Constitutive models for peat - a review

This paper presents a review of the main constitutive models for peat and other highly organic soils having extremely high water content. At present, predictions of the geomechanical behaviour of such soils for design practice are mostly based on constitutive theories developed for fine-grained mineral soils. Concepts of primary consolidation and secondary compression as applied to peat are explained using the two-level structure assumption of micropores and macropores [1]. As background, the historical development of consolidation hypotheses A&B [24] regarding the concepts of primary consolidation and secondary compression is reviewed for both mineral and organic soils. Based on microscopic examinations and in-situ testing, it is generally accepted that hypothesis B is more suitable for peat. The micro-mechanical rheological model proposed by Berry and Poskitt [2] and the isotache-compression model developed by den Haan [6] were reported to have good agreement with experimental laboratory results for fibrous and amorphous peats. Attention is given to the structural anisotropy of peat material, inherent by its fibrous nature, in these constitutive frameworks

Municipal solid waste management under Covid-19: Challenges and recommendations

Covid-19 is proving to be an unprecedented disaster for human health, social contacts and the economy worldwide. It is evident that SARS-CoV-2 may spread through municipal solid waste (MSW), if collected, bagged, handled, transported or disposed of inappropriately. Under the stress placed by the current pandemic on the sanitary performance across all MSW management (MSWM) chains, this industry needs to re-examine its infrastructure resilience with respect to all processes, from waste identification, classification, collection, separation, storage, transportation, recycling, treatment and disposal. The current paper provides an overview of the severe challenges placed by Covid-19 onto MSW systems, highlighting the essential role of waste management in public health protection during the ongoing pandemic. It also discusses the measures issued by various international organisations and countries for the protection of MSWM employees (MSWEs), identifying gaps, especially for developing countries, where personal protection equipment and clear guidelines to MSWEs may not have been provided, and the general public may not be well informed. In countries with high recycling rates of MSW, the need to protect MSWEs' health has affected the supply stream of the recycling industry. The article concludes with recommendations for the MSW industry operating under public health crisis conditions

Phyllite clay–cement composites having improved engineering properties and material applications

Phyllite clays contain clay minerals (chlorite, illite and mixed-layer illite smectite), quartz and feldspars. In this experimental laboratory study, new composites of phyllite clay and cement (5, 7 and 9 wt.%) were prepared and tested to determine their Atterberg limits, dry density and optimum water content for modified Proctor (MP) compaction, California Bearing ratio, swelling potential after soakage in water, unconfined compressive strength (UCS) and water-permeability coefficient. From the mixes investigated, the composite with 5 wt.% cement was deemed most suitable for certain construction material applications, having a plasticity index of 10.5%, maximum dry density of 2.17 Mg/m3 and optimum water content of 8% for MP compaction (undergoing no swelling under soakage), a UCS of 0.74 MPa, and a very low permeability coefficient value of 7.4 × 10− 11 m/s. Potential material applications for these new composites include for building construction, roofs, and flexible pavements.Peer reviewe

NovADEC: Novel approach for determination of the elemental content of organic matter

Organic matter (OM) significantly influences the physico-chemico-biological properties of geomaterials (viz., soils, sediments, municipal solid waste) and hence its accurate determination has profuse applications in agriculture, environmental and geotechnical engineering fields. OM mainly consists of carbon, hydrogen, nitrogen, and oxygen, collectively known as elemental content (EC), and these elements can be determined to estimate OM and its variation in several processes, including decomposition under the actions of thermal and biological activities. Usually, EC is determined by employing an elemental analyser, wherein the sample is exposed to an elevated temperature for the conversion of the elements to their respective gases (viz., CO2, H2O, N2, and NyOx) followed by detection of these gases to quantify the percentage of C, H, N, and O. However, this technique has limitations, including time-consuming process, expertise required for instrument operation, issues related to sample preparation and analysis of heterogeneous materials and the destruction of the analysed specimen. These provided the impetus for the development and validation of a Novel Approach for Determination of the Elemental Content, NovADEC, which employs Fourier-transform infrared (FTIR) spectroscopy and multiple regression analysis (viz., partial least-squares regression), as presented in the present manuscript. To develop NovADEC, five samples of different natures, including geomaterials and two standard materials (viz., cellulose and its derivative), with volatile solids ranging between 13% and 85% have been considered. Further, to create a wide range in ECs, sub-samples were thermally treated at furnace temperatures ranging between 150°C and 700°C. These sub-samples were subsequently analysed by employing elemental analyser and FTIR-spectroscopy techniques. A critical synthesis of the results demonstrates that the NovADEC predictive model facilitates a quick determination of the OM of geomaterials

Determination of soil permeability coefficient following an updated grading entropy method

This paper presents a critical review of the grading entropy approach of permeability-coefficient predictions (k P) for coarse-grained soils. The approach applies the grading entropy theory to particle-size distributions (PSDs), such that the entirety of each gradation curve can be interpreted as a single point on a grading entropy chart, plotting its normalised entropy increment (B) against relative base grading entropy (A) values. Published data sets of measured permeability-coefficient (k M) values for saturated compacted silty sand, sand and gravel materials are examined to understand the dependence of A and B on various gradation parameters and the void ratio (e). In particular, log k M negatively correlates with log B and positively correlates with log A and e (log e). As such, power functions of the formkP=C1AC2BC3eC4 prove statistically superior, noting that the fitting coefficient C 1 to C 4 values are specific to the PSD range and densification (compaction) states investigated for the permeability tests. Recommendations are given for increasing the predictive power, including separate models for well-graded and poorly graded materials and the addition of a particle shape factor and specific surface parameters in the regression correlation.Integral Design and Managemen