Experimental Study of Heave Control Technique for Expansive Soil Using Micropiles and Geotextile Layers
01 Jan 2019-pp 35-43
TL;DR: In this article, the effectiveness of micropile and performance of geotextile to resist upward movement of structures built over expansive soil was evaluated with two different methods to control heaving of soil, and the results showed that maximum heave reduction was 79% for 20 mm diameter micropiles with frictional resistance.
Abstract: Heaving of expansive soil is a crucial phenomenon due to their excessive volume changes with variation in moisture regime, which in turn leads to substantial distress to the structures built on them The main objective of this study is to evaluate the effectiveness of micropile and performance of geotextile to resists upward movement of structures built over expansive soil For this study, the expansive clay compacted in a steel box of size 50 cm × 50 cm × 50 cm to a depth of 20 cm and analyzed with two different methods to control heaving of soil Firstly, four micropiles of 16 and 20 mm in diameter were inserted into the soil with and without frictional resistance The micropiles were fastened to the corners of footing of size 15 cm × 15 cm × 05 cm, with nut and bolt system Further, Geotextiles were reinforced below the footing at a vertical spacing of 01B and 03B as single and double layers Then the soil was saturated with water and the upward movement of model footings (swelling) was monitored with time Test results showed that maximum heave reduction was 79% for 20 mm diameter micropiles with frictional resistance
TL;DR: In this paper, the effect of both sand and sand-lime piles on the behavior of expansive clay soil was investigated and a series of laboratory tests were carried out using the conventional Oedometer apparatus.
Abstract: Expansive clay soil causes serious problems to many structures due to its swelling and shrinkage during wet and dry seasons. With the existence of expansive soil in Ahkmim new city, Sohag governorate, Egypt, some light buildings, road pavements, and buried pipelines have shown some damage. To avoid such damage, prior to construction, expansive clay soils should be stabilized. Different methods are available to improve the engineering properties of these soils such as densification, chemical stabilization, reinforcement, and techniques of pore water pressure reduction. The chemical stabilization of clay using lime is one of the widespread methods that can be used to improve the behavior of expansive clay soil. This study aims to investigate the effect of both sand and sand-lime piles on the behavior of expansive clay soil. A series of laboratory tests were carried out using the conventional Oedometer apparatus. Sand piles with different replacement area ratios (RARs) (4.68%, 10.16%, 24.6%, 35.84%, and 56.9%) were used. Also, sand piles stabilized with different percentages of lime (3%, 6%, 9%, 12%, 15%, and 20%) and with a replacement area ratio of 35.84% were used. The experimental results showed there is a significant improvement in reducing the swelling potential of expansive clay soil reinforced with sand or sand-lime piles. This improvement increases with the increase of both replacement area ratio and lime content.
TL;DR: In this article, the relative performance of different remedial techniques in vogue and those proposed in the recent years was studied in a site on NIT Warangal campus where natural expansive clay bed is present.
Abstract: Expansive soils being susceptible for moisture variations undergo cyclic seasonal movements that pose serious stability concerns for structures resting on them, especially when they are lightly loaded ones. The concerted efforts made by various researchers across the world enabled them to develop remedial solutions to mitigate these problems with varied degree of success. The present work is an effort to study the relative performance of the different remedial techniques in vogue and those proposed in the recent years. These techniques were adopted below the shallow footings at a site on NIT Warangal campus where natural expansive clay bed is present. This study revealed that the sand cushion and CNS cushion could reduce the heave by 56 to 64%; but in case of sand cushion, an increasing trend of heave with number of cycles of wetting and drying was observed. The chemical alteration by lime could reduce the heave by 59% and by CaCl2 and CaCl2–Na2SiO3 the heave could be reduced by 70 and 73%, respectively. The recently promulgated concrete and granular anchor piled footings have shown the heave reduction up to 63 and 78%, respectively. Further, it is found that the combined effect of CNS cushion along with chemical modification and/or tension/anchor piled footing systems were found to be synergistically more effective than individual techniques in controlling the seasonal movements of footings and flooring/lining panels. Interestingly, none of these remedial techniques could overcome the shrinkage movements though these movements are observed to be insignificant in case of piled footings.
TL;DR: In this article, a simplified analytical formulation for the mechanism by which micropiles surrounded by compacted sand control the upward movement of lightweight buildings over expansive soils is presented, which identifies the significant variables influencing the performance of micropile reinforcement.
Abstract: A simplified analytical formulation is presented for the mechanism by which micropiles surrounded by compacted sand control the upward movement of lightweight buildings over expansive soils. This formulation identifies the significant variables influencing the performance of micropile reinforcement. A design methodology for micropile reinforcement utilizing the resulting formulation is proposed and illustrated by a hypothetical example.
TL;DR: In this paper, it was shown that high concentrations of sodium hydroxide causes abnormal changes on the volume change behavior of illite-smectite (interstratified mineral) soil due to mineralogical changes.
Abstract: The results presented in this paper shows that high concentrations of sodium hydroxide causes abnormal changes on the volume change behaviour of illite–smectite (interstratified mineral) soil due to mineralogical changes. The higher swell that occurs is shown in the form of a new second stage of swelling. Increase in negative charges on soil particles and mineralogical changes after interaction with soil, respectively, are responsible for the swelling in these two stages. However, potassium hydroxide does not induce such high swelling in soils. This is mainly due to the fixation of potassium ions. Hence an attempt has been made to control the swelling induced by sodium hydroxide by making used of potassium chloride as an additive. Potassium fixation which is not substantial at neutral pH is favoured at higher pH Addition of potassium chloride salt solution (as 2 and 5% solution) can reduce only the first stage of swelling by linking the unit layers of mineral by reducing development diffuse double layer near clay surface. Potassium chloride is unable to prevent the formation of mineralogical alteration due to soil alkali interaction and hence the swelling associated with mineralogical changes. X-ray diffraction studies have revealed that mineralogical changes leading to formation of zeolite by soil alkali interaction is not inhibited by potassium ions. Morphological changes studied by scanning electron microscope corroborate these observations. Also the compressibility of soil which is increased in alkali solution is reduced in the presence of potassium salts. This reduction is due to reduction in the first stage of swelling.
01 Jan 2011
TL;DR: In this article, the authors examined the effectiveness of using micropiles as a technique to control upward movement of lightweight structures resting over expansive soils and found that the percentage reduction in heave due to micropile reinforcement was more for small-scale steel model-micropiles surrounded by sand in predrilled holes of 25 mm diameter.
Abstract: Lightweight reinforced concrete structures over expansive soils may be subjected to significant upward movement which may cause undesirable cracks in the structure. Repair activities for these cracks should be repeated annually and in some cases the cost is significant. The design alternatives include the use of stiff mat foundation, drilled pier foundation, isolated footings placed at depths exceeding the depth of seasonal variation of moisture content, soil replacement, and the use of stabilizing agents and micropiles. The type of soil and structure, environmental conditions, estimated surface heave, induced distresses and cost-effectiveness govern the selection and implementation of any of these techniques. The main purpose of this study was to examine the effectiveness of using micropiles as a technique to control upward movement of lightweight structures resting over expansive soils. For this purpose, expansive clay was compacted in a steel box of size 50cm x 50cm x 50cm to a height of 20cm in which small-scale steel model micropiles of diameter 12,16 and 20 mm were inserted in predrilled holes of 25mm diameter surrounded with and without sand. The heads of the model micropiles were fastened to the steel plate (steel plate are used as model footing) of size 25cm x 25cm x 1cm with nut and bolt arrangements. Then the boxes were filled with water and the upward movement of model footings (swelling) was monitored with time. The results showed that the percentage reduction in heave due to micropile reinforcement was more for micropiles surrounded by sand in predrilled holes of 25 mm diameter. The maximum measured reduction in heave was 94 % obtained when four 20 mm diameter micropiles surrounded by sand were used.