Centrifuge modelling of wet deep mixing processes in soft clays

Abstract

This paper assesses the feasibility of studying wet deep mixing processes using centrifuge modelling. The scaling relationships relevant to modelling of the deep mixing were first established, and the likelihood of satisfying them in centrifuge modelling was then examined. The relationships between most of the significant forces in deep mixing processes can be satisfied using centrifuge modelling, with the exception of the Reynolds number. The latter cannot be preserved, owing to the non-Newtonian characteristics of cement slurry as well as of the soil−cement mix. However, viscosity scale effects can be mitigated by using a liquid tracer of lower viscosity in place of cement slurry. Deep mixing model tests were conducted to examine the effects of viscosity of the tracer, density of the tracer and work done in mixing. Comparison between 1g and centrifuge model test results shows that the former results have significantly poorer mixing quality than the latter. This can be attributed to the larger viscous forces relative to the other forces, in the 1g models. Lowering the viscosity of the tracer, increasing the work done in mixing and minimising density differences between soil and slurry can all contribute to enhancing the quality of mixing. The effect of density differences between soil and slurry was shown to be a possible reason for the large variation in reported field unconfined compressive strength as the water−cement ratio increases.

Earthquake-induced bending moment in fixed-head piles in soft clay

“…Under such conditions, soil viscosity is not correctly scaled (Lee, 2006). However, Ishihara (1996) and Banerjee (2010) noted that rate-dependent viscous damping in the soft clay is much smaller than strain-dependent hysteretic damping.…”

Statistical evaluation of the overall strength of a soil-cement column under axial compression

“…(3) and (4) can be readily unified as F c ¼ b  q u , of which the coefficient b from both equations were plotted against the COV of UCS as shown in Fig. 13.…”

“…These techniques involve mixing admixtures, usually cementitous, into soft soils by way of hollow rotating shafts with cutting tools, mixing paddles and/or augers mounted at various locations along the shafts (e.g. among others, [1][2][3][4][5]). It is well known that this process of chemical improvement can introduce significant heterogeneity into the improved ground.…”

“…The anisotropy of heterogeneity was considered by adopting different scales of fluctuation (SOFs) in the cross-section plane and along the axial direction (see illustrations in Figs. [1][2][3]. Finite element analysis software of ABAQUS/Standard Version 6.13 was used to aid in this simulation.…”

Some issues in core strength measurement in cement-soil treatment for deep excavation - Field data study

“…In a similar way, significant non-uniformities can result from chemical improvement using cement slurry (e.g. Lee et al 2005Lee et al , 2006Lee et al , 2008. Chen et al (2011) also reported that the unconfined compressive strength (UCS) of core samples varies from about 700 kPa to about 5 MPa for the deep mixing work at the Marina Bay Financial Centre (MBFC) project in Singapore.…”