Scientifi c Review – Engineering and Environmental Sciences (2019), 28 (2), 235–243 Sci. Rev. Eng. Env. Sci. (2019), 28 (2) Przegląd Naukowy – Inżynieria i Kształtowanie Środowiska (2019), 28 (2), 235–243 Prz. Nauk. Inż. Kszt. Środ. (2019), 28 (2) http://iks.pn.sggw.pl DOI 10.22630/PNIKS.2019.28.2.22 Anna MISZKOWSKA Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences – SGGW A study on soil-geotextile interaction using gradient ratio tests Key words: nonwoven geotextile, soil, gra- Kim, 2016; Miszkowska & Koda, 2017; dient ratio, clogging, permeability, fi lter Palmeira & Trejos Galvis, 2018). A geotextile performs the fi ltration function by limiting migration of soil Introduction particles across its plane, while allow- ing relatively unrestricted liquid fl ow Nonwoven geotextiles are made of through the fi lter over a projected service randomly or directionally orientated fi - lifetime of the application under consid- bres, fi laments or other element, chemi- eration. Filtration function also provides cally and/or thermally and/or mechani- separation benefi ts (Giroud, 1981; Koda, cally bonded (PN-EN ISO 10318). They Szymański & Wolski, 1989; Koerner, have been widely used as fi lters in geoen- 2012). Figure 1 shows that a geotextile vironmental and geotechnical works for allows passage of water from a soil mass over 50 years. This type of geosynthetics while preventing the uncontrolled migra- gathers special features that commonly tion of soil particles. lead to applications with faster execution It is also worth mentioning that when and lower costs in comparison with tradi- a geotextile fi lter is placed adjacent to tional, granular fi lters. What is more, the a base soil, between the natural soil use of nonwoven geotextiles can bring structure and the structure of the geotex- benefi ts for environment due to less emis- tile arises a discontinuity, which allows sion of harmful gases to the atmosphere, some soil particles to migrate through the less water consumption and energy and geotextile under the infl uence of seepage more environmentally friendly construc- fl ows. It is important that a condition of tion procedures, for instance (Heibaum, equilibrium is established at the soil- 2014; Koerner & Koerner, 2015; Yoo & -geotextile interface as soon as possible A study on soil-geotextile interaction using gradient ratio tests 235 FIGURE 1. Geotextile fi lter (Wesolowski, Krzywosz & Brandyk, 2000) to prevent soil particles being piped for ging. Physical clogging is the accumula- an indefi nite period through the geosyn- tion of soil particles within the openings thetic. At equilibrium, three zones may of a geotextile, thereby reducing its hy- be identifi ed: the undisturbed soil, a soil draulic conductivity (Fig. 2). Clogging layer, and a bridging layer (Wesolowski can be also caused by chemical and/or et al., 2000; Shukla, 2016; Miszkowska, biological processes (Stępień, Jędryszek Lenart & Koda, 2017). & Koda, 2012; Koda, Miszkowska & The successful use of a synthetic Stępień, 2016; Miszkowska, Koda, fi lter is dependent on knowledge of the Krzywosz, Król, & Boruc, 2016; Sabiri, interaction between the base soil and the Caylet, Montillet, Le Coq & Durkheim, geotextile that is complex because of the 2017; Fatema & Bhatia, 2018). large number of parameters involved. One of the methods to evaluate com- The essential properties to be determined patibility between a granular base mate- are particle-size distribution and perme- rial and a geotextile fi lter is to use the ability of soil and water permeability gradient ratio (GR) test (Calhoun, 1972; normal to the plane, characteristic open- Palmeira, Beirigo & Gardoni, 2000; Caz- ing size, the number of constrictions in zuffi et al., 2016). case of nonwoven (Giroud, 2010; Caz- Fannin, Vaid, and Shi (1994) de- zuffi , Moraci, Mandaglio & Ielo, 2016). fi ned a modifi ed gradient ratio using What is more, nonwoven geotextiles a port located 8 mm above the geotextile are the fi rst in contact with soil in fi lters layer. Gardoni (2000) proposed a defi ni- applications, the design must be pre- tion of GR using a port 3 mm above the pared to avoid the negative phenomenon geotextile fi lter to evaluate soil-geotex- causing a decrease of the permeability tile interaction closer to the soil-fi lter in- of the geotextile fi lter in time like clog- terface. However, the defi nition of is in 236 A. Miszkowska FIGURE 2. Physical clogging (Shukla, 2016) both cases is the same as that proposed The main properties of the geotextile are by ASTM. summarised in Table 1. To avoid clogging, gradient ratio The soil used in gradient ratio test was should be less than 3 (Haliburton & classifi ed as silty sand (siSa). According Wood, 1982; Carroll, 1983). But accord- ing to ASTM D5101-12, a gradient ratio TABLE 1. Properties of the geotextile tested (own greater than 1.0 indicates system clog- and manufacturer studies) ging or restriction at or near the surface Properties Value of the geotextile. tensile strength – machine 25 The main aim of this study was to direction [kN·m–1] present the laboratory gradient ratio test tensile strength – cross machine 25 results to evaluate soil-geotextile inter- direction [kN·m–1] action. The following hypothesis can be elongation at maximum load 50 proposed: gradient ratio, GR is changing – machine direction [%] with time and apart from gradient ratio Mechanical elongation at maximum load 60 also soil-gradient ratio, SGR should be – cross machine direction [%] determined to carry out a detailed analy- dynamic perforation resistance 12 sis of soil-geotextile interactions. [mm] water permeability normal to the 55 plane [l·m–2·s–1] Material and methods characteristic opening size – O 90 65 Hydraulic [μm] In this study nonwoven geotextile, thickness under 2 kPa [mm] 1.6 needle punched and made of continu- weight [g·m–2] 300 ous polypropylene fi bres, was tested. Physical number of constrictions 22 A study on soil-geotextile interaction using gradient ratio tests 237 to Kenney and Lau (1985) method the nical Engineering at Warsaw University assessment of internal stability soils, the of Life Sciences – SGGW using ASTM tested soil was internally unstable. The modifi ed apparatus. Piezometers (6 and soil properties are shown in Table 2. 7) were installed to obtain additional pressure measurements in the layer of TABLE 2. Soil properties soil situated close to nonwoven geotex- Properties Value tile layer. Figure 3 shows a detailed sche- matic view of the device. Soil particle d10 [mm] 0.012 Soil particle d [mm] 0.04 At the beginning of test, the soil was 15 dried (in 105°C for 24 h) and sieved Soil particle d [mm] 0.12 30 through a two-millimeter mesh. Then, Soil particle d50 [mm] 0.18 the soil sample was placed on the non- Soil particle d85 [mm] 0.27 woven geotextile sample. After that, wa- Coeffi cient of curvature – Cc [-] 6 ter was delivered into the apparatus from Coeffi cient of uniformity – CU [-] 16.7 bottom to top for 24 h. In the next step Coeffi cient of soil permeability – k of the test, fl ow direction was changed s 0.000079 [m·s–1] (Fig. 4). When the water fl ow reached dn – the soil particle diameter that n% of all soil a steady condition, the pressure of indi- particles are fi ner by weight. vidual piezometer (Δh), temperature of the water fl ow (T), volume of the fl ow (V) The gradient ratio was determined in and time of the fl ow (t) were measured the laboratory of Department of Geotech- for each of the hydraulic gradients at 1.0, FIGURE 3. Scheme of gradient ratio test apparatus: g – nonwoven geotextile, Ln – distance be- tween piezometer n-th and the bottom of geotextile, hn – the piezometer reading for n-th piezometer (Wojtasik, 2008) 238 A. Miszkowska • zone 4.5–6 (17 mm layer of soil within the distance from 8 to 25 mm above nonwoven geo- textile between piezometers 4.5 and 6), • zone 2.3–4.5 (50 mm layer of soil within the distance from 25 to 75 mm above nonwoven geotex- tile between piezometers 2 and 3 as well as 4 and 5). The value of the gradient ratio can be generally defi ned as (ASTM D-5101-12): iLG GR is where: GR – the gradient ratio, i – the hydraulic gradient across a soil FIGURE 4. Front view of gradient ratio test de- LG vice (photo by the author) thickness (L) and the geotextile, is – the reference hydraulic gradient in 2.5, 5.0, 7.5 and 10.0 until the change of the soil, measured in a region away from these parameters was not observed. The the geotextile (calculated for the segment test was done in triplicate. of the soil specimen between 25 and The following piezometer readings 75 mm above the geotextile fi lter). were taken in individual zones: In the presented test, the gradient ra- – for soil-geotextile: tio in soil-geotextile system was calcu- • zone 7–8 (geotextile and 4 mm lated according the formula: layer of soil between piezom- 'h L eters 7 and 8), GR 4.5 8 24 Lh • zone 6–8 (geotextile and 8 mm 42.34.5' layer of soil between piezometrs 6 and 8), where: • zone 4.5–8 (geotextile and 25 GR – the gradient ratio, mm layer of soil between pi- Δh4.5–8 – the difference manometer read- ezometers 4 and 5 to 8), ings between average reading of 4 and – for soil: 5 piezometers and 8 piezometer [mm], • zone 6–7 (4 mm layer of soil L4 – the distance between piezometer 4 within the distance from 4 to and the bottom of geotextiles [mm], 8 mm above nonwoven geotextile L2–4 – the distance between piezometers between piezometers 6 and 7), 2 to 4 [mm], A study on soil-geotextile interaction using gradient ratio tests 239 Δh2.3–4.5 – the distance in manometer ning of the tests (GRs, SGR17s; where: readings between average reading of 2 s – start) as well as when the water and 3 piezometers and average reading fl ow reached a steady condition (i.e.