Abstract
The efficiency of stabilizing loose sandy subgrades by deep soil mixing (DSM) depends on various parameters such as sand density, the water to cement ratio of injecting slurry, and the number of blades in a drilling auger. Moreover, increasing the strength of sandy–cement columns over time is another issue which has been given less attention in the past. In order to better examine the mentioned shortages, the present study is devoted to evaluating DSM efficiency in loose sand stabilization by developing a laboratory scaled apparatus. To do so, this study used two types of 4 and 6 blade augers into loose sand of 0.4 to 1 mm grading size with two different densities of 50 and 70 %. In total, 78 soil–cement columns were prepared with diameter and height of 10 and 20 cm, respectively. The stabilization was performed by using cement slurry with three values of 0.8, 1, and 1.3 for the water to cement ratio. In order to show the DSM effect on sandy soil shear strength as well as deformability parameters during time, unconfined and triaxial compression tests were performed on the specimens at the ages of 7, 14, and 28 days. The results indicate that sand density had a minor effect on increasing the uniaxial compressive strength as well as elasticity modulus of sandy–cement samples, whereas the 6 blade augers had a better performance than 4 blades. In comparison to pure sand, a considerable increase was observed in the values of friction angle and cohesion by DSM. Finally, by statistical analysis of the results, two practical equations were derived between uniaxial strength and elasticity modulus of sand–cement columns with sand density, water to cement ratio, and time with acceptable precision which may be used for prediction of DSM performance in loose sand.
