Regression Models for Dynamic Properties of Highly Organic Soils

Regression models are presented for the dynamic properties of highly organic soils. The models are based on a database of triaxial and resonant-column/torsional-shear cyclic loading tests on thin walled tube samples mainly retrieved from the Sacramento-San Joaquin Delta. The soils in this database range from highly fibrous peat to amorphous organic clays with organic contents (OC) ranging from 14–81%, water contents ranging from 88–495%, total densities (ρ) ranging from 1.056–1.450?Mg/m3, and effective consolidation stresses (σvc′) ranging from 11–135?kPa. The secant shear modulus (G) and equivalent damping ratio (ξ) were modeled as variables dependent on the shear strain amplitude (γc), consolidation stress (σvc′), and OC. The residuals of the regression models were analyzed against other predictor variables including undisturbed density (ρ), loading frequency (f), and number of loading cycles (N). A regression model for ρ was developed, and conditional probabilities were used to improve the estimation of G and ξ when ρ measurements were available. The database of in situ measurements of shear wave velocity (Vs) was used to adjust the regression model for in situ conditions. Variances and correlations in the regression models are presented.     

Dynamic Properties of Highly Organic Soils from Montezuma Slough and Clifton Court

The nonlinear dynamic properties of highly organic soils from two levee sites in the Sacramento-San Joaquin Delta in California are described. Cyclic triaxial, resonant column and torsional shear tests were performed on thin-walled tube samples obtained from beneath levee crests, beneath adjacent berms, and in the free field such that the in situ vertical effective stresses (σvo′) ranged from about 16?to?67?kPa. These highly organic soils had considerably different organic characteristics from those used in previous studies of dynamic properties. The tested samples had organic contents of 14 to 61%, initial water contents (wo) of 88 to 496%, shear wave velocities (Vs) of 20?to?130?m/s, and organic components that ranged from highly fibrous to highly decomposed and amorphous. Secant shear modulus (G), normalized secant shear modulus (G/Gmax), and equivalent damping ratio (ξ) versus cyclic shear strain amplitude (γc) relations are presented, and their dependence on variables such as consolidation stress, organic content, prior loading history, testing device, and loading frequency are illustrated. Findings are compared to previously published results.     

Assessment of Soil Stiffness Properties by Dynamic Tests on Bridges

This paper presents a method to determine soil stiffness properties using measured structural modes of bridges. Normally, the identified mode shapes have to be smoothed. The mode shapes are approximated using functions describing the transverse vibration of distributed–parameter systems. Artificial coefficients are introduced into this solution in order to sum up the error contributions of displacements and its derivatives up to second order. Then, a pier-soil model based on normalized mechanical impedance functions is used. Applying this method along with more than one vertical mode shape leads to acceptable and more accurate results. The amplitudes of pier bottom vibrations are chosen as the suitable weights for the averaging procedure. For the Warth Bridge situated near Vienna, shear wave velocities and shear moduli at the pier foundations have been estimated. The results correspond quite well to the geological investigation.     

Strain-Dependent Dynamic Properties of Remolded Sand-Clay Mixtures

A series of undrained cyclic torsional simple shear tests using hollow cylindrical torsional shear apparatus was carried out to investigate the dynamic shear moduli and damping properties of clayey specimens with various sand contents and plasticity indices. The clayey soils used were collected from various sites along the coast of west Japan. Among these clayey soils, a clay sample with intermediate plasticity and another with high plasticity were mixed with silica sand at different proportions in order to examine the dynamic properties of sand-clay mixtures. In addition, experiments were carried out on undisturbed and remolded natural clay specimens with various plasticities. The effects of plasticity, loading frequency and confining pressure on the strain dependent normalized shear modulus and damping ratio were examined. Based on the results, empirical correlations for predicting the normalized shear modulus and damping ratio of remolded sand-clay mixtures at various shear strain levels were proposed.     

Prediction of Soil Properties from the Concepts of Energy Transfer in Dynamic Penetration Tests

Results from dynamic penetration tests are traditionally interpreted on the basis of empirical correlations, this being a frequent criticism to these tests. An alternative rational method of interpretation is proposed in this paper from which the energy delivered to the composition of rods is used to calculate a dynamic force that represents the reaction of the soil to the penetration of the sampler (Fd). Interpretation of soil properties both in sand and clay is based on this calculated dynamic force from which the internal friction angle and the undrained shear strength can be estimated. This is achieved from a simple combination of limit equilibrium analysis and cavity expansion theory. Case studies gathered from the Brazilian experience are reported in this paper to illustrate the applicability of the proposed approach.     

Engineering Properties of Fibrous Peats

This state-of-the-art paper presents an interpretation of the permeability, compressibility, and shear strength of fibrous peats using data from laboratory tests on undisturbed block samples of two fibrous peats, as well as extensive laboratory and field data from the literature on fibrous peat deposits. Engineering properties of fibrous peats are significantly different from those of most inorganic soils. However, the same fundamental mechanisms and factors determine behavior of both inorganic soils and fibrous peats. Fibrous peat deposits possess very high initial permeability, typically 1,000 times the initial permeability of soft clay and silt deposits. Upon compression, the permeability of fibrous peats decreases dramatically, with a ratio of permeability change index to in situ void ratio equal to 0.25, as compared to 0.50 for soft clay and silt deposits. Fibrous peats display extreme compressibility to the increase in effective vertical stress, with compression index values right after preconsolidation pressure 5 to 20 times the corresponding compressibility of typical soft clay and silt deposits. Among geotechnical materials, fibrous peats display the highest ratios of secondary compression index to compression index, in the range of 0.05 to 0.07. The values of coefficient of earth pressure at rest for normally consolidated young fibrous peat deposits are in the range of 0.30 to 0.35, as compared to 0.45 to 0.65 for inorganic soils. The values of friction angle from triaxial compression tests for fibrous peats are in the range of 40 to 60°, as compared to less than 35° for soft clay and silt compositions. For fibrous peats, the ratios of undrained shear strength in compression to preconsolidation pressure are usually in the range of 0.50 to 0.75, as compared to 0.32 for soft clay and silt deposits. For surficial fibrous peat deposits the ratio of vane shear strength to preconsolidation pressure is near 1.0, as compared to 0.12 to 0.35 for inorganic soft clay and silt deposits. For fibrous peats, the ratio of undrained Young’s modulus to undrained shear strength is in the range of 20 to 80.     

Best-Fit Models to Estimate Modified Proctor Properties of Compacted Soil

Regression models were developed to estimate the optimum moisture content and maximum dry density of clayey and fine-grained soils using physical and index properties from 30 soil samples collected in Central Italy and 41 soils described in the literature. The liquid limit of the soils analyzed ranged between 18 and 82%, the plasticity index between 1 and 51%, and specific gravity between 2.47 and 3.09. The most significant regression variables were the specific gravity and the Atterberg limits. The developed models are accurate and can be used as a simple tool to approximate the maximum dry density and optimum water content of clayey and fine-grained soils.     

On-Site Nonlinear Hysteresis Curves and Dynamic Soil Properties

Strong motion records at five vertical array sites in Japan are used to examine soil shear modulus and material damping as a function of shear strain during large earthquakes. Acceleration data from the sites are processed directly for evaluation of site shear stress-strain hysteresis curves for different time windows of the record. Results of the analysis demonstrate a significant nonlinear ground response at the sites with surface peak ground accelerations exceeding 90 gal. The results of shear stress-strain hysteresis curves are also used to estimate variation of soil shear modulus and material damping characteristics with shear strain amplitude at each site. The identified shear modulus-shear strain and damping ratio-shear strain relationships are in general agreement with published laboratory results. These response interpretations are also compared with the results of a frequency-domain analysis by using the spectral ratio (uphole∕downhole) technique. There is general agreement between the time- and frequency-domain results. The results illustrate the significance of the site nonlinearity during strong ground motions as well as the accuracy of the dynamic soil properties obtained from laboratory tests.     

Complex Dielectric Permittivity of Soil–Organic Mixtures (20 MHz–1.3 GHz)

The dielectric permittivity of soils can be significantly modified by the presence of organic contaminant in the pore fluid. Thus, nondestructive techniques based on the propagation of electromagnetic waves may be used to detect contaminant plumes and to evaluate decontamination processes. Ground penetrating radar (GPR) and time domain reflectometry are two of the most relevant geophysical tools working in the frequency range of interest here. In this work, the complex dielectric permittivity of some soil–organic mixtures are measured in the frequency range of 20 MHz to 1.3 GHz. Tests are conducted in samples of silica sand, loess, and kaolinite mixed with varied amount of paraffin oil and lubricant oil. Additional tests are performed in soil–water samples for comparison. Mixtures formulas reported in the literature are extended from two to three and four phases in order to model the measured dielectric response of the contaminated soil samples. The results allow us to study the effect of the volumetric liquid content, organic type, mineral composition, and specific surface of soil particles on the dielectric permittivity of the mixtures. It is concluded in this work that the value of dielectric permittivity in soils is sensitive to the detection of contaminants when the organic concentration is high. On the other hand, the organic content can be determined providing that the total volume of fluid in the pores is known. The detection limits of organics in soils are discussed. Finally, a contamination process is monitored with GPR at the frequency of 1 GHz in a laboratory cell. The results show that organic contaminants are easily detected in dry sand, yet detection becomes very difficult in wet sand.     

Mars Soil Mechanical Properties and Suitability of Mars Soil Simulants

Determination of Mars soil mechanical properties will improve future lander mission success and provide narrower constraints for geomorphological modeling. A soil mechanics investigation was conducted wherein soil mechanical properties were determined by computer reconstruction of mass wasting features observed in photographs of Mars Exploration Rover landing sites and analysis of natural slope stability. Mars soil mechanical properties were compared with thermal inertia measurements and a correlation is presented. Tests with rovers and equipment for Mars surface exploration and various past laboratory experiments have incorporated a number of different Mars soil simulants. Standard laboratory measurements were conducted to characterize the shear strength, grain size distribution, and densities of various Mars soil simulants. From these measurements, the ability of a given simulant to appropriately represent the mechanical properties of in situ Mars soils was judged. Specific simulants are recommended for certain regions of Mars.     

Measurement of Frequency-Dependent Dynamic Properties of Soils Using the Resonant-Column Device

Dynamic properties of soils are commonly evaluated at resonance; thus, their variation with frequency is difficult to measure. A nonresonance (NR) method has been recently used for testing soils at low frequencies and strain levels below the linear threshold shear strain. However, the NR method has not been validated with the standard resonant method for different shear strain levels. In this study, the NR method is used to measure the dynamic properties of soils at low and midstrain levels for a maximum frequency bandwidth between 5 and 100?Hz using the resonant-column device. A new transfer function (NTF) equation is introduced to compare the dynamic properties measured using the NR method and the conventional transfer function approach. Experimental results for two sands and a sand–bentonite–mud mixture are presented for different strain and stress confinement levels. Results from the NR method compare well with the standard resonant column method at the resonant frequency if the strain levels are the same. The NTF approach can be used to measure the dependence of phase velocity of shear waves with frequency. However, the NTF method cannot be used to measure the variation of material damping with frequency. On the other hand, the NR method can be used to measure the degradation curves of wave velocity and material damping ratio as a function of frequency.     

Learning of Dynamic Soil Behavior from Downhole Arrays

An increasing number of downhole arrays are deployed to measure motions at the ground surface and within the soil profile. Measurements from these arrays provide an opportunity to improve site response models and to better understand underlying dynamic soil behavior. Parametric inverse analysis approaches have been used to identify constitutive model parameters to achieve a better match with field observations. However, they are limited by the selected material model. Nonparametric inverse analysis approaches identify averaged soil behavior between measurement locations. A novel inverse analysis framework, self-learning simulations (SelfSim), is employed to reproduce the measured downhole array response while extracting the underlying soil behavior of individual soil layers unconstrained by prior assumptions of soil behavior. SelfSim is successfully applied to recordings from Lotung and La Cienega. The extracted soil behavior from few events can be used to reliably predict the measured response for other events. The field extracted soil behavior shows dependencies of shear modulus and damping on cyclic shear strain level, number of loading cycles, and strain rate that are similar qualitatively to those reported from laboratory studies but differ quantitatively.     

Geotechnical Properties of JSC-1A Lunar Soil Simulant

For the success of planned missions to the moon in the near future, it is essential to have a thorough understanding of the geotechnical behavior of lunar soil. However, only a limited amount of information is available about geotechnical properties of lunar soils. In addition, the amount of lunar soils brought back to Earth is small. To help the development of new regolith moving machines and vehicles that will be used in future missions, a new lunar soil similant JSC-1A has been developed. A group of conventional geotechnical laboratory tests was conducted to characterize the geotechnical properties of the simulant, such as particle size distribution, maximum and minimum bulk densities, compaction characteristics, shear strength parameters, and compressibility.     

Modeling the Erosion of Mixtures of Organic and Granular In-Sewer Sediments

The release of fine-grained organic sediments from sediment deposits can have a detrimental impact on water quality in a number of situations. This paper examines the release of such sediment in the context of the erosion of mixed organic/granular sediment in-sewer deposits. In the European Union, sewer flow quality modeling software uses equations derived from uniform granular sediment studies. Actual sewer sediments are mixtures of organic and granular material and interactions between these fractions may account for the poor performance of current models. Laboratory experiments were carried out using surrogate sewer sediment mixtures. Impaction of the bed surface by saltating granular particles increased the erosion of fine-grained organic sediments. Changes in the composition of the bed surface over the duration of a test resulted in change in the availability of fine-grained sediment. A model that attempted to simulate these mechanisms, using an empirically based correction factor to account for the impaction mechanism and an active bed layer to account for changes in the bed surface composition was developed. The limited success of the simulations indicated that such simple modeling approaches may not be appropriate for organic/granular deposits in which grain sorting occurs.     

Determination of Honeycomb Material Properties: Existing Theories and an Alternative Dynamic Approach

This paper examines several available analytic and experimental methods to determine the orthotropic material properties of honeycomb. Fifteen published sets of simple equations for the material properties were reviewed and their values calculated for a specific honeycomb aluminum core. The same core was tested with ASTM standard methods and the agreement between the theoretical material properties and the experimental results was considered. To reduce the time and cost for the experimental determination, a simple technique for measuring the main dynamic material properties of honeycomb is introduced. A good agreement was found between the major theoretical out-of-plane material properties of honeycomb, the experimental ASTM methods, and the presented dynamic approach.     

Sensitivity Analysis of Soil Hydraulic Properties on Subsurface Water Flow in Furrows

Knowledge of the sensitivity of various soil hydraulic properties is beneficial for model development and application purposes. It can lead to better estimated values, better understanding, and thus reduced uncertainty. In the present study, an extensive sensitivity analysis was performed to investigate the effects that various soil hydraulic properties have on subsurface water flow below furrows during two successive irrigation events to see which irrigation event was more sensitive and to analyze the effect of spatial variations in the initial soil water contents within the soil profile. Testing the sensitivity of the various soil hydraulic parameters in the van Genuchten-Mualem expression was carried out using the HYDRUS-2D model for two irrigation events 10?days apart. Results showed that the first irrigation event was clearly more sensitive than the second one. The latter event was mainly associated with the nonuniformity of the initial soil water contents within the soil profile. Pressure heads in the soil profile were more sensitive than cumulative outlet fluxes and soil water contents. Sensitivity analysis results for pressure heads, cumulative fluxes, and water contents indicated that in every case the most sensitive parameter was the hydraulic property shape factor (n) followed by the saturated water content (θs), the saturated hydraulic conductivity (Ks), the residual water content (θr), and the shape factor in the soil water retention curve (α), with the pore-connectivity parameter (l) the least sensitive parameter during both irrigation events. Pressure head sensitivity analysis for all parameters studied showed that the least sensitivity was linked with the wetting front as it gradually moved deeper with time, and the highest sensitivity was observed in those regions where the initial soil water contents were lower. Similarly, for water contents, higher sensitivity occurred in the drier regions during the first irrigation event and near the moisture front in the second irrigation event. Both pressure heads and water contents showed some sensitivity near the soil surface during both irrigation events, suggesting the importance of evaporation from the soil surface.     

Modeling Uncoupled Solute Transport in Natural Organic Matter Size Fractionation by Ultrafiltration

Physicochemical separation of organic macrosolutes and colloidal particles is routinely required during the analysis of natural, waste, and process waters derived from aquatic and terrestrial environmental samples. This study was conducted to demonstrate the utility of a two-parameter nonlinear permeation coefficient model (PCM) in describing the uncoupled transport of solutes in dilute heterogeneous solutions subjected to batch ultrafiltration (UF). The PCM was used in conjunction with natural organic matter (NOM) permeate data for a natural water and six hydrophobic and hydrophilic subfractions to determine permeation coefficients p and NOM concentrations Cr0 with apparent molecular weight less than membrane specific cutoff values of moderately hydrophilic YC/YM series Amicon? UF membranes. Experimentally measured permeation coefficients p determined for the whole water were found to correlate well with composite permeation coefficients p? calculated using a mass-fraction weighted average of individual NOM subfraction permeation coefficient values. Correlation of experimentally measured and calculated permeation coefficient values (p and p?) indicated that the PCM can adequately describe uncoupled transport of chemically distinct solute fractions during batch UF of heterogeneous dilute solutions.     

Microwave Sintering of Lunar Soil: Properties, Theory, and Practice

The unique properties of lunar regolith make for the extreme coupling of the soil to microwave radiation. Space weathering of lunar regolith has produced myriads of nanophase-sized Fe0 grains set within silicate glass, especially on the surfaces of grains, but also within the abundant agglutinitic glass of the soil. It is possible to melt lunar soil (i.e., 1,200–1,500°C) in minutes in a normal kitchen-type 2.45?GHz microwave, almost as fast as your tea-water is heated. No lunar simulants exist to study these microwave effects; in fact, previous studies of the effects of microwave radiation on lunar simulants, MLS-1 and JSC-1, have been misleading. Using real Apollo 17 soil has demonstrated the uniqueness of the interaction of microwave radiation with the soil. The applications that can be made of the microwave treatment of lunar soil for in situ resource utilization on the Moon are unlimited.     

Modeling Soil Water Uptake by Plants Using Nonlinear Dynamic Root Density Distribution Function

Water uptake by plants is one of the major components of water balance of the vadose zone that greatly influences the contaminant and moisture movement in variably saturated soils. In this study, a nonlinear macroscopic root water uptake model that includes the impact of soil moisture stress is developed. The model incorporates the spatial and temporal variation of root density in addition to the dynamic root depth considerations. The governing moisture flow equation coupled with the water extraction by plants term is solved numerically by an implicit finite-difference method. The simulation is performed for various physical scenarios subjected to different boundary conditions. The model is tested first without considering the water uptake and results are compared with observed data available in the literature for two cases. A nonlinear water uptake term is subsequently incorporated in the model which is then simulated for corn crop for constant root depth under various characteristic moisture availability environments. Results show that the water extraction rate is closely related to the soil moisture availability in addition to the root density. The plants are observed to extract moisture mainly from the upper root dense soil profile when water content is in an optimal range, otherwise, the peak of the uptake moves to other soil layers where the moisture is easily available. Finally, the model is applied to a corn field and simulated results are validated with field data. The simulated moisture content for 2 months of crop growing season shows a reasonably good agreement with the observed data.     

Soil and Rock Properties in a Young Volcanic Deposit on the Island of Hawaii

Deeply weathered lava flows of oceanic basalt reflect the mode and sequence of volcanic deposition, parent mineralogy, and postdepositional erosional and weathering processes. In turn, these are controlled by geology, geography, and climate. One particular site on the Island of Hawaii has been the focus of study to gain a better understanding of complex residual soil deposits, particularly in connection with a need to characterize seismic strong-motion propagation through decomposed surface soil and rock sequences. Materials at the site range from fully weathered volcanic soils, sometimes with unusual mineralogy and plasticity properties, to saprolite, weathered rock, vesicular basalt, and hard rock. Seismic surveys were conducted to investigate the distribution of these materials at the study site. Laboratory tests focused on saprolite and vesicular rock as two materials that are seldom reported on and that remain poorly characterized, at least with regard to conditions found in Hawaii.