R. W. I. Brachman

Barrier Systems for Waste Disposal Facilities

1. Basic Concepts. 2. Leachate Characteristics and Collection. 3. Clay Liners: Compaction, Hydraulic Conductivity and Clay Mineralogy. 4. Clay/Leachate Compatibility by Measurement of Hydraulic Conductivity. 5. Flow Modelling. 6. Chemical Transfer by Diffusion. 7. Contaminant Transport Modelling. 8. Evaluation of Diffusion and Distribution Coefficients. 9. Field Studies of Diffusion and Hydraulic Conductivity. 10. Contaminant Migration in Intact Porous Media: Analysis and Design Considerations. 11. Migration in Fractured Media: Analysis and Design Considerations. 12. Geosynthetic Clay Liners (GCLs). 13. Geomembrane Liners. 14. Covers. 15. Geotechnical and Related Design Issues. 16. Integration of Hydrogeology and Engineering in Barrier Design and Impact Assessment. Index.

Estimating liquefaction-induced ground settlements from CPT for level ground

An integrated approach to estimate liquefaction-induced ground settlements using CPT data for sites with level ground is presented. The approach combines an existing CPT-based method to estimate liquefaction resistance with laboratory test results on clean sand to evaluate the liquefaction-induced volumetric strains for sandy and silty soils. The proposed method was used to estimate the settlements at both the Marina District and Treasure Island sites damaged by liquefaction during the Loma Prieta, California, earthquake on 17 October 1989. Good agreement between the calculated and measured liquefaction-induced ground settlements was found. The major factors that affect the estimation of liquefaction-induced ground settlements are also discussed in detail. The recommendations for taking the effects of these factors into account in estimating liquefaction-induced ground settlements using the proposed CPTbased approach are presented. It is suggested that the proposed method may be used to estimate liquefaction-induced settlements for lowto medium-risk projects and also to provide preliminary estimates for higher risk projects.

Evaluation of side wall friction for a buried pipe testing facility

Abstract Methods of limiting the mobilization of boundary friction during large-scale laboratory testing of buried pipes (geopipes) are investigated. A small scale investigation using a direct shear apparatus examined the effectiveness of different configurations of unlubricated and lubricated geosynthetic treatments intended to reduce the boundary friction mobilized between a steel–soil interface. Results from direct shear tests indicated that applying a double layer of thin polyethylene sheeting lubricated with silicon grease yielded an angle of friction of about 5°, provided that the interface treatment received adequate protection from the backfill material. Tests conducted in the large-scale test facility suggest that this interface treatment successfully limits boundary effects arising from interface friction.

Antioxidant Depletion from a High Density Polyethylene Geomembrane under Simulated Landfill Conditions

Accelerated aging tests to evaluate the depletion of antioxidants from a high density polyethylene geomembrane are described. The effects of temperature, high pressure, and continuous leachate circulation on the aging of geomembranes in composite liner systems are examined. The antioxidant depletion rates (0.05, 0.19, and 0.41  month−1 at 55, 70, and 85°C , respectively) obtained for the simulated landfill liner at 250 kPa vertical pressure are consistently lower than that obtained from traditional leachate immersion tests on the same geomembrane (0.12, 0.39, and 1.1  month−1 at 55, 70, and 85°C ). This difference leads to a substantial increase in antioxidant depletion times at a typical landfill liner temperature ( 35°C ) with 40 years predicted based on the data from the landfill liner simulators tests, compared to 15 years predicted for the same geomembrane based on leachate immersion tests. In these tests, the crystallinity and tensile yield strain of the geomembrane increased in the early stages of ...

Thermal Expansion and Contraction of Geomembrane Liners Subjected to Solar Exposure and Backfilling

AbstractGeomembranes (GMBs) are widely used as advective barriers in landfill liner systems. When exposed to the sun, GMBs exhibit a network of wrinkles as a result of thermal expansion. These wrinkles disrupt the intimate contact between the GMB and the underlying layer. If a hole is coincident with a GMB wrinkle then the space under the wrinkle has the potential to act as a preferential pathway for flow of contaminants. Thus, the size and shape of GMB wrinkles have implications for leakage rates through the composite liner system. However, wrinkles are only a concern if they persist after placement of backfill, which is currently a subject of debate. In this paper, wrinkles are induced in a 1.5-mm-thick, black high-density polyethylene strip GMB specimen overlying a geosynthetic clay liner using natural solar and laboratory energy sources. Particle image velocimetry techniques are employed to record cross-sectional wrinkle geometry during growth and subsequent backfilling. This cross-sectional geometry ...

Ground Displacements from a Pipe-Bursting Experiment in Well-Graded Sand and Gravel

Pipe bursting is a construction technique that involves the replacement of an existing buried pipe with potentially much less surface disturbance than traditional cut and cover construction. However, excessive ground movements associated with pipe-bursting operations may lead to damage to surrounding infrastructure. A static pipe-bursting experiment was performed in sand and gravel within an 8-m-long, 8-m-wide, and 3-m-deep test pit to quantify the ground displacements from pipe bursting. An existing unreinforced concrete pipe buried 1.385 m below the ground surface was replaced with a high-density polyethylene pipe. Pulling force and the three-dimensional nature of surface displacements associated with pipe bursting are examined. The 4-m wide surface response had a peak vertical displacement of 6 mm. In addition, transverse displacements of 1.2 mm resulted in the formation of a tension crack in the ground above the concrete pipe. This experiment offers data that improves the understanding of the mechanisms of ground disturbance, and provides unique experimental data for calibration of numerical models.

Service Life of a High-Density Polyethylene Geomembrane under Simulated Landfill Conditions at 85°C

AbstractThe time to rupture of a 1.5-mm-thick high-density polyethylene geomembrane aged in a typical landfill composite liner configuration is investigated under a pressure of 250 kPa at 85°C. The geomembrane was underlain with a geosynthetic clay liner and had a 560 g/m2 needle-pinched nonwoven geotextile protection layer separating it from 50 mm of drainage gravel containing leachate. Seventeen (0.6-m-diameter) tests were conducted. In addition to 9 months required to deplete antioxidants (Stage I), the tests indicated a lag period (Stage II) of 5.5 months and a time from the start of degradation to rupture (Stage III) of 20 months, giving a total inferred time to rupture of 34.5 months (2.9 years). There were up to 61 brittle ruptures per sample (i.e., >2 million cracks per hectare). The ruptures were predominately oriented in the machine direction and located (1) directly beneath a gravel contact, (2) at the side of a gravel indentation, or (3) between gravel indentations. The ruptures between gravel...

Ultimate Limit State of Deep-Corrugated Large-Span Box Culvert

Limit state design requires independent assessment of both load and resistance. Although much is known about the live and dead loads that may act on box culverts, there is no known measurement of the resistance (or capacity) at the ultimate limit state. The objective of this study is to present results from a full-scale experiment conducted on a buried, deep-corrugated, large-span box culvert under controlled laboratory conditions—the first conducted to its ultimate limit state. The box culvert had a 2.4-m rise and 10-m span (7.9 × 32.8 ft) and was fabricated from steel plate 6 mm thick with corrugations 150 mm deep at a 400-mm pitch (0.24 × 6 × 16 in.). The box culvert was backfilled to a minimum cover depth of 0.45 m (1.5 ft) with densely compacted well-graded sand and gravel. Tandem-axle loading was then applied by an actuator until an ultimate limit state was attained. The ultimate limit state of the box culvert involved the formation of plastic hinges at the crown and shoulders at a total applied force of 1,100 kN (250 kips). The force required to reach the ultimate limit state was 1.8 times larger than the factored design tandem-axle load from the AASHTO bridge design specifications. Similarly, the factored resistance at the ultimate limit state was 1.7 times larger than the factored CL-625-ONT tandem-axle load from the Canadian highway bridge design code.

Laboratory Study of Downslope Erosion for 10 Different GCLs

AbstractThe potential for downslope bentonite erosion from a geosynthetic clay liner (GCL) subjected to an imposed daily surface flow of deionized water is examined for 10 GCLs with different carrier and cover geotextiles, bentonite (powdered and fine and coarse grained and some with a polymer-enhancement additive), and a polypropylene coating on the carrier geotextile. The erosion was similar but more visible in products with a white geotextile than in those with a black geotextile. Also, the erosion features were similar but more visible with nonwoven geotextiles than with woven geotextiles. Polymer-enhanced sodium bentonite substantially slowed the formation of erosion features. A polypropylene coating over the upper geotextile prevented erosion features from developing by keeping water from penetrating into the bentonite layer when subjected to 60 daily imposed-flow/air-drying cycles.

Thickness and Hydraulic Performance of Geosynthetic Clay Liners Overlying a Geonet

Experimental results from physical testing are reported to examine the thickness and hydraulic performance of three geosynthetic clay liners (GCLs) overlying a geonet when subjected to vertical stresses (e.g., as may be found in a secondary leachate collection layer or hydraulic control layer in solid waste landfills). The GCL was found to intrude into the underlying geonet and the effects of GCL type and water content, temperature, applied pressure, and test duration on the final GCL thickness are examined. The results are consistent with GCL deformation from the beneficial consolidation of bentonite as opposed to lateral extrusion of bentonite. Results from fixed ring flow tests suggest that the indentations in the GCL caused by intrusion into the underlying geonet do not appear to negatively impact the hydraulic performance (permittivity or resistance to internal erosion) of the particular GCLs tested for the conditions examined. The flow capacity of the geonet in these tests was found to depend not only on the amount of GCL intrusion but also on the orientation of the geonet relative to the flow direction.