Effects of Colloidal Silica Grouting on Geotechnical Properties of Liquefiable Soils: A Review

Abstract

Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in different branches of civil engineering. Many studies have recently been performed to investigate the potential of CS in improving the mechanical behavior of cohesionless soils and mitigating the risk of seismic liquefaction in urbanized areas. CS grout is chemically and biologically inert and, when injected into a subsoil, it can form a silica gel and stabilize the desired soil layer, thus representing an attractive, environmentally friendly alternative to standard chemical grouting techniques. This paper firstly describes the characteristics of CS grout, the gelation process and the main features of the behavior of the pure gelled material. The grout delivery mechanisms through porous media are then explained, pointing out the crucial issues for practical application of CS grouting. All the grouting-induced effects on the soil behavior, which have been investigated by laboratory tests on small-sized soil elements, are reviewed, including the modifications to soil strength and stiffness under both static and seismic loading conditions, to soil compressibility and hydraulic conductivity. Published results from physical model tests and in situ applications are also presented. Finally, some aspects related to the mechanism of soil improvement are discussed. A critical discussion of each topic is presented, drawing particular attention to the controversial or not yet fully examined aspects to which future research on colloidal silica grouting should be directed.

Effects of initial static shear stress on cyclic behaviour of sand stabilised with colloidal silica

“…However, as shown in representative plots for both materials (untreated and stabilised, Figs. 4,5,6,7,8,9), the way both the axial strain and the pore pressure build-up develop shows distinctive features depending on CS W . For this reason, both the axial strain and the pore water pressure response are more in-depth analysed in the following Sections.…”

“…by natural or augmented groundwater flow). This mixture becomes a silica gel after a certain time; once gelled among the soil grains, the gel modifies the soil mechanical response, increasing the liquefaction resistance of the stabilised soil [4,6,11]. The main features of colloidal silica grouting, inferred from the relevant literature, can be summarised as follows:…”

“…Although laboratory investigations have been thoroughly carried out to analyse the cyclic response of soils stabilised by CS, none of the experimental studies deals with the effects of anisotropic initial stress on the cyclic behaviour of stabilised sand [4]. On the other hand, in most in situ conditions a soil element is subjected to an initial anisotropic stress state [49,55,57].…”

Innovative Ground Improvement with Chemical Grouts: Potential and Limits of Partial Saturation with Polymers

“…Comparable values are determined in experimental laboratory tests by Chhun et al (2019) on a grouted silty sand. For colloidal silica grouts the unconfined compressive strength (UCS) is about 0.3-0.5 MPa (Persoff et al 1999;Kutzner 1991;Ciardi et al 2021). In particular, the review by Ciardi et al (2021) on studies of colloidal silica grouts indicates an increase in load-bearing capacity with increasing curing time.…”

“…For colloidal silica grouts the unconfined compressive strength (UCS) is about 0.3-0.5 MPa (Persoff et al 1999;Kutzner 1991;Ciardi et al 2021). In particular, the review by Ciardi et al (2021) on studies of colloidal silica grouts indicates an increase in load-bearing capacity with increasing curing time. The value range of about 0.3-0.5 MPa represents a curing time of 7 to 30 days, which is comparable to the samples of this research work.…”