Research Of Soft Soil Depth Treated By Lime On Subgrade Resilient Modulus

The resilient modulus of subgrade is an important parameter for pavement structure design, and the higher modulus is also the important guarantee of pavement bearing capacity. The resilient modulus of soft soil can hardly meet the requirement which is negative to bearing capacity and stability. The method of using lime to treate soft soil subgrade to enhance the resilient modulus of subgrade is frequently used in engineers. The water content, soil texture, lime content, compactness and the depth of lime treated soil of soft soil have great influence on the resilient modulus which causes blindness and conceptions during designing. The following topics were studied:(1) the regularity of distribution of of soft soil and its physico-mechanical indexs, the treated methods of soft soil and the transportation and axle load in Tianjin were studied. The results show that, the traffic is very heavy, and truck overload phenomenon is very common. Although the soft soil subgrade is stabilized by various ways, the pavement structure is prone to damage.(2) The inliuence of the water content, soil texture, lime content, compaction on the CBR, resilient modulus, compressive strength and splitting strength of soft soil treated by lime were studied by lab test. The results show that, to the soft soil of different water content, the mechanical indexs of 8%~12% lime content of limestone soil increase with the increase of the drgee of compaction, decrease with the increase of water content; the treated soil can be used in subgrade paving; Due to the different soft soil composition is different, on the mechanical properties of lime improved effect is also different, design and construction should be according to the soil to adjust.(3) The paper found that the equivalent modulus of resilience conversion formula of current specification is not suit to low modulus ratio of limestone soil subgrade by calculation analysis. According to the elastic layered system theory and the principles of displacement equivalence, a new calculation method of equivalent modulus of elasticity was established whose load radius is 15 cm using Kenapve and Minitab sofeware. The new formula is suit for that the modulus ratio which is less than 8 between soil treated by lime and soft soil and the treated thickness is more than 20 cm. The error verification shows that the accuracy and reliability is very high. The regression formula was verified by test road subgrade displacement test.(4) In accordance with the “Urban road embankment design specifications”(CJJ 194-2013) to the requirements of subgrade resilient modulus, the reasonable processing depth were calculatedunder different water content, lime content and degree of compaction by the regression formula; the engineering cost were calculated and the working life were calculated by the US AI design method of every program; the response surface optimization method was used to getting the best way to deal with the soft soil under different water content.