Shear Modulus Of Soil Research Articles

Probabilistic analysis of wave-induced dynamic response in a poroelastic sloping seabed using random finite element method

Wave loading can lead to transient liquefaction and instability in a porous seabed and can therefore cause marine structures to fail. The failure mechanism of seabed involving many complex factors and uncertainties has not been fully revealed. The properties of marine sediments, usually assessed as constant parameters in traditional deterministic analyses, actually vary spatially because of geomorphic processes and loading history. This study therefore presents a probabilistic analysis of wave-induced dynamic responses in a poroelastic sloping seabed by applying a random finite element method. Spatial variabilities of the cross-correlated permeability and shear modulus of marine soils are taken into account using random field theory. The response of poroelastic sloping seabed is analyzed based on Biot's theory and linear wave theory considering changes in wave height and length when propagated from relatively deep to shallower water. A LiveLink code is written to integrate the random field simulation and the finite element model for the probabilistic analysis of a spatially heterogeneous seabed. Monte Carlo simulations are carried out to obtain the statistics and associated uncertainties of the seabed response. Effects of cross-correlation of random fields and the slope angle on the response of a poroelastic sloping seabed were also investigated.

Development of Constitutive Models for Linear and Nonlinear Shear Modulus and Material Damping Ratio of Uncemented Soils

Development of Constitutive Models for Linear and Nonlinear Shear Modulus and Material Damping Ratio of Uncemented Soils

Prediction the shear strength and shear modulus of sand-clay mixture using bender element

Employing the conventional laboratory geotechnical methods such as shear box test to measure shear strength and shear modulus require destroying the samples which is seen as time consuming and costly. Whilst the bender element technique (BE) maintains the sample condition, time, and cost efficiency. Several sand-clay mixtures were compacted and subjected to bender element test as well as sheared using shear box test to measure and correlate shear modulus (t), shear strength (G) and the maximum shear modulus (Gmax). The results showed the critical stage (transition fines-grained) at fine-grained (FG) equal to 50% where any further increment beyond this value led to decrement the soil mixture strength. Both t and G were normalized using moisture content, density, and applied normal stress. Five empirical equations from the normalized shear strength tN were applied on the previous field data to exam their reliable and limitations. The equations indicated the importance of including the effect of overburden pressure for the natural sample as well as the in-situ moisture content and field density to avoid uncertainty in the predicted value of the soil shear strength and modulus. At no depth limitation, all empirical equations (tN1, tN2, tN3, tN4, and tN5) exceed ±20% lines which indicated a large variation in results. At depth limitation (< 5 m), only one equation corresponding to N4 showed reasonable validity and reliability to predict the shear strength. Similar was on the prediction of the shear modulus. The 5 m depth limit was recommended to apply the equation consistently.

Investigation on the Effect of Probability Distribution on the Dynamic Response of Liquefiable Soils

This study investigated the effect of different probabilistic distributions (Lognormal, Gamma, and Beta) to characterize the spatial variability of shear modulus on the soil liquefiable response. The parameter sensitivity analysis included the coefficient of variation and scale of fluctuation of soil shear modulus. The results revealed that the distribution type had no significant influence on the liquefication zone. In particular, the estimation with Beta distribution is the worst scenario. It illuminated that the estimation with Beta distribution can provide a conservative design if site investigation is absent.

Stress history and time effect on shear modulus of expansive soils

Stress history and time effect on shear modulus of expansive soils

Characterizing the Effect of Water Content on Small-Strain Shear Modulus of Qiantang Silt

Due to the impact of natural and artificial influence, such as waves, tides, and artificial dewatering, the small-strain shear modulus of soils may vary with the water content of soil, causing deformation of excavations and other earth structures. The present study used a resonant column device to investigate the effects of water content, void ratio, and confining pressure on the small-strain shear modulus of a silt extracted from an excavation site near Qiantang River in Hangzhou, China. The test results revealed that the effects of the three factors are not coupled and can be characterized by three individual equations. In particular, the small-strain shear modulus decreases with increasing water content under otherwise similar conditions, which can be characterized by a power function. The classical Hardin’s equation is modified to consider the effect of water content by introducing an additional function of water content.

Effects of construction sequence of double basement excavations on an existing floating pile

Deep excavations inevitably induce stress relief and ground movement, which may affect the safety and serviceability of nearby pile foundations. Although research attention was paid to the basement-soil-pile interaction, most of the previous studies focused on responses of end-bearing piles due to a single basement excavation. In this study, centrifuge tests and numerical analyses were conducted to investigate effects of construction sequence of double basement excavations on an existing floating pile in dry sand. For basements excavated sequentially (i.e., multi-propped excavation is conducted before cantilever excavation), the measured pile settlements due to multi-propped and cantilever excavations are 0.42% dp and 0.72% dp (pile diameter), respectively. This is because multi-propped excavation causes a reduction of soil shear modulus, and cantilever basement has much smaller support system stiffness than multi-propped basement. The horizontal soil movement and pile bending moment due to multi-propped excavation are reversed during cantilever excavation. Upon completion of double basement excavations, construction sequence of double basements (i.e., excavated sequentially and simultaneously) has limited effects on pile head settlement. But the maximum bending moment due to double basements excavated simultaneously is only 18.9% of that due to double basements excavated sequentially. To ensure the safety and serviceability of existing pile foundation, it is suggested to construct double basements simultaneously rather than sequentially.

Normalized Shear Modulus and Damping Ratio of Soil–Rock Mixtures With Different Volumetric Block Proportions

The volume fraction of rock blocks plays a particularly significant role in static/dynamic shear behaviors of soil–rock mixtures (SRM). Large-scale cyclic triaxial tests for SRM with different volumetric block proportions (VBPs) were performed at different confining pressures to investigate the reduction of dynamic shear modulus (G) and the increase of damping ratio (λ). Results indicate that VBP has a significant effect on the dynamic behaviors of SRM. The higher VBP is more likely to result in a gentler reduction of G and a faster increase of λ. The variations of dynamic shear modulus ratio (G/G0) and normalized damping ratio (λnor) fall within relatively narrow bands but are very different with gravelly soils and sands due to VBP with particle size larger than 2 mm. The G/G0 and λnor can be characterized by empirical functions about normalized shear strain amplitude (γnor).

Site Investigations of the Lacustrine Clay in Taihu Lake, China, Using Self-Boring Pressuremeter Test

Site investigations of the soils are considered very important for evaluation of the site conditions, as well as the design and construction for the project built in it. Taihu tunnel is thus far the longest tunnel constructed in the lake in China, with an entire length of over 10 km. However, due to the very insufficient site data obtained for the lacustrine clay in the Taihu lake area, a series of self-boring pressuremeter (SBPM) field tests was therefore carried out. Undrained shear strengths were deduced from the SBPM test, with the results showing generally higher than those obtained from the laboratory tests, which may be attributed to the disturbance to the soil mass during the sampling process. Degradation characteristics of the soil shear modulus (Gs) were mainly investigated, via a thorough comparison between different soil layers, and generally, the shear modulus would cease its decreasing trends and become stable when the shear strain reaches over 1%. Meanwhile, it was found that a linear relationship between the plasticity index and the shear modulus, and between the decay rate of the shear modulus and the plasticity index as well, could be developed. Further statistical analysis over the undrained shear strength and shear modulus distribution of the soils shows that the undrained shear strength of the soils follows a normal distribution, while the shear modulus follows a log-normal distribution. More importantly, the spatial correlation length of the shear modulus is found much smaller than that of the undrained strength.

Reliability Analysis of Soil Liquefaction Considering Spatial Variability of Soil Property

The objective of this study was to investigate the liquefaction response of soil using the spatial variability of the shear modulus by considering different values of the coefficient of variation (COV) and the horizontal scale of fluctuation (SOF). For this purpose, a Monte Carlo simulation, combining the digital generation of a non-Gaussian random field with finite difference analyses, was utilized. Parametric studies were performed from the perspectives of the liquefaction area, excess pore water pressure (EPWP), and displacement at the ground surface. We found that a larger COV of the soil shear modulus was correlated with a slower reduction of liquefaction area and a lower EPWP ratio. To explain the influence from the perspective of the spatial distribution characteristics of the shear modulus, a deterministic model test was carried out. Additionally, it was found that the displacement history and the differential settlement at the end of shaking were regularly affected by the COV and the horizontal SOF, especially for large COV and horizontal SOF.

Impact of bedding plane direction and type of plastic microparticles on stiffness of inherently anisotropic gap-graded soils: Index, wave propagation and micromechanical-based interpretations

Sand-clay mixtures are often encountered in natural deposits and compacted soils in earth structures in the form of gap-graded soils. They commonly display anisotropic fabric which markedly influences their wave propagation and mechanical properties. In this study, a comprehensive experimental program is carried out to thoroughly examine the influence of the inclined bedding plane and clay type on the small strain shear modulus (Gmax) of granular soils mixed with various portions of low and high plasticity fines, controlling in this way the double diffuse layer of the microparticles. To this end, cylindrical samples containing different fines contents are prepared with their corresponding optimum water contents and maximum dry densities in a standard proctor mold. Undisturbed specimens are then extracted by the continuous coring method and wave propagation tests with bender elements are applied at different angles with respect to the bedding plane (α-direction), evaluating in this way shear wave velocity and Gmax. The test results suggested that α-direction has a significant influence on Gmax of sand-clay mixtures and this influence is amplified at lower fines contents and higher confining pressures. Mixtures of sand with high plasticity clay are observed to have lower degree of anisotropy compared to those containing low plasticity clay, specifically at lower confining pressures. The contribution of fines in the load carrying structure of the solid skeleton decreases for high plasticity clays; the phenomenon which is primarily attributed to the thick diffuse double layer of the microparticles. This trend becomes more pronounced at higher contents of fines inclusion where the sand-in-fine structure dominates. A previously proposed expression for sands is rectified and extended so as to develop a Gmax model of sand-cohesive clay mixtures taking into account the bedding plane direction. Micromechanical-based interpretations are further elaborated considering the intervention of the microparticles on the contact response of sand grains altering their normal and tangential contact behavior, so as to supplement the findings, from the wave propagation tests, with multi-scale insights.

Strength and Deformation Behavior of Fine-Grained Soils Reinforced with Hair Fibers and Its Application in Pavement Design

ABSTRACT Although waste hair fibers are consumed in agricultural and pharmaceutical industries, etc., their use in civil engineering is very limited. Because of fibrous nature, it can be used as reinforcement material in soil for sustainable development, similar to other commercially used fibers in practice. In this study, an effort is made to improve the properties of the Delhi silt and Dhanauri clay using the human hair fiber. All the tests on Delhi silt and Dhanauri clay were performed with optimum fiber content, i.e., 2%. The results indicate that the shear strength, modulus and CBR value of soil reinforced with human hair fibers have increased considerably. And then, the suitability of human hair fibers in pavement engineering is examined by designing both rigid and flexible pavements using improved properties. Results indicate that there is a reduction in thickness of both pavements, which means that there can be saving of cost in major projects, when human hair fiber is used.

Numerical study on the frequency response of offshore monopile foundation to seismic excitation

The potential vulnerability of the monopile foundation for the offshore structures during seismic events is a valuableresearchtopic. In this study, an integrated 3-D numerical model is set up to investigate the dynamic behavior of monopile-seawater-seabed coupling system in the frequency domain. The pile is considered as linear viscoelastic material and Biot model is used for porous seabed. The dynamic interactions among various components including pile, seabed, and seawater, are fully considered and the perfectly matched layer is adopted as an absorbing boundary condition. The seismic responses of the coupling system, such as hydrodynamic pressure of seawater, pore pressure in seabed, acceleration amplitudes in pile and seabed, are discussed. In addition, the transient liquefaction in the seabed around the monopile foundation is investigated. At the first three peak frequencies, transient liquefaction occurs in more than about two-thirds area around the pile, rather than the whole pile circumference. In particular, only less than about two thirds of the soil around the pile could be transiently liquefied along the vertical direction. Additionally, the influences of embedment depth, pile diameter, soil shear modulus, soil damping ratio, and water depth on the earthquake-induced pore pressure around the pile are significant.

The effect of bogie track and forwarder design on rut formation in a peatland

ABSTRACT The effect of forest machinery on the rut formation on extraction trails is an important aspect of forest operations. The aim of this study was to compare how track design and vehicle configuration affects rut formation on straight and curved test trails with no slash mats on peatland. Rut depth was observed from five machine-track combinations on several test plots after several passes and two different trail configurations, straight and curve. The observations (N = 760) were modeled using a mixed model approach to include the variation between the combinations. The results show that rut depth decreases exponentially with soil shear modulus, increases linearly with the number of passes and is not affected with the trail section configuration. The overall coefficient of determination is R2 = 0.55. A first generation Ponsse Elk with Fomatec tracks (EFwo) showed the lowest rut formation, followed by a first generation Ponsse Elk with Fomatec tracks equipped with add-on track shoes (EFw), a Ponsse Buffalo with KOPA high flotation tracks (Kopa) and a Ponsse Elk 10 W with Olofsfors mixed tracks (E10W), while a Ponsse Elk with long wheelbase bogie and Olofsfors high-flotation tracks (LWB) showed the deepest rut formation. Vehicle dynamics on peatlands are still far from being fully understood and the paper highlights the complexity of the interactions of the variables studied while providing a valid modeling tool with applications in planning of forest operations and simulation.

A 3-D numerical study of the random wave-induced response in a spatially heterogenous seabed

The seabed failure poses a significant threat to the stability of marine structures. The actual wave-induced dynamic response in a porous seabed is a complex issue due to the randomness in hydrodynamic pressure and the spatial variability in soil properties. A probabilistic framework was proposed based on a 3-D stochastic finite element model for the investigation of the random wave-induced responses in a spatially heterogenous seabed. The framework integrates the generation of random waves as well as the random soil and the finite element analysis of poroelasticity via a Livelink code. A decomposed Karhunen-Loève expansion method was proposed, making the generation of multi-dimensional random fields with high resolution and large scale possible. Contrastive analyses of different scenarios were conducted to study the effects of the randomness of wave pressure and the spatial variability of the soil shear modulus on the seabed response. Monte Carlo simulations were used for the statistics of seabed response, and then the effects of the correlation length of random fields on the liquefaction depth were investigated. The results of the analysis highlighted the significant impacts of the randomness of ocean waves and the spatial variability in soil properties, which were often ignored in previous studies.

Piezoelectric Ring Bender for Characterization of Shear Waves in Compacted Sandy Soils.

Shear wave velocity and small-strain shear modulus are widely used as the mechanical properties of soil. The objective of this study is to develop a new shear wave monitoring system using a pair of piezoelectric ring benders (RBs) and to evaluate the suitability of RB in compacted soils compared with the bender element and ultrasonic transducer. The RB is a multilayered piezoelectric actuator, which can generate shear waves without disturbing soils. For five compacted soil specimens, the shear waves are monitored by using three different piezoelectric transducers. Results of time-domain response show that the output signals measured from the RB vary according to the water content of the specimen and the frequency of the input signal. Except at the water content of 9.3%, the difference in the resonant frequencies between the three transducers is not significant. The shear wave velocities for the RB are slightly greater than those for the other transducers. For the RB, the exponential relationship between the shear wave velocity and dry unit weight is better established compared with that of the other transducers. The newly proposed piezoelectric transducer RB may be useful for the evaluation of the shear wave velocity and small-strain shear modulus of compacted soils.

Influence of site conditions on seismic design parameters for foundations as determined via nonlinear site response analysis

Site conditions, including geotechnical properties and the geological setting, influence the near-surface response of strata subjected to seismic excitation. The geotechnical parameters required for the design of foundations include mass density (ρ), damping ratio (βs), shear wave velocity (Vs), and soil shear modulus (Gs). The values of the last three parameters are sensitive to the level of nonlinear strain induced in the strata due to seismic ground motion. In this study, the effect of variations in soil properties, such as plasticity index (PI), effective stress (σ′), over consolidation ratio (OCR), impedance contrast ratio (ICR) between the bedrock and the overlying strata, and depth of soil strata over bedrock (H), on seismic design parameters (βs, Vs, and Gs) was investigated for National Earthquake Hazards Reduction Program (NEHRP) site classes C and D, through 1D nonlinear seismic site response analysis. The Morris one-at-a-time (OAT) sensitivity analysis indicated that βs, Vs, and Gs were significantly influenced by variations in PI, while ICR affected βs more than it affected Vs and Gs. However, the influence of H on these parameters was less significant. It was also found that variations in soil properties influenced seismic design parameters in soil type D more significantly than in soil type C. Predictive relationships for βs, Vs, and Gs were derived based on the 1D seismic site response analysis and sensitivity analysis results. The βs, Vs, and Gs values obtained from the analysis were compared with the corresponding values in NEHRP to determine the similarities and differences between the two sets of values. The need to incorporate PI and ICR in the metrics for determining βs, Vs, and Gs for the seismic design of foundations was highlighted.

Warsaw Glacial Quartz Sand with Different Grain-Size Characteristics and Its Shear Wave Velocity from Various Interpretation Methods of BET.

After obtaining the value of shear wave velocity (VS) from the bender elements test (BET), the shear modulus of soils at small strains (Gmax) can be estimated. Shear wave velocity is an important parameter in the design of geo-structures subjected to static and dynamic loading. While bender elements are increasingly used in both academic and commercial laboratory test systems, there remains a lack of agreement when interpreting the shear wave travel time from these tests. Based on the test data of 12 Warsaw glacial quartz samples of sand, primarily two different approaches were examined for determining VS. They are both related to the observation of the source and received BE signal, namely, the first time of arrival and the peak-to-peak method. These methods were performed through visual analysis of BET data by the authors, so that subjective travel time estimates were produced. Subsequently, automated analysis methods from the GDS Bender Element Analysis Tool (BEAT) were applied. Here, three techniques in the time-domain (TD) were selected, namely, the peak-to-peak, the zero-crossing, and the cross-correlation function. Additionally, a cross-power spectrum calculation of the signals was completed, viewed as a frequency-domain (FD) method. Final comparisons between subjective observational analyses and automated interpretations of BET results showed good agreement. There is compatibility especially between the two methods: the first time of arrival and the cross-correlation, which the authors considered the best interpreting techniques for their soils. Moreover, the laboratory tests were performed on compact, medium, and well-grained sand samples with different curvature coefficient and mean grain size. Investigation of the influence of the grain-size characteristics of quartz sand on shear wave velocity demonstrated that VS is larger for higher values of the uniformity coefficient, while it is rather independent of the curvature coefficient and the mean grain size.

Seismic behavior of underground station and surface building interaction system in earth fissure environment

Earth fissures, special engineering geological hazards, destroy the integrity of the ground and enlarge seismic responses of structures. Because of this, the safety of structures in the earth fissure environment is hard to guarantee, especially in bustling areas of the city in which underground stations and surface structures are affected by each other under earthquakes. In this paper, the 3D finite element models of the surface structure, underground station, and ground soil with earth fissure were built, taking into account the interaction between structures and soil. Then, the artificial boundary was verified, and seismic behaviors of earth fissure ground were compared with the test result. The experiment and the calculation result showed the same tendency. Moreover, the key parameters of the simulation model were modified, and the acceleration amplification factors of the underground station were analyzed. Finally, based on the most unfavorable condition, the failure mechanism of the underground station was analyzed. The numerical results indicate that the existence of earth fissure and surface structure amplifies the seismic responses of the underground station. The increase in floor number of surface structure and decrease in shear modulus of soil also enlarge the seismic responses of the underground station, and this amplification effect is more obvious in the earth fissure environment. The columns of the underground station in the hanging wall are one of the crucial parts to the bearing capacity of the station, and are destroyed due to the P-Δ effect and the uneven vertical settlement of the underground station. These results are significant for studying the effect of earth fissure on the seismic responses of the underground station.

Effect of soil microstructure on the small-strain shear modulus of saline soil

The behavior of soils at small strains (< 10−5) is of significant interest for geotechnical engineers. Compared with the small-strain properties of sand or clay, those of saline soil have been investigated less extensively and therefore remain poorly understood. Accordingly, this study investigates the influence of microstructure on the small-strain shear modulus (G0) of saline soil. A series of specifically designed experiments was conducted on saline soil specimens under unsaturated conditions via the resonant column technique and scanning electron microscopy. The results showed that the G0 of saline soil increases with the dry density. The obtained values of the fitting parameter, A, are between 52.06 and 63.42, with an average value of 58.82, while those of the fitting parameter, n, are between 0.284 and 0.363, with an average value of 0.322. The Na2SO4 content was employed as a state variable, using which Hardin’s equation was modified for proper consideration of the influence of the Na2SO4 content on the prediction of G0. The results show that G0 increases with the Na2SO4 content. The inflection point of the Na2SO4 content with a significant change in G0 is 20%. The main contact forms of soil particles are edge–edge, edge–surface, and surface–surface contacts. With increasing Na2SO4 content, the cementation of soil particles by salt crystals gradually replaces the inter-particle contact, and sulfate crystal cementation becomes the dominant factor affecting G0.