Abstract—The behavior of model piles embedded in a very high expansive soil was investigated, a specially manufactured saturation- drying tank was used to apply three cycles of wetting and drying to the expansive soil surrounding the model straight shaft and under reamed piles, the relative movement of the piles with respect to the soil surface was recorded with time, also the exerted uplift pressure of the piles due to soil swelling was recorded. The behavior of unloaded straight shaft and under reamed piles was investigated. Two design charts were presented for straight shaft and under reamed piles one for the required pile depth for zero upward movement due to soil swelling, while the other for the required pile depth to exert zero uplift pressure when the soil swells. Under reamed piles showed a decrease in upward movement of 20% to 30%, and an uplift pressure decrease of 10% to 30%. Keywords—Expansive Soil, Piles, under reamed, wetting drying cycles. I. INTRODUCTION XPANSIVE soils and rocks undergo volumetric changes upon wetting and drying, thereby causing ground heave and settlement problems, these characteristics cause considerable defects if not adequately taken care of, for swelling to occur, these soils must be initially unsaturated at some water content, if the unsaturated soil gains water content, it swells, on the other hand, if a decrease in water content occurs the soil will shrink [1]. It is widely distributed around the world, the deformation of structure above an expansive soil is caused by apparent swelling-shrinkage behavior of the soils with changes in water content, which is different from the common foundation systems whose settlement are controlled by soil compressibility and strength. For engineering construction on the area of expansive soil, piles are commonly used to be digged into deeper soil layers which may greatly decrease the upward movement of the structure. Since piles are inserted into expansive soils, it must be pulled by upward shear force transmitted from the soil to the piles. If the upward shear force is great enough, the pile may even be broken by such great tension [2].Therefore, a more comprehensive investigation of tension-resistant foundations such as under reamed piles should be done with comparing to the conventional straight shaft piles. Many researchers had recommended studying the effect of cycles of wetting and drying on behavior of piles embedded in Bushra Suhale Al-Busoda is Assistant Professor, College of Civil Engineering, Baghdad University, Iraq (e-mail: albusoda@yahoo.com). Laith Kadim is Geotechnical Engineering M.Sc. Student, College of Civil Engineering, Baghdad University, Iraq (e-mail: laith.anbarry@gmail.com). expansive soil. II. MATERIAL PROPERTIES A. Expansive Soil The expansive soil used in this research is brought from Al- Anbar region western Iraq, 300 km west of the capital Baghdad, the expansive soil covers large regions of that area and they are mainly bentonite soils with high percentage of montmorillonite mineral. To shorten the period of soil saturation, the soil had been mixed with 10% sand. The final mix produced a very high expansive soil with swelling pressure of (312 kPa); the following table gives the physical properties of the used expansive soil: TABLE I PHYSICAL PROPERTIES OF EXPANSIVE SOIL Soil Property Test Specification Value Soil Classification USCS CH Maximum Dry Density (MDD) ASTM D698 - 12 1.23 g/cm 3 Optimum Moisture Content (OMC) 34 % Specific Gravity Gs ASTM D854 - 10 2.805 Liquid Limit ASTM D4318 - 10 102 % Plastic Limit 45 % Plasticity Index 57 Swelling Pressure Standard 6.9kPaOedometer 312 kPa B. Soil Containers Fifteen steel containers of 4mm thickness with dimensions of 25cm * 25cm *35cm were manufactured to contain the expansive soil and the piles within. These containers were perforated with 25 holes on each side, the hole diameter was 3mm, to allow water seeping through them. C. Model Piles Six straight shaft piles and six under reamed piles with one bulb were formed from solid aluminum with a diameter of 10mm and embedment length to depth ratio (L/D) of 10, 15 and 20 respectively. D. Saturation-Drying Tank Two saturation-drying systems were manufactured with dimensions of 150 cm* 80cm *40cm to apply cycles of wetting and drying to eight soil containers at the same time. One tank is dedicated for piles movement monitoring due to soil swelling and shrinkage, the other is to determine the exerted uplift pressure due to soil swelling for different wetting-drying cycles. Fig. 1 shows the saturation-drying tank for pile uplift pressure determination during saturation period and Fig. 2 shows saturation-drying tank during drying process. Bushra Suhale Al-Busoda, Laith Kadim Al-Anbarry Wetting-Drying Cycles Effect on Piles Embedded in a Very High Expansive Soil E World Academy of Science, Engineering and Technology International Journal of Civil, Architectural, Structural and Construction Engineering Vol:8 No:1, 2014 61 International Science Index Vol:8, No:1, 2014 waset.org/Publication/9997192