Gravel Drainage Research Articles

Development of a simplified method for the assessment of liquefaction mitigation via vertical gravel drains

Development of a simplified method for the assessment of liquefaction mitigation via vertical gravel drains

Parameters affecting the development of capillary barriers due to conventional geotextiles

The objective of this study is to assess the formation of capillary barriers on unsaturated soils in contact with geotextiles that have been placed with the primary function of acting as a separator between soil or drainage layers, including the geotextile component of a geocomposite. A comprehensive experimental program involving soil column infiltration tests was conducted using a variety of material combinations to assess the hydraulic performance of interfaces between unsaturated clay and geotextiles. Soil moisture was recorded using time domain reflectometers. Custom made acrylic soil columns were comparatively small (20 cm diameter and 33 cm tall) in order to facilitate test setup and reduce total testing time. Multiple column tests were conducted, which included woven and nonwoven geotextiles selected to identify which geotextile characteristics may affect the formation of a capillary barrier. Other tests were conducted to assess the effect of varying relative compaction and inflow rate on the hydraulic performance. Based on data from the moisture sensors, all tests were found to clearly show the formation of a capillary barrier, which resulted in additional moisture storage in the overlying finegrained soil layer. The test results show that currently available conventional geotextiles create a capillary barrier and restrict moisture flow into the underlying soil or drainage layer until the overlying fine-grained soil has become essentially saturated. This includes nonwoven geotextiles that are commonly used as the top layer in geocomposite drainage products or as separators between a soil layer and an underlying gravel drainage layer. The strength of the capillary barrier was found to be similar for the multiple conventional polypropylene geotextiles investigated in this study.

Assessing water dynamics and net percolation rates within engineered cover systems for mine waste rock piles: A long-term field monitoring study

Mine waste rock piles (WRPs) typically contain trace sulfidic minerals that can react with the atmosphere and produce toxic acid mine drainage (AMD) leachate. Water flow through the waste rock affects both the chemistry and transport of the leachate, and a common remedial solution is the installation of engineered cover systems over the WRP to control net percolation (NP) into the waste rock. As NP is mainly controlled by meteorological conditions and the hydrological properties of cover materials, the water balance (WB) method can be employed to investigate NP and water dynamics within cover systems. However, studies on comprehensive WBs at full-scale WRPs have been limited, and most NP studies have relied on controlled, small-scale laboratory and field tests. This unique study contains the long-term field monitoring data at multiple WRPs needed to comprehensively assess NP rates within cover systems. Field monitoring data with high temporal resolution (hourly) was collected from 2012 to 2018 at four covered WRPs located within the Sydney Coalfield (Nova Scotia, Canada), consisting of one simple soil cover and three multi-layer covers lined with the same geomembrane but differing drainage layer materials. Each WB component – precipitation (PPT), evapotranspiration (ET), water/snow storage, surface runoff, and interflow – was determined, with the residual inferred to be NP into the waste rock. The simple soil cover was not very effective, only reducing NP from the pre-cover 34% PPT to 30% PPT. In contrast, the geomembrane-lined cover systems reduced NP to 4% PPT (no drainage layer), 1.6% PPT (thick gravel drainage), and 1.8% PPT (geocomposite drainage net). While ET and water/snow storage changes at all WRPs were similar, the biggest influence on NP was runoff and interflow. This study provides new field information on the performance of cover systems for controlling NP and water dynamics at full-scale WRPs.

The need to consider the service life of all components of a modern MSW landfill liner system

The long-term performance of a geosynthetic clay liner (GCL) above a drainage layer and a geocomposite drain (GCD) are investigated. Full-scale tests are used to: (i) assess the integrity of GCL and GCD in a double composite liner below a defect in the primary geomembrane with ageing, and (ii) establish the head at which there was internal erosion in GCL without a carrier geotextile (GTX) such that the bentonite is in direct contact with the underlying gravel drainage. Six years after contact with simulated landfill leachate at 85 °C through an intentional defect on the geomembrane, the GCL resting on the GCD had failed due to degradation of the GTX between the bentonite and the core of the GCD and subsequent erosion of the bentonite into the core structure of the GCD was observed. In addition to complete degradation of its GTX at some locations, the GCD had also experienced extensive stress cracking and rib rollover. The second test demonstrates that if a suitable gravel drainage layer had been used instead of the GCD, the GTX component of the GCL would not have been required for acceptable long-term performance under normal design conditions and indeed could withstand a head of up to 15 m before problems became evident. The findings serve as a warning landfill designers and regulators that more attention must be paid to the service life of all components of double liner systems used in Municipal Solid Waste (MSW) landfills.

A Novel Multipurpose Self-Irrigated Green Roof with Innovative Drainage Layer

Climate change is a significant problem that many countries are currently facing, and green roofs (GRs) are one of the suitable choices to confront it and decrease its impacts. The advantages of GRs are numerous, such as stormwater management, thermal need reduction, runoff quality, and life quality improvement. However, there are some limitations, including the weight, limits in water retention, irrigation in the drought period, suitability of harvested water for building usages, installation on sloped roofs, and high cost. Therefore, developing a novel system and design for GRs with higher efficiency and fewer negative points seems necessary and is the main scope of this research. In this regard, a novel multipurpose self-irrigated green roof with an innovative drainage layer combined with specific multilayer filters has been developed. The application of the proposed system in terms of water retention capacity, water storage volume, runoff treatment performance, irrigation system, drainage layer, application of the harvested water for domestic purposes, and some other aspects has been analyzed and compared with the conventional systems with a focus on extensive green roofs. The results demonstrate that this novel green roof would have many advantages including less weight due to the replacement of the gravel drainage layer with a pipeline network for water storage, higher water retention capacity due to the specific design, higher impacts on runoff treatment due to the existence of multilayer filters that can be changed periodically, easier installation on flat and sloped roofs, the possibility of using the collected rainfall for domestic use, and fewer irrigation water demands due to the sub-surface self-irrigation system.

Пути повышения гидрологической эффективности осушения земляного полотна железных дорог

Purpose: Hydrological rationale for drainage system buildings that effectively drain poorly permeable subgrade soils. As a result of watering of soils by rainfalls and groundwaters, track upper structure undergoes deformation and loses its strength. To exclude adverse processes, various drainage devices and drainage systems are used. In the modern world, traffic speed and freight transportation quantity have risen and the load on track superstructure has significantly increased. To reduce risk for drainage system buildings it is necessary to apply hydrological requirements to ensure moisturizing regime of subgrade soils. Methods: For new structures, traditional water-balance method for drainage efficiency assessment is used. The method takes into account two main types of moisturizing: atmospheric and mixed ones. For atmospheric watering, we used the data on water estimated inflow to a drainage in Russia North-West zone. Atmospheric nutrition may be absent in the case of geomembrane usage on subgrade major platform. The distance between collectors is determined by the author’s methodology obtained by an analytical method. Results: The new structure of gravel drain is proposed. It has been proven that the proposed structure in poorly permeable soils drains a subgrade more efficiently than a subditch drainage does. An example of a hydraulic calculation of such a drain is given, the distance between outlet collectors in the set conditions is determined. Practical significance: Due to the use of gravel drainage, subgrade soil moisture will decrease that will lead to the subgrade bearing capacity increase. The results can be used in poorly permeable soils which prevalence is quite high. Structures, including gravel drainage, can be applied in combination with traditional ones.

Use of plastic geocellular modules as a replacement gravel layer for natural turf rootzones

AbstractA trial was conducted to assess the suitability of a novel plastic geocellular drainage layer (Permavoid) as a replacement for a conventional gravel layer in a high‐quality sports pitch. The trial was conducted during the 2014–2015 and 2015–2016 United Kingdom football (soccer) seasons. Perennial ryegrass (Lolium perenne L.) was grown under five different rootzone depth treatments (50, 100, 200, and 300 mm over Permavoid and 300 mm over gravel as a control representing current practices). These were repeated for two contrasting rootzone types. The trial area was subjected to artificial football‐style wear throughout each playing season, with irrigation and nutritional inputs as would be normal for a high‐quality football pitch. Infiltration rates, rootzone moisture content, turf cover and tractional strength for the 200‐ to 300‐mm rootzone over Permavoid and 300 mm over gravel were the same throughout the trial. The replacement of the gravel drainage layer with Permavoid had no negative effect on the rootzone's hydraulic characteristics or turfgrass growth over the 2‐yr study period. In addition, it may be possible to use shallower rootzone depths in some circumstances, reducing the volume of material needed for construction. Shallower rootzones (50–100 mm) experienced greater fluctuations in rootzone moisture content, which was likely to be directly related to rootzone depth. Rootzone type had a minor effect, with finer rootzones holding onto more moisture and allowing slightly stronger turf. Therefore, when managing shallower and/or coarser rootzones, maintenance programs need to reflect the moisture and nutrient retention characteristics of these growing media.

Performance Comparison of Geodrain Drainage and Gravel Drainage Layers Embedded in a Horizontal Plane.

Drainage materials are widely used, among other uses, in the construction of landfills. Regulations require a drainage layer in the base and a covering for the landfill. The implementation of a gravel drain requires a lot of material and financial outlays. New geocomposite materials are an alternative, and facilitate construction. The aim of the research was to compare the drainage properties of the Pozidrain 7S250D/NW8 geocomposite and gravel drainage. The model test was performed on a specially prepared test stand. The research was carried out for model #1, in which the gravel drainage was built. Model #2 had a drainage geocomposite built into it. The test results show the values of the volumetric flow rate for geodrains, with a maximum value of 40 dm3·min−1. For the gravel layer, values of up to 140 dm3·min−1 were recorded. Another parameter recorded during the damming of water by the embankment was the speed of water suction by the geosynthetic and gravel drainage; the values were 0.067 and 0.024 m3·s−1, respectively. The efficiency of water drainage through the geocomposite was sufficient. It is possible to use the slopes of the landfill for drainage, which will reduce material and financial outlays.

Verification of effectiveness and design procedure of gravel drains for liquefaction remediation

The current design practice of using gravel drains as a liquefaction countermeasure involves the selection of the drain spacing and drain diameter to keep the peak excess pore water pressure ratio low. As it has mostly been verified through small-scale 1 g shaking tests, its validity for the field-scale prototype has yet to be well investigated. In this study, a series of centrifuge tests was conducted to gain insight into the stress-dependent behavior of loose sand deposits with a level surface improved by gravel drains. Meanwhile, the current design procedure was validated with experimental data. The results revealed that the effects of gravel drains in suppressing the excess pore pressures depend significantly on the depth of the drains. The current design procedure has failed to elucidate the depth-dependent behavior of sand deposits. One of the important features of the mechanical properties of the soil used for the design of gravel drains was revealed through laboratory tests in which the coefficient of volumetric compressibility, mv, was found to be highly dependent on the stress level, while mv was assumed to be fixed in the design procedure. It was also found that the water flow regime in gravel drains can be a turbulent flow. The Reynolds number in drains increases from the bottom to the top, and the permeability coefficient decreases accordingly, resulting in more significant well resistance than expected based on the current design procedure. In the present study, when stress level-dependent mv and Reynolds number-dependent kw were used as input soil parameters, the axisymmetric diffusion equation, with consideration given to the well resistance, satisfactorily predicted the excess pore pressures in sand with gravel drains.

Shaking table tests on wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand

In this paper, the seismic performance of wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand has been addressed using a series of 1 g shaking table tests. In these tests, the liquefaction resistance of silty sand was studied by changing soil relative density, silt content, number of walls, and materials of drainage walls. In order to evaluate shear wave propagation, the generation and dissipation of pore water pressure (PWP), and the ground surface settlement, various accelerometers, displacement and PWP transducers were placed. The obtained results indicated that an increase in the relative density and the number of wall-type gravel and rubber drains in liquefiable silty sand reduces the settlement, liquefaction-induced deformations, as well as the excess PWP and eventually improves the liquefaction resistance. Totally, it can be noted that the reinforced silty sand with wall-type gravel drains revealed less excess PWP and settlement than that with wall-type rubber drains.

Relationships that Govern Changes in Permeability and Microstructure of Leachate Drainage Layer Under Loading

To examine the changes in the permeability and the microstructure of the gravel layer under different overburden stresses, samples of leachate are taken from the Yanqun landfill in Xuzhou, China, which are used as the seepage fluid in an experiment in a physical model established by using similarity theory. A mathematical model of the relationship between the permeability coefficient gradient per unit stress of overburden stress and seepage time is established. The results show that the porosity and permeability coefficient of the drainage layer, the occupied pore space after clogging, rate of reduction in porosity, pore surface area and pore volume of the gravel (drainage medium) all decrease with an increase in the overburden stress. Increases in the overburden stress can lead to a substantial reduction in the permeability and porosity of the drainage layer, and as the permeability of the drainage layer gradually decreases, there is an increase in occupied pore space after clogging as the seepage time is increased, while the drainage porosity of the seepage section near the inlet where the leachate is poured in the lowest under the same overburden stress. The findings of this study can act as a reference source for analyses on the changes in the permeability of the drainage layer in engineering barriers for municipal solid waste landfills and for the optimal environmental operation of landfills.

Coupled smoothed particle hydrodynamics-discrete element method simulations of soil liquefaction and its mitigation using gravel drains

In this paper, a fully Lagrangian particle-based method for coupled fluid-particle interaction is utilized to evaluate liquefaction of saturated granular soils subjected to dynamic base excitations. The discrete element method (DEM) is employed to model the solid particles and the fluid motion is simulated using the smoothed particle hydrodynamics (SPH). A coupled SPH-DEM scheme is achieved through local averaging techniques and well-established semi-empirical formulas for fluid-particle interaction. A key feature of the employed technique is that it does not presume undrained conditions for the granular deposit and allows for spatial fluid movements within the deposit. The responses of loose and dense granular deposits to seismic excitation are first analyzed. As expected, the loose deposit exhibited significant pore pressure development and liquefaction while the dense deposit barely showed any considerable buildup of pore pressure and did not liquefy. Liquefaction of the loose deposit resulted in significant surface settlement while that experienced by the dense deposit was within tolerable limits. A liquefaction mitigation technique through the installation of gravel drains was then introduced to the loose deposit and its effect on mitigating pore pressure buildup was examined. Results of conducted simulations show that the installation of gravel drains effectively reduced pore-pressure buildup and, for the most part, the soil maintained its strength. However, the drains did not reduce the overall surface settlement of the deposit to acceptable levels.

Large-Scale Prototype Testing of a Composite Geosynthetics Reinforced Earth Structure for Riverbank Slope Protection Using Fine Grained Sandy Soil

This paper presents the field evaluation of large scale prototypes of an innovative composite geosynthetic reinforced earth (CGRE) structure as an alternative for the conventional earth retaining structures, hence a green engineering design for riverbank slope protection. This reinforced earth structure comprises of a geogrid that serves as the main reinforcement and the cover of the facing member of the structure; and a geotextile as separator medium between the infill soil and intermediate horizontal gravel drainage. Three large scale prototypes at full, half, and no gravel drainage were built, monitored, and tested. Clayey sand soil was the fill material used and a 3/2” to 2” sub-rounded gravel was used for the drainage and facing members. CGRE prototypes were evaluated in saturated conditions, and tested under incremental surcharge loadings with a total applied stress of 40 kPa. Lateral displacements for every layer of the structure were determined using horizontal rods where readings were taken from line gauges. Results showed that prototypes with gravel drainage displaced lower than the permissible limit of 4.0%. The CGRE prototype with full gravel drainage had the smallest average total lateral displacement of 1.28%. Hence, it had a higher interface friction resistance, and pull-out capacity than the one with less or no gravel drainage. Overall, the incorporation of gravel drainage improved the performance of the reinforced earth system by reducing the lateral movements of the structure. Therefore, the CGRE structure is a viable slope protection alternative even under saturated conditions.

The BioChemical Clogging of Landfill Leachate Collection System: Based on Laboratory Studies.

Leachate collection system (LCS) clogging is a common operational problem in municipal solid waste (MSW) landfills in China, which can result in high leachate levels that threaten the safety of landfill operations and subsequently increase the leachate leakage risk. In our previous research, a filtration test was conducted and the physical clogging effect was evaluated. To fully analyze the LCS failure, in this study, a set of column experiments were carried out to investigate the biochemical clogging development and mechanisms. Results showed that the biofilm and deposited CaCO3 composed the primary clogging materials. During the experimental period, the hydraulic conductivities in simulated gravel and nonwoven geotextile drainage layers were observed (91.7% and five orders of magnitude reduction), and decreased to 10−4 and 10−8 m s−1, respectively. Therefore, the significance of the geotextile layer in LCS designing needs to be reconsidered. The biochemical clogging was positively correlated with volatile fatty acids (VFAs), and Ca2+ loading and the Ca2+ played the dominant role. Meanwhile, an improved method for analyzing biochemical clogging development was proposed.

Centrifuge modeling of hybrid foundation to mitigate liquefaction-induced effects on shallow foundation resting on liquefiable ground

A hybrid foundation is developed in this study to mitigate the liquefaction-induced effects on shallow foundations. The proposed hybrid foundation is a combination of a gravel drainage system and friction steel piles with spiral blades, framed under the footing. The motivation behind having a gravel drainage system, as an integral part of the hybrid foundation, is its ability to improve the liquefaction resistance of the ground in the most economical way. However, case histories and the development of recent research have highlighted that gravel drainage systems have exhibited poor performances and could not prevent ground liquefaction during strong ground motion. To counteract these shortcomings, friction steel piles are provided which are supposed to yield frictional resistance during earthquakes and are presumed to minimize the rocking/tilting behavior of the foundation-structure system even if the ground undergoes liquefaction. The evolution of excess pore water pressure, specifically in the vicinity of the foundation-structure system, dominatingly influences the settlement mechanism of shallow foundations. Centrifuge test results show that the presence of gravel drainage can minimize the post-liquefaction settlement of shallow foundations through the rapid dissipation of excess pore water pressure. Moreover, friction piles are able to minimize the tilting/differential settlement of shallow foundations. It is found that the proposed hybrid foundation provides the desired function of reducing the overall liquefaction-induced effects on shallow foundations resting on liquefiable grounds.

Dynamic Centrifuge Tests on Dissipation Effects of Excess Pore Water Pressure by Gravel Drains

グラベルドレーンによる液状化対策はこれまで多数の実績を有するものの, その液状化抑制効果を実際の応力レベルで実験的に検証した例は少なく, 未解明な部分が残されている．その中で, 本研究はドレーンと液状化層の透水性および有効拘束圧がドレーンによる過剰間隙水圧の消散効果に与える影響に着目し, 層厚8m相当のドレーン改良地盤を再現した遠心模型実験により検討を行った．計5ケースの実験結果から, 液状化層の透水性が高いほど, また有効拘束圧の高い液状化層の深部ほど, ドレーンによる消散効果は高まることが明らかとなった．一方で, 透水性が低く, 液状化の発生を抑制できない条件においても, 液状化の継続時間は大幅に短縮されることが確認された．

A comparative study between gravel and rubber drainage columns for mitigation of liquefaction hazards

Liquefaction is one of the most destructive natural hazards that cause damage to engineering structures during an earthquake. This study aims to examine the effect of rubber and gravel drainage columns on the reduction of liquefaction potential of saturated sandy soils using a shaking table. Experiments were carried out in various conditions such as construction materials, different arrangements and diameters of drainage columns. Effects of the relative density and the input motion on the base test were investigated as well. The results demonstrate that rubber drainage columns have slightly better performance compared to gravel drainage columns at high relative density and high input acceleration. Soil improvement using gravel drainage columns, which leads to reduction in liquefaction effects at moderate input acceleration and low relative density, is a more effective method than that using rubber drainage columns. By increasing the number and diameter of gravel and rubber drainage columns, deformations due to liquefaction are reduced. The drainage rate of gravel drains is higher than that of rubber drains after shaking. Totally, the outcomes indicate that densification is the most important factor controlling liquefaction.

Geological explorations and laboratory testing at the site designated for installation the vertical gravel drains

Vertical gravel drainages are used to improve the geomechanical characteristics of sedimented dusty and sandy soils where the application of gravity drainage is not possible. They are formed in a membrane made of a cylindrical woven geotextile (GEC - geotextile encased columns). They are intended to improve the geomechanical properties of the soil by lowering the groundwater level. Their practical application was realized on a part of an unstable internal landfill at the open pit of lignite 'Drmno' in Kostolac. At the sites planned for the production of vertical gravel drains, it is necessary to perform the complex hydrogeological, geotechnical and laboratory tests, and this is shown in this paper.

Sound insulation of lightweight extensive green roofs

This paper examines factors affecting the sound insulation of lightweight extensive green roofs. The research had three objectives: (1) To examine the extent to which the sound insulation of lightweight extensive green roofs is affected by the variable conditions of their substrate and vegetation layer (soil's distribution, water content and compaction level); (2) To quantify how sound insulation is affected by the main elements making up the roof (substrate and vegetation layer, drainage layer and added cavity); (3) To identify applications for such roofs in relation to their sound insulation performance. For objective 1, it was found that the variable conditions of the substrate and vegetation layer do not significantly affect the sound insulation properties of lightweight extensive green roofs (variations in Rw of no more than 1 dB). For objective 2, results indicated that the addition of a cavity represents the most effective solution for improving sound insulation (+13 dB in Rw for a 50 mm deep cavity with mineral wool), whilst increasing the amount of substrate or using heavier drainage layers tend to provide more limited improvements in Rw (+3 dB for 25 mm of substrate and +2 dB for gravel vs. lightweight drainage membrane). Finally, regarding objective 3, the systems tested were found to provide appropriate sound insulation for both commercial and residential types of constructions. All the results were obtained from tests carried out on small 1 m2 samples, so their accuracy and validity will need to be identified through comparisons with large scale tests.

Stormwater Suspended Solids Reduction in Sand-Zelbrite Filter Media

The use of the filtration process based on zeolite for stormwater treating has been recently increased. This study reports the results obtained from a laboratory experimental testing on a treatment unit consisting of a gravel drainage layer, a filtering media composed of zelbrite (a synthetic zeolite) and silica sand. The filter media is fed with typical stormwater particulate matter (PM) loadings. The treatment performance is evaluated in terms of total suspended solids (TSS) reduction. In addition, the transformation of PM particle size distribution (PSD) through the filtering media is also determined. The findings show that TSS reduction varies from 76% to 91% for different influent PM loads.