Numerical Simulation Of The Deformation Of The Seasonal Soaking Subgrade And The Pavement Disign Coordinating The Deformation

Alternation of dry and wet seasons exits in typical rainforest regions of Africa and Southeast Asia.The rainfall is abundant in the rainy season which indicates a high ground water table.The rainfall in the dry season has plummeted and the groundwater level is reduced.The roadbed in such a region may face seasonal infiltration and humidity.On the other hand,several kinds of soft soil are widely distributed in this area.The complex soft base contains humus soil,peat soil,silt and muddy soil.These have led to the problems of large subsidence and uneven settlement deformation in the subgrade which is a huge challenge to the pavement design.The aim of this paper is to reduce the influence of water infiltration on the seasonal soaking subgrade,and provide a feasible solution for the pavement structure design in this area by controlling the water infiltration,reducing the uneven deformation and the properly pavement design method.First of all,numerical simulation was carried out for seepage field and seepage control measures.Based on the unsaturated soils theory,the seepage analysis model of subgrade was established by Abaqus finite element software.The influence of three kinds of subgrade fillings,including clay,silt and gravel,on the infiltration of subgrade slope was analyzed.The average consistency index of subgrades with slope protection,gravel drainage layer,sewer drainage were evaluated.The results show that "lag" of the water infiltration in the low permeability clay subgrade was the greatest and the change range of the infiltration line in the subgrade was the smallest;the shallow and deep buried sewer could control the humidity of the subgrade in the moderate wet or dry state respectively.Therefore,low permeability material and the integrated use of slope protection and ditch should be used.Secondly,the deformation rules of seasonal subgrade are studied by numerical methods.Based on the Abaqus finite element software,the calculation model of soil settlement was established.Through the UMAT subroutine,the modified bounding surface constitutive model was implemented and applied to the first layer of soft soil to record its cumulative plastic deformation under the dry wet cycle.The effects of two kinds of water boundary conditions(single and double side),three kinds of replacement thickness(0.5m,1m and 2m),two kinds of replacement materials(clay and sand)and the effect of reinforced concrete square pile on the deformation of the subgrade were analyzed.The results indicate that the differential settlement of the subgrade shows a typical "bend basin" form and the vertical and horizontal displacement fluctuates with time.As difference settlement control index was set as 0.37%,the 2m thick clay or the 1m thick sand replacement could effectively treat the differential settlement of the shallow soft foundation,however,the sand replacement will increase the deformation wave of the subgrade.When the deep soft soil foundation(8m)was treated with reinforced concrete piles,the settlement value of the top surface of the roadbed was only 0.94 cm,and the differential slope of the settlement was only 0.06%.Clay materials replacement is recommended for the shallow soft soil and the deep soft soil must be treated with reinforced concrete square piles.Finally,the pavement structure for seasonal soaking subgrade was designed based on the deformation of the seasonal subgrade and the principle of coordinating the deformation between subgrade and pavement.The pavement design process for seasonal soaking subgrade was formulated.Dynamic differential settlement was applied to different pavement structures as displacement load through the Abaqus finite element software Considering the mechanical response of pavement under the wheel load and the most disadvantageous differential deformation,the adaptability evaluation and structure optimization of the inverted base asphalt pavement structure,the semi rigid base asphalt pavement structure and the combined base asphalt pavement were carried out.The results show that the combined base and optimized inverted asphalt pavement structure could adapt to the maximum 0.54% differential settlement.The settlement adaptability of the composite base asphalt pavement was optimal and the overall thickness of it was the smallest.It was recommended for the seasonal soaking subgrade.