Analysis And Control Of Differential Settlement Of Old Road Widening Pavement In Thick Marine Soft Foundation

Due to economic development and increasing traffic volume,the existing roads have been unable to meet the traffic demand which means it is imperative to widen the old roads.In the road widening project of thick layer Marine soft foundation area,as the settlement of the old subgrade is nearly completed under the action of traffic load for many years,the soil properties have changed greatly,while the settlement of the new subgrade has not started yet.In this case,under the action of load,there will be differential settlement between new and old subgrade in soft foundation area over time which will lead to longitudinal dislocation cracks along the patchwork joints and even affect the road safety.It has become a problem that must be solved to widen the old road of soft soil foundation.Based on the reconstruction and expansion project of Zhong Shan Sha Gang highway,through the methods of field investigation,indoor soil test,numerical simulation and real time monitoring,this paper systematically studies the differential settlement control technology of roadbed in the reconstruction and expansion project of urban section without embankment.First of all,this paper introduces the general engineering and geological and hydrological situation of Shagang highway,using the undisturbed soil samples of Shagang highway scene for indoor creep test,based on the existing widening form and the roadbed treatment,proposes the design scheme of anti-differential settlement of the reinforced structure of the upper part of the double-layer reinforcement network with soil-cement,gives the specific technical parameters and construction requirements,and applies it to the actual project.,the laboratory creep test was carried out on the undisturbed soil samples obtained from the site of Shagang highway,and the creep parameters of soft soil were obtained by fitting the test data with the creep law of the power function of "time hardening",which provided a constitutive relation for the numerical simulation of the time-related deformation of subgrade pavement and soil.The unconfined compressive strength test of soil-cement was carried out on site,and the optimal cement incorporation ratio was determined for strengthening soil-cement structure.Secondly,the finite element model of bearing deformation of the old and new roadbed is established by using the large universal finite element program ABAQUS,and the differential settlement rule of the old and new roadbed under the influence of multiple factors is analyzed from two aspects.On the one hand,considering the elasticplastic properties of soil,The Mohr-Coulomb constitutive model is used to analyze the settlement law of the road surface and the lateral displacement law of the road surface in two cases of treatments of subgrade soil with different modulus ratio under load: the untreated condition,the mixing pile treatment.And then obtained the optimal treatment of pile length under various modulus ratios,and the equivalent depth of the deformation basis of the old and new roads in terms of road table level.On the other hand,considering the rheological properties of the deep soft soil,the Drucker-Prager soil constitutive model with time correlation was used to analyze the settlement law of the new and old subgrade with each modulus ratio under the disposal of 12 m pile length.Thirdly,based on the existing widening form and the established roadbed treatment method,the anti-differential settlement design plan for the double-layer reinforced mesh sandwiched cement-soil upper reinforcement structure was proposed.On the one hand,considering the elastic-plastic properties of soil,The Mohr-Coulomb constitutive model is used to analyze the settlement law of the road surface and the lateral displacement law of the road surface in two cases of treatments of subgrade soil with different modulus ratio under load: the upper reinforces structural layer treatment,and the upper reinforced structure combined mixing pile treatment.On the other hand,considering the rheological properties of the deep soft soil,the Drucker-Prager soil constitutive model with time correlation was used to analyze the settlement based on the engineering practice,the settlement law of the road surface with time is discussed when the upper reinforced structure is used alone and the upper reinforced structure is used in combination with cement mixing pile for the new and old soil foundation with a modulus ratio of 1:3.The comprehensive analysis of the two aspects indicates that the design of strengthening structure on the upper part of cement soil with double reinforcement network has a good effect on the differential settlement of the old and new joints.The optimum cement content was obtained through the compressive strength test of cement soil.According to the results of numerical simulation and the cement soil test,the specific technical parameters and construction requirements of the double-strength mesh-clamped cement-soil reinforced structure were given and applied actual engineering.Finally,according to the engineering practice,the typical section is selected,the monitoring scheme is made and the real-time monitoring is implemented.The existing field monitoring results show that it is feasible to treat the differential settlement of the new and old roadbed with deep Marine soft soil by using cement mixing piles combined with the reinforced upper layer of the double-layer reinforcement network with cement soil,and it can effectively control the uneven settlement of the new and old roadbed and the lateral displacement of the roadbed surface.