Tensar Technical Presentation June 19 Tensar Technical Presentations June 19 How geogrids improve pavement performance John Buckley Business Manager – Aust./NZ Tensar International Limited Support and training offered by Tensar / Geofabrics - Geofabrics can provide preliminary evaluation assistance and certified designs (if required, for additional cost) for the following applications: - Pavements – temporary and permanent roads - Working platforms for tracked cranes and piling rigs - Mining haul roads - Heavy duty pavements – ports / container yards / airports - Reinforced soil retaining walls / slopes - Geofabrics can assist with technical advice, in-house or seminar training on various Tensar software design packages Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Presentation Outline - PAVEMENTS - Stabilisation concept & explanation - “SmartRock” & other full scale research - Practical considerations? - Available design methods Mechanical Stabilisation June 19 Demo – Extreme Stabilisation Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Explanation of Concepts - Stabilisation History of geosynthetics in roads The Problem The Solution • Wide variety of geosynthetics available since 1970’s • Woven geotextiles • Woven geogrids • Welded geogrids • Punched & drawn geogrids • What are the differences in performance? • How does performance of different products relate to pavement applications? Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Identifying the Problem The Problem Simplified – improve performance (reduce rutting, cracking) of pavement structure within a given design life or traffic loading Considerations: • Unlike most reinforced soil applications, in pavements, geosynthetic is NORMAL to load • Geosynthetics for retaining walls, slopes, embankments are PARALLEL to applied loads to provide stability • Tensar TriAx geogrids work by STABILISING aggregate particles • Established mechanism known as MECHANICAL STABILISATION Mechanical Stabilisation June 19 Benefits of stabilisation with TriAx geogrids Concept of the mechanically stabilised layer - MSL Benefits of Mechanical Stabilisation - Key mechanisms: Interlock Confinement & Lateral Restraint - Low deformation response – load is perpendicular to geogrid - Main aim is thickness reduction or increased life plus protection of subgrade Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 How other products behave? Spec sheets or Index properties – will not provide a true indication of product behaviour in pavements Considerations: • Unlike most reinforced soil applications, in pavements, geosynthetic is NORMAL to load • Geosynthetics for retaining walls, slopes, embankments are PARALLEL to applied loads to provide stability • In pavements, geosynthetics designed on strength need large strains to support wheel loads • Large geosynthetic strain = Large subgrade deformation • This mechanism is known as Tensioned Membrane, MUST HAVE Anchorage & Friction • Suited to unpaved, haul roads under channelised traffic Mechanical Stabilisation June 19 Demonstration of tensioned membrane The tensioned membrane Importance of strength • If the function of the geogrid is something like this • Then strength is important 10 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Where can Tensar geogrids be used? • Subgrade Stabilisation • Soft subgrades to stabilise lower sub-base layers or construction platforms • In combination with non-woven geotextile below for separation, particularly for clay subgrades • Temporary platforms to construct permanent works e.g piling / crane working platforms • Pavement Optimisation • Over firmer subgrades and can be installed higher in pavement to extend pavement life and reduce construction costs • Asphalt Reinforcement • Under deeper asphalt layers to prevent reflective cracking from underlying rigid bases, e.g CTB’s 11 Mechanical Stabilisation June 19 Heavily loaded pavements • Triaxial geogrids have stabilised very heavily loaded platforms • Typical applications are working platforms and heavy duty pavements for container yards 12 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 I want to use TriAx but how I defend the spec? REMEMBER - Spec sheets not provide a true indication of product behaviour in pavements • Have you seen a product sample – what type of product is it? • How will it interact with aggregate? Is there a history of full scale testing for the relevant application? • Junction Efficiency for superior load distribution – specify a value of at least 90% • Radial Secant Stiffness Ratio • This value relates to how geogrid rib stiffness changes around each junction and differentiates between biaxial and triaxial geogrids • For biaxial geogrids, the values range from 0.3 – 0.5 • For triaxial geogrids, the values range from 0.6 – 0.8 • Contact ISCL, Tensar or Geofabrics for a NON-COMMERCIAL triaxial geogrid specification 13 Mechanical Stabilisation June 19 Stabilisation Research – “SmartRock” Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast – Phase I - 2014 ▪ Rail ballast consists of large size angular aggregate particles with uniform gradation to facilitate drainage and load distribution ▪ Fouling of ballast with fines has been a major issue of railway track maintenance Approximately 70-76% of fouling comes from ballast breakdown ▪ Breakdown of ballast occurs due to mechanical wear of sharp edges through repeated loading ▪ Research Objective: Investigate the effect of geogrid on particle movement inside railroad ballast under cyclic loading 15 Mechanical Stabilisation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast – Phase I - 2014 ▪ ▪ ▪ ▪ Test set-up: 250mm of AREMA No Ballast over TX190L Wireless 3D printed “SmartRock” embedded in ballast Control section also constructed 500 cycles of 130 kN applied per test ▪ Measurements carried out: ▪ Smart Rock rotation and displacement on three axes ▪ Sleeper deflection 16 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast ▪ SmartRock is installed above geogrid and records real-time ~ 60mm particle movement including translation and rotation 17 Mechanical Stabilisation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast 18 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 Tensar Technical Presentation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast In translation In rotation So we can see what is actually going on inside the aggregate layer! 19 Mechanical Stabilisation June 19 Composite behaviour “SmartRock” Pennsylvania State University Test of rail ballast ▪ Test set-up Test set-up models this part of the track Sleeper deflection Smart Rocks 20 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 10 Tensar Technical Presentation June 19 Full scale pavement trial carried out by University of Iowa to investigate stresses in pavement layers • Clay subgrade supporting crushed limestone sub-base • Instruments included to measure vertical and horizontal total stresses • Investigation of effects of different geosynthetic layers at subgrade/sub-base interface Stresses in pavement during & after construction Sub-base Subgrade Pressure cell Mechanical Stabilisation - Copyright © Tensar International Limited 2019 15 Tensar Technical Presentation June 19 Horizontal Stress - Subbase Total Horizontal Stress (kPa) 25 Lift Roller Lift Roller Truck Location: Subbase Layer 20 Truck 15 10 W-PP-GT BX1200 Control Section TX160 0 20 40 60 80 100 120 140 160 180 Roller/Truck Cumulative Pass Count Horizontal Stress - Subgrade Total Horizontal Stress (kPa) 25 Lift Roller 20 Lift Location: Subgrade Layer Truck Roller Truck 15 10 W-PP-GT BX1200 Control Section TX160 0 20 40 60 80 100 120 140 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 160 180 16 Tensar Technical Presentation June 19 Subgrade Soil Strength • Soil modulus decreases in proportion to the increasing stress levels thus exhibiting stress-softening type behavior Stabilized case CBR=5% Unstabilized case CBR=3% Stress reduction through TX stabilisation Thompson and Elliot, 1985 BACK Other Full Scale Testing Tensar has a > 30 year involvement in full scale performance trafficking trials to establish the benefits of stabilisation using geogrids Some examples of this include: - U.S Army Corps of Engineers– 800,000 ESAL’s over phases - TRL (UK)- 80,000 ESAL’s over phases - Webster (USACE)– ~100,000 ESAL’s over phases BACK Mechanical Stabilisation - Copyright © Tensar International Limited 2019 17 Tensar Technical Presentation June 19 Other Full Scale Testing - TRL Investigation of pavement performance – Welded Geogrid • 60kN/m biaxial welded geogrid • Investigation of performance under 300mm sub-base layer • Target subgrade CBR 2% Before Trafficking Trafficking After Trafficking Other Full Scale Testing - TRL Control Welded grid 60kN/m Depth below datum (m) 0.1 -0.1 2000 passes -0.2 9000 passes -0.3 -0.4 0.4 0.8 1.2 1.6 0.4 0.8 1.2 1.6 2.4 Passes Distance across section (m) Distance across section (m) 2000 4000 6000 8000 10000 2.4 Welded grid Control Mean rut depth (mm) -20 -40 -60 -80 -100 -120 Tensioned membrane -140 36 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 18 Tensar Technical Presentation June 19 Other Full Scale Testing - TRL Control Tensar TriAx Depth below datum (m) 0.2 4,000 0.1 11,500 passes -0.1 -0.2 -0.3 -0.4 11,500 -0.5 0.4 0.8 1.2 1.6 Distance across section (m) 2000 4000 2.4 Passes 6000 0.4 0.8 1.2 1.6 Distance across section (m) 8000 10000 2.4 12000 Control TX Mean rut depth (mm) -20 -40 -60 Confinement -80 -100 -120 -140 -160 -180 37 Mechanical Stabilisation June 19 Practical Considerations Mechanical Stabilisation - Copyright © Tensar International Limited 2019 19 Tensar Technical Presentation June 19 Construction Details Important construction details: - 300mm overlap both directions, generally - 150mm compacted cover between geogrid & plant - To prevent bow-wave, cascade 1st fill layer onto grid - 75mm max particle size, well graded aggregate for std aperture geogrids, ie TX160 - Multi-tyred roller on initial lift can encourage interlock by ‘kneading’ action 39 Mechanical Stabilisation June 19 Construction Details – Service Trench Reinstatement Service trench width C/L Extent of excavation above geogrid 200mm Surfacing Surfacing Base Base Sub-base 200mm Sub-base Tensar geogrid Subgrade Tensar geogrid Subgrade Establish width of service trench and alignment of centre-line Extent of excavation above Tensar geogrid = Trench Width + 2x200mm Surfacing Base Base 100mm Surfacing Sub-base Excavate by hand Sub-base Cut geogrid at edges Tensar geogrid Subgrade Subgrade Carefully excavate last 100mm over geogrid by hand 40 Tensar geogrid Mechanical Stabilisation Cut geogrid at edges of service trench June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 20 Tensar Technical Presentation June 19 Construction Details – Service Trench Reinstatement (cont’d) Surfacing Surfacing Base Base Sub-base Installed services Excavated service Sub-base trench Tensar geogrid Subgrade Tensar geogrid Subgrade Excavate remaining service trench depth Install services, backfill and compact trench to geogrid level Surfacing Surfacing Base Base Reinstated pavement layers Sub-base Replacement geogrid Sub-base Tensar geogrid Tensar geogrid Subgrade Subgrade Reinstate Tensar geogrid with 200mm overlap 41 Replace and compact remaining pavement layers Mechanical Stabilisation June 19 Available Design Methods Mechanical Stabilisation - Copyright © Tensar International Limited 2019 21 Tensar Technical Presentation June 19 Summary of available software and design approaches Standard Flexible Pavements (15t axle loads): - The Structural Design of Heavy Duty Pavements for Ports and other Industries, Edition (John Knapton-Dec 2007) - PCASE (Pavement-Transportation Computer Assisted Structural Engineering) design software, USACE Mine Haul Roads: - Guideline for Mine Haul Road Design (Tannant & Regensburg-2001), Section 3.20 Design based on CBR - Design of Surface Mine Haulage Roads (Kaufman & Ault) 43 Mechanical Stabilisation June 19 SPOTLIGHT – Heavy Duty Pavements 44 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 22 Tensar Technical Presentation June 19 Container Yard Pavements – Loading Types 45 RTG Front lift truck Straddle carrier Reach stacker Trailer Containers Mechanical Stabilisation June 19 Container Yard Pavements – Possible Failures Trailer jockey wheels indented surfacing Failure of container corner castings Pavement failure – inadequate support 46 foundation? Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 23 Tensar Technical Presentation June 19 Container Yard Pavements – Design Method 47 Mechanical Stabilisation June 19 Container Yard Pavements – Design Input • Wheel Load • Obtained from manufacturer’s data • Repetitions for critical plant • Account for dynamic effects, ie cornering, braking • Allow for asymmetric vehicle loading • Allow for container corner casting loads • Subgrade Conditions • Assessed in the ‘usual’ way – e.g roads • CBR or su • Capping layer (CBR 15%) required if CBR < 5% • Material Parameters • Base material – assumed CBR 80% • Sub-base material – assumed CBR 30% • Surfacing – either concrete slab or pavers (80mm) 48 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 24 Tensar Technical Presentation June 19 Container Yard Pavements – Application Suggestion • Input sheet available • Contact ISCL / Geofabrics / Tensar • Application Suggestion done inhouse by Tensar (KL) • Application Suggestion • Typical output 49 Mechanical Stabilisation June 19 SPOTLIGHT – TensarPave AustRoads module • Inputs • Subgrade CBR – 2-30% • Design Traffic • Fig 12.2 - 1,000 – 100,000 DESA • Fig 8.4 – 100,000 – 100,000,000 DESA • Surfacing – Chip Seal or 40mm Asphalt 50 Mechanical Stabilisation June 19 Mechanical Stabilisation - Copyright © Tensar International Limited 2019 25 ... consists of large size angular aggregate particles with uniform gradation to facilitate drainage and load distribution ▪ Fouling of ballast with fines has been a major issue of railway track... working platforms • Pavement Optimisation • Over firmer subgrades and can be installed higher in pavement to extend pavement life and reduce construction costs • Asphalt Reinforcement • Under deeper... • This value relates to how geogrid rib stiffness changes around each junction and differentiates between biaxial and triaxial geogrids • For biaxial geogrids, the values range from 0.3 – 0.5