Model Experimental Investigation Of Transparent Soil On Soil Arching In Piled Embankment

Appropriate methods should be utilized to treat the foundation in the process of civil engineering construction for the sake of poor permeability performance,high compressibility,low strength and high water content.The shearing strength of local field can be fully utilized to decrease the total settlement and differential settlement when pile-supported embankments are applied in the soft foundation.This is owing the fact that the compressive stiffness of piles is significantly larger than that of the soft soil,leading to the settlement difference.Partial deadweight of the soil would transfer to the pile in the process of settlement making the compressive stress concentrate around the pile,which is the phenomenon of soil arching effect.The soil arching effect has drawn wide attention from researchers in aspect of reveal the distribution of stress in the embankment,while little studies have been carried out for the settlement of pile-supported embankment.Deformation on surface of the soil can be determined through the conventional measuring methods.However,the deformation inside the soil cannot be depicted owing to the characteristic of nontransparent soil.Traditionally,the deformation inside the soil can be determined by the imbedded displacement measurement devices.For the case of model tests,bearing capacities of the soil may be affected following the traditional measure method with only a few data,which shows limited potential to reveal the real displacement field of the embankment.The particle image velocimetry and photogrammetry technique is adopted to conduct the transparent media model tests,aiming to reveal the deformation distribution inside the soft soil and numerical analyses conducted by the ABAQUS software are applied to verify the validity of the model tests.Major findings can be concluded as follows:(1)The double model test equipment with characteristics of visualization is developed and the test method is designed for the pile-supported embankment in the soft soil to measure soil arch effect.Then analyze the advantages of this method.(2)Model tests are conducted to analyze the settlement regularity of the pile-supported embankment in the process of loading application,based on the developed test equipment.The results showed that the deformation of pile-supported embankment is three-dimensional issue.Little deformation is observed in the soil media around the pile in the process of model tests.In contrast,the largest settlement of the pile-supported embankment occurs in the middle zone of inter-pile soil approximately,leading to a deformation shaped like a basin at surface of the embankment.(3)Based on the depicted deformation figure,the embankment can be divided into 3 parts with obvious arch dividing line.Settlement of the embankment beyond the arch dividing line shows little variation in the process of model tests,while the settlement inside the line is increased obviously.Moreover,the displacement of the surrounding soil in the area of semicircle with diameter of the pile side length shows little variation,due to the pile-soil interaction.(4)The settlement curve of pile is shaped like a special inverted Chinese character ?JI? at bottom of the embankment.The settlement distribution of the soil shows characteristics of regional change.From the vertical direction,the settlement of soil are increased with the increasing z,for the area with soil and pile interaction.While for the area with soil only,the settlement tends to decrease with the gradual increase of z.Skewback of the soil arching is located at head of the pile,shaped like a parabola approximately.The maximum settlement and steady settlement are increased with the gradual increase of pile spacing,and settlement tend to be stable.(5)The concept of relative differential settlement is proposed to use as a quantization discriminant standard for the equal settlement section.The equal settlement section is a plane with the relative settlement difference less than 5%.The height of the equal settlement section which equals to ?2?2 pile spacing for approximation tends to increase with the increase of pile spacing.(6)The settlement distribution obtain by the numerical examples shows well match with the model test,signifying the validity of the proposed experimental scheme.The maximum settlement and the steady settlement of the embankment tend to increase with the decrease of pile side length,modulus of the filled soil and modulus of the inter-pile soil.While it is increased with the height of the embankment,pile spacing.Load sharing ratio shows tendency of decrease with the decrease of pile side length,modulus of the filled soil,while it tends to decrease with the increasing modulus of inter-pile soil and pile spacing.It is sensitive for the soil arching effect,which is affected by the pile spacing and pile side length.While for the height of filled soils,modulus of the soil,it shows little influence to the soil arching effect.