Comprehensive Review of Geotechnical Engineering Properties of Recycled Polyethylene Terephthalate Fibers and Strips for Soil Stabilization.

The waste management of plastic has become a pressing environmental issue, with polyethylene terephthalate (PET) being one of the major contributors. To address this challenge, the utilization of recycled PET fibers and strips in geotechnical engineering applications for soil stabilization has gained considerable attention. This review aims to provide a comprehensive study of the geotechnical engineering properties of recycled-PET-reinforced soils. The review examines various factors influencing the performance of PET-reinforced soils, including PET percent content, fiber length, and aspect ratio. It evaluates the mechanical properties, like shear strength, compressibility, bearing capacity, hydraulic behavior, and durability of recycled-PET-reinforced soils. The findings reveal PET reinforcement enhances shear strength, reduces settlement, and increases the bearing capacity and stability of the soil. However, it is observed that the incorporation of recycled PET fibers and strips does not lead to a significant impact on the dry density of the soil. Finally, an environmental and cost comparison analysis of recycled PET fibers and strips was conducted. This review serves as a valuable resource for researchers, engineers, and practitioners involved in the field, offering insights into the geotechnical properties of PET-reinforced soils and outlining future research directions to maximize their effectiveness and sustainability.

Improvement of Geotechnical Properties of Clayey Soil Using Biopolymer and Ferrochromium Slag Additives.

The geotechnical properties of clay soil and its mixtures with different proportions (0.75%, 0.85%, 1%, and 1.15%) of Agar Gum biopolymer and Ferrochromium Slag (0.25%, 0.50%, 0.75%, and 1%), having various curing times and freeze-thaw cycles, were studied through a series of soil mechanical tests to investigate possibilities to improve its undesired/problematic plasticity, compaction, and shear strength characteristics. The results revealed that treatment with an optimal ratio of 1% Agar Gum and 1% Ferrochromium Slag alone, as well as together with, improved the geotechnical properties of the clay soil considerably. Both the unconfined and shear strength properties, along with the cohesion and internal friction angle, increased as much as 47 to 173%, depending on the curing time. The higher the curing time, the higher the shear strength, cohesion, and internal friction angle are up to 21 days. Deteriorating the soil structure and/or fabric, freeze-thaw cycles, however, seem to have an adverse effect on the strength. The higher the freeze-thaw cycle, the lower the shear strength, cohesion, and internal friction angle. Also, some improvements in the plasticity and compaction properties were determined, and environmental concerns regarding Ferrochromium Slag usage have been addressed.

Marble Powder as a Soil Stabilizer: An Experimental Investigation of the Geotechnical Properties and Unconfined Compressive Strength Analysis.

Fine-grained soils present engineering challenges. Stabilization with marble powder has shown promise for improving engineering properties. Understanding the temporal evolution of Unconfined Compressive Strength (UCS) and geotechnical properties in stabilized soils could aid strength assessment. This study investigates the stabilization of fine-grained clayey soils using waste marble powder as an alternative binder. Laboratory experiments were conducted to evaluate the geotechnical properties of soil-marble powder mixtures, including Atterberg's limits, compaction characteristics, California Bearing Ratio (CBR), Indirect Tensile Strength (ITS), and Unconfined Compressive Strength (UCS). The effects of various factors, such as curing time, molding water content, and composition ratios, on UCS, were analyzed using Exploratory Data Analysis (EDA) techniques, including histograms, box plots, and statistical modeling. The results show that the CBR increased from 10.43 to 22.94% for unsoaked and 4.68 to 12.46% for soaked conditions with 60% marble powder, ITS rose from 100 to 208 kN/m2 with 60-75% marble powder, and UCS rose from 170 to 661 kN/m2 after 28 days of curing, molding water content (optimum at 22.5%), and composition ratios (optimum at 60% marble powder). Complex modeling yielded R2 (0.954) and RMSE (29.82 kN/m2) between predicted and experimental values. This study demonstrates the potential of utilizing waste marble powder as a sustainable and cost-effective binder for soil stabilization, transforming weak soils into viable construction materials.

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material.

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress-strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm3 to 1.72 g/cm3 with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10-9 cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd2+, Mn2+ and Cu2+ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Qmax) of Cu2+, Cd2+ and Mn2+ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu2+, Cd2+, and Mn2+ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills.

Pond ash as a potential material for sustainable geotechnical applications - a review.

Energy-harnessing sources significantly influence a country's infrastructure and economic development. Though nuclear and hydel power sources are used for energy harnessing, thermal sources are still the primary power source in India and contribute to 75% of the demand. Thermal power plants exploit large volumes of coal reserves. The combustion of coal leads to 30%-40% of waste ash residues such as Fly ash and Bottom ash. Though Fly ash finds greater applicability, pond ash poses a severe environmental hazard due to its large occupancy of terrain in ash dykes and lagoons. Many research efforts are underway to utilize pond ash in various structural and geotechnical infrastructure projects; however, there are still limitations and apprehensions about its properties and determination. The present study provides a detailed review of the morphological and chemical properties. Further, the geotechnical attributes of pond ash, including strength characteristics, consolidation parameters, and durability aspects, are critically reviewed for the probable application as fill material for backfill and many other applications. Based on the earlier research on pond ash, it could be comprehended that pond ash has wide property variability and finds compatibility with many other pozzolanic admixtures and, in this way, finds broader applicability in geotechnical projects. The way forwards could be a significant step towards cleaner and greener technology.

An integrated characterisation of incineration bottom ashes towards sustainable application: Physicochemical, ecotoxicological, and mechanical properties.

Environmental protection is a central concern regarding municipal solid waste incineration bottom ash (IBA) management, but the assessment of waste Hazardous Property HP14 (ecotoxicity) is still under debate. Civil engineering applications may be a suitable management strategy. This work aimed at evaluating IBA regarding mechanical behaviour and environmental hazardous potential, including a biotest battery for ecotoxicity assessment (comprising miniaturised tests), to explore its potential for safe utilization. Physical, chemical, ecotoxicological (Aliivibrio fischeri, Raphidocelis subcapitata, Lemna minor, Daphnia magna, Lepidium sativum), and mechanical (one-dimensional compressibility, shear strength) analyses were performed. The low leaching for potentially toxic metals and ions complied with European Union (EU) limit values for non-hazardous waste landfills. No relevant ecotoxicological effects were found. The biotest battery seems suitable for ecotoxicological assessment in the aquatic ecosystem, providing wide information on waste impact on different trophic/functional levels and chemical uptake routes, simultaneously involving short-duration tests and reduced amounts of waste. IBA presented more compressibility than sand, but its mixture with sand (30%:70%) was closer to sand compressibility. IBA (lower stresses) and the mixture (higher stresses) showed slightly higher shear strength than sand. Overall, IBA presented the potential for valorisation as loose aggregates from an environmental and mechanical viewpoint in a circular economy framework.

Geotechnical and environmental radioactivity investigations at Al Sadis Min Uktober city, Cairo municipality (Egypt), for the high-speed railway construction.

The present study aims to evaluate the possibility of constructing a new high-speed railway (HSR) at Al Sadis Min Uktober city, Cairo (Egypt): geotechnical and environmental radiological hazards are estimated from several collected soil and water samples. A variety of laboratory geotechnical tests such as grain size, free swelling test, liquid and plastic limits, chemical analysis and uniaxial compression strength are applied to sixty-one drill holes. A geotechnical examination of the coarse-grained soil at the foundation level classified it as poorly graded soil. The results of the investigation of fine-grained soil at the foundation level shown that the liquid limit ranges from 22% to 55%, the plastic limit ranges from 12% to 28%, the plasticity index varies from 11% to 33%, free swelling varies from 51% to 71%. Mechanically, the uniaxial compressive strength values on rock samples range from 6.96 MPa to 142.39 MPa. The radioactive study is performed to detect the 226Ra, 232Th, and 40 K activity concentrations of the soil samples: their mean values are 34 ± 10 Bq·kg-1, 14 ± 5 Bq·kg-1 and 552 ± 20 Bq·kg-1, respectively. The values of radiological hazard indexes are not exceeded the permissible limits: e.g. the mean value of absorbed dose rate is 47 ± 6 nGy h-1; the annual gonadal dose equivalent is 0.3 ± 0.04 mSv·y-1; the lifetime cancer risk is 02 ± 0.2·10-3. Thus, the soil in the studied railway area is safe to use in building materials and infrastructure applications: the radiological hazards and the geotechnical studies confirmed the studied area is suitable to construct a new community having a HSR. According to the SWOT-PEST and environmental impact analyses, the construction of the HSR meets the criteria of the Kyoto Protocol, the EU Climate and Energy policy, and other international treaties.

Geotechnical and Shear Behavior of Novel Lunar Regolith Simulants TUBS-M, TUBS-T, and TUBS-I.

The return to the Moon is an important short-term goal of NASA and other international space agencies. To minimize mission risks, technologies, such as rovers or regolith processing systems, must be developed and tested on Earth using lunar regolith simulants that closely resemble the properties of real lunar soil. So far, no singular lunar simulant can cover the multitude of use cases that lunar regolith involves, and most available materials are poorly characterized. To overcome this major gap, a unique modular system for flexible adaptable novel lunar regolith simulants was developed and chemically characterized in earlier works. To supplement this, the present study provides comprehensive investigations regarding geotechnical properties of the three base regolith simulant systems: TUBS-M, TUBS-T, and TUBS-I. To evaluate the engineering and flow properties of these heterogeneous materials under various conditions, shear tests, particle size analyses, scanning electron microscope observations, and density investigations were conducted. It was shown that small grains <25 µm (lunar dust) are highly compressive and cohesive even at low external stress. They are particularly important as a large amount of fine dust is present in lunar regolith and simulants (x50 = 76.7 to 96.0 µm). Further, ring shear and densification tests revealed correlations with damage mechanisms caused by local stress peaks for grains in the mm range. In addition, an explanation for the occurrence of considerable differences in the literature-based data for particle sizes was established by comparing various measurement procedures. The present study shows detailed geotechnical investigations of novel lunar regolith simulants, which can be used for the development of equipment for future lunar exploration missions and in situ resource utilization under realistic conditions. The results also provide evidence about possible correlations and causes of known soil-induced mission risks that so far have mostly been described phenomenologically.

A Critical Review on the Feasibility of Synthetic Polymers Inclusion in Enhancing the Geotechnical Behavior of Soils.

Polymers have attracted widespread interest as soil stabilizers and are proposed as an ecologically acceptable means for enhancing the geotechnical properties of soils. They have found profound applications in diverse fields such as the food industry, textile, medicine, agriculture, construction, and many more. Various polymers are proven to increase soil shear strength, improve volume stability, promote water retention, and prevent erosion, at extremely low concentrations within soils through the formation of a polymer membrane around the soil particles upon hydration. The purpose of this work is to provide an overview of existing research on synthetic polymers for soil improvement. A fundamental evaluation of many synthetic polymers used in soil stabilization is provided, Furthermore, the impact of different polymer types on the geotechnical parameters of treated soil was assessed and compared. Limiting factors like polymer durability and the effect of changing climatic conditions on the engineering behavior of the polymer-treated soils have been critically reviewed. The dominant mechanisms responsible for the alteration in the behavior of polymer-soil admixture are reviewed and discussed. This review article will allow practicing engineers to better understand the intrinsic and extrinsic parameters of targeted polymers before employing them in real-field scenarios for better long-term performance.

Geotechnical properties of fresh municipal solid wastes with different compositions under leachate exposure.

This paper investigates the geotechnical properties of a type of synthetic municipal solid waste (MSW). The tests were conducted on five groups of synthetic MSW compositions, based on the field characterization of fresh MSW samples collected from Mugga Lane landfill site, ACT, Australia. Compaction, hydraulic conductivity, compression, drained and undrained shear properties of the MSWs with water and leachate addition to the field moisture content were studied. The study shows that adding leachate could increase the maximum dry density of the MSWs under given moisture contents and compaction energies. The hydraulic conductivity of the MSWs could decrease by 100-fold when the confining pressure increases from 15 kPa to 240 kPa. The shear behaviours of the MSW samples follow the strain hardening behaviours of loose sand. The cohesion of the MSWs decreases but the friction angle of the MSWs increases with leachate addition due to the change in the surface tension and viscosity of the pore liquids and the loss of cementitious components. The addition of leachate increases the compression ratios of the MSWs by around 10% to 30% due to the change in the pH of the pore liquids. The most significant components affecting the shear and compression behaviours of the MSW were paper and wood. The effects of leachate exposure on the geotechnical properties of the MSWs is not very significant. It is important to consider the variation of MSW properties to the leachate properties (viscosity, pH and surface tension) in the large body of MSWs in the landfills.

Post hurricane Harvey dataset: Portable free fall penetrometer and chirp sonar measurements of Texas rivers.

This data article includes datasets collected at three sections of the Guadalupe River, Brazos River, and Colorado River in Texas, USA, almost ten months post Hurricane Harvey. Instruments used include a Portable Free Fall Penetrometer (PFFP), Chirp Sonar, Side Scan Sonar (SSS), Acoustic Doppler Current Profiler (ADCP) and sediment grab sampler. Measurements were collected from small vessels such as canoes and a 6-feet inflatable zodiac and were supported by long term hydrodynamic data from local river water level and discharge gages. Laboratory testing performed on samples collected included grain size analysis, Atterberg test, and erodibility testing using an Erosion Function Apparatus (EFA). Data collected were analyzed to estimate sediment strength derived from the PFFP, backscatter intensity recorded by the chirp sonar, and soil sample characteristics. The dataset includes raw and processed data for the measurements recorded by the instruments, location of measurements, and laboratory testing grouped for each river with a readme file which gives a potential for reuse by other researchers for further analysis if needed. This data article is representing supplementary data to the following research article published in Engineering Geology [1]: Jaber, R., Stark, N., Jafari, N., & Ravichandran, N. "Combined Portable Free Fall Penetrometer and Chirp Sonar Measurements of three Texas River Sections Post Hurricane Harvey." Raw data was published [2]: Stark, N. Jafari, N. Ravichandran, R. Jaber, R. (2020). Combined Geotechnical and Geophysical Investigation of Texas Rivers Post Hurricane Harvey. in Combined Geotechnical and Geophysical Investigation of Texas Rivers Post Hurricane Harvey. DesignSafe-CI. https://doi.org/10.17603/ds2-835m-zp94.

Properties of Lime-Cement Concrete Containing Various Amounts of Waste Tire Powder under Different Ground Moisture Conditions.

Lime-cement concrete (LCC) is a non-structural concrete in which lime and cement are used as the main binders. However, although LCC has many applications in reducing the settlement of foundations and providing a support layer for shallow foundations, little research has been conducted to evaluate its behaviour in various moisture conditions. Previous researchers have studied the feasibility of using waste tires in conventional concrete to alleviate their negative environmental impacts. However, in field projects, rubber has not been widely used because its application leads to the strength reduction of concrete. In the case of LCC, attaining high strengths is not required and thus application of waste tire particles sounds reasonable. This research evaluated the impact of various rubber powder contents on the fresh, geotechnical and durability properties of LCC at different saturation degrees induced by the capillary action and groundwater level increment, which has not been studied before. The results of more than 320 tests showed that the application of tire powder increases workability and decreases the water absorption of LCC. Moreover, all 60-day cured specimens exposed to 100% saturation degree experienced a strength reduction of less than 10% by using rubber powder contents varying from 0 to 20%. Moreover, increasing the saturation degree from 0 to 100% decreased the average compressive strength by 13.5 and 22% for 60-day cured samples of two different mix designs. The results of this research confirm that LCC containing up to 10% rubber powder could be promisingly used underneath or close to the groundwater table without its strength and geotechnical properties being jeopardized due to rubber employment and/or exposure to ground moisture.

Geotechnical properties of oil-polluted soil: a review.

Soil polluted by oil and its derivatives is a critical environmental issue worldwide that jeopardizes ecological systems and causes geotechnical problems. This review paper focuses on the previous studies concerning the impacts of oil pollution on soil geotechnical properties. To this end, related academic literature on this topic was investigated and discussed. The findings of this study demonstrated that the addition of oil pollution in coarse-grained soils significantly reduces particle surface roughness. On the other hand, in fine-grained soils, it results in flocculation and secondary aggregation of clay particles, less aggregated and loose packing in the soil matrix, the formation of isometric pores, the formation of fissure-like pores, and an increase in mesoporosity. In general, it was found that the geotechnical properties of oil-polluted soils are mostly determined by the physicochemical and/or physical interactions between the soil and contaminant. Additionally, previous research has demonstrated that oil pollutants alter the geotechnical properties of cohesive and non-cohesive soils significantly, including the Atterberg limits, particle-size distribution, compaction behavior, unconfined compressive strength, friction angle, cohesion, hydraulic conductivity, and consolidation characteristics. However, no general pattern could be established for the majority of them. Besides, it was found that the degree of geotechnical property alteration of oil-polluted soil is strongly influenced by the soil type and features, as well as the quantity, type, and chemical composition of oil pollutants.

Assessment of the reuse of Covid-19 healthy personal protective materials in enhancing geotechnical properties of Najran's soil for road construction: Numerical and experimental study.

The COVID-19 pandemic has not only caused a global health crisis, but it has also had significant environmental and human consequences. During the COVID-19 pandemic, this study focused on emerging challenges in managing healthy personal protective materials (HPPM) in Kingdom of Saudi Arabia, using silty sand (SM) soil as an example since it covers large areas in KSA and in the whole world. The main objective of this paper is to find a novel way to minimize pandemic-related waste by using HPPM as waste materials in road construction. For the first time, a series of experiments was conducted on a mixture of different percentages of shredded HPPM (0, 0.5, 1 and 2%) added to the silty sand (SM) soil for road applications, including soil classification according to the USCS, modified compaction, UCS, UPV, and CBR. In addition, a numerical simulation was performed using geotechnical-based software Plaxis 3D to study the performance of the soil-HPPM mix as a subbase layer in the paving structure under heavy traffic loading. The modified compaction test results show that there is an increase in the optimum moisture content with increasing the HPPM contents from 0.5% to 1% and 2%. However, a reduction in the maximum dry density is observed. The values of dry density and water content at 0%, 0.5%, 1% and 2% pf HPPM are 2.045, 1.98, 1.86 and 1.8 g/cm3 and 7.65% 8%, 8.5% and 9.5%, respectively. The soaked CBR values at 0, 0.5, 1 and 2% HPPM are 23, 30, 8, 2% with the maximum value attained with the addition of 0.5% HPPM. The results of UCS were with the same percentages of HPPM 430, 450, 430 and 415 kPa, respectively, with the maximum value attained with 0.5% HPPM addition as well. In contrast, the values of UVP at 0%, 0.5%, 1% and 2% are 978.5, 680.3, 489.4 and 323.6 m/s, respectively, confirming the trends obtained by modified compaction test results. The simulation results confirm this conclusion that the soil-HPPM mix show a superior performance when used as a subbase layer and reduced vertical displacement by a percentage of 11% compared to the normal subbase material. By eliminating HPPM especially facemasks from the landfill lifecycle, incorporating them into high quality construction material production has the potential to deliver significant environmental benefits.

Reuse of waste tyre products as a soil reinforcing material: a critical review.

All over the globe, the generation of industrial waste has been increased due to the increasing demand for modern civilisation. In the developing countries like India, it is growing vigorously which eventually increases the production of vehicles and results in the more number of waste tyres. Despite the dumping such hazardous waste in landfills, stockpiling, and burning, their feasible utilisation in the modification of soil and concrete can be a good alternative option for their disposal. This paper enlightens the published work carried out by various researchers to enhance the mechanical properties of clayey soil using various forms of waste tyres. The effects of different forms of waste tyres on consistency limits, compaction characteristics, strength characteristics, compressibility characteristics, permeability and California-bearing ratio of cohesive soils have been reviewed. The review results show that the use of waste tyre products in ground improvement can be an economical solution for the construction industries and optimistic future as its disposal option. Still, further investigations and more research studies are required to consolidate the remarks drawn by the past researchers for its utilisation in the construction of highway/railway embankments and other field applications.

Geotechnical properties of products of alternative fuel combustion and co-firing with hard coal in the context of their use as solidifying dense mixtures.

Efforts directed to reduction of greenhouse gas emissions have led to the introduction of new firing/co-firing technologies and alternative fuels in the coal-based power industry. This has resulted in the formation of combustion products with new properties that can affect the reuse of these wastes and/or pose a hazard to the environment. One of the power-plant fly ash (FA) reuse options is its application as a solidifying dense mixture with water for backfilling mine workings or in engineering constructions. In this comparative study, geotechnical properties of three groups of FA were evaluated: (i) weathered and freshly generated ash from hard coal combustion in conventional pulverized coal boilers without (C-PCA, C-PFA) and with selective non-catalytic reduction installations for NO x reduction (NC-PFA); (ii) FA from hard coal co-firing with alternative fuels: off gases (GC-PFA) or biomass (BC-PFA) in pulverized coal boilers; (iii) FA from coal (C-FFA) or biomass combustion (B-FFA) in fluidized-bed boilers. The transportability, bonding and solidification properties, uniaxial compression strength, and rewetting of dense mixtures were evaluated by measurements of volumetric density, fluidity, water retention capacity, bonding time, solidification time, uniaxial compression test, and slakeability at the background of the FA chemical composition. Calcareous C-FFA > B-FFA displayed the best geotechnical properties. Other materials showed poorer geotechnical properties than FFA and could be aligned in the order BC-PFA > GC-PFA > NC-PFA > C-PFA > C-PCA.

Use of waste paper sludge ash as a calcium-based stabiliser for clay soils.

Chemical ground improvement of soils of poor quality for construction has been increasingly used as a means of promoting sustainable construction practices. The production of conventional soil stabilisers such as cement or lime involves non-renewable natural resource and energy consumption and high carbon dioxide emissions; therefore, alternative stabilisers are sought. This study used waste paper sludge ash (PSA) to treat three different clays. The aim was to assess PSA effectiveness as an alternative to lime or cement for clay stabilisation based on plasticity characteristics, unconfined compressive strength (UCS), water retention and volumetric stability. PSA-treated soil specimens were shown to perform well compared to lime-treated or cement-treated ones: (a) PSA considerably lowered the plasticity indices of the two expansive clays, in a similar way as lime; (b) in most cases PSA dosages equal to or greater than the initial consumption of lime gave UCS at least twice as high compared to those obtained using commercial limes at equivalent dosages (> 1 MPa for the two expansive soils after 7 or 28 days of curing) and in the inspected cases also higher UCS than cement; and (c) consistently with the plasticity results PSA-treated specimens swelled less during wetting and had lower volumetric strains upon drying (better volumetric stability) compared to lime-treated or cement-treated soils. Overall the results give promise for a valorisation route of this waste material in the field of ground improvement.

Geotechnical properties of municipal solid waste at Laogang Landfill, China.

Landfills have been widely constructed all around the world in order to properly dispose municipal solid waste (MSW). Understanding geotechnical properties of MSW is essential for the design and operation of landfills. A comprehensive investigation of geotechnical properties of MSW at the largest landfill in China was conducted, including waste composition, unit weight, void ratio, water content, hydraulic conductivity, and shear behavior. A large-scale rigid-wall permeameter and a direct-shear apparatus were adopted to test the hydraulic conductivity and shear behavior of the MSW, respectively. The composition of the MSW varied with age. With the depth increasing from 0 to 16m, the unit weight increased from 7.2 to 12.5kN/m3, while the void ratio decreased from 2.5 to 1.76. The water content ranged between 30.0% and 68.9% but did not show a trend with depth. The hydraulic conductivity of the MSW ranged between 4.6×10-4 and 6.7×10-3cm/s. It decreased as the dry unit weight increased and was sensitive to changes in dry unit weight in deeper layers. Displacement-hardening was observed during the whole shearing process and the shear strength increased with the normal stress, the displacement rate, and the unit weight. The friction angle and cohesion varied from (15.7°, 29.1kPa) to (21.9°, 18.3kPa) with depth increasing from 4 to 16m. The shear strength of the MSW obtained in this study was lower than the reported values in other countries, which was caused by the less fibrous materials in the specimens in this study. The results in this study will provide guidance in the design and operation of the landfills in China.

Interrelationships among geotechnical and leaching properties of a cement-stabilized contaminated soil.

Relationships among selected performance properties have been established using experimental data from a cement-stabilized mixed contaminated soil. The sandy soil was spiked with 3,000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel. It was then treated with 5%, 10%, 15%, and 20% dosages of Portland cement. Different water contents were considered for lower dosage mixes. Selected geotechnical and leaching properties were determined on 28-day old samples. These include unconfined compressive strength (UCS), bulk density, porosity, hydraulic conductivity, leachate pH and granular leachability of contaminants. Interrelationships among these properties were deduced using the most reasonable best fits determined by specialized curve fitting software. Strong quadratic and log-linear relationships exist between hydraulic conductivity and UCS, with increasing binder and water contents, respectively. However, the strength of interrelationships between hydraulic conductivity and porosity, UCS and porosity, and UCS and bulk density varies with binder and water contents. Leachate pH and granular leachability of contaminants are best related to UCS and hydraulic conductivity by a power law and an exponential function, respectively. These results suggest how the accuracy of not-easily-measurable performance properties may be constrained from simpler ones. Comparisons with some published performance properties data support this.

Mini-review of the geotechnical parameters of municipal solid waste: Mechanical and biological pre-treated versus raw untreated waste.

The most viable option for biostabilisation of old sanitary landfills, filled with raw municipal solid waste, is the so-called bioreactor landfill. Even today, bioreactor landfills are viable options in many economically developing countries. However, in order to reduce the biodegradable component of landfilled waste, mechanical and biological treatment has become a widely accepted waste treatment technology, especially in more prosperous countries. Given that mechanical and biological treatment alters the geotechnical properties of raw waste material, the design of sanitary landfills which accepts mechanically and biologically treated waste, should be carried out with a distinct set of geotechnical parameters. However, under the assumption that 'waste is waste', some design engineers might be tempted to use geotechnical parameters of untreated raw municipal solid waste and mechanical and biological pre-treated municipal solid waste interchangeably. Therefore, to provide guidelines for use and to provide an aggregated source of this information, this mini-review provides comparisons of geotechnical parameters of mechanical and biological pre-treated waste and raw untreated waste at various decomposition stages. This comparison reveals reasonable correlations between the hydraulic conductivity values of untreated and mechanical and biological pre-treated municipal solid waste. It is recognised that particle size might have a significant influence on the hydraulic conductivity of both municipal solid waste types. However, the compression ratios and shear strengths of untreated and pre-treated municipal solid waste do not show such strong correlations. Furthermore, another emerging topic that requires appropriate attention is the recovery of resources that are embedded in old landfills. Therefore, the presented results provide a valuable tool for engineers designing landfills for mechanical and biological pre-treated waste or bioreactor landfills for untreated raw waste as well as planning landfill mining projects.