Proposal for an initial screening method for identifying microplastics in marine sediments

Marine debris, which is often called microplastics, is widespread in marine environments, particularly in sediments, and is recognized as an environmental hazard because it concentrates contaminants, forms biofilms, and sinks into marine sediments. In sediments, it may be ingested by benthos and have a negative impact on higher food chain levels. In this study, a new protocol was developed to identify microplastics in various sediment fractions. This protocol combined sieving and staining based on ordinal geotechnical/geological testing methods. The sieving process was derived from the conventional particle size distribution test, and nontoxic dyes were employed in the staining process. The protocol is safe and easy to perform as it merely involves the use of conventional geological/geotechnical testing equipment. The new protocol was successfully employed to stain and categorize different types and sizes of microplastic particles from contaminated sediments. This safe, easy-to-use, and efficient protocol can serve as the basis for a new alternative approach to study microplastics present in sediments, which can be performed using basic materials familiar to geotechnical/geological engineers.

Unsaturated structured soils: constitutive modelling and stability analyses

The paper presents a new single-surface elasto-plastic model for unsaturated cemented soils, formulated within the critical state soil mechanics framework, which should be considered as an extension to unsaturated conditions of a recently proposed constitutive law for saturated structured soils. The model has been developed with the main purpose of inspecting the mechanical instabilities induced in natural soils by bond degradation resulting from the accumulation of plastic strains and/or the changes in pore saturation. At this scope, the constitutive equations are used to simulate typical geotechnical testing conditions, whose results are then analysed in light of the controllability theory. The results of triaxial tests on an ideal fully saturated cemented soil and on the corresponding unsaturated uncemented one are first discussed, aiming at detecting the evidence of potentially unstable conditions throughout the numerical simulations. This is followed by similar analyses considering the combined effects of both the above features. For each analysed case, a simple analytical stability criterion is proposed and validated against the numerical results, generalizing the results, and highlighting the crucial role of state variables and model parameters on the possible occurrence of failure conditions.

The Suitability of Granite and Granite-Gneiss of part of Minna Sheet 164 SW North-Central Nigeria as Construction Aggregates

Geotechnical tests were performed on granite and granite-gneiss rock samples of parts of Minna to know their suitability as construction aggregates. Eight rock samples were selected for porosity test, impact value, specific gravity and absorption capacity. The average porosity of the samples is 0.21, 0.12, 0.30, 0.10, 0.25, 0.25, 0.24 and 0.11 respectively for L1, L14, L15, L19, L21, L23, L25 and L29 which shows they are normal except L15 with a high porosity. Average impact value of the samples show they are suitable for wearing surface course in road and bridge construction, except samples L14 and L19 with average impact value of 32.8 and 34.9 respectively making them suitable only as bituminous macadam (maximum value = 35%). Sample L1 is not suitable as construction aggregates because it exceeds the maximum value specified for that purpose. The average specific gravity of the rocks are L1=2.68, L14=2.65, L15=2.65, L19=2.67, L21= 2.63, L23= 2.71, L25=2.65, and L29=2.69 respectively and which make them suitable as normal weight materials for construction. The average absorption capacity values of the rock samples are 0.20%, 0.20%, 0.50%, 0.10%, 0.25%, 0.10%, 0.50% and 0.20% respectively for samples L1, L14, L15, L19, L21, L23, L25, and L29. All testing followed the respective ASTM standards. Keywords: Geotechnical testing, construction aggregates, granite, granite-gneiss, Minna, Nigeria.

Sustainable soil stabilization using combination of geotextile, fly-ash and saw dust for pavement subgrade

Purpose: This paper investigates the combined effect of fly ash, sawdust and geotextile in stabilizing the soil. Design/methodology/approach: A thorough geotechnical testing was carried out in order to study the potent characteristics of soil and soil mixes. The present investigation was set up in two stages. In the first stage, effects of fly ash (5, 10, 15 and 20%), sawdust (2.5, 5 and 7.5%) and layers of geotextile placed at different depths were studied separately to determine their effect on soil stabilization. In the second stage, fly ash, sawdust and geotextile were mixed with soil sample in order to obtain the optimum dosage which can be used for stabilization of soil i.e. their combined effect as stabilizer on soil stabilization. Findings: It was observed that by introducing fly ash, sawdust and geotextile to the soil, the CBR values increase and thickness of pavement layer decreases. It also decreases the amount of stress on subgrade leading to enhancement of pavement stability with cost effectiveness. Research limitations/implications: Economical use of industrial waste has been proposed in the present research which otherwise prove to be a malady to climatic change and human health. From the study, an optimum dosage of fly ash (2.5%) and saw dust (5%) and depth for geotextile (6 cm) has been proposed. Originality/value: The article explores the possibility of a ternary blend, i.e., geotextile, flyash and saw dust on effectively stabilizing pavement subgrade. Limited literature was available to address the issue of utilizing the industrial wastes that otherwise pose disposal issues.

Geomechanical Behaviour of Uncemented Expanded Polystyrene (EPS) Beads–Clayey Soil Mixtures as Lightweight Fill

Lightweight fill can be advantageous in embankment construction for the purposes of reducing the (i) bearing pressures on the underlying soil foundation, (ii) destabilizing moments for constructed earthen slopes, and (iii) earth pressures acting behind retaining walls. This paper investigates the merits/limitations of particulate expanded polystyrene (EPS) beads mixed with clayey sand (CS) soil as lightweight fill, considering both geotechnical and environmental perspectives. The bench-scale geotechnical testing programme included standard Proctor (SP) compaction, California bearing ratio (CBR), direct shear (sheardox), oedometer and permeability testing performed on two different gradation CS soils amended with 0.5, 1.5 and 3.0 wt.% EPS, investigating two nominal bead sizes equivalent to poorly-graded medium and coarse sands. Compared to the unamended soils, the compacted dry density substantially decreased with increasing EPS beads content, from 2.09 t/m3 (0 wt.% EPS) to as low as 0.33 t/m3 for 3 wt.% (73 v.%) of larger-sized EPS beads. However, from analyses of the test results for the investigated 50 to 400 kPa applied stress range, even 0.5 wt.% (21 v.%) EPS beads caused a substantial mechanical failure, with a drastic decay of the CBR and compressibility parameters for the studied CS soils. Given the more detrimental environmental cost of leaving myriads of separate EPS beads mixed forever among the soil, it is concluded that the approach of adding particulate EPS beads to soils for producing uncemented lightened fill should not be employed in geotechnical engineering practice.

Mineralogical and Micro-structural Investigation into the Mechanical Behaviour of a Soft Calcareous Mudstone

The construction industry in Abu Dhabi is thriving and its coastline has some of the most ambitious structures in the world. Whilst the subsurface evaporitic and calcareous soft rocks of this region are of great geological interest, they are relatively poorly understood from a geotechnical engineering perspective, forcing foundation designs to be overly conservative. Understanding the stiffness of the underlying geology at small strains is of great importance for the accurate estimation of ground movements around excavations and foundations, and yet routine post-SI laboratory testing programmes tend to focus on basic rock mechanics tests such as UCS tests. These procedures are generally unsuitable for use with calcareous rocks due to their friable and moisture sensitive nature, and rarely obtain parameters representative of actual in situ behaviour. The calcareous mudstone investigated in this paper has mechanical and structural characteristics falling between those of a soil and those typical of a rock and, as such, requires a geotechnical testing approach that combines methods from both soil and rock mechanics disciplines. The mineralogical, micro-structural and mechanical characteristics of this lithology have been examined via a suite of testing techniques, including XRPD, SEM, advanced triaxial with bender elements, along with industry standard procedures. Shearing, tensile and consolidation behaviours have been explored. Examination of the micro- and macro-scale features of this material shows it to be highly structured, with strength and stiffness being controlled by inter-granular bonding of Dolomite grains, as well as by mean effective stress state and rate of strain. The presence of fibrous Palygorskite acts to reduce the degree of bonding, causing specimens rich in this clay mineral to have a more ductile mechanical behaviour.

Impact of sample scaling on shear strength: coupled effects of grains size and shape

Size limitations of geotechnical testing equipment often require that samples of coarse granular materials have to be scaled in order to be tested in the laboratory. Scaling implies a convenient modification of the particle size distribution (PSD) to reduce particle sizes. However, it is well known that particle size and shape may be correlated in nature, due to geological factors (as an example). By means of two-dimensional contact dynamics simulations, we analyzed the effect of altering the size span on the shear strength of granular materials when particle size and shape are correlated. Two different systems were considered: one made of only circular particles, and the second made of size-shape correlated particles. By varying systematically the size span we observed that the resulting alteration of material strength is not due to the change in particle sizes. It results instead from the variation of the particle shapes induced by the modification of the PSD, when particle size and particle shape are correlated. This finding suggests that particle shape distribution is a higher order factor than PSD for the shear strength of granular materials. It also highlights the importance of particle shape quantification in soil classification and the case for its consideration in activities such as sampling, subsampling, and scaling of coarse materials for geotechnical testing

Small-scale Geotechnical Testing Using a Six-axis Robot

Single-gravity (1-g) small-scale testing is a widely used method to investigate geomechanics problems that involve the interactions between soils and objects (e.g., structures or machine parts). This letter presents a new approach for performing 1-g model tests where a six-axis industrial robot functions as a versatile actuator capable of moving objects along virtually arbitrary trajectories, while simultaneously tracking multiple components of force and moment acting on the objects. A performance evaluation confirms that the robot's motion control and force measurement are sufficiently accurate for geotechnical model tests. This assessment is completed through two benchmarking exercises: (1) determining the failure envelope of a strip foundation subjected to combined loading and (2) quantifying the force-displacement history for the soil cutting process (e.g., for applications in soil-machine interaction).