Research On The Design Method Of Subgrade Filler With The Overall Stiffness Of Subgrade As The Target

Subgrade is the foundation of pavement structure,which should have enough strength and stability.In the construction of subgrade filling,due to the improper selection of subgrade filler,the subgrade stiffness after filling is low.It is easy to produce large deformation.In the past,the engineering experience method was used in the design of subgrade filler.Due to the lack of relevant theoretical support,in order to meet the requirements of the overall design of subgrade,many test roads need to be laid,which is time-consuming and difficult to ensure the overall stiffness of subgrade.Therefore,how to design subgrade filler economically and reasonably,formulate subgrade filling scheme,improve the overall stiffness of subgrade,and make it meet the requirements of design acceptance.It is great significance for highway engineering construction in China.In order to solve the problem that it is difficult to ensure the overall stiffness of subgrade in the existing design of subgrade filler,based on the elastic mechanics theory and displacement equivalence principle,this paper puts forward a design method of subgrade filler with the overall stiffness of subgrade as the target.It includes the rapid determination of lower embankment resilient modulus in situ and the design of filling materials for upper embankment and roadbed.In the past,the bearing plate method was often used in the field measurement of lower embankment,which was inefficient and time-consuming.In this paper,the portable falling weight deflectometer(PFWD)is introduced to consider the deformation lag effect of subgrade under impact load,and the back calculation method of subgrade modulus based on viscoelastic model is established.It is used for rapid determination of lower embankment resilient modulus.In the test section,the field verification shows that the detection efficiency is high,and it is very close to the measured results of the bearing plate.The upper embankment and roadbed filler design is based on the following calculation parameters:lower embankment resilient modulus and comprehensive resilient modulus of subgrade top surface.The target resilient modulus of upper embankment and roadbed top surface is determined.The required resilient modulus and filling thickness of each filling layer are determined by combining with the nomograph of filler design for subgrade filling layer.According to the on-site filler supply situation,select the appropriate filler,and formulate a reasonable subgrade filling scheme.During the field construction,the filling scheme can be adjusted dynamically in real time according to the measured resilient modulus and resilient deflection of the upper embankment and roadbed top surface.It is used to control the quality of subgrade construction.The resilient modulus of subgrade filler is required as the design parameter in the design of subgrade filler.It is difficult to determine the resilient modulus of subgrade filler directly due to the limited construction site test conditions.In this paper,the field subgrade filling material of G360 National Highway in Hainan is taken as the research object.The basic physical properties of fillers are analyzed.The road performance test and dynamic resilient modulus test were carried out.The regression equations between the soaked CBR and the resilient modulus,and the regression equations between the non-soaked CBR and the resilient modulus were established respectively.The relationship curve between CBR and resilient modulus fits well,and the correlation between non-soaked CBR and resilient modulus is better.Therefore,a prediction method of subgrade filler resilient modulus is proposed.According to the non-soaked CBR of the field filler,combining with the formula E=2.0004CBR1.1017,the resilient modulus can be quickly estimated.It provides parameters for subgrade filling design.Based on G360 National Highway in Hainan,according to the subgrade filler design method and subgrade filler resilient modulus prediction method proposed in this paper,combined with the on-site filler supply,the subgrade filling scheme in test section is designed.Through the field test,the effectiveness of the new design method of subgrade filler is further verified by comparing with the original subgrade filling scheme.The method can effectively improve the overall stiffness of subgrade,select site filler economically and reasonably,and reduce the waste of resources.The engineering application effect is good and can be popularized.The research results of this paper have important scientific significance and reference value for the design and construction of highway subgrade.