Conference Agenda

<p>Geogrid reinforcement of pavements is becoming common practice in civil engineering. But in Australia no design method was available that relates directly to Australian pavement design methodology. A simple design method has been developed that allows rapid, effective geogrid-reinforced pavement design with reference to Austroads pavement design methodology. Case histories are presented that prove the usefulness of this method.</p>

Forest roads are fundamental infrastructures to provide the necessary access to the forest. Most forest roads are unpaved, formed using a superficial layer of unsealed gravel or aggregate, and often local soils or a mix of these two types of material. Herein, two local Portuguese soils were studied, assessing their potential use in unpaved forest roads, namely by including reinforcement with a geocomposites, and by performing CBR and triaxial tests, and estimating key design properties using proposals from the literature. The CBR test results indicate little improvement of the response due to the reinforcement. The triaxial test results show a clear effect of the reinforcement, namely for higher axial strains. The stiffness of the composite material increased relative to the unreinforced soil, particularly for higher strains, and decreased the post-peak softening. The correlations used for estimating the resilient modulus of the soils led to a large scatter of values. Thus, they must be quantified using tests or by proposing adequate relations to other geotechnical properties, extending existing databases.

<p>This paper presents a two-dimensional approach to numerical modeling with finite elements (FE) using PLAXIS 2D Software, where the behavior of three biaxial geogrids located at different depths in a base layer of a flexible pavement structure. The influence of different factors were assessed including the subgrade strength, the geogrid stiffness, the placement depth of geogrid and the strength reduction factor at the interfaces of the flexible pavement structure. Results indicate that the reinforcement with geogrid is more relevant on a weak compressible subgrade. Also, a geogrid with greater stiffness reduces strains in the subgrade and results in a better load distribution. The placement of a geogrid as reinforcement at the base / subgrade interface is recommended to improve the reinforcement results.</p>

<p>For decades, geogrids have been used successfully to improve performance in both paved and unpaved road construction. Even though the current state of practice differentiates between the design methodology incorporating geogrids in paved and unpaved roadways, the true improvement contribution of geogrids is to the base layer, or to the layer that is placed directly on top of it. It has been established that the three reinforcement mechanisms by which geogrids enhance roadway performance are: lateral restraint, bearing capacity increase and membrane tension support. In order to quantify these mechanisms and their contribution to the roadway performance improvement, twelve Cyclic Plate Load (CPL) tests are carried out directly on unsurfaced (no asphalt) roadway section. The tests include control and reinforced sections, as well as two subgrade strengths and three base layer thicknesses. Each test is instrumented with Linear Variable Differential Transducers (LVDTs) at the surface and subgrade levels, and stress transducers at the subgrade level. For the reinforced tests, the geogrids are instrumented with stress and strain gauges. The paper presents the results of these tests, emphasizing the relationship between roadway section configuration, geogrid properties, and the mechanism by which the geogrid contributes to the roadway performance improvement. The results could be used empirically to modify the current state of practice for geogrid contribution in paved and unpaved roadways.</p>

<p>The use of geosynthetic materials has noticeable effects on reducing the growth of reflective cracks in asphalt pavements. Meanwhile, in spite of the positive effects and increasing the number of loads that can be tolerated by the overlay before cracking start, as well as reducing the crack growth rate, due to the reduction of shear strength between asphalt paving layers, some other parameters can be changed. One of the most important effects of changes in shear strength between pavement layers strengthened by geosynthetics is the change in resistance to other failures like rutting. Based on the study conducted in this research, the shear strength between the pavement layers was measured using the AUT-SFT device and then the resistance against rutting was tested for the same samples using a wheel track device. The results showed that the lower the shear strength of the geosynthetic reinforced specimens, shows the higher rut depth in AUT-SLT machine after the end of 600 load cycles.</p>

<p>Several previous studies revealed the benefits of using geogrid and the possibility of using fine lateritic soils abundant in some tropical regions. These materials are being utilized, especially in roads with low traffic volumes, and they present an acceptable mechanic behaviour, which results in a lower overall pavement cost. The analysis of nonconventional materials in pavements is complex, and further investigation is required to understand their performance better. One of the questions that remain is the effectiveness of geogrid when comparing lateritic gravel and granular material. This study presents a laboratory study on seven different test configurations subjected to cycling moving wheels load by using an accelerated pavement test. Tests were conducted on two different base type and thickness, with and without the inclusion of the geogrid, the geogrid position was investigated. All test sections were constructed on a low California bearing ratio clay subgrade, and the reinforced sections had the same geogrid material. Each pavement section performance was evaluated by measuring the surface rutting and the subgrade vertical pressure at different cycles. Findings indicated that the lateritic gravel base pavement sections had lower surface rutting than the granular base, mainly because the lateritic increases the material stability, delaying the occurrence of damage on the gravel. Furthermore, sections modified with geogrids were found to have improved performance than the control sections. Although the 10 cm base reinforced section showed reduced surface rutting than the control section, it did not present similar performance than a 20 cm base control section. Lastly, the traffic benefit ratio showed significantly higher values with the granular base than the lateritic gravel base, indicating that a better interlocking between the geogrid and gravel can be achieved with the granular base.</p>

Biaxial geogrids are often used to reinforce unpaved roads over low strength subgrades. By allowing the unsuitable subgrade to remain in place and allowing for reduced road thick-nesses, substantial reductions in cost and improvements in performance can be achieved. This paper reviews research undertaken at Technological University Dublin where small model testing boxes and instrumented geogrids have been used in combination with representative samples of weak subgrades and high-quality granular fill to simulate the response of biaxial geogrids to monotonic and cyclic plate loading. It was found that the tensile strain measured in the geogrid under test was only a small fraction of the geogrid’s ultimate tensile strain, indicating that the ultimate strength of the geogrid is less important than its interaction with the fill. The magnitude of loading was found to have a more significant effect on displacement than the number of load cycles suffered. It was also found that in-creasing the number of geogrids in the road had a very significant impact on strain and displacement suffered.

<p>The ability to quantify the performance benefits of geosynthetic inclusions in granular pavement layers is a unique challenge. Geosynthetic products in the current market have varying aperture sizes, material types, and manufacturing processes that intend to improve pavement performance through a variety of mechanisms, making quantification of the potential of individual geosynthetic products and the development of a universal design procedure problematic. One approach to quantifying performance benefits is the assessment of geosynthetic inclusions in full-scale testing. While it could be argued that full-scale evaluations provide the most realistic assessment of anticipated performance, full-scale experiments can be logistically burdensome and, at times, cost prohibitive. On the other hand, large-scale laboratory box testing reduces the amount of required materials, reduces required testing time, and reduces required capital investments. Large-scale laboratory box testing has been used for well over 30 years to investigate geosynthetic stabilized pavement structures with well-documented success.   However, a comprehensive testing program to assess the repeatability of large-scale laboratory box testing has not been conducted. In the absence of a comprehensive testing program, two historical studies with multiple test items conducted at the U.S. Army Engineer Research and Development Center were selected to assess the repeatability of current large-scale laboratory test procedures. The two historical studies included multiple pavement profiles representative of both a thick airfield pavement subjected to heavy loading conditions and an aggregate surfaced pavement subjected to highway loading conditions. The assessment of the test procedure included a statistical and engineering evaluation of the reported surface deformation data to estimate repeatability in large-scale box test results and an investigation of potential sources of variability that could influence performance outcomes. The results of these assessments of the large-scale laboratory box experimental procedure represent an initial step to identify expected variability in large-scale box testing.</p>

<p>Analyzing the operation of a pavement with GRC (Geoweb reinforced concrete) and its modeling according to the initial variables: applied loads, traffic, climate, condition of the subgrade, properties of the concrete and the Geoweb base polymer. With this, it is possible to determine the behavior of the GRC pavement through time. This analysis is carried out detailing how the pavement modeling is performed through a mechanisistic methodology of pavement design. Thermal effects and horizontal stress effects are determined. To study fatigue, an analysis of forces and moments is carried out, obtaining the maximal deformation of the subgrade and determining the maximum tensile stress in the system, from which the PCA method and the one proposed in the French pavement manual are implemented. Through this the modeling of the pavement is carried out obtaining the cycles it should be able to withstand.</p>

<p>Roadways include stiff aggregate layers, which support and dissipate traffic loads before reaching the subgrade soil. The aggregate stiffness must be preserved to reduce rutting se-verity. Geosynthetic-stabilisation can preserve the aggregate stiffness through aggregate-geosynthetic interaction at small strains. The performance of geosynthetic-stabilised road-ways depends on the properties of both the geosynthetic and the selected aggregate. A study was completed at the University of Saskatchewan to determine the relative performance of two geogrids used to stabilise two types of aggregate. A recently built full-scale wheel trafficker system applies accelerated traffic loading to 1.5 m wide unsurfaced test sections. Accelerometers were installed on the surface to measure changes in the aggregate stiffness with traffic loading using multichannel analysis of surface waves (MASW). This method facilitates non-destructive measurements of stiffness at numerous depths through-out the aggregate. The average shear wave velocity and rutting performance are presented for each soil-geogrid composite.</p>