Expansive Clay Mineralogy Effect on the Subgrade Stabilization Efficiency

Understanding of factors affecting unsuccessful road projects is a valuable experience to avoid their repetition in future. So, in this paper the reason of pavement failure of a road in north part of Hamedan province was studied. Also, the macro and micro structure tests were used to monitor the impact of quality and quantity of clay mineral on the chemical stabilization efficiency of expansive soil. The results indicate that the presence of montmorillonite and subgrade mineralogy anisotropy cause the road destruction. Due to variation in clay type of natural soil samples obtaining from the site, the differential heave in the pavement subsoil is grater than 80%. This condition contributes to uneven ground deformation and tension stress which has made pavement failure. On the other hand, whit respect to mineralogy variation of studied materials and aiming to evaluate its effect on soil stabilization process, in the laboratory controlled condition effect of lime on the behaviour of samples with various amounts of kaolinite and montmorillonite clays was investigated. The results of the experimental tests demonstrate that soil-lime interaction through short-term and long-term reactions reduces the swelling potential and improves the soil strength. It was observed that the rate of these reactions impact on the kaolinite and montmorillonite properties is different. It is governed by the type and amount of clay mineral, lime contents, and time of curing. With increase of montmorillonite, the threshold of lime to soil improvement and pozzolanic reactions is increased. The results of Atterberg limits, swelling and compressive strength tests indicate that the soil engineering properties changes after treatment are not similar. Addition of 8 percent lime and passing 24 hours are sufficient for a short-term reaction and swelling control while the strength increasing is limited. According to X-ray diffraction (XRD) analysis, sufficient amount of lime and appropriate curing time cause growth cement compounds and bonding adjacent soil particles together (solidification) which reduce 30% the lime consumption for swelling control. The study concludes that the optimum of lime should be selected based on the main objective of improvement and time of curing which is needed to complete the reactions.