Experimental Study on Dynamic Elastic Modulus and Damping Ratio of Soil-cement Modified by Nano-SiO2 in Corrosive Environment
Objective Most construction projects in offshore areas are affected by seawater corrosion and dynamic loads.Many of these projects have caused a series of accidents due to the corrosion of cement soil,such as the swelling and collapse of road bases and the cracking and destruction of found-ations.From the perspective of dynamic load,cement soil is subjected to various stresses,including earthquakes,typhoons,vehicle-induced crush-ing,wave impacts,and other loads during construction and use,which inevitably aggravate the deterioration of the cement soil foundation.Methods In order to improve the mechanical properties of cement soil foundations in offshore areas,a coastal engineering clay from Guangzhou is selected to prepare nano-SiO2-improved cement soil specimens.The GDS true(dynamic)triaxial instrument is employed to conduct cyclic loading tests on the improved cement soil.The specimens are saturated in a vacuum using a saturator,placed in a seawater solution for corrosion after saturation,and then subjected to counterpressure saturation using the GDS true(dynamic)triaxial instrument.The peripheral pressure is set at 200 kPa,with a loading frequency of 1 Hz(sine wave),an initial axial force of 2 200 N,and a dynamic stress amplitude(σd)of 100,200,300,400,500,600,700,800,900,and 1 000 kPa.The specimens are loaded in ten stages and vibrated 10 times in each stage to investigate the effect of nano-SiO2 on the mechanical properties of cement soil under corrosion conditions.To study the dynamic elastic modulus and damping character-istics of the improved cement soil under varying corrosion durations and concentrations,the changes in the dynamic elastic modulus of cement soil before and after improvement are compared.A dynamic elastic modulus ratio decay model is established,and the influence of changes in the damping ratio is analyzed.Results and Discussions The results showed that under the combined effects of cyclic loading and seawater corrosion,the dynamic elastic modu-lus of cement soil before and after nano-SiO2 improvement decreased with increasing seawater concentration.When the dynamic strain(εd)was less than 0.3%,the rate of decrease of the dynamic elastic modulus was faster,whereas the decrease rate slowed when εd exceeded 0.3%.Under similar corrosive conditions,the dynamic elastic modulus of cement soil increased gradually with the rise in the corrosion time,but the growth rate decreased over time.The dynamic elastic modulus of nano-SiO2-improved cement soil was consistently greater than that of ordinary cement soil in all corrosion cycles.A good linear relationship was observed between the inverse of the dynamic elastic modulus and the dynamic strain of the cement soil when the Konder model was used.The maximum dynamic elastic modulus(Ed0)of nano-SiO2-modified cement soil was signific-antly higher than that of ordinary cement soil.The Darendeli model was utilized to analyze the dynamic elastic modulus of cement soil,and the decay model of the dynamic modulus ratio of cement soil before and after nano-SiO2 improvement was obtained.This model better describes the variation in the dynamic elastic modulus of cement soil with dynamic strain under a corrosive environment.The hysteresis loop area(S)increases continuously with the increase in dynamic strain.The S-εd curve gradually moves downward with time and rises with the increase in sea salt con-centration.Under the corrosion of seawater solutions with different concentrations,the damping ratio(λ)of cement soil before and after nano-SiO2 modification increases with dynamic strain and gradually levels off,while the λ-εd curve shifts upward as the corrosion concentration increases.The overall trends of the S-εd and λ-εd curves for nano-SiO2-modified cement soil are slower than those for ordinary cement soil.For the same corrosion time,the hysteresis loop area(S)and damping ratio(λ)of nano-SiO2-modified cement soil are smaller than those of ordinary cement soil and increase with the increase in the concentration.After mixing an appropriate amount of nano-SiO2 into the soil,nano-SiO2 reacts with cement to generate cementitious substances that fill and refine some of the soil's pores.This enhances the structural stability of the soil,in-creases the force between particles,improves load transfer efficiency,reduces energy loss during loading,and lowers energy consumption.A large quantity of cementitious substances is rapidly produced on the surface of soil particles.These substances,which appear as rods,bars,and spheres,increase with the concentration.Compared to ordinary hydraulic soil,the surface of soil particles rapidly produces a large number of gel-like sub-stances in the form of rods,bars,and spheres that stack together to fill pores and particle gaps.This forms a dense spatial network,effectively en-hancing the strength and structural stability of cement soil,reducing seawater erosion,improving corrosion resistance,and increasing resistance to the coupling effects of dynamic loading and seawater corrosion.Most current research on nano-SiO2 cement soil focuses on its engineering prop-erties under static load in ordinary environments,while studies on its dynamic properties in seawater corrosive environments remain limited.Conclusions This experiment investigates the effects of different seawater concentrations and corrosion durations on the kinetic properties of nano-SiO2-modified cement soil under the coupling of dynamic loading and seawater corrosion.It reveals the deterioration patterns of the mech-anical properties of cement soil under these conditions and examines the improvement mechanism of nano-SiO2,providing a reference for future studies on cement soil base structures in coastal areas.
sea salt solutioncement soilnano-SiO2dynamic triaxial testdynamic elastic modulusdamping ratio
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