Search

Pore-size distribution (PSD) of soil is a fundamental property that determines flows of water, heat, chemicals, and electricity and controls distributions of stress and deformation. PSD can be intrinsically related to the soil–water retention curve (SWRC), which is a constitutive relationship describing how the soil skeleton retains pore water via adsorption and capillarity. A general framework to quantify soil's PSD is proposed by first fitting an analytical SWRC model to experimental water retention curves that explicitly separate the SWRC into an adsorptive SWRC and a capillary SWRC. The PSD is then estimated at incremental steps by combining the capillary SWRC and the conventional Young–Laplace equation relating capillary pressure to pore size. Cumulative and density PSD curves for 11 soils covering a wide spectrum of soil types are determined and compared with the PSD functions independently measured using mercury intrusion porosimetry (MIP). Good agreement is observed in the estimated pore size range, distribution pattern, and peak position determined from the two different methods. Differences observed in the methods are attributed to differences inherent in the use of wetting and nonwetting fluids to probe the pore space. The SWRC-based method generally characterizes pore sizes ranging from 100 to 0.02 μm with a major peak located within a pore diameter range of 1–10 μm. As the clay content increases, a secondary peak becomes evident at smaller pore sizes (about 0.01–0.1 μm), where the bimodal pattern reflects the dual-porosity microstructure commonly observed for clayey soils. For soils containing swelling clays, PSD can change substantially with variation in water content; thus, the water-based method is more appropriate than MIP for applications to geotechnical engineering practice. [ABSTRACT FROM AUTHOR]

In addition to creating environmental threats, the leakage and entrance of chemical fertilizers into soil, which is possible in various ways, dramatically changes the physical and mechanical properties of soil. Furthermore, clay soils in the vicinity of monoammonium phosphate (MAP) contamination show substantially negative behavior, thus, improving the engineering geological factors of soil has become a huge challenge for engineers. Extensive programs such as triaxial compression test, consolidation test, compaction test, Atterberg limits, and collapse tests, in addition to X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on samples containing 10%–30% MAP over 7 days, 1, and 3 months. The mentioned trend was repeated when 0.5%–3% nano A (Al2O3 in alpha phase), nano F (Fe2O3 in alpha phase), and AF in form of a nanohybrid were added to soil which had been contaminated by MAP. Gained reports demonstrated significant declines in maximum dry density, plasticity index, and shear strength of contaminated soil when compared with natural soil. Conversely, increases in liquid limit, plastic limit, consolidation settlement, as well as soil collapse index were observed. Furthermore, a decrease in the amount of minerals in the XRD results and the formation of a flocculated structure in the SEM images in MAP-contaminated soil are evident. According to microstructural analysis, adding nano A, nano F, and AF nanohybrid as an improvement phase caused remediation of the soil structure and created cementation bonds between soil particles, thereby increasing the maximum dry density and soil shear strength, and decreasing the consolidation settlement and soil collapse index. Therefore, the use of AF as an efficient additive to remediate physical and mechanical properties of soils that have been contaminated with MAP, and to decrease the geological hazards of these kinds of contamination is recommended. [ABSTRACT FROM AUTHOR]

In this paper, a constitutive model is presented to model the behavior of various soils (sand and clay) in different loading conditions and the minimum required parameters are obtained. Although some practical features (concepts) of the bounding surface framework and modified Cam-Clay have been employed in its formulations, the model is developed mainly based on the generalized plasticity framework. Moreover, some concepts such as dilatancy relation and loading history surface are redefined. Finally, the proposed constitutive model is evaluated using the experimental data related to two different sandy soils and three different clays under different loading conditions. Finally, it is concluded that the proposed constitutive model can easily be calibrated for various clayey and sandy soils. It can depict different behavioral aspects of these soils under different monotonic and cyclic loading conditions. [ABSTRACT FROM AUTHOR]

This paper presents an iterative horizontal method of slices (iterative HMS) for the global stability analysis of a slurry trench in layered cohesive-frictional soils. The iterative HMS differs from existing HMS models in terms of the assumptions on interslice forces. Preceding HMS techniques postulate that normal interslice forces can be evaluated from overburden pressures, which can lead to the violation of failure criteria along interslice boundaries. The iterative HMS ensures that a limit equilibrium system is established without violating the failure criterion throughout the entire soil mass. This is achieved by iteratively adjusting interslice forces by means of enforcing the failure criterion for the aforementioned problematic slice boundaries violating the failure conditions. The performance of the iterative HMS is evaluated in example problems of a slurry trench in uniform clayey soils and cohesive-frictional strata. The results are compared against solutions obtained using finite-element limit analysis (FELA) and a shear strength reduction FEM (SSRFEM). This comparative analysis shows that the adjustment in interslice forces is important for reasonably assessing trench stability conditions. A parametric analysis is performed by using the iterative HMS to show under what trench construction parameters the adjustment of interslice forces cannot be neglected in the stability analysis of a slurry trench. [ABSTRACT FROM AUTHOR]

Several widely used field methods for estimating postliquefaction ground deformation are based on the laboratory data from one series of cyclic simple shear tests performed on one uniform clean sand reconstituted to three relative densities. It is not clear if the trends of this one data set are applicable to other clean sands, nonplastic silty sands, and nonplastic silts. A database of 579 test results on postliquefaction volumetric strain, including 299 test results that relate maximum shear strain to the factor of safety against liquefaction triggering, was compiled and used to examine trends for these soils. The database includes postcyclic test data on 10 clean sands, 2 gravels, 3 silty sands, 5 silts, and 3 clayey soils. The enlarged cyclic testing database was used to develop models that estimate postliquefaction volumetric strain and maximum shear strain as a function of soil type, state, and seismic demand. The models are applicable to uniform nonplastic soil. The state parameter was used in addition to relative density and void ratio to characterize the state of the soil. Correlations between these parameters enable the full data set to inform the models. [ABSTRACT FROM AUTHOR]

In this paper, the compressive and tensile ultimate bearing capacity of helical piles, in the load range required for designing 63-kV transmission towers, are studied by conducting analytical and numerical investigations. In this light, an explicit easy-to-use analytical framework was developed by considering the unsaturated soil condition that was validated against experimental records. Also, finite-element models were constructed for fully saturated and fully dry soil conditions. Then, to validate the analytical and numerical solutions in fully saturated and fully dry soil conditions, three compressive and one tensile field tests were carried out, and the results were compared quantitatively with analytical and numerical calculations. Comparative studies showed that the analytical, numerical, and experimental results have a high level of conformity. In accordance with the load ranges of transmission towers, analytical parametric studies were conducted for different geometrical aspects of the helical piles in different soils. Also, for two typical unsaturated sand and clay soils, the ultimate load of helical piles was calculated versus matric suction. Moreover, a vast numerical parametric study was performed to investigate the role of the geometrical aspects of helical piles and soil characteristics on the load-transfer mechanism and ultimate bearing-capacity values for helical piles driven in sandy and undrained saturated clayey soils. Results showed that the maximum load capacity of helical piles occurred in a matric suction less than that of a fully dry soil. In addition, the soil type and the geometrical aspects of the helical pile were shown to have significant effects on the load–displacement behavior and ultimate bearing-capacity values. [ABSTRACT FROM AUTHOR]

This paper examines the accuracy of a new elastic–thermoviscoplastic (E-TVP) constitutive model developed based on critical state soil mechanics. The model can be used for simulating the temperature-dependent and strain-rate-dependent behavior of clay soils. The study compares the E-TVP behavior of a single soil element with previously published thermo-mechanical experimental results performed on saturated clay specimens at different temperatures. Suggestions regarding unloading and reloading at constant temperatures as well as thermal consolidation under constant loads are presented. A modification for unloading–reloading adds a new criterion to the volumetric thermoviscoplastic strain rate formulation. A physics-based term is added to the current specific volume of the soil to include the viscous effect induced by temperature change. These modifications improve the convergence of laboratory data and simulated model responses. Comparisons of results from an earlier E-TVP model and the newly improved model provide evidence of improved predictive capabilities. [ABSTRACT FROM AUTHOR]

Pore-water pressure in soil is caused by three physically distinguishable sources: ambient (environmental) pressure, surface tension–induced capillary pressure, and the soil's electromagnetic potential–induced adsorptive pressure. The former two form the conventional concept of pore-water pressure, which is considered a constant within a soil-water-air representative elementary volume and can be directly measured by piezometer (under saturated and compressive states) or tensiometer (under unsaturated and tensile states). The third one can be called adsorption-induced pore-water pressure and is localized within a certain distance to the particle surface of soil or intercrystalline surface of swelling clay. The adsorption-induced pore-water pressure is always compressive and dictates the water phase transition in soil by altering water's freezing point, density, and viscosity, among other physical properties. A framework of quantifying the adsorption-induced pore-water distribution via the measured soil water isotherm is presented for any soil type under any given water content. It is demonstrated that the adsorption-induced pore-water pressure can be up to 1.6 GPa in the first few layers of hydration, but will diminish to zero at a distance equivalent to the gravimetric water content >1% for sandy soil and greater than a few percent for silty soil. In clayey soil, the adsorption-induced pore-water pressure can sustain tens of megapascals even at much farther distance, equivalent to ∼30% water content. In expansive clay, the adsorption-induced pore-water pressure inside the crystalline lamellae can exceed 800 MPa. The soil water density functions of a silty soil and a bentonite clay predicted by the proposed framework matched well with that measured independently from the conventional consolidation testing, validating the framework to determine the spatial distribution of the adsorption-induced pore-water pressure in soil. [ABSTRACT FROM AUTHOR]

2 of the original paper" and that "For soils and rocks under undrained condition, HT ht has been proven theoretically to be equal to 0.5 when the Skempton ([22]) HT ht parameter is equal to 1 at fully saturated conditions." For instance, for very stiff clays at high confining pressures, the theoretical HT ht value may barely exceed 0.9 even at fully saturated conditions. The Skempton HT ht parameter depends on both the degree of saturation and the stiffness of the soil skeleton. 1, HT ht is more affected by changes in degree of saturation and confining pressure at small strain conditions compared to large strain conditions (e.g., [10]). [Extracted from the article]

To estimate the cyclic shear-induced ground settlement of clay layers, cyclic simple shear tests were carried out on three normally consolidated clays with different plasticity. The pore water pressure accumulation during cyclic shear and the settlement at the postcyclic recompression stage were measured in tests with unidirectional and two-directional shearing, with different phase shifts between the shear strains applied in the two orthogonal directions and a wide range of shear strain amplitudes. All tests were performed with 200 cycles. In conclusion, firstly, the discrepancies of the pore water pressure accumulation and postcyclic settlement between unidirectional and two-directional cyclic shear were quantified, and the effects of cyclic shear direction on these properties were then described by the total length of strain path. Secondly, a method for estimating the cyclic shear-induced pore water pressure accumulation and postcyclic settlement of clayey soils with different plasticities was then developed considering the effect of cyclic shear direction. [ABSTRACT FROM AUTHOR]

The unconfined compressive strength (UCS) of soils is essential for both researchers and practitioner geotechnical engineers. UCS is well-understood and standardized for laboratory and field tests. Nevertheless, the large number of environmental and physical governing factors makes the reasonable prediction of UCS complicated. In this paper, a deep learning approach using the multilayer perceptron regressor (MLP) method along with the genetic expression programming (GEP) are used to assess nine variables that contribute to form a reflective multivariate formulation of the UCS. These variables include clay mineral percent (CF), specific gravity (Gs), dry unit weight (γd), saturated unit weight (γsat), natural unit weight (γt), moisture content (MC), void ratio (e), degree of saturation (S), and porosity (n). MLP and GEP are implemented to classify, correlate, rank, and reduce the number of variables that govern the UCS through the application of classification algorithms, importance analysis, interrelations and interdependency analysis of the variables, and functional indicators that shape the UCS. The changes of UCS in line with the variations of void ratio are analytically formulated according to both the critical state soil mechanics and the inverse proportionality between the voided area and soil strength. Moreover, the validity of the UCS principle is examined as opposed to the variation of the clay percent in the soil. Findings show that there shall be a breakpoint (clay percentage) after which the concept of UCS is radically changed due to the presence of a significant amount of frictional and drainable materials in the soil. The breakpoint appears to be centralized between 40% and 55%. The study is concluded by identifying the fundamental soil parameters, providing practical models to evaluate UCS, developing fundamental relationships between UCS and void ratio, and defining the breakpoint of clay content. [ABSTRACT FROM AUTHOR]

This paper presents an analytical three-dimensional rotational mechanism for the limit analysis on the overall stability of slurry trenches in layered cohesive soils. The proposed mechanism differs from the traditional torus mechanism in terms of the assumption on the shapes of cross section. The proposed rotational mechanism can have cross section with arbitrary shapes that are described by a smooth rotation radius function. The factor of safety for the overall stability of slurry trenches is obtained by using the new kinematic mechanism. The performance of the proposed mechanism is evaluated by analyzing the overall stability of trenches in single-layered, uniform and nonuniform clayey soils. The computed results are compared with the solutions given by finite-element limit analysis (FELA), which show that the proposed mechanism can give better solutions than the traditional torus mechanism when the length-to-depth ratio of the trench is relatively small. Based on the proposed mechanism, the stability of slurry trenches in layered undrained clay is investigated. The results show that, for trenches in two-layered undrained clay, the strength ratio between the shallow and deep layers can significantly influence the depth of the collapse mechanism. For trenches in three-layered undrained clay with a weak interlayer, the thickness of the interlayer can greatly affect the modes of failure in terms of global or local instability. [ABSTRACT FROM AUTHOR]

Desiccation cracking in clayey soils occurs when they lose moisture, leading to an increase in their compressibility and hydraulic conductivity and hence a significant reduction of soil strength. The prediction of desiccation cracking in soils is challenging due to the lack of insights into the complex coupled hydromechanical process at the grain scale. In this paper, a new hybrid discrete-continuum numerical framework, capable of capturing hydromechanical behavior of soil at both grain-scale and macroscale, is proposed for predicting desiccation cracking in clayey soil. In this framework, a soil layer is represented by an assembly of discrete element method (DEM) particles, where each occupies an equivalent continuum space and carries physical properties governing unsaturated flow. These particles move freely in the computational space following the DEM, and their contact network and the continuum mixture theory are used to model the unsaturated flow. The dependence of particle-to-particle contact behavior on water content is represented by a cohesive-frictional contact model, whose material properties are governed by the water content. In parallel with the theoretical development is a series of experiments on three-dimensional (3D) soil desiccation cracking to determine essential properties and provide data for the validation of mechanical and physical behavior. Very good agreement in both physical behavior (e.g., evolution of water content) and mechanical behavior (e.g., occurrence and development of cracks, and distribution of compressive and tensile strains) demonstrates that the proposed framework is capable of capturing the hydromechanical behavior of soil during desiccation. The capability of the proposed framework facilitates numerical experiments for insights into the hydromechanical behavior of unsaturated soils that have not been possible before. [ABSTRACT FROM AUTHOR]

Soil suction–based analyses are paramount to proper design of foundations in expansive soils, yet availability of field soil suction profiles from direct measurement is limited. A method was developed, using directly measured suction profiles obtained from sites across the US, by which routine geotechnical tests can be used to estimate soil suction to expand the database for estimation of field suction profiles. Herein, the expanded database is used to develop best-estimate clay soil suction envelopes for boundary conditions associated with covered or uncovered ground surface subjected to natural climatic surface flux. Where appropriate for site conditions, the proposed soil suction profile envelopes can be used with any suction-based heave/shrinkage analysis. Key features of the field suction envelopes, consistent with current popular approaches, include climate-dependent estimates for equilibrium suction at depth, depth to equilibrium (stable) suction, and variation in soil suction at the ground surface. Comparisons to existing soil suction envelope recommendations are made. Finally, a limited number of cases of developed/irrigated sites are presented for comparison to soil suction profiles obtained for natural climatic surface flux conditions. [ABSTRACT FROM AUTHOR]

This paper analytically investigates the postconstruction load-carrying capacity of a cast-in-place pile in clayey soil. The stress release induced by borehole excavation, the slurry supporting effects, and the dissipation of the negative excess pore-water pressure after construction, all of which have significant effects on the effective stresses of the soil around the pile, are the main concerns of this study, which aim to establish a method to reasonably evaluate the load-carrying capacity of a cast-in-place pile after construction. The stress release due to borehole excavation is modeled by cylindrical cavity contraction theory, which employs a K0-consolidated anisotropic modified Cam-clay (K0-AMCC) model to represent the mechanical behavior of the soil. Considering the dissipation of the negative excess pore pressure, the load-carrying capacity after construction is determined by the total stress method, with consideration of the three-dimensional strength of the soil adjacent to the pile. The proposed method was verified by finite-element (FE) numerical simulations. The results indicate that the soil properties and the factors involved in pile construction, such as the stress release due to borehole excavation, the slurry supporting effects, and the dissipation of negative excess pore-water pressure, have substantial influences on the postconstruction load-carrying capacity of the pile. [ABSTRACT FROM AUTHOR]

Pressure-dispersed compression anchor consists of several anchor units fitted with an end plate. Limited field tests have been conducted to investigate the performance of a pressure-dispersed compression anchor system in cohesive soil. This paper conducted a series of field pullout loading test of pressure-dispersed compression anchors in clay soils, considering the following influence factors of stressing sequence, grouting method and compensation load. The simultaneous stressing yielded less pullout capacity than the individual stressing because of the relatively large interaction between the units. With the increase of the load level, the movement ratio decreased with a gradually decreased rate, followed by a slight increase when the load level exceeded 0.7. The rebound stiffness declined as the load level increased and the individual stressing yielded smaller reduction in the rebound stiffness than the simultaneous stressing. The back calculation indicated that the effective anchor diameter was enlarged by 10% due to the post grouting with a grouting factor of 0.2. [ABSTRACT FROM AUTHOR]

Design of flexible pavements over fine-grained soils requires determination of subgrade resilient modulus over a wide range of degree of saturation and suction for different soils. A novel experimental setup was developed by integrating a cyclic triaxial apparatus with capability to control suction using axis-translation and automated vapor pressure control to the specimen gas phase. System performance was evaluated through repeated load triaxial (RLT) tests for suction ranging from 0 kPa at saturation to 600 MPa at drier conditions. Replicate tests performed on a silty soil and a high-plasticity clayey soil indicated excellent repeatability. Resilient modulus of the materials is essentially unaffected with drying at low-suction range near the air-entry value and the optimum moisture content condition. This property then increases rapidly with subsequent drying until reaching a residual state after which the rate of increase in resilient modulus with respect to suction decreases to a low value. Limitations of a recent prediction model in capturing this trend demonstrated the need to determine resilient moduli over a wider range of suction for developing robust resilient moduli prediction model. [ABSTRACT FROM AUTHOR]

Frost heave of soil is a highly nonuniform problem, in which the local deformation is much more severe and meaningful compared with the overall deformation. When soil is upon freezing, a water–ice phase change occurs and induces the migration of pore water. Subsequently, the distribution of temperature, water content, ice content, and fabric is highly nonuniform in frozen soil. The local frost deformation of soil mainly depends on the local temperature, soil water content, and ice content. In this study, the particle image velocimetry (PIV) method is introduced into the soil column test to monitor the local frost deformation. Several tracer particles are tested to overcome the difficulty that the deformation field is not clear in clay soil. The results demonstrate that the mixed sand is a suitable choice of tracer particles and can lead to clear contours of vertical displacement and strain. Such local deformation information is valuable and can be synthetically analyzed with the local temperature, soil water content, and ice content. The PIV technique is considered to be a good choice for monitoring the local frost deformation field in frozen soil. [ABSTRACT FROM AUTHOR]

In most geotechnical construction works, compacted soils of cohesive-frictional nature are expected to remain mostly under partially saturated conditions and hence experience continuous changes in the suction state (negative pore-water pressure) stemming from seasonal weather and temperature variations throughout any given year. Over the last decade, a few studies have demonstrated that the suction stress characteristic curve (SSCC) can be used to describe the state of stress in partially saturated soils and therefore assess, with reasonable accuracy, the additional shear strength contribution resulting from matric or total suction. However, limited experimental data are available to conclusively verify the magnitude of suction stress at rather high values of suction, especially well beyond the residual suction. In the present work, the SSCC for compacted silty sand has been thoroughly assessed in light of recent experimental data obtained from suction-controlled triaxial testing over a wide range of matric and total suction values (0.05–300 MPa). The suction stress in the test soil was observed to increase with increasing suction even beyond the residual suction state, in contrast with findings from previous works reported in the literature for predominantly sandy or clayey soils. In addition, experimental data from suction-controlled true triaxial, ring shear, and plane strain (biaxial) tests, recently conducted on six different types of cohesive-frictional soils in the low-to-medium matric suction range, were also analyzed to obtain the corresponding SSCCs. Finally, suitable model equations are presented in order to best fit the multiple experimental data sets and hence predict the SSCC for each of the test soils under the different suction-controlled testing techniques. [ABSTRACT FROM AUTHOR]

The writers appreciate the discussers' recognition of the pioneering and novel nature of the original work, which provides a unified effective stress equation for all types of soils under all saturation conditions. However, the discussers fail to appreciate the importance of the roles of soil water adsorption mechanisms in soil water retention and effective stress, given the ample experimental evidence presented in our work and other previously published work. Instead, they raise some points, which are academically thought-provoking notions that are largely reflections of the misunderstanding of the importance of the soil sorptive potential (SSP) concept and the roles of SSP in the effective stress in soils, as detailed subsequently, following the order outlined by the discussers. The discussers consider that the sole mechanical energy in soil water is capillary pressure as they state "That [capillary water] is presumably why many researchers have previously suggested that capillary water, solely, plays a role in the mechanical behavior of unsaturated soil.". [Extracted from the article]

This paper presents a closure to "Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils" by Anand J. Puppala, Raja S. Madhyannapu, and Soheil Nazarain. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002647. The discusser pointed out that the presence of alkalines and acids in the soil or groundwater could influence the performance of deep soil mixing based on lime and cement stabilizers. [Extracted from the article]

This paper presents a discussion of "Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils" by Anand J. Puppala, Raja S. Madhyannapu, and Soheil Nazarain. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002647. The authors utilized the deep soil mixing (DSM) technology to modify a heavily overconsolidated swelling clay soil in situ to determine the efficacy of the DSM treatment of expansive soils and presented the results obtained from the instrumented full-scale field tests undertaken. [Extracted from the article]

As discussed by Been and Jefferies, normally consolidated soil specimens with the same HT ht exhibit similar consolidation stress-normalized stress-strain-strength behavior (i.e., similar stress paths and critical state shear strengths). Consider a soil specimen at the preshearing effective vertical stress, HT ht , after unloading from a maximum effective vertical stress, HT ht . [Extracted from the article]

Theoretical curves for different values of HT ht , 0.6, 0.8, and 1.0 are superimposed on the graph and can be seen to encapsulate the data. Yet, even without these separate curves, Wroth ([14]) noted that the parameter HT ht would track well with I ' i alone according to CSSM, and recommended the approximation HT ht (5) Graph: Fig. [Extracted from the article]

The writers would like to thank the discussers for their acknowledgment of the research presented in the original paper, for the interesting model to predict soil-cement strength they presented, and for their question about kambara reactor (KR) slag properties. It is quite interesting to see the excellent correlation among the normalized soil strength with adjusted porosity/cement index for S1 and S2 soils and curing periods (7 and 28 days) considered in the original paper, demonstrating the efficiency of the model to predict the soil-cement strength as a function of soil characteristics and percentage of cement addition. For low percentages of cement addition, the soil-stabilized mixtures are treated under the category of "soil improved by cement". [Extracted from the article]

Eq. (2) is similar to the unconfined compressive strength empirical correlation found by Consoli et al. ([2]) [Eq. (3)] HT ht (3) where HT ht , HT ht , and HT ht = scalars; and HT ht = volumetric cement content in relation to the total specimen volume. The value of HT ht was chosen to normalize the results. [Extracted from the article]

Das and Deb ([5]) argued that the stress concentration ratio (SCR) increased as the modular ratio (the elastic modulus of support pile and soft soil, i.e., HT ht ) increased. The HT ht was derived about 10,000 from the original Table 1, and the monitored SCR reached a maximum value of 6.6 at the end of embankment construction shown in Fig. In practice, HT ht could be calculated using the HT ht method ([9]; [12]), the HT ht method (the effective stress method, [17], [15], [16]), or the HT ht method ([13]). [Extracted from the article]

Rapid load pile testing (RLT) techniques such as Statnamic were developed as an alternative to more frequently adopted static and dynamic tests. The existing unloading point method (UPM) for deriving equivalent static load-settlement behavior from rapid load tests seems to be adequate in coarse-grained soils but may result in poor prediction in clays and silts. To address these shortcomings, the UPM has been improved to reflect soil type, and new analysis techniques have been developed. To test the performance of the improved UPM and new analysis techniques, pile tests from two clay sites were analyzed. The first case study site was underlain by very to extremely high-plasticity Quaternary London clay, and the second site was underlain by low- to intermediate-plasticity matrix dominant glacial till. The best predictions of static equivalent load-settlement behavior for very-high-plasticity clay were obtained from a new analysis technique that incorporated a soil-specific rate effect parameter (selected on the basis of the clays' plasticity index) that varied with pile settlement. In general, the UPM performed better for tests undertaken in the low- to intermediate-plasticity glacial till, as there is greater experience of RLT in these soils. The results of the study suggest that the development of analysis techniques would benefit greatly from tests in a wider variety of soil types. On the basis of the findings of this study, improvements to the UPM and Schmuker techniques are presented, which include pile settlement-dependent variation of the damping and rate effect parameters. [ABSTRACT FROM AUTHOR]

The purpose of this study is to evaluate the adequacy of the 100-year discharge along with the Froehlich bridge abutment scour equation adopted by the U.S. Federal Highway Administration (FHwA) in predicting abutment scour for bridge design purposes in South Carolina streams. The analysis utilized bridge properties, stream cross-sectional and hydraulic data, local flood frequency equations, a one-dimensional steady river flow computer model (WSPRO), and procedures recommended by the FHwA for predicting abutment scour. A method was developed to identify the single stream-discharge at each bridge that can cause the abutment scour that was observed at 73 bridge abutments. Analysis of the results revealed that for one-third of the abutments in the sandy soil region of South Carolina, the flow rates required to produce the observed scour depths had return periods greater than 100 years. Although for bridges in the region dominated by clay soil, the return periods were significantly smaller than 100 years. [ABSTRACT FROM AUTHOR]

The effectiveness of structural fuse mechanisms used to improve the performance of buildings during seismic loading depends on their capacity, ductility, energy dissipation, isolation, and self-centering characteristics. Although rocking shallow footings could also be designed to possess many of these desirable characteristics, current civil engineering practice often avoids nonlinear behavior of soil in design, due to the lack of confidence and knowledge about cyclic rocking. Several centrifuge experiments were conducted to study the rocking behavior of shallow footings, supported by sand and clay soil stratums, during slow lateral cyclic loading and dynamic shaking. The ratio of the footing area to the footing contact area required to support the applied vertical loads (A/Ac), related to the factor of safety with respect to vertical loading, is correlated with moment capacity, energy dissipation, and permanent settlement measured in centrifuge and 1 g model tests. Results show that a footing with large A/Ac ratio (about 10) possesses a moment capacity that is insensitive to soil properties, does not suffer large permanent settlements, has a self-centering characteristic associated with uplift and gap closure, and dissipates seismic energy that corresponds to about 20% damping ratio. Thus, there is promise to use rocking footings in place of, or in combination with, structural base isolation and energy dissipation devices to improve the performance of the structure during seismic loading. [ABSTRACT FROM AUTHOR]

In the present note, the susceptibility to necking of a subsurface barrier installed by the vibrating beam method in fine-grained soils is investigated by physical model tests. Two soils are investigated, a clayey soil and a silty soil. The model soil is prepared by moist tamping. The recipe of slurry in the model tests is widely used in the foundation engineering industry. The dynamic loading exerted by the vibration of the adjacent panel is simulated by a shake table. The test results show that soil plasticity and water content are the major influence factors on the susceptibility to necking. The plasticity index can be used as an indicator for the susceptibility to necking of subsurface barrier installed by the vibrating beam method in fine-grained soils. Other influence factors on necking are also investigated and their implications for practice are discussed. [ABSTRACT FROM AUTHOR]

Over the last 50 years, the city of Venice, Italy, has observed a significant increase in the frequency of flooding. Numerous engineering solutions have been proposed, including the use of movable gates located at the three lagoon inlets. A key element in the prediction of performance is the estimation of settlements of the foundation system of the gates. The soils of Venice Lagoon are characterized by very erratic depositional patterns of clayey silts, resulting in an extremely heterogeneous stratigraphy with discontinuous layering. The soils are also characterized by varying contents of coarse and fine-grained particles. In contrast, the mineralogical composition of these deposits is quite uniform, which allows us to separate the influence of mineralogy from that of grain size distribution. A comprehensive geotechnical testing program was performed to assess the one-dimensional compression of Venice soils and examine the factors affecting the response in the transition from one material type to another. The compressibility of these natural silty clayey soils can be described by a single set of constitutive laws incorporating the relative fraction of granular to cohesive material. [ABSTRACT FROM AUTHOR]

Alibey Dam is located near Istanbul in Turkey on the Alibey Stream, 4.5 km north of its point of confluence with Golden Horn, an ancient submerged river mouth. It was constructed as an earthfill dam over 30-m-thick soft valley sediments. Before the construction of the dam, field and laboratory tests were performed to determine the geotechnical characteristics of the foundation soils. During the construction and many years after the construction of the earthfill embankments, including the cofferdams and the intermediate fills, the response of the foundation soils was monitored by extensive field instrumentation generating a unique long-term (over 25 years) database. With proper instrumentation and careful monitoring of the collected data, field construction rates could be adjusted and the earth dam was safely constructed on the thick soft deposits. Approaches to settlement prediction were evaluated in a historical context, starting with the simplified one-dimensional approach available at the time of construction to more sophisticated analyses including the employment of modern numerical methods, in terms of the recorded data. Standard subsurface exploration and field testing supplemented with conventional laboratory testing provided the relevant material parameters that were used in the finite element method. The only exception to this was the overall hydraulic conductivity of the deposit, which controlled the rate of consolidation. Early field observations were used to assign the appropriate hydraulic conductivity. An elastoplastic soil model in a coupled analysis of consolidation was employed in the analysis that yielded realistic predictions of field behavior in response to the complex construction history. The accurate prediction and monitoring of the behavior of soft and thick soil layers subjected to staged construction, as in the case of Alibey Dam, is very important for planning of the construction as well as the expected behavior after construction. [ABSTRACT FROM AUTHOR]

Tests for determining the water retention curve (WRC) can be time-consuming and tedious, especially with deformable soils for which volume change and water content have to be simultaneously monitored. In some cases, predictive models can become a practical alternative to obtain an estimate of the WRC. However, very few models are available to predict the WRC of deformable materials under increasing suction. In this paper, the modified Kovács (MK) model, developed initially for incompressible soils, is extended to describe and, in some cases, predict the WRC of deformable clayey soils. This generalization of the MK model is performed by introducing the volumetric shrinkage curve (VSC) in its formulation. A curvilinear equation is proposed to represent the void ratio-suction function e(ψ) corresponding to the VSC. This VSC model and the extended MK model (MKd) are validated using experimental data taken from the literature. Empirical relationships are developed for predictive purposes to estimate the parameters involved, using basic geotechnical properties. Applications show a good agreement between measured and calculated WRC. [ABSTRACT FROM AUTHOR]

Comments on several discussion regarding geotechnical and geoenvironmental engineering. Role of momentum in pile driving and pile specifications; Analysis on the issues regarding the two compacted earth fill sites that were shaken by a significant earthquake in 1994; Consistence of reference to the fill soils being composed of clay soil.

The effects of large sample spacing associated with evaluating the vertical strength variability of a clayey soil are discussed in this paper. The research concerns 0.2 m sample spaced cone penetration data profiles analyzed by means of statistical treatment. The aim is to verify the effects of this sample spacing, or that greater than 0.2 m, on trend definition and on parameters which describe the vertical strength variability of the soil. We consider the variance and the scale of fluctuation of the strength values compared to the trend. This investigation also involves the effects of large sample spacing on the location of geostatistical boundaries and the importance of the trend removal technique for obtaining a sound set of residuals. The results of this research provide both theoretical indications and engineering prescriptions for planning a site characterization program. [ABSTRACT FROM AUTHOR]

Tensile strength of soil plays an important role in controlling the cracking and tensile failure of many earth structures. In this investigation, a direct tensile test apparatus was developed to determine the tensile strength of compacted clayey soil over a broad range of water contents (4.3-28.5%) and with different dry densities (). The results show that the tensile strength of compacted clayey soil significantly depends on water content. The tensile strength characteristic curve (TSCC) exhibits one peak value occurring at the critical water content around 11.5%. With increasing water content, the tensile strength increases at the dry side of and then decreases at the wet side of it. Generally, with the increase of dry density, the tensile strength also increases. Moreover, a modified model is proposed to describe the tensile strength characteristics of compacted clayey soil, and it is validated by the obtained test data. [ABSTRACT FROM AUTHOR]

The authors focus on research into deep building foundations and its behavior under axial and lateral loading. They mention that the prediction of load-transfer curves, both for side resistance and for end bearing, allow for the analysis of deep foundations under a range of conditions. They talk about soil properties around deep foundations after installation and how the pile capacity under axial load differs depending on if the pile was driven into consolidated clay or loose cohesionless soil. They state that research can lead to an improvement of design methods of deep foundations.