Simulation of seismic response of passively stabilised sand

Konstantinos I Andrianopoulos,Georgia I Agapoulaki,Achilleas G Papadimitriou

doi:10.1680/jgere.16.00003

Konstantinos I Andrianopoulos, Georgia I Agapoulaki + Show 1 more

Open Access

https://doi.org/10.1680/jgere.16.00003

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Abstract

Passive (site) stabilisation is a novel technique for mitigating the risk of seismic liquefaction in the non-cohesive foundation soil of existing structures. It comprises the low-pressure injection (in the soil pores) of colloidal silica grout, a very low-viscosity material that transforms into a firm gel after a well-controlled time. This gelation improves macroscopically the mechanical response of the soil skeleton–pore fluid system. Owing to the lack of a dedicated constitutive model, this paper explores the potential of using existing constitutive models for sands for simulating the cyclic response of sands (passively) stabilised with colloidal silica. Hence, a well-established plasticity model for sands (named NTUA-Sand) is used for the simulation of pertinent element tests and of a dynamic centrifuge test modelling the seismic response of a stabilised sand layer. It is used in coupled analyses either after recalibration for simulating the stabilised sand response or in combination with a reduced pore fluid modulus. The latter numerical approach simulates the seemingly compressible colloidal silica in the soil pores, instead of incompressible water, and successful comparisons of its phenomenological simulations with test data underline its potential for use in practice.

Highlights

For developed sites, the large majority of conventional liquefaction mitigation techniques cannot be applied, due to vibration
Owing to the lack of a dedicated constitutive model, this paper explores the potential of using existing constitutive models for sands for simulating the cyclic response of sands stabilised with colloidal silica
The novelty of the method is its requirement of low-pressure injection, since colloidal silica initially has a viscosity slightly higher than that of water (

Summary

Introduction

The large majority of conventional liquefaction mitigation techniques cannot be applied, due to vibration Simulating stabilisation by focusing on its effects on the pore fluid This section evaluates the simulation of stabilisation, by enforcing a reduction in the fluid bulk modulus K, as per Equation 4 This is performed in terms of horizontal accelerations, where the recording near the ground surface (depth of 2 m) from the centrifuge test on stabilised sand (Gallagher et al, 2007b) is compared with pertinent simulations performed with NTUA-Sand after adopting different values of the denominator n, namely n = 50 (Figure 16(a)), n = 500 (Figure 16(b)), n = 1000 (Figure 16(c)) and n → ∞ (Figure 16(d)) to simulate the fully drained conditions – that is, conditions that do not appear in nature, but are considered here only for comparison purposes.

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