No abstract

A new method of evaluating strains and predicting required protection layers that are placed over geomembranes is developed based on the combined effects of the clay strength and stiffness and the cushioning effect of a nonwoven protection layer. Plots giving the required geotextile protection for different maximum strains are presented for expected landfill pressures under 300 kPa for angular, 38 mm gravel placed above a geomembrane liner for both drained and undrained loading conditions of the clay. A similar plot is also given for tire-derived aggregate placed above the liner for pressures under 500 kPa for undrained loading conditions. All tests were conducted at room temperature. For all cases, nonwoven geosynthetic protection layers with mass per unit area (MUA) exceeding at least 1200 g/m2 were required to limit long-term strains below current threshold levels. The MUA of the protection layer, for the particular aggregates and geomembranes tested, is dependent on the loading rate, water content relative to optimum, the silt content, and the activity of the clay below.

High localized strain in geomembranes caused by indentations from coarse, uniform drainage aggregate is associated with long-term stress cracking and has been widely studied. A number of large-scale lab tests were carried out with direct measurement of the distribution of the major and minor principal (engineering) strain across the area of a large laboratory sample of geomembrane. This ‘grid-point’ method of strain estimation is compared to the method developed by Tognon et al. which has been recommended as the best available approach at this time. It has been found that the method by Tognon et al. tends to over- and under-predict geomembrane strain depending on the aggregate and protection layers used. Indentations with higher smaller ratios of membrane to bending strains tend to be underestimated. A correction factor is proposed based on the ratio of membrane to bending strains and fits the measured grid strain method used in this study well.

Reliable, low-cost datalogging alternatives promote transfer of knowledge and technology to the wider geotechnical and geoscientist community. Alternative systems can ease increased data resolution on large projects, operate in remote locations with restricted site access, or allow developing countries access to reliable and cost-effective datalogging solutions. A low-cost prototype datalogger was developed and tested in the laboratory with the use of open-source materials. Open-source example code is provided at the permanent links included in this paper. The materials for the prototype were 20 % the cost of commercial datalogging units with similar capabilities. With labor, these custom-built units were 35–45 % the cost of a purchased datalogger. Measurements from commercial units and the prototype datalogger were compared to determine the prototype’s accuracy. The datalogger was deployed in place of commercially available dataloggers at three sites across western Canada in the past two years. Laboratory and field testing of the low-cost datalogger has shown the prototype to be easily adaptable to various sensor types. The study experimented with negative pore water pressure (matric suction), volumetric water content, and temperatures from SDI-12 sensors as well as positive pore water pressure and temperature from vibrating wire piezometers. Telemetry modules have been attached to remote dataloggers, transmitting occasional data points, and periodically verifying system operation. Assembly, installation, and monitoring with the low-cost datalogging system over the past two years has demonstrated their durability in field applications. The implementation of a low-cost, open-source geotechnical datalogging system can be a challenge in some locations and requires the consideration of limitations, which are addressed.

No abstract