Geotextile Separators Research Articles

Evaluation of intermixing application of geotextiles at subgrade-base interface using accelerated pavement testing

This study focuses on identifying and quantifying the potential benefits of a geotextile separator in flexible pavements placed at the interface between a granular base and an underlying soft subgrade with high water content and a granular base. While benefits of using separators in roadway applications have been generally acknowledged, quantification of such benefits has been limited. The evaluation in this study is based on the results from two accelerated pavement tests using a one-third scale Model Mobile Load Simulator (MMLS3) device. Both models have identical configuration except that a non-woven geotextile was placed at the interface between the subgrade and base layer to serve as a separator in one of the pavement models. The subgrade material used in this study involved a soil mixture containing fifty percent kaolin and fifty percent Monterey sand #30. The base material was an angular AASHTO #8 aggregate. Additionally, an instrumentation program was implemented involving sensors to track the earth pressure distribution, the subgrade excess pore pressures generation, the change in moisture content of the subgrade and the horizontal particle displacement of the base layer. During exhumation of the pavement models, base and subgrade samples were collected to quantify the levels of intermixing. The results of the APT were quantified in terms of the traffic benefit ratio (TBR), which was as high as 6.4 for 25.4 mm rutting showing the significant benefit of using a non-woven geotextile as a separator to extend the design life of flexible pavements. The differences in performance observed between the control and the separation pavement models were found to correlate well with the amount of intermixing observed at the interface between subgrade and base layers. A series of soil columns were tested using cyclic loading to extend the intermixing analysis to different subgrade types with different fine content and geotextiles. The study concluded that higher levels of fine contain in the subgrade would lead to higher levels of intermixing. A correlation between the pore size of the geotextiles and the pumping of subgrade into the base was identified suggesting that smaller pore size would mitigate the pumping intermixing mechanism more efficiently.

Geotextile filtration opening size under tension and confinement

Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested.

Physical model study on the clay–sand interface without and with geotextile separator

In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice.

Reduction of subgrade fines migration into subbase of flexible pavement using geotextile

Pumping in pavement is defined as traffic-induced migration of saturated subgrade fines into overlying granular layers or onto the surface of the pavement, negatively impacting the performance and service life of the pavement. The objective of this study was to assess the capability of geotextile as a separation and filtration layer in reducing subgrade fines migration. A one-third scale Model Mobile Load Simulator, an accelerated pavement testing device, was used to simulate the cyclic traffic loading on a scaled model of a flexible pavement. The results from three scaled pavement tests were compared to evaluate the effectiveness of geotextile separation and filtration in reducing subgrade fines migration. The three tests had identical configurations, except that a geotextile layer was placed at the interface of subgrade and subbase in one of the tests. The lab testing revealed that, under cyclic traffic conditions, the migration of subgrade fines into subbase was significant. However, using a geotextile at the subgrade-subbase interface significantly reduced the subgrade pumping. At the end of the test, the fines that migrated to the subbase, based on % mass of subbase, were 6.39% in the tests without geotextile and 1.81% in the test with geotextile. An approximately 30% reduction was observed in the amount of pavement rutting when using geotextile at the top of the subgrade. The subgrade soil migration in mass percentage increased with the traffic loading cycles, and more migration occurred in the bottom half than in the top half of the subbase. The study concludes that geotextile can be used as an effective means to reduce pumping of subgrade fines in pavement by providing both separation and filtration.

Model Studies on Encased Fly Ash Column–Geocell Composite Systems in Soft Clay

This study narrates the use of postconsumer waste plastic water bottles for developing a new type of encasement to confine fly-ash columns fully penetrated in soft clay. Geocell-reinforced fly-ash beds along with a jute geotextile separator were also placed over the fly-ash columns, while the cellular mattresses were also made of the same type of plastic water bottles. A series of systematic model tests were carried out on encased fly-ash columns, geocell composite systems, and encased fly-ash column–geocell composite systems in soft clay, while the three different systems produced improved footing capacity of about 5-fold, 8.5 times, and 12-fold, respectively, as compared to the untreated clay bed. It was observed that with the increase in mattress height over the encased fly-ash column, the contribution from the encased column decreased accompanying the higher contribution from the geocell mattress in the overall footing capacity over the encased fly-ash column–geocell composite systems. Moreover, model tests were performed on groups of three and four end-bearing encased fly-ash columns in triangular and square patterns, respectively, to determine the efficacy of the proposed plastic bottle encasement in a group column situation. The group of four columns showed better footing capacity than that over single columns and the group of three columns.

Numerical Analyses on Cellular Mattress–Reinforced Fly Ash Beds Overlying Soft Clay

AbstractThis paper presents the results of large-scale numerical modeling of cellular mattress–reinforced fly ash beds overlying soft clay using a finite-element program. The cellular mattress was a honeycomb structure consisting of interconnected multiple circular cells. The influence of the height, diameter, and tensile stiffness of the cell and the width of the entire mattress on the pressure-settlement response of footing, surface deformation during footing settlement, and mobilization of hoop tension in the cell walls are illustrated. Results from the numerical analyses indicate an improvement in footing capacity of approximately1.4 times greater over fly ash bed by inclusion of a single geotextile separator representing jute geotextile in between the fly ash bed and underlying clay. The cellular mattress–fly ash composite bed produced an approximately sevenfold increment in the footing capacity compared with the unreinforced fly ash bed both in presence of the jute separator. The mattress-reinforced...

Model Studies on Geocell-Reinforced Fly Ash Bed Overlying Soft Clay

AbstractThis paper addresses the effectiveness of geocell mattress prepared with waste plastic bottles with fly ash as a filling material overlying soft clay bed through laboratory model tests. The test beds were subjected to loading by means of a square rigid steel plate as a footing. The effect of height and width of geocell mattress as well as basal bamboo geogrid underneath geocell mattress on overall performance of the system in terms of footing pressure, settlement, and the adjacent surface deformation (heave/settlement) has been systematically studied through a series of tests. Test results indicate around twofold increases in the bearing pressure by placing a jute geotextile separator beneath the unreinforced fly ash bed, whereas reinforcing the fly ash bed with geocell mattress in presence of a basal bamboo geogrid and jute geotextile separator can produce sevenfold increases in the footing pressure. Inclusion of a basal bamboo geogrid improves overall behavior of the reinforced bed. No surface d...

Field investigation of granular base rehabilitation project incorporating a woven geotextile separation layer, sand, and cement stabilization

Full-depth reclamation and cement strengthening has been used successfully to dry and strengthen granular pavements. However, some thin pavements fail due to severe wetting-up of the subgrade, thus requiring additional substructure strengthening and (or) drainage systems. This research investigated the laboratory characterization and in situ field mechanical behaviour of full-depth reclaimed and cement-stabilized granular materials in conjunction with a woven geotextile and sand drainage system. This research showed that the integration of cement-stabilized reclaimed granular materials with a geotextile separation layer and sand drainage system significantly improved the mechanical primary response and climatic durability properties of the reclaimed road structure. The cement-stabilized and geotextile separation–drainage system improved the structural asset management test results from a completely failed road structure to primary plus load-carrying capacity. This research also demonstrated an improved correlation between the mechanistic material constitutive properties of the stabilized aggregate to the end-product field structural assessment relative to conventional California bearing ratio and unconfined compressive strength test results.

Geotextile Separators for Dust Suppression in Unbound (Gravel) Roads

Dust is a health concern because of its potential to contain respirable particles, especially particles less than 10 microns in diameter (PM10). It is also a nuisance issue for residents living in the vicinity of unbound, unsealed (gravel) roads. Numerous techniques are used in attempts to reduce the dust generated from unbound roads, but all have limitations. Anecdotal evidence suggests that dust from unbound roads can be reduced for roads that incorporate a geotextile separator. A program to document the effect of the geotextile separators quantitatively is under way, with several test sections in central Missouri. A test section including a nonwoven, needle-punched geotextile; a non-woven, spun-bonded geotextile; and a new aggregate-only layer was installed; dust measurements were made over a 6-month period, during which the road experienced more than 3,600 vehicle passes. Dust levels were lowest immediately following the placement of new aggregate for the unbound layer and increased with time (traffic passes). Initially the sections containing a geotextile separator produced slightly less dust than the control (no geotextile) section. After 6 months of service, dust levels from the geotextile and control sections were similar, but the percentages of fines in the unbound layer above the geotextiles were about one-half that in the control section. Geotextile separators are likely to reduce dust for unbound roads when the source of particulate is fines migrating from the subgrade into the unbound layer. When the fines are developed because of degradation of the aggregate in the unbound layer, geotextile separators may be less effective in reducing dust from the roadway.

Performance of Geotextile Separators Five Years after Installation

During the reconstruction of a state highway in 1991, a full-scale test section was established at a site with a history of poor pavement performance, most likely because of a soft silty clay subgrade, high ground-water table, and heavy logging truck traffic. Five different separator geotextiles and a soil-only control section were installed in each lane. Excavations were made in the test section 5 years after installation, and samples of geotextiles, subgrade, and base course materials were exhumed for visual observation and laboratory testing. In addition, in situ soil tests were performed on the exposed subgrade soils. This paper summarizes these observations and test results. Although some fines from the subgrade had migrated through the geotextiles into the bottom of the base course, there was no evidence after 5 years of any adverse effect on the pavement itself. Minor geotextile damage that apparently occurred during construction had little effect on the pavement performance. In all of the sections with geotextiles, the subgrade soils were found to have consolidated significantly in comparison with the soil-only sections. Overall, the geotextiles performed their intended function well.

Use of a geotextile separator to minimize intrusion of clay into a coarse stone layer

Experiments were conducted to study the effectiveness of a geotextile separator for minimizing the intrusion of a compacted clayey till into a layer of coarse stone under applied pressures. For comparison purposes, intrusion was also studied for the case of a graded granular filter/separator and in the absence of a filter/separator between the soil and the stone. Both the selected geotextile and graded granular filter efficiently minimized intrusion of the soil mass into the stone void space, and the actual quantity of fines which passed through the geotextile or granular filter/separator was insignificant with respect to the void space in the stone. It is considered that most of the fines passed through the geotextile due to compaction during installation of the clayey soil in the test cell and not due to the applied pressures. In the absence of a filter-separator, a significant amount of clay soil intruded into the voids of the stone layer. The results of this study suggested that both the geotextile and graded granular filter/separator could be successfully used in practice, however the geotextile occupies substantially less air space and is likely to be easier to construct and more cost effective.

Design approaches for geotextile separators beneath the granular sub-bases of unpaved roads

The purpose of a geotextile separator beneath a granular sub-baisse to prevent the road aggregate and the underlying subgrade soil from intermixing. In the absence of a geotextile, contamination of the sub-base aggregate by soft subgrade soil could reduce its load bearing capacity and thereby limit the life of the pavement A number of different approaches have been proposed for the design of geotextile separators beneath unpaved roads. The most widely accepted of the methods based on simple hand calculations are those of Giroud and Noiray, and Sellmeijer et al. This Technical Note presents a simplified summary of these two design approaches and suggests some modifications.

Geotextiles as separators: an introductory overview

The largest use of geotextiles in civil engineering, in terms of the total area of material used, is for separation. Yet it is one of the most difficult of geotextile functions to define and describe. This set of technical notes was prepared in order to provide guidance on specific aspects of design, construction and use of geotextile separators. The authors of the notes are well known members of the profession with a combined experience of more than a hundred years of geotextile design. This note introduces the subjects covered in the set of notes and highlights the lessons which may be learned from them. Since the early stages of geotextile engineering it has been considered that the three main functions of a geotextile are (a) filtration (b) separation (c) reinforcement.

Designing with geotextiles

This paper deals with three current functions of geotextiles: geotextile drains; geotextile filters; geotextile separators.