Lessons Learned on Geosynthetics Applications in Road Structures in Silesia Mining Region in Poland

applied sciences

Article Lessons Learned on Geosynthetics Applications in Road Structures in Silesia Mining Region in Poland

Jacek Kawalec 1 , Marcin Grygierek 1 , Eugeniusz Koda 2 and Piotr Osi ´nski 2,*

1 Department of Geotechnics and Roads, Faculty of Civil Engineering, Silesian University of Technology, 44-100 Gliwice, Poland; [email protected] (J.K.); [email protected] (M.G.) 2 Department of Geotechnical Engineering, Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences, 02-776 Warsaw, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-22-535-213

Received: 1 February 2019; Accepted: 12 March 2019; Published: 17 March 2019

Featured Application: Authors are encouraged to provide a concise description of the speciﬁc application or a potential application of the work. This section is not mandatory.

Abstract: The paper aims at the research of pioneering applications of geosynthetic materials used for improvement of anthropogenic material for road contraction challenges in Poland. The presented case study concerns a road embankment construction process within an area of underground mining coal extraction for which significant deformations have been frequently recorded. To improve the bearing capacity of the structure base, the geosynthetic materials were used. The question; however, was how the anthropogenic materials, filling the embankment, will interact with each other over time. The assessment of the structural condition of the motorway surface was performed using the falling weight deflectometer and the calculated modules based on the back-analysis method. They confirmed the effectiveness of the geosynthetics used in the study. They also revealed that the mining exploitation, with simultaneous use of aggregate stabilization with geogrids, did not cause significant changes in the stiffness of the pavement layers. All observations, based on both field and laboratory tests, did not show any negative impact of anthropogenic soils on the structural behavior of geogrids.

Keywords: geosynthetics; anthropogenic materials; stabilisation by geogrid

1. Introduction In Europe in late 80’s, after the Iron Curtain collapsed, such countries as Poland started a new chapter in economical development. The infrastructure was one of the key areas where Poland was far behind Western Europe standards. Almost all the construction technologies were outdated, non-efﬁcient, and in many cases unsafe for use [1–3]. Becoming open to new technologies and structural materials provided a strong impact for modernization of the entire construction industry, and until nowadays this trend is still being observed [4–8]. Lack of planning and poor economy management resulted in a huge production of waste, both municipal and industrial, which in many cases were deposited without any control [3–5]. The waste deposition became a serious issue, mainly in well-developed regions like Warsaw or Silesia, where the amount of by-products was rapidly increasing. A typical solution of the problem, back in the days was just enlarging the area used to deposit waste materials. In those days, the use of materials such as geosynthetics were barely noticeable [9–13]. Until 1990’s only a few non-woven textiles manufacturers were operating, but the material quality and durability was insufﬁcient for large scale road construction projects. Simultaneously, in Poland a boom in new geosynthetics applications has started. Now, after over two decades of gaining experience on

Appl. Sci. 2019, 9, 1122; doi:10.3390/app9061122 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 1122 2 of 14 Appl. Sci. 2018, 8, x FOR PEER REVIEW 2 of 15 atwo number decades of infrastructure of gaining experience projects, we on are a ablenumber to make of infrastructure scientifically based projects, conclusions we are andable comments to make onscientifically most of them. based conclusions and comments on most of them. The present paper paper describes describes a a case case study study on on road road construction construction works works on on post-mining post-mining areas. areas. It Itconcerns concerns an an underground underground mining mining coal coal extraction extraction site site where where a a new new motorway motorway was was planned planned to to be constructed. However,However, due due to to significant significant deformation deformation of the of groundthe ground surface, surface, caused caused by former by miningformer excavations,mining excavations, the sophisticated the sophisticated ground ground improvement improvement methods methods were necessary were necessary to be applied. to be applied. For the linearFor the structures, linear structures, like roads, like orroads, other or geotechnical other geotechnical investments investments the mining the mining activity activity is a major is a safetymajor threat,safety threat, thus the thus need the of need maintenance of maintenanc effortse efforts increase increase significantly significantly [14–17 ].[14–17]. Recently, a peculiar revolution in the fieldfield ofof understandingunderstanding and describing the geogrid interaction with the unbound aggregate has been observed.observed. It mainly concerns the road construction and ground mechanical mechanical condition condition improvement. improvement. An An improved improved performance performance of ofthe the pavement pavement due due to tothe the geosynthetic geosynthetic reinforcement reinforcement and and bearing bearing capacity capacity improvement improvement [18–23] [18–23 ]depends depends on on main mechanisms [[24–26]:24–26]: • Lateral confinement of the unbound aggregate in the base course; • Lateral confinement of the unbound aggregate in the base course; • Increased bearing capacity; • Increased bearing capacity; • Tensioned membrane effect. • Tensioned membrane effect. The road pavement is made of layers, which distributes traffic generated loads, disabling excessiveThe roaddeformation pavement of the is madesubsoil. of The layers, major which role of distributes a road pavement traffic generated is bearing loads, high frequency disabling excessiveloads. The deformation pavement works of the provide subsoil. a The very major small role range of a of road deformation, pavement isbetween bearing 10 high−6 and frequency 10−3 m, −6 −3 loads.when considering The pavement the worksvehicles provide load and a very stiffness small of range pavement of deformation, layers [3,11]. between The time 10 gapand between 10 m, a whenroad opening considering and the the asphalt vehicles resurfacing load and stiffnessis determin of pavemented by the fatigue layers life. [3,11 A]. depletion The time of gap the between fatigue alife road of the opening pavement and thecauses asphalt characteristic resurfacing cracks is determined and structural by the rutting. fatigue A life. significant A depletion issue ofwhen the fatigueconstructing life of a the road pavement is the location causes characteristicwithin mining cracks areas and where structural subsoil rutting. deformation A significant occurs, issue including when constructingdeformation of a road the surface. is the location Mining within deformations mining areasusually where affect subsoil working deformation conditions occurs, of the pavement including deformationlayers, cause ofpavement the surface. stiffness Mining reduction, deformations and the usually decrease affect of workingfatigue life. conditions The deformations of the pavement of the layers,ground cause surface pavement can take stiffness the form reduction, of continuous and the [27] decrease or discontinuous of fatigue life. mechanisms The deformations [28–31]. of The the groundcracks observed surface can on takethe road the formpavement of continuous as a result [27 of] orthe discontinuous subsoil deformations mechanisms are presented [28–31]. The in Figure cracks observed1. on the road pavement as a result of the subsoil deformations are presented in Figure1.

Figure 1. Typical damages observed on pavements.

In thethe casecase of of continuous continuous deformation, deformation, there there is ais subsidence a subsidence on the onsurface the surface of the of ground the ground on which on thewhich continuity the continuity of the subsurfaceof the subsur rockface layer rock does layer not does cease. not cease. Such subsidence,subsidence, inin general, general, is describedis described by severalby several surface surface deformation deformation indicators indicators among among which thewhich horizontal the horizontal deformation deformationε [mm/m] ε [mm/m] should beshould distinguished, be distinguished, as they areas includedthey are included in the design in the of design of pavements, particularly in mining areas [27]. The horizontal deformation determines changes in the stiffness of the subsoil and pavement layers. On the convex part of subsidence, the Appl. Sci. 2019, 9, 1122 3 of 14 pavements,Appl. Sci. 2018, particularly8, x FOR PEER REVIEW in mining areas [27]. The horizontal deformation determines changes3 in of the 15 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 15 stiffness of the subsoil and pavement layers. On the convex part of subsidence, the loosening effect (stretching)loosening effect is activated, (stretching) and is in activated, the bottom and part in the of thebottom subsidence, part of the the subsidence, re-compaction the re-compaction (compression) loosening effect (stretching) is activated, and in the bottom part of the subsidence, the re-compaction process(compression) may occur. process The may presentation occur. The of speciﬁc presentation indicators of specific usually affectingindicators the usually subsidence affecting is given the (compression) process may occur. The presentation of specific indicators usually affecting the subsidencein Figure2. Theseis given are in the Figure conditions 2. These that are always the cond needitions to be that considered always whenneed to analyzing be considered the working when subsidence is given in Figure 2. These are the conditions that always need to be considered when analyzingconditions the of theworking road surfacesconditions designed of the road in post-mining surfaces designed areas. in post-mining areas. analyzing the working conditions of the road surfaces designed in post-mining areas.

Figure 2. Mining induced subsidence trough: w—vertical displacement (m), T—inclination (mm/m), Figure 2. Mining induced subsidence trough: w—vertical displacement (m), T—inclination (mm/m), R—radiusFigure 2. Mining of curvature induced (km), subsidence ε—horizontal trough: strain w—vertical (mm/m), displacement u—horizontal (m), displacement T—inclination (m) (mm/m),[32]. R—radius of curvature (km), ε—horizontal strain (mm/m), u—horizontal displacement (m) [32]. R—radius of curvature (km), ε—horizontal strain (mm/m), u—horizontal displacement (m) [32]. The impactimpact of of mining mining deformation deformation can can affect affect thepavement the pavement by reducing by reducing the modules the modules and reducing and The impact of mining deformation can affect the pavement by reducing the modules and reducingthe fatigue the life fatigue of the pavement.life of the pavement. For non-reinforced For non- pavementreinforced (i.e., pavement no geogrid), (i.e., looseningno geogrid), deformations loosening reducing the fatigue life of the pavement. For non-reinforced pavement (i.e., no geogrid), loosening deformationscause a signiﬁcant cause increase a significant of the increase horizontal of the deformations horizontal deformations due to signiﬁcant due to reduction significant of thereduction layers’ deformations cause a significant increase of the horizontal deformations due to significant reduction ofrigidity the layers’ and the rigidity subsequent and the fatigue subsequent life. The fatigu deformatione life. The ranges, deformation experienced ranges, in the experienced past and analyzed in the of the layers’ rigidity and the subsequent fatigue life. The deformation ranges, experienced in the pastby authors and analyzed on a number by authors of different on a number case studies of diff [32erent–34 ],case are studies presented [32–34], in Figure are presented3. The case in studies Figure past and analyzed by authors on a number of different case studies [32–34], are presented in Figure 3.represented The case studies different represented pavement categoriesdifferent pavement (from 1 to categories 7) and concerned (from 1 twoto 7) types and concerned of construction two types layer 3. The case studies represented different pavement categories (from 1 to 7) and concerned two types ofcompositions, construction for layer mining compositions, and non-mining for mining areas and [34 ].non-mining areas [34]. of construction layer compositions, for mining and non-mining areas [34].

Pavement categories based on traffic Horizontal deformation beneathPavement asphalt layers, categories outside based the minion trafficng area Horizontal deformation beneath asphalt layers, withinoutside the the minin miningg area area Horizontal deformation beneath aggregateasphalt layers, layers, within outside the theminin migning area area Horizontal deformation beneath aggregate layers, withinoutside the the min mininging area area Horizontal deformation beneath aggregate layers, within the mining area

Figure 3. Horizontal deformation in selected pavement layers taking into account mining impact. Figure 3. Horizontal deformation in selected pavement layers taking into account mining impact. 2. Materials and Methods 2. Materials and Methods 2. Materials and Methods 2.1. Stabilisation of the Embankment Base 2.1. Stabilisation of the Embankment Base 2.1. StabilisationIn this particular of the Embankment application, Base a base layer of the embankment was placed over the geomattress, madeIn of this unbound particular aggregates application, stabilized a base withlayer two of the layers embankment of a monolithic was placed geogrid. over Due the togeomattress, the project madeIn of this unbound particular aggregates application, stabilized a base with layer two of the layers embankment of a monolithic was placed geogrid. over Due the to geomattress, the project requirementsmade of unbound the aggregates aggregates of stabilized anthropogenic with two wast laeyers material of a monolithicwas made ofgeog polypropylenerid. Due to the [34]. project Such arequirements geomattress thecreates aggregates a quasi-stiff of anthropogenic platform at the wast base,e material reducing was most made deep of polypropylene mining deformations [34]. Such on a surface,geomattress and allowingcreates a quasi-stiffrapid construction. platform Theat the instal base,lation reducing of the most geomattress deep mining is shown deformations in Figure 4.on a surface, and allowing rapid construction. The installation of the geomattress is shown in Figure 4. Appl. Sci. 2019, 9, 1122 4 of 14 requirements the aggregates of anthropogenic waste material was made of polypropylene [34]. Such a geomattress creates a quasi-stiff platform at the base, reducing most deep mining deformations on a surface, and allowing rapid construction. The installation of the geomattress is shown in Figure4. Appl. Sci. 2018, 8, x FOR PEER REVIEW 4 of 15

Figure 4.4. InstallationInstallation of of the the geomattress, geomattress, made made of of two two layers layers of of monolithic geogrids and anthropogenic aggregates.

The fillfill material for the geomattress in most ca casesses was either slag or burned mining mining shale. shale. Below the slag, the red colored aggregate was burnt mining shale. The stabilizing effect of the geomattress was achieved by interlocking the aggregateaggregate particles in apertures of the geogrid. It was achieved onlyonly ifif thethe geogrid geogrid was was stiff stiff and and the the aperture aperture shape shape was was not not deformable deformable under under load, load, which which was appliedwas applied during during the compaction the compaction of the aggregateof the aggregat layer.e The layer. interlocking The interlocking effect of theeffect geogrid of the makes geogrid the aggregatemakes the layeraggregate confined layer for confined some depth for some [10,27 depth]. In case[10,27]. of mining In case influences,of mining influences, it becomes it a becomes barrier for a abarrier deformation for a deformation propagation propagation in directions in fromdirections the below from tothe the below above to layers. the above layers.

2.2. Evaluation of Mining Waste Mechanical Parameters Part of the complex preparation of the motorway design was the determination of the strength parametersPart of ofthe the complex mining preparation waste materials of the that motorway were to be design used forwas the the construction determination of an of embankment the strength body.parameters In this of case the a fullmining scale in-situwaste test,materials based onthat the were method to ofbe trialused loading for the was construction performed [29of– 32an]. Theembankment applied methodology body. In this guaranteed case a full a comprehensivescale in-situ test, distribution based on of the the method stress paths of trial that loading were crucial was forperformed the proper [29–32]. identiﬁcation The applied of themethodology design parameters. guaranteed With a comprehens reference toive the distribution trial loading of the of slopes, stress thepaths in-situ that testswere enabledcrucial for appropriate the proper simulation identification of the of failure the design process, parameters incomparable. With to reference any laboratory to the teststrial orloading numerical of slopes, analyses. the Thein-situ technical tests issuesenabled here appropriate referred to simulation difﬁculties of in achievingthe failure boundary process, equilibrium,incomparable corresponding to any laboratory with thetests most or realisticnumerical estimations analyses. ofThe the technical strength parameters:issues here thereferred internal to frictiondifficulties angle in achieving (ϕ) and the boundary cohesion equilibrium, (c)[33]. The corresponding tests performed with on the an most experimental realistic estimations embankment of allowedthe strength the measurementparameters: the of internal the “load-settlement” friction angle relationship.(φ) and the cohesion It was necessary (c) [33]. The for furthertests performed analyses byon meansan experimental of an elastic—ideally embankment the allowed plastic soilthe model.measurement of the “load-settlement” relationship. It was necessaryThe model for was further used analyses to measure by means the slope of an geometry elastic—ideally before the and plastic after thesoil failure,model. taking into accountThe amodel destructive was used load. to The measure loading the of theslope top geomet surfacery of before the slope and withafter a the pile failure, of pavement takingslabs into withaccount a measurement a destructive of load. the settlementsThe loading after of the each top incremental surface of the step slope was consideredwith a pile toof bepavement the optimum slabs solution.with a measurement To be capable of of the considering settlements the problemafter each as incremental linear (planar step strain), was aconsidered load was assumed to be the to beoptimum applied solution. on the length To be of capable a minimum of considering of three pavement the problem slabs, as usedlinear as (planar a surcharge. strain), The a load model was is presentedassumed to in be Figure applied5. on the length of a minimum of three pavement slabs, used as a surcharge. The model is presented in Figure 5. The computations included estimations of the φ and c values, as parameters of an elastic (ideally plastic) Coulomb–Mohr model, based on back analyses applying the finite element method (FEM) method and the Janbu method, respectively. The results obtained for the mechanical parameters, using the modeling, and also the physical parameters are listed in Table 1. Appl. Sci. 2019, 9, 1122 5 of 14

The computations included estimations of the ϕ and c values, as parameters of an elastic (ideally plastic) Coulomb–Mohr model, based on back analyses applying the ﬁnite element method (FEM) method and the Janbu method, respectively. The results obtained for the mechanical parameters, usingAppl. Sci. the 2018 modeling,, 8, x FOR andPEER also REVIEW the physical parameters are listed in Table1. 5 of 15

FigureFigure 5. 5. Finite element method method (FEM) (FEM) model model used used for for mechanical mechanical parameters parameters determination: determination: (a) (aModel) Model geometry; geometry; and and (b (b) )calculation calculation characteristic characteristic curve ofof mechanicalmechanical parametersparameters referringreferring to to monitoringmonitoring results. results. Table 1. Physical and mechanical parameters (based on back analysis) of the ﬁlling material. Table 1. Physical and mechanical parameters (based on back analysis) of the filling material. Characteristics Embankment Material Aggregate in Mattresses Characteristics Embankment Material Aggregate in Mattresses physical physical dmax (mm) <150 63 dmax (mm) < 150 63 U = d60/d10 (-) 8.6–41.0 11.4–15.3 U = d60/d10 (-)Type Unburned 8.6–41.0 coal mining shales Blast furnace 11.4–15.3 slag CarbonType cont. fC (%) Unburned coal 8.8 mining shales n/a Blast furnace slag Carbonw cont.opt (%) fC (%) ac. Proctor 9.65 8.8 25.7 n/a ρds (g/cm3) ac. Proctor 1.85 1.46 wopt (%) ac. Proctor 9.65 25.7 Passive capillary (m) 1.75 n/a ds (g/cm3) ac. Proctor 1.85 1.46 ρ Frost resistance (%) 71 99.7 Passive capillary (m) 1.75 n/a mechanical Frost resistance (%) 71 99.7 Internal friction angle ϕ [◦] 22.7 40 mechanical Cohesion c [kPa] 50 4 Internal friction angle φ [°] 22.7 40 Cohesion c [kPa] 50 4 The modeling part refers directly to the reliability assessment of waste strength parameters results, obtainedThe on modeling the basis part of trial refers loading directly of the to road the embankmentreliability assessment slope in the of naturalwaste strength scale. The parameters full-scale trialresults, loading obtained test was on carriedthe basis out of usingtrial loading 18,000 tonsof the of road material embankment on the 100 slope m long, in the 20 mnatural wide, scale. and 5 The m highfull-scale road embankment,trial loading test presented was carried in Figure out6 .using 18,000 tons of material on the 100 m long, 20 m wide,The and results 5 m ofhigh the road strength embankment, parameters presented evaluation, in withFigure relatively 6. low values of standard deviation, were usedThe toresults design of athe motorway strength embankment parameters inevaluati a sectionon, located with relatively near the mine.low values In 1990, of the standard Polish governmentdeviation, were decided used to to constructdesign a motorway a new section embank of ament motorway in a section passing located through near the the Silesia mine. In region 1990, withthe Polish over 50 government active deep decided coal mines. to construct The length a new of the section Silesian of a part motorway of the motorway passing through is 45 km the and Silesia the majorityregion with of it runsover over50 active the mining deep coal areas. mines. The onlyThe materiallength of used the Silesian for the embankment part of the motorway construction is 45 was km anthropogenicand the majority soil. of At it this runs stage over a decision the mining was madeareas. thatThe the only impact material of the used mining for inﬂuencesthe embankment on the motorwayconstruction should was beanthropogenic reduced and soil. protective At this layersstage a with decision geogrids was shouldmade that be designedthe impact [31 of]. the Based mining on observedinfluences reduction on the motorway in the pavement should durability be reduced by 20%and andprotective more (higherlayers designedwith geogrids deformations), should be itdesigned was necessary [31]. Based to apply on solutionsobserved that reduction minimize in th thee impactpavement of miningdurability deformations. by 20% and Due more to a (higher small designed deformations), it was necessary to apply solutions that minimize the impact of mining deformations. Due to a small range of the deformations, it was also necessary to mobilize the geosynthetics at the initial stage of the deformation. Therefore, for the purposes of constructing the motorway in mining areas, a completely innovative approach was applied. The typical parameters for geogrids used for reinforcement are Appl. Sci. 2019, 9, 1122 6 of 14 range of the deformations, it was also necessary to mobilize the geosynthetics at the initial stage of the deformation. Appl. Sci.Therefore, 2018, 8, x forFOR the PEER purposes REVIEW of constructing the motorway in mining areas, a completely innovative6 of 15 approach was applied. The typical parameters for geogrids used for reinforcement are tensile strength tensile strength Rmax [kN/m] and elongations at 2% and 5% (R2% i R5%), respectively. Commonly the Rmax [kN/m] and elongations at 2% and 5% (R2% i R5%), respectively. Commonly the elongation at the elongation at the breaking point εmax is also determined. breaking point εmax is also determined.

Figure 6. Full scale trial test to determine mechanical parameters of waste material.

In Figure 77,, twotwo extremelyextremely different behavioral models models of of geogrids geogrids are are presented. presented. Model Model (1) (1) is characterizedis characterized by by high high initial initial stiffness stiffness EEi i(1)(1) and and moderate moderate strength strength Rmax (1).(1). In In contrast, contrast, the the high strength Rmax (2)(2) of of model model (2) (2) is is accompanied accompanied by by low initial stiffness Eii (2).(2). Figure Figure 77,, showsshows aa typicaltypical presentation of material material characteristics, characteristics, that that usually usually are are insufficient insufﬁcient for for a fully a fully covered covered description description of theof the material’s material’s mechanical mechanical performance. performance. From From the the point point of ofview view of of a aproper proper protection protection of of the motorway, mobilizationmobilization at at a verya very small small deformation deformatio isn very is very much much of interest. of interest. Thus, theThus, initial the rigidity initial rigidityis Ei tangential is Ei tangential to the “force-elongation” to the “force-elongation” curve, at thecurv beginninge, at the ofbeginning the stress–strain of the stress–strain relationship, relationship,or the ES secant or stiffnessthe ES secant is a limited, stiffness deformable is a limited, interval, deformable up to 0.5%. interval, The geogrid’sup to 0.5%. built-in The aggregategeogrid’s built-inlayer behaves aggregate differently layer behaves to a geogrid differently tested in to an a in-situgeogrid condition.Thanks tested in an in-situ to mechanical condition.Thanks compaction, to mechanicalthe grains of compaction, sizes no bigger the grains than the of sizes apertures no bigger get clogged than the in apertures the apertures, get clogged practically in the eliminating apertures, practicallythe ability toeliminating deform. The the stiffness ability to of adeform. geogrid The built stiffness into the of aggregate a geogrid is; built therefore, into the greater aggregate than theis; therefore,standardsample greater inthan the the laboratory. standard sample in the laboratory.

2.3. Stabilization of Motorway Pavement Another example of a pioneer application of geomattresses is presented for the pavement stabilization in areas of deep coal mining. The construction of the pavement is as follows: • 5 cm asphalt wearing course Stone Mastic Asphalt (SMA) 0/12.8 mm • 10 cm asphalt base layer z Asphalt Concrete (AC) 0/25 • 12 cm asphalt sub base layer 0/31.5 mm • 22 cm aggregate sub base layer from crushed unbound aggregate 0/31.5 mm, • monolithic geogrid • 20 cm technological layer made from natural unbound aggregate 0/31.5 mm • 30 cm frost protective layer California Bearing Ratio (CBR) = 25% The geomatress with two layers of geogrids installed under the embankment, used in the study, was the main solution to protect the motorway against the mining deformations. However, it was

Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 15 tensile strength Rmax [kN/m] and elongations at 2% and 5% (R2% i R5%), respectively. Commonly the elongation at the breaking point εmax is also determined.

Figure 6. Full scale trial test to determine mechanical parameters of waste material.

Appl. Sci.In 2019Figure, 9, 1122 7, two extremely different behavioral models of geogrids are presented. Model 7(1) of 14is characterized by high initial stiffness Ei (1) and moderate strength Rmax (1). In contrast, the high strength Rmax (2) of model (2) is accompanied by low initial stiffness Ei (2). Figure 7, shows a typical believedpresentation that of the material geomatress characteristics, would not that fully usually stop the are deformation insufficient propagation,for a fully covered so another description layer of stabilizingthe material’s geogrid mechanical was needed, performance. filled within From the pavementthe point structure.of view Theof a entire proper installation protection process of the is presented in Figure8. A falling weight deflectometer (FWD) was used for further evaluation of the Appl.motorway, Sci. 2018 , mobilization8, x FOR PEER REVIEW at a very small deformation is very much of interest. Thus, the 7initial of 15 deformationrigidity is E processi tangential and effectivenessto the “force-elongation” of the applied curv solution.e, at Thethe methodbeginning is used of the to imitate stress–strain actual conditions of traffic load. The FWD device measures the vertical deflection of the road pavement relationship,Figure 7. orStress–strain the ES secant relationship stiffness for is di afferent limited, types deformable of geogrids: interval, (1) high upinitial to 0.5%.stiffness; The (2) geogrid’s low structurebuilt-ininitial aggregate caused stiffness. by layer falling behaves of a fixed differently mass load to from a geogrid a set height. tested The in mass an in-situ falls naturally condition.Thanks and transfers to impulsemechanical to acompaction, bearing device. the grains The vertical of sizes deflection no bigger induced than the by apertures the plate get is clogged registered in bythe aapertures, group of geophones2.3.practically Stabilization placedeliminating of Motorway in different the ability Pavement distances to deform. from theThe axis. stiffness The load of a impulsegeogrid valuebuilt rangesinto the from aggregate 7 to even is; 300 kN, depending on the type of pavement structure. therefore,Another greater example than theof standarda pioneer sample application in the oflaboratory. geomattresses is presented for the pavement stabilization in areas of deep coal mining. The construction of the pavement is as follows: • 5 cm asphalt wearing course Stone Mastic Asphalt (SMA) 0/12.8 mm • 10 cm asphalt base layer z Asphalt Concrete (AC) 0/25 • 12 cm asphalt sub base layer 0/31.5 mm • 22 cm aggregate sub base layer from crushed unbound aggregate 0/31,5 mm, • monolithic geogrid • 20 cm technological layer made from natural unbound aggregate 0/31,5 mm • 30 cm frost protective layer California Bearing Ratio (CBR) = 25% The geomatress with two layers of geogrids installed under the embankment, used in the study, was the main solution to protect the motorway against the mining deformations. However, it was believed that the geomatress would not fully stop the deformation propagation, so another layer of stabilizing geogrid was needed, filled within the pavement structure. The entire installation process is presented in Figure 8. A falling weight deflectometer (FWD) was used for further evaluation of the deformation process and effectiveness of the applied solution. The method is used to imitate actual conditions of traffic load. The FWD device measures the vertical deflection of the road pavement structure caused by falling of a fixed mass load from a set height. The mass falls naturally and transfers impulse to a bearing device. The vertical deflection induced by the plate is registered by a groupFigure of geophones 7. Stress–strain placed relationship in different for distances different typesfrom ofthe geogrids: axis. The (1) load high impulse initial stiffness; value ranges (2) low from 7 to eveninitial 300 stiffness. kN, depending on the type of pavement structure.

Second layer of the geogrid to be installed

First layer of the geogrid

Figure 8. View of the pavement section where the geogrid was installed. Figure 8. View of the pavement section where the geogrid was installed.

3. Results and Discussion on the Research Outputs To understand how the geomattress could limit the influences from the mining activity, there was a sophisticated monitoring system designed on the pavement. As shown on Figure 9, two inclinometric-type pipes were installed beneath and above the geomattress. The site monitoring readings, collected simultaneously, showed significant differences in profiles beneath the geomatress, while the readings from the profile above were even. In some of the motorway sections, Appl. Sci. 2019, 9, 1122 8 of 14

3. Results and Discussion on the Research Outputs To understand how the geomattress could limit the influences from the mining activity, there was a sophisticated monitoring system designed on the pavement. As shown on Figure9, two inclinometric-type pipes were installed beneath and above the geomattress. The site monitoring readings, collected simultaneously, showed significant differences in profiles beneath the geomatress,

Appl.while Sci. the 2018 readings, 8, x FOR PEER from REVIEW the profile above were even. In some of the motorway sections, after8 of the 15 base was constructed, a significant ground subsidence took place. The biggest subsidence reached up reached100 cm; however,up 100 cm; the however, base profile the above basethe profile geomattress above the was geomattress not seriously was affected, not seriously which proved affected, the whichprotective proved role ofthe the protective material role used. of A the similar material observation used. A onsimilar the differences observation between on the deflection differences of betweendeeper profiles deflection were of reported deeper profiles by Huckert were et reported al. [35]. Afterby Huckert the experiment et al. [35]. on After the first the section,experiment similar on thegeomattresses first section, were similar designed geomattresses and installed were for alldesi othergned sections and installed of the motorway, for all other especially sections where of the motorway,risk of mining especially subsidence where was the high. risk of mining subsidence was high.

Figure 9. Cross-sectionCross-section of oftesting testing set setdesigned designed to monitor to monitor geomattress geomattress deformations deformations below below the embankment.the embankment.

Between years years 1995 1995 and and 2008 2008 the the motorway motorway sections sections in Silesia in Silesia were werecompleted, completed, and until and today until thetoday geomattresses the geomattresses helped helped keep keepthe pavement the pavement in an in anundamaged undamaged condition. condition. To To provide provide a a better understanding of collected deformation readings, readings, a a graph presenting the moni monitoringtoring results for the firstfirst year of observation is given on Figure 1010.. Bearing in mind that the permissible value of deformation is 1.5 mm/m, according to the standards of [7,20], the readings proved the sufficient bearing capacity of the used material. The mining works located near the control sections were carried out to the south of the motorway and they reached three different levels: level 418—wall 130 in years 2006–2007; level 502—wall 796 in year 2008; and level 504—wall 006 in years 2010–2011. The location of wall 006 and the measure subsidence is presented in Figure 11. Taking into consideration the location of the excavation walls in the south, it is important to highlight that the motorway was subjected to continuous horizontal deformations in the west direction. When analyzing measured values of the subsidence, it was noted that the summarized vertical deformation of the north line reached 30 cm. The technical assessment indicated that the surface remained preserved in sufficient conditions, and only in two locations single longitudinal cracks were

Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 15

reached up 100 cm; however, the base profile above the geomattress was not seriously affected, which proved the protective role of the material used. A similar observation on the differences between deflection of deeper profiles were reported by Huckert et al. [35]. After the experiment on the first section, similar geomattresses were designed and installed for all other sections of the motorway, especially where the risk of mining subsidence was high.

Figure 9. Cross-section of testing set designed to monitor geomattress deformations below the embankment. Appl. Sci. 2019, 9, 1122 9 of 14

Between years 1995 and 2008 the motorway sections in Silesia were completed, and until today observed.the geomattresses After 10 yearshelped of use,keep the the surface pavement was evaluatedin an undamaged on the basis condition. of the deﬂection To provide measurements a better usingunderstanding FWD, The of measurementcollected deformation was made readings, in the righta graph wheel presenting track, onlythe moni on thetoring outer, results on thefor mostthe loadedfirst year lines. of observation is given on Figure 10.

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Figure 10. Analysis of strain changes in lower and upper (rods) ties of the geomattress built into the embankment, for the first year of exploitation.

Bearing in mind that the permissible value of deformation is 1.5 mm/m, according to the standards of [7,20], the readings proved the sufficient bearing capacity of the used material. The mining works located near the control sections were carried out to the south of the motorway and they reached three different levels: level 418—wall 130 in years 2006–2007; level 502—wall 796 in year 2008; and level 504—wall 006 in years 2010–2011. The location of wall 006 and the measure subsidence is presented in Figure 11. Taking into consideration the location of the excavation walls in the south, it is important to highlight that the motorway was subjected to continuous horizontal deformations in the west direction. When analyzing measured values of the subsidence, it was noted that the summarized vertical deformation of the north line reached 30 cm. The technical assessment indicated that the surface remained preserved in sufficient conditions, and only in two locations single longitudinal cracks were observed. After 10 years of use, the surface was evaluated on the basis of the deflection measurementsFigure 10. Analysisusing FWD, of strain The changesmeasurement in lower was and made upper in (rods) the tiesright of wheel the geomattress track, only built on into the the outer, on theembankment, most loaded for lines. the ﬁrst year of exploitation.

FigureFigure 11. 11. Subsidence ofof the the southern southern roadway roadway with with the location the location of the 006of the wall 006 (300 wall m from (300 the m motorway). from the motorway). Based on deflections measured every 50 m, the standardized deflections were compared with the permissibleBased on values deflections for the measured surface with every the highest50 m, the traffic standardized load (KR7) deflections [27]. The results were compared are presented with in the permissible values for the surface with the highest traffic load (KR7) [27]. The results are presented in Figure 12. The deflections were calculated based on corrected measured deflections of used testing force 50 kN, at temperature of 20 °C, taking into account the month of the measurement. The formula is given below:

DST = D0·(50/F)·fT·fS·fP where: DST—standardized deflection, D0—measured deflection (FWD), fT—coefficient of temperature, Appl. Sci. 2019, 9, 1122 10 of 14

Figure 12. The deﬂections were calculated based on corrected measured deﬂections of used testing force 50 kN, at temperature of 20 ◦C, taking into account the month of the measurement. The formula is given below: DST = D0·(50/F)·fT·fS·fP where:

DST—standardized deﬂection,

Appl.D0—measured Sci. 2018, 8, x FOR deflection PEER REVIEW (FWD), 10 of 15 fT—coefficient of temperature, fS—coefficient of season (September, fS = 1,20), fS—coefficient of season (September, fS = 1.20), fS—coefficient of subbase (flexible pavement, fS = 1,0). fS—coefficient of subbase (flexible pavement, fS = 1.0). The assessment of the pavement deflections (Figure 12) indicates the good technical condition The assessment of the pavement deflections (Figure 12) indicates the good technical condition of of the pavement. Despite the 10-year period of use and additional load, caused by mining the pavement. Despite the 10-year period of use and additional load, caused by mining deformations, deformations, the calculated deflections were lower than the permissible values, assumed for the the calculated deflections were lower than the permissible values, assumed for the highest class of the highest class of the technical condition. However, it should be noted that in the area from 323 + 800 technical condition. However, it should be noted that in the area from 323 + 800 km to 323 + 400 km, km to 323 + 400 km, larger deflections were observed, especially on the southern section, which is larger deflections were observed, especially on the southern section, which is closer to the so-called closer to the so-called zone of the main impacts of mining operations. Such observations could also zone of the main impacts of mining operations. Such observations could also be found in researches be found in researches conducted worldwide [36–38]. The major difference between the different conducted worldwide [36–38]. The major difference between the different studies is that the mining studies is that the mining influenced area studied in the present paper was much more complex and influenced area studied in the present paper was much more complex and specific for this particular specific for this particular region. Despite the difficult working conditions, the material allowed for region. Despite the difficult working conditions, the material allowed for the significant limitation of the significant limitation of the subsidence effect. the subsidence effect.

Figure 12.12. MeasuredMeasured (using (using Falling Falling Weight Weight Deflectometer) Deflectometer and permissible) and permissible deflections deflections of the motorway of the motorwaypavement loadedpavement with loaded KR7 traffic, with KR7 after traffic, 10 years after of 10 exploitation. years of exploitation.

Further analysis of of the technical condition of of the pavement was was based on FWD results, by performing inverse calculations to determine th thee elastic modules for surface layers, using such parameters as as loading loading magnitude, magnitude, circular circular loading loading plain plain radius, radius, and and deformations deformations measured measured using using a geophonea geophone located located within within the the loading loading axis. axis. The The results results of of calculations calculations for for each each layer layer is is presented presented in Figure 13.13. Detailed analysis of the values for the calculated pavement elastic modules indicated that the pavement and the subsoil were of high rigidity, which is in agreement with the assumptions made by Zornberg et al. [39] and Sudarsanan, et al. [40]. At the same time, in the section of increased deflections (i.e., from 323 + 800 km to 324 + 00 km—southern section), the value of modules was reduced. Whereas, the minimum modules did not exceed the minimum value, taking into account the loosening of the substrate with the mining deformations (Figure 13c). The embankment sections, additionally, had a layer of aggregate stabilized by two layers of monolithic geogrids, in the form of geomattresses. The same solution was also included within the dipper layers of the pavement structure. The durability of the applied solution was proved by the values obtained from calculations on the basis of FWD field measurements [18]. To estimate the Appl. Sci. 2018, 8, x FOR PEER REVIEW 11 of 15

Appl.reduction Sci. 2019 of, 9 ,the 1122 module due to the loosening effect, a value of 1,5 mm/m was used. This value11 is ofin 14 line with Polish Mining Area Category I.

Appl. Sci. 2018, 8, x FOR PEER REVIEW 12 of 15

FigureFigure 13.13. CalculationCalculation of moduli for: ( (aa)) Mineral Mineral asphalt asphalt mix, mix, ( (bb)) aggregate aggregate layers, layers, and and (c ()c )subgrade. subgrade.

4. Conclusions In the present paper the geosynthetic applications in road construction in Poland were presented. The use of geosynthetics in the present study concerns the areas of mining influences. The paper aimed at proving the application reliability of such materials in linear infrastructures based on the presented case study. Based on the laboratory tests, the conclusion was that a careful and reasonable determination of vertical deformation of the filing materials is crucial, especially for such working conditions as those met at post-mining sites. When it comes to the present case study, after over 15 years of use the solution still remains effective. The main conclusions drawn from the research were: • The applied measurement system installed at the site allowed a qualitative assessment, indicating the reduction of deformations of the area where geosynthetic layers were applied. • The assessment of the condition of the motorway pavement using the FWD and the calculated modules, based on the back analysis, confirmed the effectiveness of the geomattresses used. For the motorway pavement, a reduction of a maximum of 30 cm was revealed. Nevertheless, the aggregate layer module of the surface was not reduced. The confirmation of this conclusion was the lack of damage on the pavement itself. • The results of the research confirm that mining exploitation with simultaneous use of the aggregate stabilization method with geogrid did not cause significant changes in the stiffness of the pavement layers. It seems that also in the area of the higher mining category, this conclusion can be considered appropriate. However, further research and monitoring needs to be performed at the site. The application of geogrids in combination with anthropogenic materials has proved to be very efficient in terms of a deformation measurement. An important advantage is that tens of thousands of cubic meters of anthropogenic soils have been applied and used for the construction. Such a solution meets the European standards regarding environmental and sustainable development. All the observations, both field and laboratory tests, did not show a negative impact of anthropogenic soils on the properties and behavior of the geogrids used in the study.

Author Contributions: Conceptualization, E.K. and J.K.; methodology, J.K., M.G., and E.K., software, J.K., M.G., E.K., and P.O.; validation, J.K., M.G., and P.O.; formal analysis, J.K. and E.K.; investigation, M.G. and P.O.; resources, J.K. and E.K.; data curation, J.K., M.G., and P.O.; writing—original draft preparation, J.K., M.G., Appl. Sci. 2019, 9, 1122 12 of 14

Detailed analysis of the values for the calculated pavement elastic modules indicated that the pavement and the subsoil were of high rigidity, which is in agreement with the assumptions made by Zornberg et al. [39] and Sudarsanan, et al. [40]. At the same time, in the section of increased deﬂections (i.e., from 323 + 800 km to 324 + 00 km—southern section), the value of modules was reduced. Whereas, the minimum modules did not exceed the minimum value, taking into account the loosening of the substrate with the mining deformations (Figure 13c). The embankment sections, additionally, had a layer of aggregate stabilized by two layers of monolithic geogrids, in the form of geomattresses. The same solution was also included within the dipper layers of the pavement structure. The durability of the applied solution was proved by the values obtained from calculations on the basis of FWD ﬁeld measurements [18]. To estimate the reduction of the module due to the loosening effect, a value of 1.5 mm/m was used. This value is in line with Polish Mining Area Category I.

• The applied measurement system installed at the site allowed a qualitative assessment, indicating the reduction of deformations of the area where geosynthetic layers were applied. • The assessment of the condition of the motorway pavement using the FWD and the calculated modules, based on the back analysis, confirmed the effectiveness of the geomattresses used. For the motorway pavement, a reduction of a maximum of 30 cm was revealed. Nevertheless, the aggregate layer module of the surface was not reduced. The confirmation of this conclusion was the lack of damage on the pavement itself. • The results of the research confirm that mining exploitation with simultaneous use of the aggregate stabilization method with geogrid did not cause significant changes in the stiffness of the pavement layers. It seems that also in the area of the higher mining category, this conclusion can be considered appropriate. However, further research and monitoring needs to be performed at the site.

The application of geogrids in combination with anthropogenic materials has proved to be very efﬁcient in terms of a deformation measurement. An important advantage is that tens of thousands of cubic meters of anthropogenic soils have been applied and used for the construction. Such a solution meets the European standards regarding environmental and sustainable development. All the observations, both ﬁeld and laboratory tests, did not show a negative impact of anthropogenic soils on the properties and behavior of the geogrids used in the study.

Author Contributions: Conceptualization, E.K. and J.K.; methodology, J.K., M.G. and E.K., software, J.K., M.G., E.K. and P.O.; validation, J.K., M.G. and P.O.; formal analysis, J.K. and E.K.; investigation, M.G. and P.O.; resources, J.K. and E.K.; data curation, J.K., M.G. and P.O.; writing—original draft preparation, J.K., M.G. and P.O.; writing—review and editing, P.O.; visualization, J.K. and P.O.; supervision, J.K. and E.K.; funding acquisition, J.K. and E.K. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂicts of interest. Appl. Sci. 2019, 9, 1122 13 of 14

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