The viscous properties, or loading-rate eŠects on the stress-strain behaviour, of unbound and bound soils, in particular unbound granular materials, are summarised. The viscous properties were evaluated by stepwise changing the strain rate, ·e, and performing sustained loading during otherwise monotonic loading (ML) at a constant ·e and also by performing ML tests at diŠerent constant values of ·e. Four basic viscosity types, Isotach, Combined, TESRA (or Viscous Evanescent) and Positive & Negative (P & N), which were recently found are described. The Isotach type is the most classical one and, in the case of ML, the current viscous stress component is a function of instantaneous irreversible strain, e ir and its rate, ·e ir . So, the strength during ML at a constant ·e increases with ·e. With the other three types, the viscous stress increment that has developed at a given moment, denoted as Ds v , decays with e ir towards diŠerent residual values during subsequent ML. With the TESRA type, Ds v decays eventually totally and the strength during ML at constant ·e is essentially independent of ·e. With the Combined type, Ds v decays with e ir like the TESRA type, but it does not decay totally. So, the strength during ML at constant ·e increases with ·e like the Isotach type. With the P & N type, found latest, a positive value of Ds v decays towards a negative value. So, the strength during ML at constant ·e decreases with an increase in ·e. The viscosity type tends to change with e ir : e.g., from Isotach toward TESRA and from TESRA toward P & N. A general mathematical expression that can describe these four viscosity types and transitions among them is proposed. Numerical simulations of typical drained triaxial compression tests of geomaterials based on a non-linear three-component model incorporating the general expression of the viscous stress are presented. The viscosity type is controlled by at least, grading characteristics and particle shape.

It is shown that creep failure of geomaterials can be simulated by a non-linear three-component elasto-viscoplastic model. The model is described in the case of a single stress variable and the isotach viscous property type, although the model can be applied to more general three-dimensional stress conditions and viscous property types other than isotach. Various trends of viscous behaviour, including stress relaxation and creep deformation with and without creep failure, are illustratively simulated to show that creep failure is one specific aspect of the whole viscous behaviour that can be simulated by a single model. Creep failures observed in drained triaxial compression tests on compacted moist cement-mixed gravelly soil and saturated soft clay are simulated.

e potential and efficiency of using rice husk ash (RHA) to add up or partially replace Portland cement in deep cement mixing technique are examined. A series of unconfined compression tests on cement-RHA-stabilized clay are conducted to investigate the influence of RHA on the mixture properties. Special attention is paid to its efficiency for increasing the strength by partial cement replacement to obtain high-strength soil cement, and it is compared with fly ash. Test results indicate that up to 35% of RHA could be advantageously added up to enhance the strength if the cement content in the mixture is larger than 10%. e RHA enhances the strength of cement-admixed clay by larger than 100% at 28 days. For curing time of 14 and 28 days, the RHA exhibits higher efficiency on Portland cement replacement when the cement and overall cementitious contents are not less than 20 and 35%, respectively. e optimum condition for high-strength mixture is achieved when RHA is added to the 20% cement content mixture. When compared with fly ash of similar grain size, the efficiency of RHA is higher when the content to be added is greater than 15%. is indicates the suitability of RHA for use in high-strength soil-cement.

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