of deep compaction are available for such applications; among these, dynamic compaction is one of the most effective ways of densifying granular soils to a significant depth. However, the success of dynamic compaction is affected by many factors, several of which are not yet fully understood. This paper deals with the dynamic compaction densification method utilised at the Changi East reclamation site in Singapore for the improvement of reclaimed sand fill. Field data collected are used as a basis to investigate the effectiveness of the densification method and the effect of various influencing factors critical to the success of dynamic compaction treatment.

This paper presents the results of centrifuge model tests on the behaviour of a slope subjected to seepage with and without soil nails. For this purpose, a custom-designed seepage flow simulator was developed for evaluating the deformation behaviour of slopes with and without soil nails at the onset of seepage flow at 30g. A series of centrifuge model tests was carried out on 2V:1H slopes by varying nail layout and length of soil nails. Bored and grouted soil nails including nail heads were modelled using thin aluminium tubes covered with a thin layer of sand-coated adhesive. A soil nail inclination of 15° with the horizontal was adopted with two different layouts. All the models were thoroughly instrumented with displacement transducers for measuring settlements and using pore pressure transducers to capture the development of the phreatic surface within the slope during the centrifuge test. A digital image analysis technique was employed to arrive at displacement vectors of markers placed on the front elevation of the slope. The displacements were used to compare slopes with and without soil nails and to identify the occurrence of failure surfaces. The results indicate that stabilising the earth slope using soil nails has a significant effect in improving the stability and deformation behaviour of a slope subjected to seepage. For a soil nail layout, the stabilising effect was observed to diminish with a decrease in soil nail length and increasing vertical and horizontal spacing of the soil nails in the slope surface. Stability analysis of the slope models with and without soil nails was found to be in good agreement with physically observed centrifuge test results.

Desert sands cover vast areas in Oman, and create major problems for the construction of infrastructure. The low bearing capacity of the desert sands, and their susceptibility to collapse on wetting, preclude the support of structures on them. This paper presents experimental results on the use of different additives to stabilise desert sands for possible use as a foundation-bearing soil. Stabilising agents included Portland cement and cement by-pass dust (or cement kiln dust), and were added in amounts of 2%, 4%, 8%, 10% and 12% by dry weight of soil. Laboratory tests such as compaction, unconfined compression and shear box tests were performed to measure the engineering characteristics of the stabilised material. The results showed substantial improvements in maximum dry density, unconfined compressive strength, and shear strength parameters (c and φ). Thus cement and cement by-pass dust can be used to improve the compressibility and shear strength characteristics of desert sands.