Engineering Characteristics And Reinforcement Measures Of Hard Shell Diatom Soil Foundation

In view of the many unfavorable engineering characteristics of diatomite,the diatom soil foundation needs reinforcement treatment.However,the amount of foundation treatment works is huge and the cost is high,which delays the progress of the project.The overlying hard shell layer can effectively diffuse the stress,and restrain the deformation of the underlying diatomite.Nowadays,the nature of the hard shell layer is not well understood,and the engineering characteristics of the hard shell diatom soil foundation are not fully grasped.Therefore,the double-layer foundation of hard shell diatomite is taken as the research object,through literature research,field survey,geotechnical test,field in-situ test and numerical simulation,the physical and mechanical characteristics of diatomite,the action characteristics of hard shell layer,in addition,the bearing characteristics,settlement mechanism and the strengthening principle of the hard shell diatomite foundation are deeply analyzed,and the following important conclusions are obtained:(1)The diatomite in Shengzhou area belongs to weakly expansive clay diatomite,which is specifically characterized by high porosity,high water absorption,strong structure,high strength,high plasticity,low permeability and disintegration in water.Diatomaceous earth is dense and massive,but it is easy to soften after the disturbance,the mechanical properties drop sharply,and the engineering properties are extremely poor.Surface diatomite is easily degraded into secondary diatomite,which often causes engineering accidents such as instability of shallow slopes,sliding and softening of foundation.(2)The presence of the hard shell layer can effectively reduce the vertical additional stress at the interface.The thickness and deformation modulus of the hard shell layer have a great influence on the vertical additional stress,and the thickness of the hard shell layer plays a major role.As the thickness of the hard shell layer increases,the vertical additional stress at the shell-soil interface decreases within the embankment load range,but the vertical additional stress at the interface outside the embankment increases,indicating that the hard shell layer has a significant stress diffusion effect At the same time,the analytic expression of the stress diffusion coefficient of the diatom soil in the hard shell layer is deduced to modify the settlement formula of the diatom soil base in the hard shell layer related to the layer summation method.(3)During the filling period,a settlement of 6.75 mm occurred in the center of the foundation.The settlement curve in the stationary period tended to be stable,and the value during the filling period accounted for 89.36% of the total settlement.During the same period,the compression deformation of the foundation mainly occurred within a depth of 6m below the surface,so shallow diatomite was the main area that caused the settlement of the foundation.The lateral displacement of the slope foot is obviously arcuate.The maximum horizontal displacement occurs 5m below the ground and the value is 6.19 mm.The groundwater level in this area rises and falls frequently and belongs to the weakest part of the foundation soil.(4)Under the simulated train fatigue load,the dynamic stress and vibration acceleration of the base surface of the hard shell layer are stabilized at 6.37 k Pa and 0.94m/s2,respectively,and the dynamic energy is greatly attenuated after the diffusion of the bed filler and the hard shell layer.At the same time,the post-construction settlement of the hard shell diatom soil foundation caused by dynamic loading is basically negligible;the dynamic load has little effect on the performance of the capillary drainage board,and the capillary drainage board has good waterproof and drainage characteristics.(5)While the thickness of the hard shell layer≥3m,embankment can be directly built on the diatomite natural foundation of hard shell layer,but the treatment measures still need to take into account the construction organization,construction period,meteorology and hydrology and other factors;otherwise,the foundation needs to be strengthened;the plain concrete pile can be applied to the diatom soil foundation,and the calculation shows that only 3.27 mm post construction settlement is produced after consolidation with pile-raft composite foundation,which meets the requirements of the norm.