Study On Dynamic Behavior Of Shengzhou Diatomite Under Cyclic Loading

Diatomite is a special kind of strong structured soil,but up to now,there is very little understanding of the geotechnical properties of diatomite at home and abroad,and the corresponding research is still very lacking.With the rapid development of infrastructure construction in China,some major projects will be located in or pass through the diatomite area,and engineering accidents caused by insufficient understanding of diatomite frequently occur.It is very necessary to conduct a systematic study on the geotechnical properties of diatomite.This article takes the typical natural diatomite in Shengzhou as an example,high quality sampes of Shengzhou diatomite are firsty obtained by block sampling method.a series of dynamic characteristics studies are then conducted on them through GDS dynamic triaxial test system(S/DTTA).The detailed research contents are as follows:(1)Combined with on-site field investigation,data collection and indoor physical property tests,the characteristics of Shengzhou diatomite were initially described.The sampling method and process of original diatomite samples were further improved based on the feedback from on-site sampling and laboratory tests.(2)In view of the long-term characteristics of cyclic loading,one-way cyclic triaxial tests with up to 50000 times under different confining pressures,different vibration frequencies and different cyclic stress ratios was carried out to study the changes of pore pressure and deformation,stress-strain hysteresis curve evolution,strength attenuation,damping ratio and small strain shear modulus of undisturbed diatomite under long-term undrained cyclic loading.Based on the test results,an empirical formula for the change of dynamic elastic modulus,strain accumulation,damping ratio and small strain shear modulus of undisturbed diatomite samples under long-term undrained cyclic loading is established.The effects of cyclic stress ratio,cyclic load vibration frequency and structure on the dynamic properties of undisturbed diatomite are analyzed.The study found that the residual pore pressure,strain and dynamic elastic modulus increase with the increase of confining pressure;when the confining pressure is constant,the residual pore pressure and strain increase with the increase of the cyclic stress ratio,and the dynamic elastic modulus As the cyclic stress ratio decreases,the original residual pore pressure ratio is between 0.1 and 0.4.The critical cyclic stress ratio is greatly affected by the confining pressure;the residual pore pressure ratio and the cumulative plastic strain vary with the loading frequency.The rebound strain decreases with the increase of the loading frequency,and the stable value of the dynamic elastic modulus has a linear relationship with the increase of the loading frequency;The original damping ratio decreases rapidly with the increase of dynamic strain,and is between 0.01 and 0.02.(3)In view of the long-term characteristics of cyclic loading,a unidirectional excited triaxial test with up to 30000 times under different confining pressures,different vibration frequencies and different cyclic stress ratios was carried out to study the regularity of pore pressure and deformation accumulation,stress-strain hysteresis curve evolution,strength attenuation,damping ratio and small strain shear modulus changes of undisturbed diatomite under long-term undrained cyclic loading.The applicability of empirical equations such as dynamic elastic modulus,cumulative strain,damping ratio and small strain shear modulus of undisturbed diatomite under long-term undrained cyclic loading is analyzed.The effects of cyclic stress ratio and cyclic load vibration frequency on the dynamic characteristics of remoodeled diatomite are analyzed.The study found that the boundary residual pore pressure ratio of remodeled diatomite is significantly higher than that of intact diatomite,and the residual pore pressure ratio and rebound strain development curve of reshaped samples under different loading frequencies are significantly different;The strength is significantly lower than that of the original sample,and the critical cyclic stress ratio is between 0.25 and 0.3;unlike the original sample,the dynamic elastic modulus of the reshaped sample exhibits nonlinear attenuation at the early stage of dynamic strain development,and shows the characteristics of strain softening.When showing obvious strain hardening,the ability to resist deformation increases;compared with the original diatomaceous earth,the small strain shear modulus of remodeled diatomaceous earth is significantly reduced.(4)The experimental results of undisturbed diatomite and reshaped diatomite are compared to analyze the difference in properties between remodeled diatomite and undisturbed diatomite.From the comparison results,we can see that diatomite is a special structure with strong structure.There is a big difference between the failure shape of the reshaped sample and the original sample.The original sample shows the shear failure caused by strain localization.The main feature is the shear failure along the original structural surface of the soil sample.