The latest revision of the Austroads Pavement Design Guide was issued in 2001 as a final draft for public comment. Previous Guides have been issued in 1979, 1987 and 1992. The Guide represents a major revision of the 1992 edition as it incorporates substantial improvements that have resulted from Australian and overseas research into materials characterisation, traffic assessment, pavement performance studies and design methodology. This paper summarises the work undertaken to revise the guidelines for the design of flexible pavements. (a) For the covering entry of this conference, please see ITRD abstract no. E208402.

Guidelines for the design of flexible pavements for australia

Abstract Volume change in expansive soils due to the intervention of water causes swell. A laboratory investigation using two different gbeosynthetic materials was designed to minimise the swell characteristics. The influence of three parameters, being geosynthetic material [Secutex (ST) and Combigrid (CG)], orientation (horizontal and vertical), and number of layers (1, 2, and 3) on the swell of an expansive soil was studied to better understand the potential for geosynthetics in swell control. The study on the immediate swell characteristics (limited to 24 hours) helps in gaining confidence in the use of geosynthetics in the swell control of expansive soils. From the investigation results, it was found that all three parameters, being type of material, orientation, and number of layers influenced the swell control of the soil. When two layers of ST and CG were placed both vertically and crossed, they reduced the swell of the virgin soil by almost 60% and 44%, respectively. It can, therefore, be concluded that geosynthetics can play an effective role in the swell control of expansive soils.

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A Comparative Laboratory Investigation into the Role of Geosynthetics in the Initial Swell Control of an Expansive Soil

In desert regions, aeolian sand is abundant, but it is not suitable to be used directly as the upper roadbed filler for highways. Generally, gravelly soil is mined around the desert as upper roadbed fill, resulting in high engineering expenses for road construction in the desert hinterland. Geocells have a significant reinforcing effect on aeolian sand. However, in the completed desert highway, the dynamic performance of geocell-reinforced aeolian sand as an upper layer of roadbed fill has not been studied. Using a field test method, the dynamic performance of geocell-reinforced aeolian sand as an upper roadbed fill is examined. The results show that the majority of the frequency distribution of road vibration is within 30 Hz. In the horizontal direction, the actual vibration amplitude decay on the side of geocell-reinforced aeolian sand is slower but smoother than on the side of gravelly soils. In vibration velocity, the work area depth of the geocell-reinforced aeolian sand side of the roadbed is less than that of the gravelly soil side. The maximum difference can reach 0.55 m. As far as vibration velocity is concerned, the 30 cm gravelly soils can be substituted with 15 cm geocell-reinforced aeolian sands as the upper roadbed. In summary, the dynamic attenuation characteristics of geocell-reinforced aeolian sand are superior to gravelly soils. The research results provide a reference for the design of the desert highway subgrade.

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Field Characterization of Dynamic Response of Geocell-Reinforced Aeolian Sand Subgrade under Live Traffic

ABSTRACT In this study, California Bearing Ratio (CBR) tests in a laboratory were performed to observe the effects of geotextiles on bearing capacity ratio, pavement layer thickness, and cost for geotextile reinforced soils. Fourteen geotextile samples, most of which were produced from recycled materials, were used in the experiments. Therefore, physical properties of geotextiles were compared to each other in order to find the most effective type of geotextiles by CBR tests. Then, relationship and adaptation between soil particles and geotextile types were researched by using microscope analyses. Additionally, AASTHO pavement thickness calculations were conducted and cost analysis according to reinforced pavement design were investigated either for reinforced base and for reinforced subbase layers. As a result of the study, it was found that using geotextile can increase CBR behavior, and the bearing capacity ratio values can be more almost 3.5 times than unreinforced models. Each geotextile reinforcement type has a characteristic behavior on the pavement layer and generally, they decrease the pavement thickness and as for long span they can be more economical.

Determining Geotextile Effects on Bearing Capacity Ratio and Cost of Pavement Layers by Conducting CBR Tests

Natural fibers, materials, or plants were used in the early days of geotextile production to improve the condition of roads built on unstable soil. Geofibres have just lately been put to use and tested in modern construction. A highly developed product that must meet a variety of criteria, geofibres have become increasingly popular in recent years. Suitable machinery is needed to produce custom industrial materials. Using geofibres in construction has been a huge success for over three decades. Stronger construction can be achieved by separating sub-grade from sub-base. An example of geosynthetics being utilized to reinforce clayey soil is presented in this publication. Clayey soils were used to prepare laboratory California bearing ratio (CBR) test samples. Thermally bonded nonwoven geofibre-reinforced reinforced soils demonstrate an increase in bearing ratio in these experiments. The load-penetration behaviour of geotextile-reinforced granular soils was studied in a laboratory CBR experiment. Selection and testing of granular soil samples with various gradings are out without the use of reinforcement. So by inserting geotextile at particular depth within the sample heights in one and two layers, impacts of geotextile number and grading on reinforced granular soils and geotextile performance are examined. According to the results of these studies, the bearing ratio of geotextile-reinforced granular soils rises.

Performance evaluation of geofibre sheets on cbr value of soil

The vertical stress exerted by the vehicles will be high in a populated road and to increase the bearing capacity of subgrade characteristics, geosynthetic material can be used. In the current study different geosynthetic material such as geo-grid, geo-textile and geo-membrane were used to as a subgrade reinforcement member inside the CBR mould for understanding the improvement in subgrade  for single, two and three geosynthetic layering  in the CBR mould. The results show there was a constant increase in the bearing with the increase in a number of layers and this improvement varied with type of geosynthetic materials also. Among three geosynhteic materials, geogrid shows improved CBR characteristics. Finally, Cost analysis and design of flexible pavement were carried for an optimum number of layers for geogrids. There was reduction of about 6.38% in the cost of construction when using geogrid as subgrade reinforcement member.

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Shanmugam Ganesh-Kumar

Papers

Functional and cost- benefits of geosynthetics as subgrade reinforcement in the design of flexible pavement