Laboratory Investigation on the Effect of Microsilica Additive on the Mechanical Behavior of Deep Soil Mixing Columns in Saline Dry Sand

Abstract

Since loose and salty subgrades consider as problematic barriers while constructing new transportation infrastructures such as railway tracks and roads are required, the current study aims to find a solution to stabilize these kinds of subgrades using the deep soil mixing (DSM) technique and micro silica additive. In the present study a series of experimental DSM columns were executed in a salty sand-filled chamber utilizing a laboratory scale DSM apparatuses. In the first step, by adding three salt percentages of 5, 10 and 20 into the original sand, four different sandy subgrades with a relative density of 70% were prepared. Considering three percentages of 10, 15 and 20 for micro silica additive, the water-to-cement ratio of 1, salt percentages of 0, 5, 10 and 20 totally 150 sand-cement columns were constructed in the lab environment. In continuation, unconfined compression strength (UCS) and elasticity modulus of all capped DSM columns have been determined and interpreted using scanning electron microscope (SEM) images at three ages of 7,14 and 28 days. The results indicated that increasing the salinity of subgrade soil from 0 to 20% resulted in a falling UCS and Young module by 28 and 21% for 28-days specimens. Furthermore, as a solution, adding micro silica in cement-water grout up to 15% resulted in enhancing mechanical characteristics of the DSM columns. So that adding 15% microsilica caused a 21 and 42% increase in UCS and elasticity modulus of 28-days samples respectively, executed in subgrade with 20% salt.

Improving the Properties of Saline Soil Using a Deep Soil Mixing Technique

“…Therefore, extensive literature reviews on DM operation characteristics have been conducted to define the acceptable values of auger penetration, withdrawal rate, and rotation speed. In their study, (Esmaeili et al, 2021 andFrikha et al, 2017) [10,23] selected vertical translation while penetration and withdrawal ranged from (250-1000 mm/min) and rotation rate ranged from 15 to 60 rpm. The selected rotation rates for some of these studies is corresponded to the order of magnitude utilized by AFNOR NF EN 14679 standard-December 2005.…”

“…Jung et al [9] presented the first and the only study which employed a wet DSM technique for saline soil in the UAE to reduce settlement and improve the bearing capacity of a shallow foundation as an alternative to traditional piling. The employed binder in DSM is typically cement; however, it may also occasionally be fly ash, geopolymers, microsilica, or glass powder [9][10][11][12][13][14]. The environmental impact of geotechnical engineering applications, such as grouting and soil stabilization using cement, is very harmful due to high CO 2 emissions [15].…”

“…Many studies on DSM techniques reported a traditional mechanical mixing of the soil, binder and water that are not consistent with the field methods where the soil and binder mixtures are poured into molding cylinders [11][12][13]. Very few studies, such as Esmaeili et al [10] and Frikha et al [23], presented a scaledlaboratory apparatus similar to the field deep soil mixing techniques where a vertical and rotating auger mixed the binder and the soil.…”

“…Esmaeili et al [10] presented a study treating a loose salty dry sand subgrade (artificial subgrade) with different salt percentages (0, 5, 10 and 20% salt) using microsilica additives. Three percentages micro-silica additives, 10, 15 and 20%, were added to a cement solution with a w/b ratio equal to 1.…”

“…Both studies by Esmaeili et al [10] and Frikha et al [23] applied a DSM technique in the laboratory for artificial saline dry sand and organic soft clay with 163% water content, respectively. The physical and chemical properties of the soil, including its grain size distribution, water content, Atterberg limits, clay mineral type, cation exchange capacity, soluble silica and alumina content, pore water pH, and organic matter content, first have an impact on the properties of the treatment applicability and then on the treated soil properties if successful [24].…”