Study On Mechanical Properties Of Soft Clay Considering The Influence Of Vibration Disturbance

Soft clay is widely distributed in coastal plain,delta,lake basin and valley.In these areas,the construction of various projects inevitably encounters the safety risks of vibration disturbance during construction.Because of the high natural water content,high void ratio,high compression and low strength,soft clay has poor mechanical properties such as creep and thixotropy.Once disturbed,the original structure is very susceptible to disturbance and the strength is obviously reduced.Soil structure is an important feature of natural soft clay,which has a considerable influence on its deformation and strength.The neglection of the effect of soil structure of soft clay often leads to unexpected failure without signs.If the soft ground is not treated properly in the process of construction,it will cause serious harm and loss of life and property.Therefore,this paper studies the mechanical properties of soft clay after vibration,aiming to evaluate the change rule of mechanical properties of soft clay caused by vibration,and provide necessary theoretical support and design basis for practical engineering application.The main work and conclusions are as follows:(1)The basic physical properties of the typical soft clay samples in Lianyungang city were obtained by routine laboratory soil tests,and the basic physical properties parameters(like grain size distribution curve,optimum moisture content,maximum dry density,etc.)were obtained.XRD test was carried out by X-ray diffraction apparatus.The results showed that the mineral composition of the soil samples was mainly the composed of the mixed layer of illite and montmorillonite.The soft clay samples with different disturbance degrees(undisturbed soil,disturbed soil and remolded soil)were prepared by laboratory shaking table.The detailed onedimensional compression test,unconfined compressive strength test and direct shear test were made for soft clay samples under different vibration disturbance conditions.The microstructure and morphology of samples with different disturbance degree were obtained by SEM(scanning electron microscope).(2)The one-dimensional compression tests of soft clay with different disturbance degree were carried out,and the influence law and action mechanism of different vibration frequency and elapsed time on the compression characteristics of soft clay were discussed.The results showed that the vibration frequency and vibration duration will cause different degree of disturbance to the undisturbed soil samples,which will cause structural damage and increase of compressibility.At the same frequency,soil sample compression curve for specimen with higher vibration time is located below that with lower vibration time.The slope CCLA(compression index for the compression line after yielding)and consolidation yield pressure p’y decrease with the increase of vibration time,and the slope CCLB(compression index for the compression line before yielding)and disturbance D increase with elapsed time before the consolidation yield,and p’y decreases linearly with the increase of disturbance.The compression curves of high frequency samples are located below the low frequency samples under the same vibration time,and the yield pressure p’y and CCLA of soft clay decrease with the increase of vibration time,while CCLB and D increase gradually with time.In addition,the microstructure analysis shows that vibration disturbance causes the loss of soil structure,the pore volume gradually decreases,and the particles tend to be closer.The vibration disturbance makes the soil structure change from undisturbed soil to remolded soil.The differences of microstructure and morphology of samples with different disturbance degree are analyzed by SEM test,and the reasons for the difference of macro compression characteristics of soil samples are explained from the micro point of view.(3)The unconfined compressive strength test and direct shear test were carried out for soft clay with different disturbance degree.The influence law and action mechanism of different vibration frequency and elapsed time on the shear strength characteristics of soft clay were discussed.The results showed that the larger the vibration time is,the greater is the disturbed degree of soil samples.When the vibration time is fixed,the higher the frequency is,the greater is the disturbed degree of soil sample,the stronger is the thixotropy.The magnitude of cohesive c and shear strength soil samples under different vibration disturbance conditions are between undisturbed soil and remolded soil.When the frequency is fixed,with the increase of vibration time,or when the vibration time is fixed,with the increase of vibration frequency,both the cohesion c and shear strength shown a decrease trend.In addition,the friction angle φ in each working condition varies around 20° The results showed that the vibration process does not affect the sliding and occlusion of particles.In addition,Based on Burland’s normalized compression theory and Chandler’s normalized strength theory,the compression curves and strength of soil samples under various working conditions are processed.The results showed that remolded soil can be normalized to the intrinsic compression line and intrinsic strength line,and undisturbed soil is located at the top of all lines,while disturbed soil is affected by loss of soil structure.The longer the vibration time is,the closer it is to the natural compression line and strength line.Under the same vibration duration,the higher the frequency,the closer it is to the natural compression line and strength line.