Experimental Study On The Structural Characteristics Of Cangzhou Coastal Soft Clay

The country's soft soil area is widely distributed,and most coastal areas have a large amount of marine sedimentary soft clay.Marine sedimentary soft soils will exhibit certain physical properties due to their different geological environments,but they all have the characteristics of structural characteristics.The structural strength of soft clay will affect its physical and mechanical characteristics to varying degrees,and structural damage will often occur in the absence of an omen,which will have a greater impact on engineering practice.To some extent,the structure of soft clay has become a more important topic in the study of soil mechanics.In order to better reveal the strength characteristics and deformation characteristics of regional structural soft clays,based on the summary of the current status of structural research,this paper conducted a series of indoor geotechnical tests and analysis work with Cangzhou coastal soft clays as research objects,and discussed the application The structural constitutive model and model parameters for soft clay are of reference significance to regional engineering practice.(1)In this paper,direct shear tests and consolidation shear tests were performed on local natural and remolded soils to investigate the effect of structural properties on soil shear strength.The results show that the strength of the soil after the disturbance is significantly reduced,the bonding strength of the soil is destroyed,and the cohesion and internal friction angle are both low.The shear stress-strain curve of undisturbed soil has obvious peaks,while the remodeled soil is relatively gentle and accompanied by strain hardening.In the consolidation shear test,the difference in strength between the undisturbed soil and the remolded soil is greatly reduced,and the deformation tendency becomes similar,indicating that consolidation can eliminate part of the structural effects on soil deformation and strength.(2)According to the unconfined compressive strength test,the soft clay in this area has high sensitivity,and has strong structural characteristics.In the test,the failure characteristics of the undisturbed soil were brittle failure,and cracks and rupture surfaces appeared successively.However,under the same conditions,the compressed shape of the remolded soil was drum-shaped,and no obvious fracture surface appeared.(3)Compressive tests were performed on undisturbed soil and remolded soil,and the results showed that the curve of undisturbed soil can be divided into three sections,that is,gentle section,yield section and steep drop section.The compression curve of the remolded soil has no obvious inflection point and is in a straight line.During the compression of undisturbed soil,when the vertical load reaches near the yield pressure,the structure is destroyed,the compression curve appears an inflection point,and then it tends to reshape the compression curve of soil.For structural soft clay,the in-situ compression curve was restored by a mathematical model method,and the preliminary consolidation pressure of the soil was obtained.(4)Consolidated undrained shear tests were performed on the specimens using a triaxial shear meter,and the stress-strain relationship characteristics of pores,the characteristics of pore water pressure changes,and changes in effective stress paths and total stress paths during shearing were explored.It provides experimental basis for constructing structural constitutive model.(5)Aiming at the characteristic that the modified Cambridge model does not consider the structure of the soil,this paper combines the structural test and the triaxial shear test.Based on the elasto-plastic model proposed by Yin Jie et al.,The structural Cambridge model of Cangzhou coastal soft clay is discussed and the suggested parameters are given.