Study On Settlement Deformation Mechanisms Of Coastal Highway In Soft Soil Subgrade And Disease Prevention Countermeasures

Due to consolidation and settlement of soft soil and complex environmental conditions,amounts and types of the coastal pavement disease are increasing during highway operation day by day,which has been threating seriously to road service performance and driving safety.It is an important basis for guiding the disease prevention to establish the relationship between settlement deformation and road disease.With the continuous development of China’s transportation,the overall amount of highway construction has ranked first in the world.Roads and other livelihood buildings are gradually increasing in the coastal areas,and the road section built on soft foundation is up to 40%.For meeting construction requirements of the modern comprehensive transportation system in Guangdong-Hong Kong-Macao Greater Bay Area,the high-quality construction,operation and maintenance of coastal highway are in significant demand.It is of great importance in engineering to improve settlement deformation mechanisms of the soft soil foundation,road disease identification ability,and comprehensive evaluation on treatment effect of highway diseases.Engineering background in this dissertation was based on Taishan soft foundation section of the West Coastal Highway in Guangdong Province.The study methods were used such as field investigation,in-situ monitoring,radar detection,laboratory test,numerical simulation and theoretical analysis.Five study contents were carried out,that is the settlement monitoring in road structural system after construction,the strength and deformation characteristics on soft foundation soil,the dynamic response and comprehensive time-varying prediction of soft foundation deformation under vehicle load,the disease detection and treatment measure evaluation in soft foundation road.The settlement deformation mechanism and disease distribution were revealed and some suggestions were developed for engineers.Main study contents and conclusions completed are as follows:(1)Characteristics and development laws of coastal soft foundation highway were established in detail.Based on the data from in-site monitoring,we studied the vertical settlement displacement,horizontal lateral displacement,pavement diseases and traffic features according to 8 full-amplitude monitoring sections,4 inclined pipes,1.8 km omnidirectional disease surveying,and dynamic axle load weighing system from 2015-2019.The results show that ranges of differential settlement peak in adjacent settlement piles monitored are consistent with the disease distribution section,which is mainly located between the divider of main and overtaking lane,and central divider.Lateral displacement of coastal highway is related to the soil type,soil depth and other factors.The lateral displacement decreases with the increase of soil depth,and the abrupt displacement phenomenon will exist at the boundary of soil layer.(2)Deformation characteristics and solidification effect on soft foundation soil were investigated clearly.In order to study characteristics of strength,deformation and solidification from soft foundation soil under the environment of rich water and salt,a series of model tests were designed on the filled soil and silt.The results show that the content of water and salt in soil are the important factors affecting the strength and deformation.The exponential relationship is shown between the shear strength and high-water content,or high-salt content.The compressibility is increasing with the increase of water and salt content at the compression stage,but it is decreasing at the stage of spring back and recompression.Meanwhile,the solidified experiment results of cement,quicklime and carbon nanotubes show that the shear and compression resistance of soft foundation soil are improved and the consolidation settlement is reduced fundamentally after solidifying.The larger the dosage of curing agent,the smaller the macropore amount and total pore area in micro level.In addition,the increase range of shear strength and unconfined compressive strength,and the decrease range of compression coefficient in macro level are more significant.Compared three curing measures,the curing effect of cement is best.(3)The influence mechanism of settlement deformation aimed at soft foundation road structure system under different factors was revealed.MISO and DP constitutive model were used to characterize the stress-strain relationship of pavement materials and soil materials,respectively.Three-dimensional finite element calculation models of coastal soft foundation highway were established.The results show that the calculation results are consistent with the measured results based on the elastic-plastic constitutive models.The overall road settlement deformation is cumulative and decreases with the increase of depth.In the carriageway,the overtaking lane is the vertical displacement peak area,and the main lane is the lateral displacement peak area.The positive and negative displacement boundary ranges from 5～10m are below the road surface,which will occur large lateral displacement.Based on grey relational degree method,the factors affecting the road settlement deformation from large to small are the vehicle axle load,soft foundation thickness,salt and water content of silt.Meanwhile,for overcoming the deficiency that three-dimensional large size model cannot be used to calculate the settlement deformation with large time span,a comprehensive time-varying prediction model was established on the basis of the measured settlement data by introducing variable weight idea.Therefore,the prediction accuracy of pavement post-construction settlement is improved and its long-term prediction of the development trend is also realized.(4)Efficient and nondestructive disease detection methods of coastal soft foundation highway were innovated.To solve the problem that recessive diseases caused by differential settlement or material aging were difficult to be accurately detected and interpreted,high and low frequency antennas of MALA Ground-penetrating Radar were used to detect the study region.Meanwhile,the continuous wavelet transform,absolute modulus maximum method and pixel equivalent concept were introduced to comprehensively interpret the whole detection region radargrams.The results show that the interpretation accuracy is improved from decimeter to millimeter level by using one-dimensional continuous wavelet transform and absolute mode maximum method,and the shortage of the disease omission can also be solved.Secondly,the identifiable characteristics of pavement diseases are enhanced with twodimensional discrete and continuous wavelet transforms,which is beneficial to engineers’ interpretation.Finally,A kind of volume optimization algorithm for irregular recessive diseases is proposed based on the pixel equivalent analogy.Moreover,the existence of uneven settlement in the calculation has been verified by the comprehensive radar detection results.The accurate positioning can be provided for follow-up targeted engineering treatment.(5)Countermeasures of coastal soft foundation highway diseases were proposed and the treatment effect was evaluated.To solve the engineering problems that the recessive diseases mainly occur in soft foundation and pavement layer,the grouting reinforcement,pavement resurfacing or layer adding have become the important means to treat highway diseases.Based on the characteristic parameters from solidified silt with cement,quicklime and carbon nanotube,advantages and disadvantages of three countermeasures on the overall settlement deformation of road were evaluated with finite element platform.The application range of two pavement treatment measures was also discussed.The results show that in the soft foundation disease treatment,the decrease of vertical settlement and lateral displacement is more obvious with increase of the curing agent.The solidification effect is the best when the cement content is 20 %,and the maximum decrease of settlement and deformation can reach 79 % and 74 %respectively.In the pavement disease treatment,the pavement resurfacing has better effect on the basic layer with serious cracks,etc.However,the ultra-thin abrasive layer adding has better effect on loose diseases caused by the aging of the upper layer.