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| Centrifuge modeling of seismic response of soft clay grounds improved by CDM grids |
| WANG Yongzhi1，2，Mohammad Khosravi2，Daniel W. Wilson2，WANG Hai1，Shuji Tamura3，WANG Tiqiang1 |
(1. Key Laboratory of Earthquake Engineering and Engineering Vibration，Institute of Engineering Mechanics，China Earthquake Administration，Heilongjiang，Harbin 150080，China；2. Center for Geotechnical Modeling，University of California at
Davis，Davis 95616，America；3. Department of Architecture and Building Engineering，Tokyo Institute of Technology，
Tokyo 152–8550，Japan) |
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Abstract Recent international damage surveys indicate that the performance of ground improved by cement-deep-mixing(CDM) method is generally better than expectations. Enhancing the understanding of the seismic response of CDM improved ground is important in developing suitable design methods of seismic resistance. Two series of dynamic centrifuge model tests to the composite soft clay grounds improved by CDM grids were presented. The unimproved ground and improved ground sites with embedded and floating CDM grids installed following a TRD-like method were tested. The responses and features of peak acceleration amplification，spectral ratios，ground settlement and shear stress-strain were analyzed. The results show that the acceleration responses of two embedded grid-improved grounds are linearly amplified at large and the peak accelerations are amplified by a factor of 1.4 on average，which is in contrast to the response where a floating grid was used. The unimproved soft clay below the floating grid-improved ground significantly affects the local amplification effect and limits the surface PGA especially when the clay is softening. In this case，a reduction in high frequency content were observed. The settlements of grid walls in all cases typically occur mostly due to the post shaking reconsolidation. Differential settlements were observed between the grid walls and the enclosed soils in both embedded grid-improved ground sites，indicating that the negative skin friction was generated. Conversely，the settlements of the grid walls and the enclosed soils in the floating grid-improved ground are in agreement. The results of back analysis indicate that the grid walls by SSI(Soil-Structure Interaction) restrict or mobilize the shear strain response of their enclosed soils dependent on the frequency content and intensity of seismic motions. The effect of mobilizing gave a reasonable explanation for the settlements of the enclosed soils in the two embedded grid-improved grounds during the high frequency earthquakes.
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2018, Vol. 37 
