FLY ASH FOUNDATION REINFORCED BY CEMENT–SOIL MIXING PILES

Abstract

Cement-soil mixing piles have been commonly used to enhance the bearing capacity of fly ash stratum and mitigate the settlement damage to the surrounding environment. However, only cement is used as curing agent in traditional cement-soil mixing piles. The growth rate for strength of cement-soil mixing piles decreases with the rise in the cement content. Accordingly, it is necessary to explore the combination effects of various curing agents on the strength of cement-soil mixing piles. However, rare studies for the reinforcement effect of fly ash stratum have been conducted by using lime or gypsum as effective replacement materials of cement in cement-soil mixing piles. In this study, laboratory tests were performed to compare the variation laws of unconfined compressive and shear strength of test specimens before and after replacement. Then, the reinforcement effect of cement–soil mixing piles at different lime–cement and gypsum–cement replacement ratios was evaluated. Results demonstrate that the cement–soil mixing piles with 12% cement content not only enhance the bearing capacity of cement-soil mixing piles but also decrease the amount of the cement. When the gypsum-to-cement replacement ratio is 1:2, the 28-day strength of gypsum–cement–fly ash specimens reaches the peak value of 4.5 MPa. When the lime-to-cement replacement ratio is 1:1, the 28-day unconfined compressive strength of lime–cement–fly ash specimens is 6.6 MPa, which increased by 46% compared with those of pure cement–fly ash specimens. Thus, the strength of cement–soil mixing piles in fly ash stratum can be improved due to the lime–cement combination. The rationality of design in cement-soil mixing piles on the factor is further verified by the field test. The results of this study can be referenced for the application of cement–soil mixing piles in the stratum of fly ash reinforcement. Keywords: Cement–soil mixing piles, Unconfined compressive strength, Shear strength, Fly ash stratum