Abdelmalek Bouazza

Geosynthetic clay liners

Abstract Over the past decade, geosynthetic clay liners (GCLs) have gained widespread popularity as a substitute for compacted clay liners in cover systems and composite bottom liners. They are also used as environmental protection barriers in transportation facilities or storage tanks, and as single liners for canals, ponds or surface impoundments. As a result, they are being investigated intensively, especially in regard to their hydraulic and diffusion characteristics, chemical compatibility, mechanical behaviour, durability and gas migration. In this paper, a review of the main findings is presented with the focus on the critical aspects affecting the service life of GCLs. From this work, a general insight is gained on the design implications for systems that incorporate GCLs.

Gas permeability of geosynthetic clay liners

Abstract Series of gas permeability tests were performed on partially saturated needle-punched geosynthetic clay liners (GCLs) with nitrogen (N2) as the gas permeant medium. The hydration procedure was found to have a strong influence on the gas permeability of the GCLs. For the range of overburden pressures considered in the present investigation, a reasonable linear relationship on a linear-log scale has been observed between the permeability and the volumetric water content. A decrease of around 1 to 1.5 order of magnitude in the permeability of a granular bentonite type of GCL and about 2 to 3 order of magnitude in the permeability of a powder bentonite type of GCL have been observed for the range of volumetric water content studied (46%

Field and Laboratory Investigation of a Heat Exchanger Pile

Incorporation of heat exchangers into pile foundations is a relatively novel sustainable technology for the intermittent storage of energy in soils. Energy can be utilised in this way for space heating and cooling of buildings by means of suitable systems integrated into buildings. This paper relates to an ongoing study on the impact of coupled thermo-mechanical loads on heat exchanger pile foundations. This study evaluates the performance of a laboratory scale energy pile under different vertical stress levels, temperature gradients and heat transfer modes and presents the full-scale in situ energy pile setup equipped with ground loops for heating/cooling and multi-level Osterberg cells for static load testing.

Determining Soil Thermal Conductivity Through Numerical Simulation of a Heating Test on a Heat Exchanger Pile

Heat exchanger pile foundations have a great potential of providing space heating and cooling to built structures. This technology is a variant of vertical borehole heat exchangers. A heat exchanger pile has heat absorber pipes firmly attached to its reinforcement cage. Heat carrier fluid circulates inside the pipes to transfer heat energy between the piles and the surrounding ground. Borehole heat exchangers technology is well established but the heat exchanger pile technology is relatively new and requires further investigation of its heat transfer process. The heat transfer process that affects the thermal performance of a heat exchanger pile system is highly dependent on the thermal conductivity of the surrounding ground. This paper presents a numerical prediction of a thermal conductivity ground profile based on a field heating test conducted on a heat exchanger pile. The thermal conductivity determined from the numerical simulation was compared with the ones evaluated from field and laboratory experiments. It was found that the thermal conductivity quantified numerically was in close agreement with the laboratory test results, whereas it differed from the field experimental value.

Numerical Characterization of Advective Gas Flow through GM/GCL Composite Liners Having a Circular Defect in the Geomembrane

Numerical experiments were conducted to understand the effect of geometric and transport characteristics of a geomembrane-geosynthetic clay liner (GM/GCL) composite liner on gas leakage rate through a circular defect in the geomembrane (GM). The originality of the approach proposed in this paper rests on the use of a new conceptual two-layered system for modeling of GM/GCL composite liners where the interface zone between the GM and geosynthetic clay liner (GCL) has been merged with the GCL cover geotextile and handled as one layer; the GCL bentonite layer was considered the second layer. The role of the carrier geotextile layer was ignored since it can be considered as a no pressure loss layer. Analysis of numerical simulation results shows the existence of a constitutive leakage flow surface which enables evaluation of the leakage flow state for different geometric and transport properties of GM/GCL composite liners. Furthermore, the determined surface was also exploited to evaluate gas leakage rates under the framework of the Forchheimers analytical solution. The gas leakage rate predictions were found to be in good agreement with experimental results obtained at different GCL moisture content.

Modeling and Laboratory Assessment of Capillary Rise in Stabilized Pavement Materials

Capillary rise tests were carried out on marginal material (scoria) stabilized with two cementitious additives, general purpose cement, and general blended cement up to 5.5% by dry weight. The test results indicated that capillary rise occurred along the entire specimen height of 345 mm (100%) for both specimens. The rate of rise and the water absorption reduced as the binder content was increased, and a similar trend was found for specimens cured at 7 to 28 days. The saturated hydraulic conductivity and porosity were found to be approximately 10-8 m/s and 0.3, respectively. The theoretical basis for the capillary rise is explained by using the simple capillary tube model and water retention characteristics. A simplified model was developed to analyze the capillary rise tests. The model appeared to present the capillary characteristics reasonably well. On the basis of the theoretical approach presented, the test appears to be directly relevant to the field scenario when free water is available at the base of the pavement; however, other scenarios may be simulated approximately.

SOME MECHANICAL PROPERTIES OF RECONSTITUTED BOOM CLAY

SummaryThe mechanical behaviour of reconstituted normally consolidated Boom clay was examined in a series of laboratory triaxial stress path tests. The aim was to establish some basic characteristics of this soil. The compressibility of the reconstituted Boom clay was found to be moderate, corresponding to the soils of the same plasticity. The results indicated also that the destructured Boom clay exhibited a brittle behaviour. The undrained secant stiffness was found to vary with strain level and also to be dependent on the consolidation pressure.

Thermomechanical Behavior of Saturated Geosynthetic Clay Liners

AbstractThe aim of this study is to assess experimentally the volume change behavior of geosynthetic clay liners (GCLs) under elevated temperatures. Such elevated temperatures can be generated in landfills as the result of biological decomposition of organic matter in municipal solid waste. A modified consolidometer capable of handling temperatures up to 60°C was utilized for this purpose. A series of thermomechanical consolidation tests were performed on two different GCLs at different elevated temperatures, varying from 20 to 60°C, and different vertical stress levels (50, 100, and 150 kPa). The results show that the thermally induced volume change is stress dependent. A preliminary conceptual explanation for this behavior is introduced and discussed in this study.

Friction characteristics of a nonwoven geotextile and peat

Abstract Embankments on peat present a difficult problem for present day highways because of their heavy traffic loads. It has been customary to avoid peat lands when planning the construction of a highway, and this is still the preferred solution. However, as land becomes more scarce and more areas become populated the choice of highway gets narrower. The present note pertains to peat from the Gue de Constantine area, near Algiers (Algeria), and also to reinforced peat. The site is to be developed to accommodate an extension to the eastern highway. Use of a geotextile has been recommended for the improvement of the embankment foundation and friction characteristics obtained from shear tests of a nonwoven geotextile in a peat are presented and discussed.

STRENGTH PROPERTIES OF CEMENT TREATED COODE ISLAND SILT BY THE SOIL MIXING METHOD

Coode Island Silt (CIS) is one of the youngest formed sedimentary foundations in the Melbourne geological region of the Yarra Delta. Because it is a highly compressible material, CIS imposes geotechnical constraints on the design and performance of infrastructure works. This paper investigates the effectiveness of using soil mixing technology via cement stabilization of CIS by studying the improvement of the strength of treated soils. Tests were carried out in two stages: (1) laboratory based stabilization of CIS; and (2) small scale model mixing. The improvement in terms of strength was assessed using unconfined compressive strength (UCS) test. A small-scaled model mixing was set up to mimic the actual mixing scenario on sites. Although it may not be perfect, it gives an indication on the effectiveness of the cement slurry when combining with the silty clay.