Explanation and Application of the Evolving Contact Traction Fields in Shallow Foundation Systems

The present paper provides a qualitative discussion of the evolution of contact traction fields beneath rigid shallow foundations resting on granular materials. A phenomenological similarity is recognized in the measured contact traction fields of rigid footings and at the bases of sandpiles. This observation leads to the hypothesis that the stress distributions are brought about by the same physical phenomena, namely the development of arching effects through force chains and mobilized intergranular friction. A set of semi-empirical equations are suggested for the normal and tangential components of this contact traction based on past experimental measurements and phenomenological assumptions of frictional behaviors at the foundation system scale. These equations are then applied to the prescribed boundary conditions for the analysis of the settlement, resistance, and stress fields in supporting granular materials beneath the footing. A parametric sensitivity study is performed on the proposed modelling method, highlighting solutions to the boundary-value problems in an isotropic, homogeneous elastic half-space.

Transient Two-Phase Flow in Porous Media: A Literature Review and Engineering Application in Geotechnics

This work reviews the transient two-phase flow in porous media with engineering applications in Geotechnics. It initially overviews constitutive relationships, conventional theories, and experiments. Then, corresponding limitations are discussed according to conflicting observations and multiphase interfacial dynamics. Based on those findings, the dynamic nonequilibrium effects were so defined, which could also be abbreviated as dynamic/transient effects. Four advanced theories have already been developed to resolve these effects. This review collects them and discusses their pros and cons. In addition, this work further reviews the state-of-art in terms of experimental methods, influential factors in dynamic/transient effects, and modelling performance, as well as micromodel and numerical methods at pore-scale. Last, the corresponding geotechnical applications are reviewed, discussing their applicability in effective stress, shear strength, and deformation. Finally, the entire review is briefed to identify research gaps in Geotechnics.

Seismic Hazard Assessment for a Wind Farm Offshore England

Offshore wind has become a major contributor to reducing global carbon emissions. This paper presents a probabilistic seismic hazard analysis for the Sofia Offshore Wind Farm, which is located about 200 km north-east of England in the southern North Sea and will be one of the largest offshore wind farms in the world once completed. The seismic source characterization is composed of two areal seismic source models and four seismic source models derived using smoothed gridded seismicity with earthquake catalogue data processed by different techniques. The ground motion characterization contains eight ground motion models selected based on comparisons with regional data. The main findings are (1) the variation in seismic hazard across the site is negligible; (2) the main source controlling the hazard is the source that includes the 1931 Dogger Bank earthquake; (3) earthquake scenarios controlling the hazard are Mw = 5.0–6.3 and R = 110–210 km; and (4) the peak ground accelerations on rock are lower than for previous regional studies. These results could help guide future seismic hazard assessments in the North Sea.

Cyclic Liquefaction Resistance of an Alluvial Natural Sand: A Comparison between Fully and Partially Saturated Conditions

Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the strength and stiffness of soil. The liquefaction resistance of soils increases significantly as the degree of saturation decreases, making soil desaturation an effective measure for the mitigation of this phenomenon. This paper presents a comparative analysis of liquefaction resistance of an alluvial sand from Aveiro (Portugal) under fully and partially saturated conditions. For this purpose, an in situ characterisation based on CPTu and a laboratory series of cyclic triaxial tests were carried out. The cyclic triaxial tests were conducted under undrained conditions on remoulded specimens with different degrees of saturation, including the full saturation. On the other hand, the triaxial apparatus was instrumented with Hall-effect transducers to accurately measure the strains during all testing phases. In addition, it was equipped with piezoelectric transducers to measure seismic waves velocities, namely P-wave velocity, for evaluation of the saturation level of the specimen in parallel with the Skempton’s B parameter. Hence, relations between the B-value, and P-wave velocity and cyclic strength resistance are presented. The number of cycles to trigger liquefaction, considering the pore pressure build-up criterion, is presented for the different degrees of saturation. Results confirmed the increase in liquefaction resistance for lower degrees of saturation in this soil.

Microbial-Facilitated Calcium Carbonate Precipitation as a Shallow Stabilization Alternative for Expansive Soil Treatment

Expansive soils generally recognized as swell-shrink soils have been a problem for civil infrastructure for a long time. Engineers are in search of sustainable stabilization alternatives to counter these problematic soils. Microbial-induced calcium carbonate precipitation (MICP) is a promising biocementation process that can improve the properties of expansive soil through calcium carbonate precipitation. Past research has shown promise for the use of MICP in mitigating swelling distress from expansive soils. In this research, MICP via biostimulation was attempted by mixing enrichment and cementation solutions with soils in an effort to develop a new alternative to shallow chemical stabilization. Three soils with varying clay contents (30%, 40%, and 70%) and plasticity characteristics were selected, and soils were treated by mixing with enrichment solutions followed by cementation solutions. Five different mellowing periods, three different curing periods, and two types of cementation solutions were studied to optimize the method. Treatment effectiveness was evaluated using unconfined compression tests, calcium carbonate tests, and free swell index tests. Results showed that an increase in the mellowing period beyond two days was not beneficial for any of the three soils tested in this research. It was determined that the best improvement was observed at two days of mellowing and seven days of curing.

Strength of Chemically Stabilized Sewage Sludge—Some Inferences from Recent Studies

Although there has been a substantial body of research on the chemical stabilization of sewage sludge, most of these results are project-specific and relate mainly to the use of new binders and sewage sludge from specific sources. In this sense, much of the work to date is context-specific. At present, there is still no general framework for estimating the strength of the chemically treated sludge. This paper proposes one such general framework, based on data from some recent studies. An in-depth re-interpretation of the data is first conducted, leading to the observation that sludge, which has coarse, hard particulate inclusions, such as sand, premixed into it, gives significantly higher strength. This was attributed to the hard coarse particles that lower the void ratio of treated soil, are much less susceptible to volume collapse under pressure, and contribute to the strength through frictional contacts and interlocking. This motivates the postulation of a general framework, based on the premise that coarse, hard particulate inclusions in the sludge which do not react with the binders can nonetheless contribute to the strength of the treated soil. The overall void ratio, defined as the volume of voids in the cementitious matrix normalised by the overall volume, is proposed as a parameter for quantifying the combined effect of the coarse particulate inclusions and the cementitious matrix. The binder-sludge ratio is another parameter which quantifies the strength of the cementitious matrix, excluding the hard particulate inclusions. Back-analysis of the data suggests that the significance of the binder-sludge ratio may diminish as the content of hard particulate inclusions increases.

Modeling of Seismic Energy Dissipation of Rocking Foundations Using Nonparametric Machine Learning Algorithms

The objective of this study is to develop data-driven predictive models for seismic energy dissipation of rocking shallow foundations during earthquake loading using multiple machine learning (ML) algorithms and experimental data from a rocking foundations database. Three nonlinear, nonparametric ML algorithms are considered: k-nearest neighbors regression (KNN), support vector regression (SVR) and decision tree regression (DTR). The input features to ML algorithms include critical contact area ratio, slenderness ratio and rocking coefficient of rocking system, and peak ground acceleration and Arias intensity of earthquake motion. A randomly split pair of training and testing datasets is used for initial evaluation of the models and hyperparameter tuning. Repeated k-fold cross validation technique is used to further evaluate the performance of ML models in terms of bias and variance using mean absolute percentage error. It is found that all three ML models perform better than multivariate linear regression model, and that both KNN and SVR models consistently outperform DTR model. On average, the accuracy of KNN model is about 16% higher than that of SVR model, while the variance of SVR model is about 27% smaller than that of KNN model, making them both excellent candidates for modeling the problem considered.

Investigating Sand Production Phenomena: An Appraisal of Past and Emerging Laboratory Experiments and Analytical Models

This paper provides an in-depth review of research developments on a common phenomenon in oil and gas exploration: sand production. Due to its significant impact to reservoir productivity and production efficiency, sand production has been widely researched in recent years. This paper focused on the review of historical progress in experimental and analytical studies which helped to understand the nature of the sanding mechanism and identify conditions that favour the process. Collation of the experimental data and analytical solutions and formulations enabled the authors to comment on effectiveness and also limitations of the existing experimental protocols and analytical models. Sand production models were then grouped into categories based on initiation of sanding, rate and amount of sanding as well as the failure criterion incorporated in their formulation so that it will be more convenient for future researchers to identify and adopt an appropriate model for their own research. The review also confirms that there are still some aspects of sand production requiring further investigation, and maybe a hybrid approach combining experimental, analytical and numerical methods could be the best solution for future explorations.

Effects of Colloidal Silica Grouting on Geotechnical Properties of Liquefiable Soils: A Review

Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in different branches of civil engineering. Many studies have recently been performed to investigate the potential of CS in improving the mechanical behavior of cohesionless soils and mitigating the risk of seismic liquefaction in urbanized areas. CS grout is chemically and biologically inert and, when injected into a subsoil, it can form a silica gel and stabilize the desired soil layer, thus representing an attractive, environmentally friendly alternative to standard chemical grouting techniques. This paper firstly describes the characteristics of CS grout, the gelation process and the main features of the behavior of the pure gelled material. The grout delivery mechanisms through porous media are then explained, pointing out the crucial issues for practical application of CS grouting. All the grouting-induced effects on the soil behavior, which have been investigated by laboratory tests on small-sized soil elements, are reviewed, including the modifications to soil strength and stiffness under both static and seismic loading conditions, to soil compressibility and hydraulic conductivity. Published results from physical model tests and in situ applications are also presented. Finally, some aspects related to the mechanism of soil improvement are discussed. A critical discussion of each topic is presented, drawing particular attention to the controversial or not yet fully examined aspects to which future research on colloidal silica grouting should be directed.

Geopolymers as Alternative Sustainable Binders for Stabilisation of Clays—A Review

The need to transit to greener options in soil stabilisation has revamped research on the use of industrial and agricultural by-products in order to cut down on the current carbon footprint from the use of ordinary Portland cement (OPC) and lime related binders for the treatment of problematic soils. This study is a review on the use of geopolymers constituted by alkali activation of several industrial wastes such as pulverised fuel ash (PFA), ground granulated blast furnace slag (GGBS), metakaolin (MK), glass powder (GP), palm oil fuel ash (POFA), silica fume (SF), rice husk ash (RHA), volcanic ash (VA), and marble powder (MP) for the stabilisation of weak clays. The performance of stabilised clays as subgrade and subbase materials for road pavement construction was evaluated by comparing the 7 day UCS of the treated clays with the strength requirement for stabilised materials as outlined in BS EN 16907-4. The result of the study shows that geopolymers can be employed in improving the engineering properties of problematic clays to meet practical applications. Strength improvement was observed in the stabilised clays with increased precursor content, molarity of alkaline activator, and curing period.