Elastic Soil Properties Research Articles

Determination of Elastic Properties of Soils around a Typical Erosion-Prone Area in Benin City, South-South Nigeria

Soil properties play a crucial role in understanding the mechanisms of erosion and consequently developing appropriate mitigation strategies. The aim of this study is to determine the elastic parameters of soil in an erosion-prone area using the Multichannel Analysis of Surface Wave (MASW) method of geophysical exploration. The active method MASW was adopted for this study. Data were acquired using a 24-channel ABEM Terralock MATK-6 seismograph with geophones of frequency 14Hz. An 8 Kg hammer was used as a source to generate seismic energy. Data acquired were processed with SeisImager2D refraction software developed by Geometric Earth Science Ltd and 2-D shear wave (Vs) and P-wave (Vp) velocities were generated alongside 2-D profiles of Shear Modulus, Young’s Modulus, Bulk Modulus, and Poison’s Ratio. The result of this study reveals soft to medium-stiff saturated clay/dry sand/wet sand and medium-stiff to stiff saturated clays/dry sand/wet sand with shear wave velocity values ranging from 84 m/s to 504 m/s. The bulk modulus, shear modulus, poison’s ratio, and Young’s modulus range from 3.4 GPa to 5.9 GPa, 20 kPa to 440 kPa, 0.448 to 0.498, and 50 kPa to 1.05 GPa respectively.

Analysis of the Seismic Properties for Engineering Purposes of the Shallow Subsurface: Two Case Studies from Italy and Croatia

We present two case studies of the application of seismic surveys to estimate the elastic properties of soil and rock in the shallow subsurface. The two sites present very different geological characteristics. The first test site is a town on the Croatian coast, not far from the city of Split, built on hard rock, where we acquired three seismic lines. The second site is located in the outskirts of the city of Ferrara, in Italy, in an alluvial plain, where two lines were acquired. In both sites, for detailed characterization, we acquired surface-, compressional- and shear-waves, further distinguishing the latter between horizontally (SH) and vertically (SV) polarized wavefields. We processed the data by performing a Multichannel Analysis of Surface Waves to compute a preliminary one-dimensional shear wave velocity profile. Then, we performed first-break tomography to compute P-, SH- and SV-velocity profiles. Such unusual acquisition allowed us to compute not only basic engineering parameters such as the equivalent shear-wave velocity of the first 30 m of subsurface (VS30) from the SH profiles but also other useful parameters such as the VP/VS and estimate the anisotropy of the medium thanks to the VSV/VSH. Given the level of detail of the results and their engineering value, we conclude that the method of investigation we applied in the two test sites is a valuable tool for characterizing the shallow subsurface.

COMPARATIVE ANALYSIS OF STATIC SHEAR MODULUS AND DYNAMIC SHEAR MODULUS DETERMINED BY GEOPHYSICAL AND GEOTECHNICAL INVESTIGATION

Due to the occurrence of earth tremors which leads to the vibrations of foundations and perhaps failure of buildings and roads, it is therefore important to understand and have knowledge of the geomechanical soil properties for foundation design, assessment of risks and suggestion of mitigation plans in engineering structures and road construction. A total of 3 boreholes were drilled with the Standard Penetration Test (SPT) performed and Downhole Seismic Test (DST) carried out in the boreholes located within Assa to investigate the Geomechanical soil properties in the area. For the geophysical survey, the downhole seismic test was carried out to determine the P-wave and S-wave. The results were processed using the generalized reciprocal method (GRM) with the Seisimager program. The results of soil dynamic modulus (shear, young and bulk modulus) and Poisson ratio recorded from DST conducted in BH1, BH2 and BH3 ranges from 7300 KPa to 72390 KPa, 0.31 to 0.41 for the Poisson ratio. Meanwhile, soil static modulus and Poisson’s ratio recorded from SPT conducted in BH1, BH2 and BH3 ranges from 2520 to 44687.0 KPa, 0.20 to 0.55 for the Poisson ratio respectively. The results of this study have shown that there is a wide variation between geomechanical properties derived from geotechnical investigations (static properties) and geophysical investigations (dynamic properties). Based on depth trend analysis, the dynamic and static soil elastic properties all increases with depth. Generally, the dynamic soil properties were significantly higher than the static elastic properties. At shallow depths (<12.0 m), the difference between static and dynamic soil modulus was relatively small, but increased with increasing depth. Meanwhile, the difference between static and dynamic Poisson ratio was high at shallow depth and it decreased with increased depths where they almost overlap. Correlation between the derived static and dynamic properties all revealed positive correlation trends. The strength of the correlation was highest for young modulus (r=0.87) which was closely followed by the shear modulus (r=0.63). Meanwhile, Poisson ratio (r=0.40) and bulk modulus (r=0.23) revealed weak positive correlation trends. The regression models generated from this study were used to derive static elastic properties and compared with the static properties obtained from geotechnical investigation thereby deriving the equations Dynamic Shear Modulus = (1.4207 x Static Shear Modulus) + 5022, Dynamic Young Modulus = (2.0241 x static young modulus) + 5054.8, Dynamic Bulk Modulus = (1.7852 x static bulk modulus) + 15458, Dynamic Poisson’s ratio = (0.1812 x Static Poisson’s ratio) + 0.3154. The results showed fairly good match between static (geotechnical) shear modulus and static (from regression model) shear modulus, static (geotechnical) young modulus and static (from regression model) young modulus. There was no good match obtained for bulk modulus and Poisson ratio generally, except at shallow depth (< 12 m depth) where Poisson ratio revealed a good match.

Catastrophic failure of submarine slopes with elastic shearing zones

Submarine landslides can be devastating to offshore facilities and coastal areas. This study explores the triggering mechanisms of catastrophic failure of an infinite planar slope in sensitive soil deposits under undrained conditions. The strain-softening behaviour of sensitive soils can cause rapid growth of the shear band along a thin layer of weak materials and ultimately lead to a large landslide. A new analytical criterion for catastrophic shear band propagation taking into account elastic shear deformation in the shear band was derived using a process zone approach. A mechanical analysis was conducted on the fully softened zone, end zone and elastic shearing zone, among which the evolution of the shear band and the development of key mechanical variables were presented to illustrate the formation mechanism of the large submarine planar landslides. The influences of the elastic properties of soils on the initiation of catastrophic failure were investigated for both clay and sand slopes, demonstrating that the consideration of the elastic properties result in a more conservative failure criterion compared with that presented in the previous study.

DETERMINATION OF THE DYNAMIC MODULE OF ELASTICITY OF PERMANENTLY FROZEN SOILS DURING DEFROST BY KINEMATIC CHARACTERISTICS OF ELASTIC WAVE

According to the data of monitoring observations of atmospheric air temperature, in the areas of permafrost distribution, the trend of temperature growth is stable. Due to the increase in atmospheric air temperature, the temperature of permafrost soils increases. As a result of changes in the temperature regime, the degradation of permafrost soils occurs. These changes lead to disruption of the operation of buildings and engineering structures. In this situation, geotechnical monitoring plays a special role. Currently, temperature, geodesic and hydrogeological methods are mainly used to solve the problems of geotechnical monitoring. The increase in the number of emergencies associated with thawing of soils indicates that the applied methods of geotechnical monitoring do not give the proper result. In this paper, we consider the possibility of using a temporary type of acoustic control to solve geotechnical monitoring problems. The paper presents a brief analysis of the currently used methods of geotechnical monitoring. The research tasks that need to be solved to assess the possibility of using a temporary type of acoustic control to solve geotechnical monitoring problems are set. Data are given of experimental studies of changes in dynamic modulus model of frozen soils during thawing, defined by equations of the relationship of the kinematic characteristics of elastic waves and elastic properties of soils.

Stiffness of granular soils under long-term multiaxial cyclic loading

Geotechnical infrastructures may be subjected over their lifetime to long-term loading cycles of varying amplitude, frequencies and direction as a result of the combination of environmental and operational processes. Soil elements surrounding the foundations of these geotechnical systems are in turn subjected to complex six-dimensional stress paths, invariably involving rotation of principal stress axes. Changes of the soil's mechanical properties can lead to changes of the overall structure dynamics, as well as to an accumulation of irreversible deformations. However, the evolution of the soil's response and stiffness under complex long-term cyclic loading scenarios is neither well known nor adequately understood. In contrast to the conditions imposed by standard laboratory tests, this research used a hollow-cylinder torsional apparatus (HCTA) to explore the evolution of the small-strain stiffness of a granular soil under long-term multiaxial drained stress cycles (up to about 6 × 105). Granular soil samples were subjected to stages of regular low-amplitude stress cycles at different anisotropic stress levels interspersed by periodic large-amplitude cyclic loops. A high-resolution local strain measurement system was employed to determine the vertical Young's modulus and shear modulus, both attained in a HCTA at different stages of the testing. It was found that low-amplitude multiaxial stress cycles, involving continuous rotation of principal stress axes, caused a degradation up to about 20% of these elastic soil properties. Within 104to 2 × 104cycles, the degraded stiffnesses reached a stable value, which was maintained up to at least 8 × 104cycles. The stiffness degradation was more pronounced for the shear modulus than the vertical Young's modulus of the soil.

Downwards force–displacement response of buried pipelines during dip–slip faulting in sandy soil

In the numerical analysis of underground pipelines against dip-slip faulting, it is common practice to model the problem as a beam surrounded by soil-equivalent nonlinear springs. Previous studies have recognised the importance of the vertical bearing soil springs (VBSS) in the modelling of pipe–fault interaction. Nevertheless, prior studies on VBSS are limited. This study presents an analytical framework for determining a hyperbolic force–displacement (P–y) curve for VBSS in dry sand. This hyperbolic criterion was established based on the ultimate bearing resistance (UBR) of pipe and the elastic subgrade modulus of the soil. Different mechanisms such as flow, arching, bearing, and friction, and various parameters like soil compressibility, pipe–soil relative stiffness, and soil elastic properties have been used in the determination of these two parameters. The P–y curves were verified and calibrated with experimental data. More reliable curves have been obtained compared to the existing methods. A numerical study was also performed to compare the current study with a pipeline seismic design guideline. The results of the current study method are in good agreement with sample experimental data compared to the seismic guideline.

Investigation of the Norcia basin (Central Italy) through ambient vibration measurements and geological surveys

During the 2016–2017, a seismic sequence struck the Central Italy, involving four regions (Umbria, Marche, Abruzzo and Lazio) and causing important damages and victims in inhabited areas such as Norcia and Amatrice towns. The strongest event of the seismic sequence was a Mw 6.5 event with epicenter at about 5 km far from the Norcia area, which is an intermontane basin prone to ground motion amplification. The historical town of Norcia and the surrounding hamlets were recently investigated by the microzonation activity, but information on the geometry and velocity are still partial considering the entire basin. Indeed, past studies aimed at reconstructing the elastic and geometrical properties focusing mainly on the northern part of the basin. Specifically in this paper, we integrated seismic and geological data to get a better knowledge of the properties of the Quaternary Norcia basin. A geological survey was carried out to provide a geological map and three geological cross-sections. We analyzed new seismic ambient vibrations data, collected by single-seismic stations, to infer the distribution of resonant frequency (f0) for the entire basin. We used passive arrays of seismic stations to better define the velocity profiles of the area. In the northern part of the basin, two 2D arrays with elliptical-like shapes were deployed showing strong discrepancies of the elastic soil properties in proximity of Norcia town. We found shear-wave velocities of the near-surface profile of about 300–400 and 500–800 m/s in presence of palustrine and alluvial fan deposits, respectively. Further, the values of f0 are abruptly varying from 0.5 Hz in the SW sector of Norcia village up to 2 Hz in its NE sector. Ambient vibration data reveal less pronounced variation of f0 in the southern part of the basin, with resonant values that are almost in the range 1–1.3 Hz. In the southern sector, a 1D array was arranged along a 5-km line and was analyzed by means of seismic noise cross-correlation analysis suggesting the presence of a deeper seismic contrast. The integration of geophysical and geological results has allowed to infer insights on the subsurface geometry of the basin.

Influence of 2D heterogeneous elastic soil properties on surface ground motion spatial variability

Spatial variability of earthquake ground motion (SVEGM) refers to the differences in amplitude and phase between recordings of the same earthquake at different locations. In the near-surface, geological processes (sedimentation, erosion) and anthropogenic activities can lead to small scale spatial heterogeneities of soil mechanical properties, which may affect SVEGM. In this paper, the effect of shallow 2D spatial variability of the shear wave velocity (Vs) on the surface ground motion is assessed through a set of numerical experiments, using a simple 2D velocity structure (a sedimentary layer over a half-space). Non-linearity or damping are not considered in the wave propagation calculation in order to solely focus on the effects of soil elastic property variability. Vs is modeled as a random field using the EOLE method (Expansion Optimal Linear Estimation) and considering three statistical parameters: the coefficient of variation, and the horizontal and vertical autocorrelation distances. Seismic ground motions are numerically simulated for a plane wave excitation with SV polarization. Modeling results clearly highlight the scattering of surface waves by ground heterogeneities, leading to large spatial variations in surface ground motion. We computed surface ground motion indicators (resonance frequency, spectral amplification, Arias intensity and duration) and we showed that their spatial variability is mainly controlled by the Vs coefficient of variation. A comparison between 2D and 1D ground motion probabilistic modeling shows that the 1D probabilistic approach may correctly reproduce average fundamental resonance frequencies and corresponding amplification. However, the 1D approach significantly under-predicts both ground motion amplification at higher frequencies and related variabilities, as well as Arias intensities and inferred durations, which are all controlled by the generation of locally diffracted surface waves.

GENETIC COUNSELING AS A WAY TO ENGAGE PEOPLE IN BEHAVIOUR CHANGE TO REDUCE RISK FOR COMMON COMPLEX DISEASE: RATIONALE FOR ITS POTENTIAL EFFECTIVENESS WHERE GENETIC INFORMATION HAS FAILED

Compressive properties of arable and forest soils are typically derived from data obtained in uniaxial confined compression tests. However, the stress field, final state of compression and thus compressive properties derived from such tests are dependent on sample dimensions, soil-cylinder wall friction and soil material properties. In this study, we analysed the stress field and bulk density distribution within a cylindrical soil sample under uniaxial compression, and how these are affected by sample dimension, soil-cylinder wall friction and elastic properties of soil. For this, we modelled a uniaxial compression test using the finite element method (FEM) and performed simulations for a range of sample diameter to height ratios (D/h), different values of soil-wall friction coefficient (μ) and different soil elastic properties (Young’s modulus and Poisson’s ratio). We use experimental data to validate the findings. The results showed a high impact of soil-cylinder wall friction on the stress field within the sample. This resulted in stress concentration at the top of sample edges (walls) and decreasing stresses at the bottom of the sample. However, the relative impact of soil-wall friction on sample average behaviour decreased with increasing D/h. These results suggest that the effect of soil-wall friction on sample-average bulk density cannot be neglected unless D/h >8. Correction of bulk density for μ and D/h could be a practical way to compare data obtained in laboratories using different sample sizes.

Impact of sample dimensions, soil-cylinder wall friction and elastic properties of soil on stress field and bulk density in uniaxial compression tests

Compressive properties of arable and forest soils are typically derived from data obtained in uniaxial confined compression tests. However, the stress field, final state of compression and thus compressive properties derived from such tests are dependent on sample dimensions, soil-cylinder wall friction and soil material properties. In this study, we analysed the stress field and bulk density distribution within a cylindrical soil sample under uniaxial compression, and how these are affected by sample dimension, soil-cylinder wall friction and elastic properties of soil. For this, we modelled a uniaxial compression test using the finite element method (FEM) and performed simulations for a range of sample diameter to height ratios (D/h), different values of soil-wall friction coefficient (μ) and different soil elastic properties (Young’s modulus and Poisson’s ratio). We use experimental data to validate the findings. The results showed a high impact of soil-cylinder wall friction on the stress field within the sample. This resulted in stress concentration at the top of sample edges (walls) and decreasing stresses at the bottom of the sample. However, the relative impact of soil-wall friction on sample average behaviour decreased with increasing D/h. These results suggest that the effect of soil-wall friction on sample-average bulk density cannot be neglected unless D/h >8. Correction of bulk density for μ and D/h could be a practical way to compare data obtained in laboratories using different sample sizes.

Spatial distribution of Winkler spring stiffness for rectangular mat foundation analysis

Structural design of mat foundations of buildings is often done by performing static analysis of a slab resting on vertical uncoupled Winkler springs. It is already well established that the simplifying assumption of a uniform modulus of subgrade reaction throughout the mat foundation leads to inaccurate results that significantly underestimate the bending moments in the mat. This paper examines the spatial variation of the Winkler spring stiffness constants that is necessary for the mat-on-springs analysis to produce the same slab deflections and bending moment diagrams as finite element analysis that treats the soil as continuum. For this purpose, three-dimensional parametric analyses of slabs resting on elastic soil are performed using the finite element method for various values of soil elastic properties, slab geometrical characteristics and column load configurations. The finite element analysis results were used for back-calculating analytically the equivalent Winkler spring constants at each node of the mat. Based on the numerical results, equations describing the spatial distribution of spring stiffness are proposed. The performance of the proposed equations is compared against existing spring stiffness spatial distribution approaches used in practice.

Reliability analysis of foundation settlement by stochastic response surface and random finite element method

This paper presents a reliability-based analysis of strip footing settlement by Stochastic Finite Element Method (SFEM). The Stochastic Response Surface Method (SRSM) and Random Finite Element Method (RFEM) are used as two formulation of SFEM. The elastic properties of soil are considered as spatial random variables and modeled as cross correlated log–normal random fields. Random field discretization is done by Karhunen–Loeve (K-L) expansion. Two programs were coded by MATLAB so as to take full advantages of its matrix operations and in an illustrative example; it was shown that the results of SRSM are close to RFEM however the consumed time in RFEM is at most 50 times longer than SRSM. Using the faster method, SRSM, it is concluded that considering the spatial variability of soil parameters in stochastic analysis is necessary.

Topographic proxies from 2-D numerical analyses

We use 2D numerical analyses at ground motion stations from the NGA-West2 dataset to develop parameters to predict the effect of surface topography on response spectra. The simplistic numerical analyses use sinusoidal input motions, uniform soil profiles, elastic soil properties, and absorbing boundary conditions. We define several topographic parameters for stations using the natural logarithm of 2D amplifications in peak ground acceleration of a sinusoidal input motion in different orientations. The natural log of 2D amplifications when averaged over multiple orientations is found to have the most predictive power among the studied parameters. We also explore the relationship between the topographic parameters developed in this study, and the topographic parameters developed at the same sites in an earlier study (Rai et al. in Earthq Spectra, 2016b).

Three-dimensional P- and S-wave velocity profiling of geotechnical sites using full-waveform inversion driven by field data

We discuss the application of a recently developed full-waveform-inversion-based technique to the imaging of geotechnical sites using field-collected data. Specifically, we address the profiling of arbitrarily heterogeneous sites in terms of P- and S-wave velocities in three dimensions, using elastic waves as probing agents. We cast the problem of finding the spacial distribution of the elastic soil properties as an inverse medium problem, directly in the time domain, and use perfectly-matched-layers (PMLs) to account for the semi-infinite extent of the site under investigation.After briefly reviewing the theoretical and computational aspects of the employed technique, we focus on the characterization of the George E. Brown Jr. Network for Earthquake Engineering Simulation site in Garner Valley, California (NEES@UCSB). We compare the profiles obtained from our full-waveform-inversion-based methodology against the profiling obtained from the Spectral-Analysis-of-Surface-Waves (SASW) method, and report agreement. In an attempt to validate our methodology, we also compare the recorded field data at select control sensors that were not used for the full-waveform inversion, against the response at the same sensors, computed based on the full-waveform-inverted profiles. We report very good agreement at the control sensors, which is a strong indicator of the correctness of the inverted profiles. Overall, the systematic framework discussed herein seems robust, general, practical, and promising for three-dimensional site characterization purposes.

Application of near-surface seismic refraction tomography and multichannel analysis of surface waves for geotechnical site characterizations: A case study

In this case study two geophysical methods based on seismic waves were employed to evaluate the geotechnical properties of the soil deposits at a site for a planned wind farm. Regional geological information shows that the study area is mainly covered by recent alluvium, which is classified as a mixture of fine sand and gravel. Twenty five seismic refraction surveys were carried out in the study area. The acquired shot gathers were processed, from which primary wave (P-wave) and shear wave (S-wave) velocities were derived. The P-wave velocities were obtained by using the Seismic Refraction Tomography method (SRT) while the S-wave velocities were extracted by utilizing the Multichannel Analysis of Surface Waves (MASW) technique, which is established based on the dispersion characteristics of Rayleigh waves. Seismic hazard at the site was evaluated according to the Iranian code using the measured S-wave velocities, and the friction angles of the soil deposits were approximated using an empirical method and by making use of Jaky's formula for earth pressure at rest, which yielded similar values. The deformation properties of the foundation soil were also estimated based on the correlations between seismic wave velocities and elastic properties of soil as well as Janbu's formula for soil modulus. The findings of this study may serve as references for economic and non-destructive geotechnical site characterizations using seismic-wave methods.

The role of compaction energy on the small strain properties of a compacted silty sand subjected to drying–wetting cycles

The elastic properties of a soil are usually investigated to describe its engineering behaviour. The results of previous studies indicate that the effect of changes in suction on the elastic response at a small strain level of soils is significant during compaction and post-compaction periods. Limited efforts have been focused on quantifying those post-compacted responses due to the changes in suction induced by wetting and drying cycles. During their service life, most earth structures experience changes in hydraulic behaviour owing to climatic changes. These seasonal fluctuations in turn impact on the geomechanical performance of compacted soil. In this paper the aspects related to the elastic properties of compacted soils subjected to cycles of drying and wetting are described. Particular emphasis is placed on the effect of compaction energy on the hysteric behaviour (i.e. amplitude of the hysteresis loop) and its dependence on the initial stress state conditions and suction history. The results not only confirm the importance of the current suction in governing the shear and compression velocities and associated moduli, but they also suggest that subsequent drying–wetting cycles or suction history can further induce hysteretic changes, particularly along the wetting paths.

Elastic Stiffness of Volcanic Sand through Resonant Column Tests

The resonant column method is established as a standard laboratory method for the study of the elastic properties of soils. The study presents low-amplitude resonant column test results on volcanic sands with intra-particle voids. The experiments were performed on dry samples prepared at variable relative densities and tested in torsional mode of vibration. In the first part of the article, the important factors that control the elastic stiffness of uncemented sands are described shortly and recent findings on granular soils dynamic properties are presented briefly. The second part describes the basic features of the resonant column used in the investigation and the materials of the study and in the third part representative results of an extensive experimental testing program on volcanic granular soils are presented and discussed with a focus on comparisons between the elastic stiffness of volcanic and quartz granular soils. The importance of the effect of the presence of intra-particle voids within the particle mass of the volcanic soils is emphasized, which in turn affects markedly the global void ratio of the samples.

Near surface geophysics: Investigating the dynamic coastal environment — Introduction

The coastal zone is a habitat for much of the world’s population, a key economic driver for fishing, shipping, recreation and tourism, and a critical wetlands ecology. However, the coastal zone is also a dynamic setting undergoing significant change at many different time scales. Large storms, for example, can restructure coastal morphology on the scale of hours or days. Rising sea level or changes in sediment supply will alter the coastline over decades to centuries and longer. These are human-relevant time scales, and such changes can have major impacts on coastal infrastructure, habitability, and ecology. Human activity also impacts the coast; e.g., hardening of coastlines and inlets, reduction in sediment supply due to damming, artificial beach replenishment, extraction of ground water for human consumption and agriculture, and the introduction of pollutants. Both land- and marine-based near-surface geophysical methods can play a significant role in understanding the many processes that impact …

Analytical Model of Soil Pulverization and Tillage Tools

The paper deals with the pulverization (fracture) model that is not based on soil elastic properties but on the physical processes of the wedge interaction with soil. The presented model agrees with the experimental data better than other models, including those based on soil elastic properties, and the tests of flat tillage tools with a variable cutting angle have proved this.