Influence of colloidal silica grout on liquefaction potential and cyclic undrained behavior of loose sand

This paper reports results of a full-scale field test to assess the performance of dilute colloidal silica stabilizer in reducing the settlement of liquefiable soil. Slow injection methods were used to treat a 2-m-thick layer of liquefiable sand. Eight injection wells were installed around the perimeter of the 9-m-diameter test area and 8% by weight colloidal silica grout was slowly injected into the upper 2 m of a 10-m-thick layer of liquefiable sand. A central extraction well was used during grout injection to direct the flow of the colloidal silica towards the center of the test area. Details of the field injection are described. Subsequently, the injection wells were used to install explosive charges and liquefaction was induced by blasting. After blasting, approximately 0.3 m of settlement occurred versus 0.5 m of settlement in a nearby untreated area. The mechanism of improvement is thought to be bonding between the colloidal silica and the individual sand particles; the colloidal silica gel encapsulates the soil structure and maintains it during dynamic loading.

Full-Scale Field Testing of Colloidal Silica Grouting for Mitigation of Liquefaction Risk

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. It is based on the concept of slowly injecting colloidal silica at the edge of a site with subsequent delivery to the target location using natural or augmented groundwater flow. Colloidal silica is an aqueous dispersion of silica nanoparticles that can be made to gel by adjusting the pH or salt concentration of the dispersion. It stabilizes liquefiable soils by cementing individual grains together in addition to reducing the hydraulic conductivity of the formation. Centrifuge modeling was used to investigate the effect of colloidal silica treatment on the liquefaction and deformation resistance of loose, liquefiable sands during centrifuge in-flight shaking. Loose sand was successfully saturated with colloidal silica grout and subsequently subjected to two shaking events to evaluate the response of the treated sand layer. The treated soil did not liquefy during either shaking event. In addition, a box model was used to investigate the ability to uniformly deliver colloidal silica to loose sands using low-head injection wells. Five injection and two extraction wells were used to deliver stabilizer in a fairly uniform pattern to the loose sand formation. The results of the box model testing will be used to design future centrifuge model tests modeling other delivery methods of the grout.

Stabilization of Liquefiable Soils Using Colloidal Silica Grout

Laboratory investigation and field evaluation of loess improvement using nanoclay – A sustainable material for construction

Method for carrying out well construction, repair and/or abandonment operations using an addition-curing silicone formulation, in particular for forming a permanent plug in a well bore or in one or more subterranean formations penetrated by the well bore by placing a mixture of cement and an addition-curing silicone formulation in said one or more subterranean formations or in said well bore at a desired location therein or placing an addition-curing silicone formulation on top of an existing non-gas tight plug and allowing the silicone formulation to set thereby producing a gas tight plug.

Compositions for use in well construction, repair and/or abandonment

Colloidal silica is a low-viscosity chemical grout. Samples of grouted sand were made by pouring sand into liquid grout in molds, with the grout diluted to concentrations ranging from 5 to 27% silica by weight. The unconfined compressive strength of the grouted sand, measured after 7 days, was proportional to the silica concentration, up to a maximum of 400 kPa. The hydraulic conductivity of the grouted sand decreased with increasing silica concentration in a nearly log-linear manner down to a minimum of 2 × 10−9 cm/s, and was below 1 × 10−7cm/s for grouts with 7.4% silica or more. Inclusion of 5% volumetric saturation of organics (tetrachloroethene, CCl4, or aniline) in the samples had little effect on the strength or hydraulic conductivity. Samples were immersed in test liquids (organics, HCl diluted to pH 3, distilled water saturated with organics, and distilled water control) for up to 1 year. All samples increased in strength except for those immersed in aniline; samples immersed in water saturated w...

/pdf/effect-of-dilution-and-contaminants-on-sand-grouted-with-18uc1ovb5m.pdf

Effect of Dilution and Contaminants on Sand Grouted with Colloidal Silica

A method for formation of subsurface barriers using viscous liquids where a viscous liquid solidifies at a controlled rate after injection into soil and forms impermeable isolation of the material enclosed within the subsurface barriers. The viscous liquid is selected from the group consisting of polybutenes, polysilotanes, colloidal silica and modified colloidal silica of which solidification is controlled by gelling, cooling or cross-linking. Solidification timing is controlled by dilution, addition of brines, coating with alumina, stabilization with various agents and by temperature.

Method for formation of subsurface barriers using viscous colloids

A first stage field injection of a new generation of barrier liquids was successfully completed. Two types of barrier liquids, colloidal silica (CS) and polysiloxane (PSX), were injected into heterogeneous unsaturated deposits of sand, silt, and gravel typical of many of the arid DOE cleanup sites and particularly analogous to the conditions of the Hanford Site. Successful injection by commercially available chemical grouting equipment and the tube-a-manchette technique was demonstrated. Excavation of the grout bulbs permitted visual evaluation of the soil permeation by the grout, as well as sample collection. Both grouts effectively permeated all of the formation. The PSX visually appeared to perform better, producing a more uniform and symmetric permeation regardless of heterogeneity, filling large as well as small pores and providing more structural strength than the CS. Numerical simulation of the injection tests incorporated a stochastic field to represent site heterogeneity and was able to replicate the general test behavior. Tiltmeters were used successfully to monitor surface displacements during grout injection.

/pdf/a-field-test-of-a-waste-containment-technology-using-a-new-714i1m3a8f.pdf

A Field Test of a Waste Containment Technology Using a New Generation of Injectable Barrier Liquids

In this paper the authors report laboratory work and numerical simulation done in support of development and demonstration of injectable barriers formed from either of two fluids: colloidal silica or polysiloxane. Two principal problems addressed here are control of gel time and control of plume emplacement in the vadose zone. Gel time must be controlled so that the viscosity of the barrier fluid remains low long enough to inject the barrier, but increases soon enough to gel the barrier in place. During injection, the viscosity must be low enough to avoid high injection pressures which could uplift or fracture the formation. To test the grout gel time in the soil, the injection pressure was monitored as grouts were injected into sandpacks. When grout is injected into the vadose zone, it slumps under the influence of gravity, and redistributes due to capillary forces as it gels. The authors have developed a new module for the reservoir simulator TOUGH2 to model grout injection into the vadose zone, taking into account the increase of liquid viscosity as a function of gel concentration and time. They have also developed a model to calculate soil properties after complete solidification of the grout. The numerical model has been used to design and analyze laboratory experiments and field pilot tests. The authors present the results of computer simulations of grout injection, redistribution, and solidification.

/pdf/injectable-barriers-for-waste-isolation-47tkwz4ota.pdf

Injectable barriers for waste isolation

Colloidal silica (CS) is a low-viscosity liquid that can be made to gel by addition of brine. This property allows it to be injected into, or mixed with, soil, so that after gelling the colloidal silica blocks the pore space in the soil and forms a barrier to the flow of contaminated groundwater or non-aqueous liquids (NAPLs). Gelled-in-place CS was first studied for the petroleum industry and later for protecting groundwater quality. Noll investigated the use of colloidal silica diluted so that its solids content was reduced from 30% (a typical nominal value for material as delivered) to values as low as 5%. The more dilute colloids could still be made to gel, although more slowly, and the resulting gel was weaker. Because the proposed application of colloidal silica grout involves emplacing it in the subsurface by permeation, jet grouting, or soil mixing where its role as a barrier will be to resist flow of contaminants, the effects of these contaminants on the properties of the grouted soil is also of interest. This work comprised four tasks. In Task 1, samples of grouted sand were prepared with a range of CS dilutions, for measurement of hydraulic conductivity and unconfined-compressive strength. In Task 2, these properties were measured on samples of grouted sand that incorporated 5% volumetric saturation of NAPLs. In Task 3, samples, prepared without any contaminants, were immersed in contaminant liquids and tested after 30 and 90 days. Task 4 was added because NAPL contamination in the samples of Tasks 2 and 3 impelled modifications in the test methods, and comparison of the results of Task 2 and Task 1 suggested that these modifications had introduced errors. In Task 4, samples were tested both ways, to confirm that in Tasks 2 and 3 strength was underestimated and hydraulic conductivity was overestimated. Despite the existence of these known systematic errors, the inclusion of control samples in Tasks 2 and 3 permits conclusions to be drawn from these data.

/pdf/effect-of-dilution-and-contaminants-on-strength-and-atueo6plp5.pdf

J.A. Apps

Papers

Effect of Dilution and Contaminants on Sand Grouted with Colloidal Silica

Method for formation of subsurface barriers using viscous colloids

A Field Test of a Waste Containment Technology Using a New Generation of Injectable Barrier Liquids

Injectable barriers for waste isolation

Effect of dilution and contaminants on strength and hydraulic conductivity of sand grouted with colloidal silica gel