Geotechnical Engineering Practice Research Articles

Exploring Shear Wave Velocity—NSPT Correlations for Geotechnical Site Characterization: A Review

Shear wave velocity (Vs) is a critical parameter in geophysical investigations, micro-zonation research, and site classification. In instances where conducting direct tests at specific locations is challenging due to equipment unavailability, limited space, or initial instrumentation costs, it becomes essential to estimate Vs directly, using empirical correlations for effective site characterization. The present review paper explores the correlations of Vs with the standard penetration test (SPT) for geotechnical site characterization. Vs, a critical parameter in geotechnical and seismic engineering, is integral to a wide range of projects, including foundation design and seismic hazard assessment. The current paper provides a detailed analysis of the key findings, implications for geotechnical engineering practice, and future research needs in this area. It emphasizes the importance of site-specific calibration, the impact of geological background, depth-dependent behavior, data quality control, and the integration of Vs data with other geophysical methods. The review underlines the continuous monitoring of Vs values due to potential changes over time. Addressing these insights and gaps in research contributes to the accuracy and safety of geotechnical projects, particularly in seismic-prone regions.

A new procedure for characterizing the critical intergranular contact state of non-plastic sand – fines mixed materials

A key and urgent scientific issue is how to characterize the complex intergranular contact state and mechanical behavior evolution of sand–fines mixed materials and then show how this state contributes to the static and dynamic properties of such materials. Both theoretical analyses and experimental data suggest that the mixes have different intergranular contact states as the fines content (FC) increases, and the mixed materials can be classified as sand-like, in-transition, or fines-like. The capability of the Rahman semi-empirical formula to predict the threshold fines content FCth—which distinguishes the regime of “fines in sand” (sand-dominated behavior) from that of “sand in fines” (fines-dominated behavior)—is verified using the basic material and mechanical properties of mixed materials from the literature. Developed from the method for determining the theoretical minimum void ratio, a new method that allows unified characterization of the critical intergranular contact state parameters FCin-min and FCin-max for in-transition soils is established based on the binary packing model, and FCin-min and FCin-max can be determined simply through explicit expressions that use some material physical indices of pure-sand and pure-fines materials. The proposed procedure offers significant advantages for evaluating the critical intergranular contact state and mechanical properties of sand–fines mixed materials in geotechnical engineering practice.

Theory of liquid and plastic limits for fine soils, methods of determination and outlook

Albert Atterberg introduced various consistency limits (state transitions) for fine-grained soil in the 1910s. Of these, the liquid limit (LL) and plastic limit (PL) are ubiquitous in geotechnical engineering practice, including their usage for soil classification and in deducing useful geotechnical parameters through correlations. Given that it is about 110 years since they were first introduced, it seems timely to review critically the current state of play regarding various definitions and theories of these index parameters and their standardised testing methods, as described in majorly used codes worldwide. Because different codes allow different LL apparatus types and employ some dissimilar criteria (e.g. in establishing the end point for the PL test), a change in method or code may produce different consistency limits results for testing the same soil. These differences are rationalised in terms of the controlling soil and test parameters. Some potential pitfalls in consistency limits testing are highlighted. Attention then turns to strength-based approaches, mostly employing fall-cone (FC) set-ups, emphasising their unsuitability for determining Atterberg’s PL. Considering the general poor reproducibility of the PL test, this paper concludes with an alternative way forward, obtaining useful FC index parameters that provide new possibilities for strength predictions and in the classification of fine-grained soils.

Deformation and failure analysis of heterogeneous slope using nonlinear spatial probabilistic finite element method

<p>Slope failures in hilly terrain impact the social and economic balance of the community. The major reasons for these slope failures are steeper slopes, climate factors, seismic activity, nearby excavations, and construction. Natural slopes show significant heterogeneity due to the inherent randomness in material properties and geometric nonlinearities. Effective slope stability analysis solutions can be achieved by incorporating probabilistic approaches. We present a comprehensive method to develop and analyze a heterogeneous two-dimensional slope model, utilizing a non-linear-spatial-probabilistic-finite element method under a plane strain condition. The developed slope model encompasses geometrical and material nonlinearity with a uniform random distribution over the space. Also, the present slope model integrates the Mohr-Coulomb's constitutive model for elastoplastic analysis to capture more realistic and complex behavior. A benchmark soil slope problem was modeled using the spatial probabilistic finite element method, comprising all six material properties with uniform spatial uncertainties. These material properties are elastic modulus, unit weight, cohesion, friction angle, and dilation angle. During the numerical simulation, the detailed deformations, stress patterns, strain patterns, potential pre-failure zone, and failure characteristics of heterogeneous slopes were achieved under self-weight and step loading sequences. Nodal failure and probability of nodal failure were introduced as two novel quantitative parameters for more insights into failure investigations. The testbench slope model was subjected to self-weight load and external 100-step loading sequences with a loading increment of -0.1 kN/m. The percentage probability of nodal failure was obtained at 40.46% considering uniformly distributed material uncertainties with a 10% coefficient of variation. The developed testbench slope model was also simulated for different values of the coefficient of variation (ranging from 0% to 50%) and comparatively investigated. The detailed deformation patterns, thorough profiles of stresses-strains, failure zones, and failure characteristics provided valuable insights into geotechnical engineering practices.</p>

Reuse of Waste Materials in Geotechnical Practice

Waste material is an inevitable outcome of most human and industrial activities, lacking enduring value. A significant amount of waste is being generated from various sources such as industrial and domestic activities, driven by population growth and economic expansion. To address these challenges, methods like re-use and recycling are crucial in mitigating the adverse impacts of waste by reducing landfill deposition. Recycling not only helps in conserving natural resources but also diminishes energy consumption. Recently, there has been increasing interest in re-using waste materials as substitutes in geotechnical and geo-environmental applications. For the efficient utilization of waste, it is essential to systematically understand its characterization, various technical aspects, and environmental implications, along with their interrelationships. This study aims to explore the potential of using different by-products and waste materials such as fly ash, shredded waste tires, and recycled concrete aggregates as geomaterials. By doing so, it endeavours to contribute to sustainable practices in geotechnical engineering. Overall, the re-use of waste materials constitutes a significant area of research aimed at fostering sustainability in geotechnical engineering practices.

Macro-micro numerical analysis of granular materials considering principal stress rotation based on DEM simulation of dynamic hollow cylinder test

The granular materials were subjected to the principal stress rotation effect induced by traffic loads, wave loads, and earthquake loads in geotechnical engineering practice. In order to reveal the influence of principal stress rotation on the macro-micro dynamic characteristics, this study proposed a numerical simulation method modeling physical dynamic hollow cylinder tests. Taking the dynamic stress state induced by traffic loading as an example, the numerical test model of the dynamic hollow cylinder was conducted on the subgrade soil, and the influence of principal stress rotation on the macro-micro evolution of dynamic characteristics was analyzed.The results showed that the principal stress rotation accelerated the development of vertical accumulative plastic strain and particle displacement, which aggravated micro-structure destruction of granular material. Moreover, the increase of confining stress declined the variations of normal contact numbers in each direction, which resisted the shear stress induced by principal stress rotation. This study provided a novel method to investigate the macro-micro dynamic characteristics of granular materials subjected to principal stress rotation, which made up for the inability of physical hollow cylinder tests to study microscopic evolution.

Discussion: Development of a Single-Point Method to Determine Soil Plastic Limit Using Fall-Cone Data [Geotech Geol Eng 41:4473–4485, 2023

This discussion article presents a critical appraisal of three empirical correlations developed via multiple regression analysis and presented in the Kayabali et al. [Geotech Geol Eng 41:4473–4485, 2023. https://doi.org/10.1007/s10706-023-02527-0] (the Authors’) investigation for the determination of the soil consistency limits. Specifically, based solely on British Standard (BS) fall-cone (FC) test data, the Authors purport that the correlations given by Equations 2 and 3 of their paper can be used to predict the ASTM rolling-plate plastic limit (i.e., PLRP), while their Equation 4 can be used to predict the BS FC liquid limit (i.e., LLFC). The Authors demonstrated that these correlations gave good predictions of the measured LLFC and PLRP water contents (i.e., wL(FC) and wP(RP), respectively) for 87 fine-grained soils they sourced from different parts of Central Turkey. Employing newly compiled large and diverse consistency limits databases assembled from the published research literature, this discussion article confirms that the Authors’ Equations 2 and 3 generally produce poor wP(RP) predictions for the fine-grained soils comprising these databases, invariably overestimating (often seriously) their measured plastic limit values. Hence, the Discussers recommend that the Authors’ Equations 2 and 3 (being generally unreliable beyond the investigated Turkish soils) should not be used in geotechnical engineering practice. While the Authors’ single-point LLFC method given by their Equation 4 broadly appears as a good wL(FC) predictor for the newly compiled database soils, it is noted that there already exist well-established and standardised single-point LLFC methods.

A Review on Soils Treated with Biopolymers Based on Unsaturated Soil Theory.

Adding different materials to soil can improve its engineering properties, but traditional materials such as cement, lime, fly ash, etc., have caused pollution to the environment. Recently, biopolymers have shown many advantages, such as economy and environmental protection, which make them applicable to geotechnical engineering. This study summarizes the effects of biopolymers on soil's engineering properties and the main directions of current research. Firstly, the advantages and disadvantages of a variety of widely used biopolymer materials and their effects on the specific engineering characteristics of soil (i.e., water retention characteristics, strength characteristics, permeability characteristics, microstructure) are introduced, as well as the source, viscosity, pH, and cost of these biopolymers. Then, based on the theory of unsaturated soil, the current research progress on the water retention characteristics of improved soil is summarized. The key factors affecting the strength of biopolymer-treated soil are introduced. Due to the actual environmental conditions, such as rainfall, the permeability and durability of biopolymer-treated soil are also worthy of attention. In summary, it is necessary to study the variation laws of the engineering properties of biopolymer-treated soil in the full suction range, and to predict such laws reasonably. The relevant results are conducive to the safer and more scientific application of biopolymers in geotechnical engineering practice.

Effect of temperature on the mechanical properties of fine-grained soils - A review

Contemporary geotechnical engineering practice encompasses design and construction of thermo-active geo-structures or structures which would encounter thermal cycles throughout its service life. Therefore, understanding the effect of temperature on soil mechanical properties becomes inevitable. Being a complex and coupled phenomenon it has been quite challenging for the researchers to study experimentally and theoretically the thermo-mechanical behaviour of fine-grained soil. Nonetheless, there are numerous studies which contribute significantly to gain insight about thermo-mechanical behaviour of soils. Incidentally, till date, on this arena of research, no comprehensive review, which provides a holistic development of the subject and its connection with the field application, is available. The prime objective of the present study is to critically appraise the state-of-the-art understanding on thermo-mechanical behaviour of fine-grained soils through a comprehensive literature review. Moreover, this paper also describes the concept of thermo-elasto-plastic strain and thermal creep behaviour of fine-grained soils.

Numerical Modeling of the Geotechnical and Structural Strengthening of Quay Structures with a Case Study

With developments in maritime trade, the need to increase port capacities has emerged. It is important that the reconstruction of such port structures be carried out without disrupting the activities of the existing port and without damaging the old structures. However, the reconstruction and strengthening of these structures require significant engineering work. Especially in the design of such structures, geotechnical and structural engineering theories and practices need to be considered together. The most important challenge in this type of engineering design is to ensure harmony in geotechnical and structural analyses. In this study, the strengthening of a port structure in Guinea is taken as a case study. First, the existing quay wall was evaluated, and then the geotechnical and structural design of the new structure to be built for capacity increase was discussed. A geotechnical design was made with the Plaxis 2D program, and the structural design was made with the Sap2000 program. The soil behavior was analyzed nonlinearly with the Plaxis program and was modeled with the same accuracy as the Sap2000 program. In addition, pile capacities were confirmed by loading tests performed on the piles. The results show that complex hybrid solutions consisting of reinforced and unreinforced piles can be modeled with the finite element method. As seen from this case study, the capacities of existing port structures can be safely increased, provided that necessary geotechnical precautions are taken.

Dynamic strength characteristics of fractured rock mass

Fractures play crucial role in the behavior of rock masses, yet the understanding of their natural distribution and impact on dynamic characteristics remain unclear. Here the effect of “natural” fractures on the dynamic impact strength of rock mass was investigated using numerical specimens with fractures prepared using the Split Hopkinson Pressure Bar (SHPB) model. These fractures were generated through biaxial compression simulation. Various axial stress levels and confining pressures replicated diverse natural rock fracture distributions. To capture the anisotropic distribution of fractures in natural rock and the randomness of impact direction, impact from 0°, 90°, 180° and 270° directions were imposed. The biaxial loading simulation showed that fracture increases with higher loading stress, and rapidly expands in the post-peak stress stage, with ∨ or ∧ shaped slip plane depending on confining pressure. The impact strength of the fractured specimen decreases as the number of prefabricated fractures increases, following a two-stage pattern, i.e., rapidly decrease with small number of fractures and gradually decrease with high number of fractures. Pre-existing fractures aligning with the impact direction provide stronger resistance compared with fractures deviated, and their location and distribution significantly affect the stress transmission. The impact from other directions has different stress transmission routes related to the fracture and macroscopic surface distribution. Importantly, a specimen’s loading history shapes its internal fracture distribution, thereby affecting its resistance to impact stress. This research provides invaluable insights into the role and mechanics of fractures in rock masses, thus enhancing our understanding of rock dynamics and potentially informing more effective geotechnical engineering practices.

Anisotropic seabed soil failure description and three-dimensional simulation method

In order to find out the underlying effect of anisotropy on the failure characteristics from the mesoscopic mechanism, using the concept of fabric tensor and assumption of mutual mapping between isotropic space and anisotropic space, a compound stress is proposed based on the combination of ordinary stress and fabric tensor. This compound stress can be used to describe the primary anisotropic properties effectively. For the difference in the effect of stress-induced anisotropy on shear strength of various geotechnical materials in the deviatoric plane, a generalized failure criterion is proposed. This failure criterion can effectively describe various criteria forms from Von-Mises criterion to SMP criterion within a relatively large range. The hydrostatic pressure effect can also be indicated by the shape of the power function on the meridional plane. A primary anisotropy generalized failure criterion can be obtained when the compound stress is used to describe the new generalized failure criterion and the corresponding transformation stress method has been proposed. This method can consider the effect of native induced anisotropy and stress induced anisotropy on the shear strength simultaneously. The comparison between predicted and tested results shows that the proposed anisotropic generalized stress failure criterion and its transformation method can be applied to the geotechnical engineering practice simply, its rationality and applicability have also been verified.

Construction practice of water conveyance tunnel among complex geotechnical conditions: a case study

The construction practice of water conveyance tunnels often encounters various complex geotechnical engineering conditions, which bring huge challenges to the design and construction of water conveyance tunnels. Based on the theory of rock elastic–plastic mechanics and finite element analysis technology, this article carried out investigations of engineering geological features, geological formations and hydrological conditions establishes a calculation model for the 3# water conveyance tunnel of the Fenhe River Diversion Project, and analyzes the variation law of surrounding rock stress and displacement during TBM excavation of the tunnel. The results indicate that the dominant direction of the rock mass principal stress measured by the hydraulic fracturing method is NE84°, and the maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress decrease sequentially, analyzing the characteristics of shield TBM construction technology, it is applied to the construction of water transfer tunnels. The numerical simulation of TBM construction using FLAC3D software shows that as the excavation surface advances, the subsidence value of the tunnel roof first slowly increases, then rapidly increases, and then tends to stabilize. The horizontal displacement of the surrounding rock is increasing. The maximum principal stress of the surrounding rock gradually increases. The final surrounding rock stress is 35 MPa. The TBM shield machine with mud water balance driven by indirectly controlled frequency conversion motor is selected for TBM construction of the tunnel. The study offers statistical information to support tunneling technology for water conveyance in the geotechnical engineering practice.

Triaxial Shear Analysis Using Discrete Element Methods for Sandy Soil with an Improved Flexible Membrane Boundary

Exploring strain localization has substantial potential to significantly impact the disaster resilience and mitigation capabilities of infrastructure, thus influencing project sustainability. Consequently, the field of sustainable geotechnical engineering is progressively directing attention toward studying soil strain localization. This research focuses on triaxial testing to deepen our understanding of this phenomenon by applying discrete element methods, thereby fostering the advancement of sustainable geotechnical engineering practices. While rigid-wall-based discrete element triaxial tests have been extensively studied, using flexible boundaries in these tests has received limited attention. This study introduces a three-stage method to enhance stress application in flexible membranes by applying confining pressure. A comparison of triaxial tests was conducted at both macroscopic and microscopic scales, utilizing flexible and rigid boundaries. Moreover, numerical simulations were performed on flexible membrane samples with various particle sizes to identify appropriate dimensions for flexible boundaries. Our results demonstrate that the improved flexible membrane provides more accurate representations of macroscopic and microscopic sample variations than rigid walls. Keeping the particle sizes for flexible membranes within the range of 0.2 to 0.8 times the characteristic particle size (r) is essential for striking a balance between simulation accuracy and computational efficiency. These findings enhance the accuracy of triaxial compression test simulations and offer a valuable foundation for studying strain localization in soils. Understanding these phenomena is essential for various geotechnical engineering applications, such as foundation design and slope stability analysis. Furthermore, these findings form a pivotal foundation for resource optimization and enhancing the reliability of engineered structures, thereby driving the advancement of sustainable geotechnical engineering practices.

Compaction Characteristics of Organo-silane Treated Soils

Abstract The extent to which hydrophobic soils can be used in geotechnical engineering practice depends upon a commensurately increased understanding of how fundamental relationships apply in hydrophobic systems, such as moisture-density. This research is to determine the compaction characteristics of organo-silane (OS) treated soils using conventional geotechnical laboratory equipment. The intrinsic difficulty in lubricating hydrophobic soils, which would allow for rearrangement of particles and subsequent compaction, arises from their inherent low surface energy. This work describes a method for compacting OS treated soils that leverages the necessary conditions such as reaction time and drying conditions for achieving hydrophobicity. Procedural steps for compacting OS treated soils are detailed by making use of a water-soluble hydrophobizing agent added to a fine-grained soil. Based on the critical dosage ratio of 1:100 (hydrophobizing agent: soil) identified, a molding water content is defined constituting of a fraction of the hydrophobizing agent. Soil water content and dry density curves are developed using the standard Proctor and Harvard miniature to contrast the resulting effect of OS. Compared to the untreated soil, a decrease in optimum water content was observed with the OS treated soil regardless of compaction technique used. For the standard Proctor test, a decrease in optimum water content from 12.0 to 9.2 % was observed, whereas compaction with the Harvard miniature showed a marginal decrease from 9.3 to 9.0 %. With the untreated soil, a relatively larger maximum dry density (2.17 g/cm3) was obtained with the standard Proctor compared to the Harvard miniature (2.05 g/cm3). The protocol defined to compact OS treated soils has shown to induce hydrophobicity spatially within the sample depth. These results suggest that engineered water repellency can be implemented in so far as treatment and compaction are largely synchronous and prior to reaction and hydrophobization.

Use of Geophysical Surveys in Geotechnical Engineering Practice — a Geotechnical Engineer’s Perspective

Use of Geophysical Surveys in Geotechnical Engineering Practice — a Geotechnical Engineer’s Perspective

Mechanical properties of a high plasticity clay mixed with sand and low-plastic silt

It is of fundamental importance in geotechnical engineering practice to have a comprehensive understanding of how the mechanical properties of widespread alluvial soils are affected with varying concentration of sand, silt, and clay particles. Moreover, among the available methods of chemical and mechanical stabilization of high plasticity cohesive soils, mixing this soil with sand and/or non-plastic silt still brings a cost-effective and environment friendly solution. In this study, clay-sand and clay-silt mixtures were prepared by adding sand and silt to the clay samples in different proportions to explore geotechnical properties of sand-clay and silt–clay mixtures and develop empirical correlations for Atterberg’s limits, compaction properties, unconfined compression strength, and consolidation characteristics for these soil mixtures. It was observed that for additive contents of up to 50%, the liquid limit and plasticity index of high plasticity clay sample decreased by 36% and 55% (with silt) and 47% and 58% (with sand), respectively. The reduction in undrained shear strength determined from unconfined compressive strength tests was about 37% with silt and 59% with sand contents. The compression index decreased by almost 13% with silt and 39% with sand. Likewise, it was also observed that the coefficient of consolidation increased with addition of silt and sand by 57% and 87%, respectively. As the increase in silt and sand content transformed the soil into a compact mass which ultimately should lead to a decreased total settlement as well as the rate of settlement of such soils. The statistical models proposed in this study have high coefficient of determination which depicts the reliability of these models in predicting the mechanical properties of sand-silt–clay mixtures.

Towards boundary conditions in concrete-rock joint shearing with STAs profile by PFC2D

Boundary conditions significantly affect the shear behavior of concrete-rock joints. Most of the joint models have been developed for the constant normal load (CNL) conditions but cannot be directly extended to the more general constant normal stiffness (CNS) conditions, as a ‘normal stiffness (K)’ serves as a spring in such a condition to constantly adjust the normal confinements in terms of the dilation. In this study, the authors attempted to set up numerical modeling of concrete-rock joint shearing by layered over-compaction method based on PFC2D. An obvious extension is that explicit spring-based kinetic equations were employed to govern the travel of the upper shear chamber, by which the system can be dynamically balanced at each timestep to permit CNS conditions. Also, an alternative joint profile consisting of multiple similar triangular asperities (STAs) was defined in the presented modeling, taking account of both varied asperity heights and sizes. The comparisons with laboratory observations, recently published by the authors, demonstrated that the model makes reasonable predictions of shear behavior, especially well capturing the essential mechanisms of STAs profile, including dilation, shearing, and local lift-off. Compared with CNL conditions, the CNS conditions can better mobilize the peak shear strength, maximum normal stress, micro-cracks, and force chain. Results indicate that an adequate choice of CNL or CNS conditions is of significance to evaluate the side resistance, loading capacity, or engineering stability in geotechnical engineering practices.

Effect of Static and Dynamic Methods of Compaction on Mechanical Properties of Silt

Engineered fills, such as roads, earthen dams, embankments, and earthen sites, are enhanced by compaction to increase strength and decrease compressibility. Static and dynamic compaction are the most popular and important methods in geotechnical engineering practice with different compaction mechanisms. However, the significant differences in the physical and mechanical properties between both compaction methods that have been reported in the literature were limited to clay or sand. Limited attempts have been made to quantify the variations in silt’s mechanical attributes that were caused by the sample preparation method. A series of consolidated drained triaxial shear tests and some mercury intrusion porosimetry (MIP) tests were constructed to interpret this. The results showed that static and dynamic compaction had a significant influence on the mechanical properties of the silt coupled with the molding water content. The shear strength of the dynamically compacted samples was higher than those of the statically compacted samples, as was cohesion (c), and the sample preparation method had little effect on the internal friction angle (φ). Furthermore, samples that were compacted at optimum water content (wot) had greater strength than those compacted on the dry or wet side of the optimum. Compared with the static compaction sample, the pore size distribution curve of the dynamic compaction sample shifted to the left with the peak pore size, distribution density, and the interaggregate pores proportion decreased. The strength discrepancy could be traced to differences in the silt structure features, for example, pore size distribution and particle orientation between statically or dynamically compacted specimens.

Comparison on the Behaviour of Bamboo and Polypropylene Fibre in Soil Stabilization

Abstract: In the practice of geotechnical engineering, soil improvement is regarded as one of the most significant solutions, particularly in the case of weak soil conditions. Expansive soil exposed to climatic changes and moisture content, experiences a significant volume shift. Building foundations, paving structures, irrigation systems, and other geotechnical engineering projects are just a few examples. To prevent swelling and shrinkage characteristics, stabilizing the expansive soil is crucial. For considerations of sustainability and economy, stabilizing material selection is crucial. In this project, the soil stabilization is accomplished using reasonably priced and easily accessible materials like bamboo fiber and polypropylene fibre. Soil is replaced by NaOH treated bamboo fibre from 0.2 to 1% at the interval of 0.2% and the same is repeated by replacing the soil with 1% to 3% at the interval of 0.5%. It was observed that, there is marginal increase in dry density of the treated soil samples and reduction compressibility. The maximum Unconfined Compressive Strength (UCS) was obtained for optimum 0.4% of bamboo fibre and 1.5% of polypropylene fibre with replacement of soil. The performance of bamboo fibre was compared with that of polypropylene fibre. The bamboo fibre showed better results than polypropylene fibre.