Journal of Geotechnical and Geoenvironmental Engineering

The design of rock engineering projects requires an estimation of the strength of intact rock blocks. These blocks can be significantly larger than the typical laboratory test specimen; thus, understanding the specimen size effect on mechanical properties is essential. In this paper, a series of uniaxial compression tests and Brazilian disc tests were conducted on cylindrical samples with diameters varying from 20 to 150 mm, and direct shear tests were conducted on cubic samples with side lengths varying from 50 to 200 mm. The results showed that the uniaxial compressive strength (UCS), cohesion, and Young’s modulus decrease with increasing specimen size, whereas the tensile strength initially increases and then decreases. Moreover, the applicability of different size effect models to experimental data was assessed. It was concluded that the fitting equations of UCS and cohesion are almost the same, whereas that of tensile strength is significantly different. The size effect law of rock mechanics parameters may be affected by the failure mode.

Ports and waterways are routinely dredged to maintain navigation channels, resulting in large quantities of dredged materials (DM) that require disposal. This study examines the reuse of a recent DM as a topsoil alternative in highway slopes. The DM met local highway administration topsoil requirements for pH, organic matter, and particle size distribution, and required application of 1,219 mm of rainwater to leach soluble salts to below limits. Column leach tests were performed on DM and topsoil to evaluate heavy metal (arsenic, barium, cadmium, chromium, copper, lead, mercury, silver, selenium, zinc) leaching behavior; extractions were performed to determine total and potentially mobile metals content. DM leached metals concentrations below drinking water maximum contaminant levels for $>95\%$ of the samples tested. Extraction data showed higher total concentrations of arsenic, chromium, and lead as compared to topsoil, but similar concentrations in the ethylenediamine tetraacetic acid (EDTA)–extracted fractions, indicating that metals are strongly bound.

Bridge or berthing structures are susceptible to accidental ship impacts that may pose a hazard to human life, property, and the environment. Therefore, fenders are often constructed around bridge piers for protection. Although efforts have been made to estimate the ship impact load, understanding of the mechanism of ship impacts on bridge fender systems is still inadequate due to insufficient experimental evidence. In this study, a comprehensive centrifuge model test program involving 60 ship impact tests was performed on a $3\times 3$ pile group to systematically examine the effect of fender systems on a bridge pile foundation subjected to ship impacts. Two types of fenders with different stiffnesses, as well as a benchmark test without fenders, were investigated under different vessel tonnage and impact velocity values. Based on the test results, the characteristics of the impact loads were analyzed. The energy transfer patterns with and without fender systems were compared. The influences of the ship tonnage, impact velocity, ship bow structure, and bridge superstructure mass on the impact load with different fender systems were studied. Finally, empirical equations are established to relate the ship impact load with key influencing factors regarding the fender system, the ship, and the bridge.

The combined influence of density and stress-induced fabric anisotropy on the nature of stress transmission in gap-graded soils with cohesionless fines has been explored using the discrete element method (DEM). Various particle size ratios and fines contents were considered in simulations of constant mean stress triaxial compression. Analysis of the available particle-scale data focused on understanding how stress was distributed among and between the finer and coarser particles. While the study confirms that stress is transferred from the coarser to the finer fraction with increasing fines content, the concept of a threshold fines content at which there is a definitive transition in the nature of stress transmission is not supported. Rather, there is a gradual evolution of the distribution of stresses between the two size fractions with increasing fines content, and the relationship between fines content and stress in the finer fraction depends on the size ratio, density, and fabric anisotropy. For the denser samples considered, the stress transmitted by the finer fraction systematically reduced during shearing. An alternate definition of granular void ratio is introduced, which accounts for the nonactive fine and coarse particles and is formulated in a consistent manner to capture both the intergranular and interfine void ratios commonly found in the literature, along with the equivalent granular void ratio. The anisotropy of the network of contacts formed by the interactions of coarse particles was observed to be the dominant contributor to fabric anisotropy.

In this study, the resistance factors ($RF$) in the load and resistance factor design (LRFD) for the drilled-shaft foundation of transmission line structures subjected to lateral loads were investigated. Various load test results were collected to establish a database and used in the reliability analysis. The first-order reliability method (FORM) was implemented to calibrate $RF$ for the Broms, Brinch-Hansen, and Prasad and Chari methods. Loads for transmission line structures were categorized and characterized statistically for calibrating $RF$. Uncertainties of the transverse tension load ($TTL$), wind-on-structure load ($W{L}_s$), and wind-on-ice-coated conductor load ($W{L}_c$), all dominant in transmission line structures, were evaluated. $RF$ varied largely with nominal load ratios of $W{L}_s/TTL$ and $W{L}_c/TTL$, which should be considered for the selection of $RF$ in the design to maintain a consistent safety margin. Increases in nominal $W{L}_s$ and $W{L}_c$ induced higher $RF$ while increasing nominal $TTL$ yielded lower $RF$. The higher $RF$ values obtained in this study were due to the low bias factors of wind-induced loads and the large load factors of the tension and wind loads. The equivalent factor of safety ($F{S}^{eq}$) was evaluated and analyzed for the proposed $RF$s.

When fully saturated sandy soil is subjected to cyclic straining in undrained conditions, pore water pressure increases and effective stress decreases. Therefore, it has been assumed that in such a case sand stiffness always degrades. However, recently published results of cyclic strain–controlled triaxial and simple shear tests reveal that, at cyclic shear strain amplitudes, ${\gamma }_c$, between 0.01% and 0.10%–0.15%, the secant shear modulus at cycle $N$, $G_{SN}$, increases with $N$ up to 10% of the initial $G_{S1}$ and then decreases, while the cyclic pore water pressure, $\mathrm{\Delta }{u}_N$, monotonically increases, and that $\mathrm{\Delta }{u}_N$ can actually reach up to 40% of the initial effective vertical stress before $G_{SN}$ drops below $G_{S1}$ and sands start to truly degrade. To investigate if such a behavior is universal and occurs under various loading conditions not tested before, new cyclic simple shear tests were conducted and analyzed. They included three sands, two different sand structures, cyclic strain–controlled single- and multistage tests with different sequences of ${\gamma }_c$ between 0.005% and 0.16%, cyclic stress–controlled tests, tests with different consolidation stresses, and several tests with a large number of cycles. The new test results revealed the same trends and confirmed that such behavior is truly universal. However, in the new tests $G_{SN}$ increased up to 15% of the initial $G_{S1}$ and $\mathrm{\Delta }{u}_N$ reached up to 50% of the initial effective vertical stress before $G_{SN}$ dropped below $G_{S1}$.

Research indicates the presence of in situ structure of soil skeleton in several natural deposits of clay. However, the effect of such in situ structure and its evolution during loading are rarely accounted for in solution of boundary value problems in geomechanics. This paper explores the effects of inherent soil structure and its degradation on bearing capacity of circular footings in structured clays. An advanced constitutive model that accounts for stress-induced anisotropy, soil structure, and their evolutions with loading is implemented within a finite element analysis (FEA) framework. FEA results demonstrate a significant increase in the bearing capacity of structured clay as compared to that in reconstituted clay. Nonetheless, such an enhancement in limit bearing capacity is subdued by destructuration of soil below the footing. A bearing capacity factor accounting for soil destructuration is proposed for inclusion in the limit bearing capacity calculation of circular footings on structured clay. Successful numerical predictions of results from an instrumented field load test on a footing resting on structured clay further substantiates the importance of considering soil destructuration in bearing capacity analysis.

This paper proposes a Bayesian network approach to predict the shear modulus and maximum friction angle of sand. The nonlinear correlations between sand parameters can be incorporated in the probability distribution represented by a Bayesian network. Extensive databases for shear modulus and friction angles of sandy soils are compiled for training the Bayesian network through maximizing the log-likelihood. The trained Bayesian network is applied to a case study in Japan (Yodo River sand). Information from multiple sources (index properties, in situ samples, and modulus logging) can be integrated in a holistic manner to decrease the uncertainty in the prediction of stiffness and shear strength. A Bayesian network also allows the calibration of the global model (model trained from a large global database) by including site-specific samples. In the Yodo River sand case, it is revealed that one to three samples are adequate to reduce the uncertainty of the global model close to the uncertainty of the site-specific model.

Monopiles are widely used as the foundation to support offshore wind turbines (OWTs). The response of monopile-supported OWTs is strongly affected by the natural frequency of the system relative to the load spectrum, and in turn, the natural frequency is governed by the initial stiffness of the foundation. Both fatigue limit state (FLS) and serviceability limit state (SLS) design are also influenced by the foundation stiffness. The stiffness of the foundation during operational loading is a function of the initial soil state postinstallation, which is influenced by the installation effect. This is the first part of a pair of companion papers that investigates the effect of different installation methods on the subsequent response of monopiles under lateral loading through extensive numerical analyse. The present paper focuses on the quantification of the effect of pile installation on the soil state in sand for three different initial relative densities. The numerical model is first validated against purpose-designed centrifuge tests. Subsequent analyses demonstrate how the soil state, including the void ratio and stresses, is altered from in-situ conditions during pile installation and is markedly different depending on whether the pile is jacked or impact driven. The results presented here and in the companion paper highlight the need to account for the effects of the installation process on the lateral pile response.

Monopiles under in-service conditions are subjected to lateral forces and resultant bending moments from the offshore environment. The subsequent lateral response following installation is significantly influenced by the initial soil state postinstallation, which is influenced by the pile installation process, as demonstrated in previous numerical studies. To date, there are no technical guidelines established for considering the installation effects on the design of laterally loaded monopiles. This paper is the second of a pair of companion papers that investigate the effect of different installation methods on the subsequent response of monopiles under lateral loading. The paper focuses on the quantification of the effect of pile installation on the initial stiffness and lateral capacity. The numerical model is first validated against purpose-designed centrifuge tests. The analysis confirms that impact driven piles have significantly higher initial stiffness and lateral capacity than jacked piles and wished-in-place piles. The effect of installation methods on the lateral response is also influenced by the initial soil density, driving distance, pile geometry, stress level, and load eccentricity. The study highlights the importance of considering the effects of the installation process on the subsequent lateral pile response.

The vast majority of surface structures are located on or surrounded by unsaturated soil deposits and may suffer excessive settlements during earthquakes. However, the fundamental understanding of the mechanisms by which the degree of saturation impacts the volumetric deformation of soils during seismic loading is still not mature. Consequently, it is critical to develop and calibrate seismic compression models while considering these mechanisms. The objective of this paper is to experimentally investigate the impacts of the degree of saturation, fines content, and desaturation technique on the seismic compression of sand and silty sands. The experimental program involved undrained cyclic direct simple shear tests on specimens prepared using suction control and wet-compaction techniques with similar relative densities but different levels of saturation. A strain-based predictive model was adapted and modified to capture the observed trends in the seismic compression of soils with different degrees of saturation. The suitability and applicability of the model were verified by comparing the measured and estimated compression values in this study with ones reported in the literature for other soils and desaturation approaches.

The severity of liquefaction-induced ejecta manifestation for the 2010–2011 Canterbury earthquakes was overestimated or underestimated using simplified liquefaction ground-failure indices at several sites in Christchurch. Nonlinear effective stress analyses of two representative level ground sites are performed to investigate the causes of these misestimations. One site has a thick, clean sand deposit, and the other site has a highly stratified silty soil deposit. The excess hydraulic head profile with depth that develops during and after earthquake shaking determines the potential of upward seepage-induced artesian flow that produces sediment ejecta. The thick, clean sand site can develop high-gradient upward seepage that is sustained after strong shaking ends to produce severe ejecta. The stratified silty soil site develops high pore water pressures in isolated soil layers, but the amount and rate of upward seepage are insufficient to produce ejecta. A proposed ejecta potential index (EPI) captures key aspects of the hydraulic mechanisms of liquefaction manifestation. EPI estimates the severity of sediment ejecta by tracking the duration in which the excess hydraulic head exceeds the hydraulic head required for artesian flow. The EPI values computed from the simulations of the two sites capture the observed trends of liquefaction manifestations during the Canterbury earthquakes.

Korea has started to build wind farms in the Yellow Sea, with the seabed consisting of a thick silty sand deposit. It is therefore important to understand the behavior of potential foundations of wind turbines. This paper reports results from a series of model tests undertaken to provide insight into the behavior of a bucket foundation subjected to monotonic horizontal and moment loading in silty sand. The tests were carried out at 70g in a beam centrifuge. The silty sand materials were cored directly from a wind farm site of Yellow Sea. The considered dimensions of the model bucket foundation and loading conditions represented those for a 3 MW wind turbine. The windward and leeward side, and inside and outside, of the model bucket was instrumented with 13 pressure transducers to obtain information in regards to soil-bucket interactions. The horizontal capacity or failure load increased with decreasing loading height due to decreasing induced moment at the load reference point (LRP). A horizontal-moment failure envelope was proposed calibrating against centrifuge test data. A loading rate 20 times faster augmented the horizontal failure load by 1.5 times. This was a consequence of dilation-induced excess pore water pressure. With the drainage valve on the lid shut, the soil inside the bucket was in tension and suction prevailed. The leeward outside of the skirt experienced significantly higher pressure, and that increased with the angle of rotation. Suction inside the skirt and resistance on the leeward outside dominate the capacity of the bucket foundation.

Sea level rise and high tide events are threatening many coastal cities, which require adequate and sustainable protection measures. The historic city centre of Venice (Italy) is often flooded during very high tide events, especially the area of St. Mark’s Island, which is at the lowest elevation among all the islands forming the city. To design cost-effective protection interventions to safeguard the historical heritage, a deep understanding of flooding mechanisms and the relationship between groundwater pressure and tidal oscillations is necessary. Geotechnical survey and analyses play an important role in this process. This paper presents the results of a recent monitoring campaign carried out in St. Mark’s Island. A simplified one-dimensional analytical model was derived for saturated conditions to understand the key parameters that govern tidal induced pressure oscillations in soil (material properties, geometrical features, and wave properties). Additional features, such as partially saturated soil conditions and two-dimensional effects, were investigated numerically. Results showed that significant pressure oscillations occur in the subsoil, which should not be neglected when considering the stability of horizontal architectural structures, such as the historical mosaics and paving. However, seepage flow rate is small, and thus its impact on the drainage system is limited in terms of water discharge.

High-resolution displacement observations of lateral spreading from optical image correlation are available for the 2011 Christchurch ($M_w=6.2$), New Zealand, earthquake, and these data were used to provide insights into the detailed displacement patterns during the earthquake and to quantitatively evaluate the performance of existing empirical models for lateral spread displacements. The observed displacements revealed important characteristics influencing the displacement patterns, including topographic terraces enhancing displacements in large regions between the terrace and the river, the combined effects of a free face and sloping ground on displacements near the river, and the effect of multiple free faces. These site characteristics can enhance displacements and should be considered when evaluating lateral spread movements. For the displacement models, on average, the Youd model underpredicts the observed displacements by more than a factor of 2, likely due to the strong magnitude scaling incorporated in the model. On average, the Zhang model is unbiased relative to the observed displacements but systematically overpredicts displacements for slopes greater than 1%. These results indicate the limitations of the existing lateral spread models and point toward the need for improvements in our understanding of lateral spread displacements.

Bentonite is planned for use as a buffer for repositories of high-level radioactive waste (HLW) because the buffer must have extremely low hydraulic conductivity to seal wastes. A Japanese HLW disposal facility might be built in a coastal area to facilitate waste transportation. Therefore, it is important to investigate the influence of seawater on bentonite buffer materials. This study used experiments to investigate the influence of artificial seawater on the hydraulic conductivities of three sodium-type bentonites and one calcium-type bentonite. This study assessed the influence of artificial seawater on hydraulic conductivities of bentonites in terms of the kinds of bentonite such as exchangeable-cation type, montmorillonite content, and the bentonite buffer dry density. Experimentally obtained results indicate a low influence of artificial seawater on hydraulic conductivities of sodium-type bentonites, provided that the compacted bentonite dry density is high. Furthermore, the author has proposed a mechanism of bentonite behavior in artificial seawater that results from cation filtration of montmorillonite mineral layers in bentonite. This study has also clarified the validity of the cations’ filtration mechanism of montmorillonite mineral layers by comparing the calculated interlayer distance of montmorillonite minerals with the hydrated diameter of main cations in artificial seawater.