Design And Construction Of Geogrid Reinforced Access Roads .
Design and Construction of Geogrid ReinforcedAccess Roads and Drill Platforms Over PeatDeposits in Northern AlbertaR. ManwaringSuncor Energy Inc., Calgary, Alberta, CanadaK. BirkettComplete Crossings Inc., Calgary, Alberta, CanadaJ. KerrTensar International Corporation Inc., Calgary, Alberta, CanadaR. AndersonGeoTrek Land Survey, Calgary, Alberta, CanadaW. DouglasNilex Inc., Calgary, Alberta, CanadaP TarrantSurface Search Inc., High River, Alberta, CanadaABSTRACTIncreased activity in northern Canada is putting pressure on the existing infrastructure in oil and gas, mining, forestrypublic highways and other industries. This is happening at the same time as the demand for materials and manpowergrows. This Increased pressure has led owners, engineers and contractors to utilize more innovative solutions in bothdesign and construction. An example of the need to meet economic and time restraints is one of Suncor Energy Inc.(Suncor) projects in Northern Alberta. The Suncor site is an in-situ oil recovery project located on leases known as"Firebag". The Steam Assisted Gravity Drainage (SAGD) technology uses underground wells to inject steam into the oilsands deposits and collect the bitumen released by the heat. The challenge is that much of the development is foundedon peat, the removal of which would present considerable environmental and cost impact. The use of modern investigative methods and new geogrid products (TriAx ) enabled design and construction to proceed expeditiously. Theuse of LIDAR (light detection and ranging) was combined with Ground Penetrating Radar (GPR) to determine the extentand depth of the peat deposit at each of the multiple sites as well as the connecting road system. This information wasthen supplemented with soils information obtained from boreholes and design was carried out using geogrid reinforcedembankments and reinforced granular surfacing. The design approach was to make the structures as light and strong aspractical in order to reduce the quantity of embankment fill and gravel required for the project. This lighter, strongerstructure was not only more economic but was also safer due the reduction of the applied dead load. The reduced crosssection also resulted in a reduction of the settlement that otherwise would have occurred. A number of these sites havebeen completed to date and more are underway. Those sites that are now in service are performing well andobservations obtained from these sites are being used to fine tune the design and construction of future sites.RÉSUMÉLa croissance de l'activité dans le nord Canadien exerce une pression sur l'infrastructure existante dans les industries dupétrole et du gaz, des mines, de la foresterie, des voies publiques et d'autres. Cela ce produit en même temps que lademande pour les matériaux et la main-d'œuvre est également en augmentation. Cette pression accrue a conduit lespropriétaires, les ingénieurs et les entrepreneurs à utiliser des solutions plus innovantes dans la conception et laconstruction. Un exemple de la nécessité de répondre aux contraintes économiques et de temps, c’est l'un des projetsde Suncor Energy Inc. (Suncor) dans le Nord de l'Alberta. Le site Suncor, c’est un projet de récupération du pétrole insitu situé sur les baux dénommés «Firebag". La technologie de drainage par gravité au moyen de vapeur (SAGD selonson sigle en anglais) utilise des puits souterrains pour injecter de la vapeur dans les gisements de sables bitumineux etpour recueillir le bitume libéré par la chaleur. Le défi réside dans le fait qu’une grande partie de ce développement estfondé sur la tourbe, dont l’extraction présenterait un impact environnemental et économique considérable. L'utilisation de méthodes d'investigation modernes et de nouveaux produits, comme des géogrilles (TriAx ), a permis àla conception et à la construction de procéder rapidement. L'utilisation de la technologie de LIDAR (détection etlocalisation par la lumière) a été combinée avec le géoradar (GPR) pour déterminer l'ampleur et la profondeur du dépôtde tourbe à chacun des multiples sites, de même que le réseau routier les reliant. Cette information a ensuite étécomplétée par des informations sur les sols provenant des forages, et la conception a été élaborée en utilisant desremblais et des revêtements granuleux renforcés avec géogrilles. La démarche de conception était de rendre desstructures aussi légères et aussi solides que possible afin de réduire la quantité de matériau de remblai et de gravierrequis pour le projet. Cette structure légère et plus forte était non seulement plus économique, mais elle était aussi plussécuritaire en raison de la réduction de la charge permanente appliquée. La section réduite a également entraîné uneréduction des tassements qui auraient eu lieu. Un certain nombre de ces sites ont déjà été exécutés à ce jour et d'autres
sont en cours. Ces sites qui sont actuellement en service sont performants et des observations obtenues à partir de cessites sont utilisées pour affiner la conception et la construction des futurs sites.1INTRODUCTION2.2Design and construction of roads and yards founded onpeat has always presented challenges. These includeinvestigation of seasonally inaccessible sites, availabilityof acceptable fill, settlement prediction, construction overextremely soft soils, rapidly rising costs of materials andlabor, to name a few.The use of advanced investigation technologies,geosynthetic reinforcement and proper constructionprocedures has enabled the construction of safer,stronger and more economic structures on a typicalproject in northern Alberta.2PROJECT OVERVIEWA typical project facing the challenges described is theSuncor Energy Inc. (Suncor) project in Northern Alberta.The Suncor site is an in-situ oil recovery project locatedon leases known as "Firebag".2.1DescriptionThe Suncor Firebag site is located 48 km northeast of FortMcMurray, Alberta as shown in Figure 1 (125 km by road).The project is an in-situ oil recovery project located onleases known as "Firebag". The Steam Assisted GravityDrainage (SAGD) technology uses underground wells toinject steam into the oil sands deposits and collect thebitumen released by the heat. The challenge is that muchof the development is founded on peat, the removal ofwhich would present considerable environmental and costimpact.ChallengesThe project presented a number of design andconstruction challenges. One of the biggest challengeswas designing to compensate for settlement. Drillingprocedures require the setting of a casing bowl at apredetermined elevation. The casing bowl is welded ontop of the casing pipe set by the drilling rig. These bowlshave to be completed before the drill rig moves off of thewell pad. Severe complications arise if the elevation ofthis bowl is set too low or two high. Investigating thefoundation conditions and accurate settlement predictionsare mandatory. The time between fill completion andsetting the bowl can be as short as 40 days.Another challenge is the prediction of settlement so asto determine the proper fill quantities and establishingproper design grades that will provide adequate fill depthfor structural purposes and, at the same time keeping thedead weight of the fill as thin (light) as possible.3SITE INVESTIGATIONSite investigation consisted of drilling test holes, groundpenetrating radar (GPR) and Laser Imaging Detection andRanging (LiDAR).3.1DrillingSite drilling was carried out using an ATV mountedcontinuous flight auger. This program was also assistedby manual probing of the muskeg to obtain additionalsamples and calibrate the depth of muskeg obtained fromthe GPR program.3.2Laser imaging Detection and Ranging (LiDAR)Laser Imaging Detection and Ranging (LiDAR) is anoptical remote sensing technology that can measure thedistance to, or other properties of, targets by illuminatingthe target with laser light and analyzing the backscatteredlight (Figure 2). Lidar was used to provide contourmapping of the sites as shown in Figure 3.LiDAR (field readings and analysis) were provided byChallenger Geomatics Ltd. The equipment used was anAirborne Challenger 3D Scout Tool. The data enabled theproject team to plan and position well sites, access roadsand pipelines from their offices in Calgary. The 3D Tooluses LiDAR Digital Terrain Model with an Orthophotooverlay to produce a detailed 3D model of a proposed siteincluding computing design elevations and cut/fillquantities. The 3D Scout Tool also utilizes Google Earth(if needed) to provide a more up to date visual aid toassess potential locations.Figure 1. Site location (Automattic Inc. - WordPress.com)
recorded every 0.5 m ( 0.2m) while driving along existingseismic trail cut-lines and exploratory well site accessroads, at speeds ranging from 3 – 5 km/hour. Surveyposition control for each GPR trace measurement wasaccomplished through real-time digital interfacing of theGPR data logs with Differentially Corrected GlobalSatellite Position (DGPS) readings.Figure 2. Example of LIDAR scanning (National Oceanicand Atmospheric Administration)Figure 4. Photo showing GPR data collection set-up with100 MHz bi-static antenna array towed behind ARGOvehicle.Figure 3. Example of drill pad mapping (ChallengerGeomatics Ltd.)3.3The GPR profile results were processed to enhance allobserved laterally continuous peat bottom signalreflections events and to supress random backgroundRadio Frequency (RF) noise (Figure 5). Peat bottomdepth picks with corresponding location coordinates (fromthe DGPS readings), were digitally extracted from eachindividual GPR data profile set and coalesced into onelarge peat bottom mapping database, which included thesite drilling data obtained within the footprint of aproposed site well pad and associated access road areas.These data were then used to create detailed depth ofpeat contour maps for each site (Figure 6).Ground Penetrating Radar (GPR)Ground Penetrating Radar was used to map the depth ofmuskeg across the site. GPR is a general term todescribe methods that use radio waves to probesubsurface objects or geologic features. GPR is a noninvasive electromagnetic (EM) geophysical technique forsubsurface exploration and characterization. Using radarprincipals, GPR systems transmit impulse electromagneticenergy (i.e. radio waves) into the ground and detectechoes, or reflected wave front energy at surface. Thisprocess is somewhat similar to p-wave seismic reflectionmethods and theoretical similarities exist between thekinematic properties of elastic and electromagnetic wavepropagation.Surface Search Inc. carried out the GPR site surveyprograms using a 100 MHz bi-static GPR antenna arrayTMsystem towed behind an all-terrain ARGO vehicle asshown in Figure 4. GPR profile measurements wereFigure 5. Example of GPR profile data recorded along asection of an existing seismic cut-line with interpreted peatbottom reflection event highlighted using red dash-line.Profile distance (m) is shown along the x-axis, and profiledepth (m) along the y-axis.
Figure 6. Example of peat bottom depth contour map derived from high-density GPR survey data coverage and sitedrilling logs. Blue-green contours reveal peat depths of 0.3 to 1.5 m approximately and red-pink reveal peat depths in theorder of 2.5 to 4.0 m.
4DESIGNThe design of each site had several aspects. First thefoundation soils had to be evaluated to determine thestability and settlement potential for the supportedembankments (roads and drill pads). Secondly, thestability of the embankment fill had to verified followed bythe design of the granular surface to support trafficloadings.4.1FoundationThe foundation for each site was predominantly finefibrous to coarse fibrous peat overlying firm clay till or theoccasional sand layer. Moisture contents of the peattypically varied from 300 to 800 percent. The odd test holeyielded moisture contents as high as 1,200 percent.Amorphous peat was rarely encountered. Peat depthsvaried from no peat to depths of up to four meters.Average depths were in the order of two meters. Inaccordance with regulatory requirements, peat depthsshallower than 0.4 meters are removed. For designpurposes the undrained shear strength of the peat wastaken as 5 kPa.Settlement was taken as a function of the depth ofpeat and the weight of the supported structure. The rateand magnitude of this settlement was monitored startingwith the construction of the earliest sites and is anongoing work in progress. The settlement is taken as afunction of the peat thickness, the applied embankmentweight and the consolidation characteristics observed onthe local fine fibrous peats observed in the geographicalarea over the years. For design purposes, observationfrom the site indicates that the long term settlement is thelesser of half the peat thickness or 37 percent of the fillthickness.4.2Embankment FillFill for the drill pad and roadways mostly consisted ofmedium plastic clay till. The borrow pits were excavatedselectively to avoid non to low plastic clay which were notideal as a fill source. The clay used had an average in situmoisture content of 13 percent with a range of 8 to 19percent and was compacted close to optimum. The3compacted fill had an average density of 20 kN/m andwas estimated to have a friction angle of 27 degrees. Nocohesion was assumed in the stability analysis if thestructure.The surface grade of the drill pad had to be designedas essentially horizontal due to the physical requirementsof the drilling rig. Minor grade slopes were used toachieve surficial drainage. The intent of the embankmentdesign was to keep the fill thickness below a maximumthickness of three meters which was determined to be themaximum thickness that could be achieved withoutresorting to staged construction. The time constraints onconstruction usually precluded the staging option. Theminimum design thickness was taken as 1.5 meters which(after settlement) would keep the traffic surface sufficientlyabove the water table to maintain trafficking serviceability.Drainage of the peat was augmented by attachingNilex Strip Drains with flex ties (two meter spacing) to theupper surface of the geogrid. The drains (3.0 mm thickand 102 mm wide) are spaced at two meter center tocenter spacing. The intent is to ensure that an efficientdrainage path is in place that will facilitate a more timelyrate of settlement.The base of the embankment fill was founded on alayer geotextile placed beneath a geogrid reinforcinglayer. The geotextile was not required for initialconstruction but was selected to facilitate removal of thefill when the site is reclaimed at the end of the service lifeof the site. A non-woven, needle punched textile wasselected for its elongation and durability characteristics. The decision to select biaxial geogrid (TensarBX1100) was based on over thirty years of successfulexperience on similar projects with similar fill thicknesses.At the time that the project started construction, BX1100 would have been replaced with the newer TriAxGeogrids but the lighter versions of these newer geogridswere not yet readily available so the project started with the older BX type geogrids. The full range of TriAxGeogrids is now available and the next series ofstructures will use TX130 instead of BX1100. The grade of TriAx used to reinforce the granular driving surfacewas, however, available.Figure 7. Typical Estimated Settlement4.3Granular Structural SurfaceOnce the data from the LiDAR, GPR and drillingprograms was available, it enabled the civil design group(Complete Crossings and GeoTrek Land Survey), tocomplete the grade drawings. The design was thenreviewed by Tensar International Corporation Inc. and thefinished stamped product was then submitted to Suncorfor approval.A crushed gravel wearing surface was placed on top ofthe clay fill. For design purposes, the strength of the clayfill was taken as having a California Bearing Ratio of twopercent. The slightly conservative CBR 2 was taken inorder to model a year round serviceable road that wouldbe less susceptible to spring-thaw softening. The gravelsurface layer was reinforced in order to achieve astronger, more cost effective surface. The cost of gravel in
this area of the province is escalating significantly. Current3prices are in the order of 100/m (compacted and inplace). The granular surface thickness was 300 mm reinforced with Tensar TriAx 140 Geogrid placed at the base of the gravel. TriAx 140 was selected as it yieldedthe optimum 300 mm design target thickness. Threehundred millimeters is considered the minimum thicknessthat should be used in order to provide ongoingserviceability year round.In accordance with AASHTO 2009 design procedures,the thickness design was based upon performancespecifications rather than material specifications. For thisproject the performance requirements were defined asfollows:61. Equivalent Single Axle Load (EASL) 1.2x102. Maximum rut depth 40mm3. Aggregate CBR 80%4. Subgrade CBR 2%Based upon the Giroud-Hann design method and full scale calibration, Tensar TX140 Geogrid was identifiedas meeting the requirements. This was determined usingTMSpectraPave4 PRO software which uses the GiroudHann method.5CONSTRUCTIONConstruction of this project goes back to 2000-2001 withthe construction of the first drill pad and associatedroadways.5.1 considerably less expensive clay fill. Tensar TriAx 140is then placed and capped with 300 mm of crushedgravel.6CONCLUSIONTo date, the completed drill sites are performing wellalthough settlement in some earlier locations has requiredgrade corrections. This has been achieved usingexpensive crushed gravel – not the ideal solution. Currentconstruction methods (described herein) are expected tomitigate future occurrences.Settlement plates have been installed on current sitesand will be, installed on future pads. An ongoing programof observation and analysis is supplementing designefforts and each completed site enables “fine tuning” forthe next site.ACKNOWLEDGEMENTSThe authors would like to thank Mr. William Redhead ofSuncor for his ongoing input to the design team and hishelp in preparing this paper. The hospitality andassistance of the site personnel at Firebag is alsogratefully acknowledged. Thanks goes to ChallengerGeomatics Ltd. for the LiDAR work done on this project.The authors are very grateful to Suncor for permission towrite this paper.Site PreparationREFERENCESIdeally, the site clearing is started during winter months.Spring construction is also avoided due to regulatoryrequirements concerning the protection of migratory birdnesting. This enables a more efficient removal and alsominimizes disturbance to the peat, the upper surfaceproviding a frozen crust. If clearing has to be carried outduring summer months, lighter equipment has to be usedand even hand clearing. Trees and taller brush areknocked down either by excavator or mulcher and laid asflat as possible over the muskeg. This vegetative mat onthe peat helps ensure that the underlying vegetationremains in an undisturbed state.5.2Embankment FillFabric, geogrid and strip drains are placed first and thenfollowed by the fill. In the winter, embankment fill is placedin lift thicknesses of about 300 mm, compacted and thedensity tested. In the summer, the peat is not strongenough to support thin lift construction methods. The firstlift is 900 mm. The surface of this lift is then compactedand tested. Subsequent fill is placed in 300 mm lifts,compacted and tested in the usual manner.5.3Granular SurfaceOnce the clay subgrade has been allowed to settle, it isthen compacted and tested. Allowing settlement to occurfirst facilitates grade corrections to be achieved using theAASHTO (2009) Standard Practice for GeosyntheticReinforcement of the Aggregate Base Course ofFlexible Pavement Structures. AASHTO PublicationR50-09. American Association of State Highway andTransportation Officials, Washington, D.C.Archer, S. P.E., Wayn
3.2 Laser imaging Detection and Ranging (LiDAR) Laser Imaging Detection and Ranging (LiDAR) is an optical remote sensing technology that can measure the distance to, or other properties of, targets by illuminating the target with laser light and analyzing the backscattered light (Figure 2). Lidar was used to provide contour
Empirical and mechanistic research performed with . the magnitude and depth of the confined zones. . 6 TriAx Geogrid handles soft soils with ease and TriAx Geogrid is easily shipped to your site. provides a strong construction
“Tensar Geogrid Roll Characteristics.” Store Tensar Geogrid rolls in a manner that prevents excessive mud, wet concrete, epoxy or other deleterious . materials from coming in contact with and affixing to . the geogrid. Store geogrids above –20 F (–29 C) and avoid handling below 14 F (–10 C) – the glass-transition
stiff geogrid. With Tensar Biaxial Geogrids, this is done through mechanical interlock,a process where the granular particles partially penetrate the apertures of the geogrid and lock into place as the material is placed and compacted (Figure 1). This process is also often referred to as “mechanical confinement.”
ABSTRACT: Cyclic pUll-out tests were conducted to measure the resistance of geogrids in embankments to dislocation during earthquakes. Two steel boxes were used as soil containers, and a piece of geogrid was laid between the two boxes. The geogrid was pulled out under the following two load conditions: (1) a static overburden pressure .
box pull-out experiments to valid ate the simulation results. They found that the optimum ratio between geogrid aperture size and aggregate size was around 1.4. This paper firstly presents large box pull-out test results with a biaxial geogrid. For the DEM simulations, four different shapes of clumps were used to represent each ballast particle in
reinforce a soil mass directly behind the retaining wall and provide connection to the concrete facing units. Geogrid properties and wall design require knowledge of wall heights, soil properties (Phi angle and moist unit weight), surcharge loads and manufacturer's requirements for specific geogrid types and strength capabilities.
drilled shaft 4 Core fill and #3 horizontal rebar in all block courses except grout and #3 horizontal rebar on top 5 courses. Geogrid Precut around drilled shaft 5 Core fill, #3 horizontal rebar in all block courses. Masonry glue on top 5 block courses Geogrid Precut around drilled shaft 6 Core fill and #3 horizontal rebar in all block
NDOT Research Report Report No. 327-12-803 Use of GEOGRID for Strengthening and Reducing the Roadway Structural
