Showing papers in "Journal of Geotechnical and Geoenvironmental Engineering in 2011"
TL;DR: In this paper, the authors present a geotechnical numerical analysis method based on the load transfer approach, which assesses the main effects of temperature changes on pile behavior and the occurrence of critical design situations.
Abstract: There is currently a lack of established calculation method for the geotechnical design of heat exchanger piles, although the technology is experiencing a fast expansion. Instead of quantifying the effects of temperature changes on the static behavior of heat exchanger piles, the common geotechnical practice is to apply a large overall security factor. This is done in order to be on the side of safety with respect to thermal effects. The few existing in situ experiments show that applying a thermal load induces a significant change in the stress-strain state of a pile. This paper presents a geotechnical numerical analysis method, based on the load transfer approach, which assesses the main effects of temperature changes on pile behavior. The method is validated on the basis of two in situ measurements of the loads and deformations experienced by heat exchanger test piles. The occurrence of critical design situations is further discussed. Some conclusions are formulated on concrete failure and the full mobilization of the pile shaft friction and base resistance during the operation of the heat exchange system.
228 citations
TL;DR: The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied in this paper, where unconfined compression and resilient modulus tests were conducted on organic soil.
Abstract: The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and CaO/SiO2...
228 citations
TL;DR: In this article, a new elastic viscoplastic model, extended from the overstress theory of Perzyna, is developed to account for inherent and induced anisotropy, interparticle bonds and bond degradation, and viscosity.
Abstract: The paper focuses on investigating the destructuration process during time-dependent stress-strain evolution. For this purpose, various oedometer tests and triaxial tests on intact and reconstituted samples of soft sensitive Vanttila clay were carried out. Based on experimental observations, a new elastic viscoplastic model, extended from the overstress theory of Perzyna, is developed. The proposed model accounts for inherent and induced anisotropy, interparticle bonds and bond degradation, and viscosity. The determination of model parameters is discussed, demonstrating how all model parameters can be determined in a straightforward way and no additional test is needed for the proposed model compared to the modified Cam clay model. The model is implemented into a finite-element code, which enables coupled consolidation analyses. The model is used to simulate various strain-rate and creep tests under one-dimensional and triaxial conditions on the intact samples of Vanttila clay. The comparisons between experimental results and simulations show that the model has good predictive ability on the time-dependent behavior of a soft sensitive clay.
227 citations
TL;DR: The results show that the bacterial cells effectively improved the geomechanical properties of the sand, owing to microbially induced precipitation and related pore volume changes.
Abstract: Biological processes may provide great and previously unexplored opportunities for cost-effective, in situ improvement of the engineering properties of soil. A laboratory study was conducted to evaluate the changes in geomechanical properties of sand attributable to the formation of calcium precipitates induced through ureolysis catalyzed by Sporosarcina pasteurii (S. pasteurii). Specifically, direct shear and California Bearing Ratio (CBR) tests were conducted on sand specimens subjected to treatment by growing, resting, and dead S. pasteurii cells in completely stirred tank reactors and completely mixed biofilm reactors, respectively. Scanning electron microscopy analyses were also conducted to evaluate microbially induced precipitation. The results of the study show that the bacterial cells effectively improved the geomechanical properties of the sand. Growing cells improved the sand properties owing to microbially induced precipitation and related pore volume changes, whereas dead and resting cells ge...
214 citations
TL;DR: In this paper, parametric studies were performed by using three typical rainfall patterns, identified by analysis of available rainfall data for Singapore and two different soil types to represent high and low-conductivity residual soils of Singapore.
Abstract: Rainfall-induced slope failure occurs in many parts of the world, especially in the tropics. Many rainfall-induced slope failures have been attributed to antecedent rainfalls. Although it has been identified as a cause of rainfall-induced slope failure, the pattern or distribution of the antecedent rainfall has not received adequate attention. In this study, parametric studies were performed by using three typical rainfall patterns, identified by analysis of available rainfall data for Singapore and two different soil types to represent high- and low-conductivity residual soils of Singapore. Antecedent rainfall patterns were applied on soil slopes and a transient seepage analysis was conducted. The computed pore-water pressures were used in stability analyses to calculate the safety factor of the slope. Results indicated that antecedent rainfall affected the stability of both high-conductivity (HC) and low-conductivity (LC) soil slopes. However, the stability of the LC soil slope was more significantly af...
168 citations
TL;DR: In this article, the authors used a hybrid method for analysis and design of slope stabilizing piles that was developed in a preceding paper by the writers and derived insights about the factors influencing the response of piles and pile-groups.
Abstract: This paper uses a hybrid method for analysis and design of slope stabilizing piles that was developed in a preceding paper by the writers. The aim of this paper is to derive insights about the factors influencing the response of piles and pile-groups. Axis-to-axis pile spacing (S), thickness of stable soil mass (Hu), depth (Le) of pile embedment, pile diameter (D), and pile group configuration are the parameters addressed in the study. It is shown that S ¼ 4D is the most cost-effective pile spacing, because it is the largest spacing that can still generate soil arching between the piles. Soil inhomogeneity (in terms of shear stiffness) was found to be unimportant, because the response is primarily affected by the strength of the unstable soil layer. For relatively small pile embedments, pile response is dominated by rigid-body rotation without substantial flexural distortion: the short pile mode of failure. In these cases, the structural capacity of the pile cannot be exploited, and the design will not be economical. The critical embedment depth to achieve fixity conditions at the base of the pile is found to range from 0:7Hu to 1:5Hu, depending on the relative strength of the unstable ground compared to that of the stable ground (i.e., the soil below the sliding plane). An example of dimensionless design charts is presented for piles embedded in rock. Results are presented for two characteristic slenderness ratios and several pile spacings. Single piles are concluded to be generally inadequate for stabilizing deep land- slides, although capped pile-groups invoking framing action may offer an efficient solution. DOI: 10.1061/(ASCE)GT.1943-5606.0000479. © 2011 American Society of Civil Engineers. CE Database subject headings: Slope stability; Embedment; Pile groups; Parameters. Author keywords: Slope stabilizing piles; Embedment depth; Simplified method; Dimensionless charts; Arching; Pile groups.
151 citations
TL;DR: In this paper, the authors developed a simplified but fairly comprehensive constitutive model for analysis of the cyclic response of shallow foundations, based on a kinematic hardening model with Von Mises failure criterion.
Abstract: The nonlinear response of shallow foundations has been studied experimentally and analytically. However, the engineering community is not yet convinced of the applicability of such concepts in practice. A key prerequisite is the ability to realistically model such effects. Although several sophisticated constitutive models are readily available in the literature, their use in practice is limited, because (1) they typically require extensive soil testing for calibration; (2) as they are implemented in highly specialized numerical codes, they are usually restricted to simple superstructures; and (3) in most cases, they can only be applied by numerical analysis specialists. Attempting to overcome some of these difficulties, this paper develops a simplified but fairly comprehensive constitutive model for analysis of the cyclic response of shallow foundations. On the basis of a kinematic hardening constitutive model with Von Mises failure criterion (readily available in commercial finite element codes), the mo...
126 citations
TL;DR: In this article, the design of the combined vacuum and surcharge fill system and the construction of the embankment are described in the Port of Brisbane and a comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge filling system highlights the clear benefits of vacuum pressure application.
Abstract: During the past decade, the application of vacuum pressure for stabilising soft coastal clay and other low-lying estuarine soils has become increasingly popular in Australia, mainly due to the proven costeffectiveness in view of the significantly reduced time for achieving a high degree of consolidation and enhanced shear strength. Due to an increase in trade activities at the Port of Brisbane, new facilities on Fisherman Islands at the mouth of the Brisbane River will be constructed on the new outer area (235ha) adjacent to the existing port facilities via land reclamation. A scheme of vacuum assisted surcharge load in conjunction with conventional surcharge and prefabricated vertical drains was selected to reduce the required consolidation time through the deeper subsoil layers. The design of the combined vacuum and surcharge fill system and the construction of the embankment are described in this paper. A comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge fill highlights the clear benefits of vacuum pressure application. A comprehensive array of field data is presented to demonstrate how the embankment had performed during construction. A new analytical solution for radial consolidation considering both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlements and associated excess pore pressures of the soft Holocene clay deposits in the Port of Brisbane, for future design of port infrastructure under increasing live loads over the next two decades.
125 citations
TL;DR: In this article, the authors present four load test databases from South Africa for driven piles in noncohesive soils (29 tests), bored piles (33 tests), driven piles (59 tests), and bored piles in cohesive soils (53 tests) and the capacity model factor is defined as the ratio of the interpreted capacity and the predicted capacity.
Abstract: Level 1 reliability methods have been internationally accepted as the basis for development of the new generation of geotechnical design codes. A key requirement of this design approach is the identification and quantification of uncertainties associated with the geotechnical design under consideration. This paper presents four load test databases from South Africa for driven piles in noncohesive soils (29 tests), bored piles in noncohesive soils (33 tests), driven piles in cohesive soils (59 tests), and bored piles in cohesive soils (53 tests). The capacity model factor is defined as the ratio of the interpreted capacity (Chin-Davisson approach) and the predicted capacity (static pile design formula). The uncertainty in the capacity model factor is modeled as a lognormal random variable. The model factor statistics reported in this study are required for reliability-based ultimate limit state design. The uncertainty in the load-settlement behavior is characterized by fitting measured load-settlement data to a hyperbolic equation and then normalizing the hyperbolic curve with the interpreted capacity. The resulting exercise reduces uncertainties in a set of nonlinear continuous curves to uncertainties in two hyperbolic curve-fitting parameters. This approach is practical and grounded realistically on the load test database with minimal assumptions. The hyperbolic parameter statistics reported in this study are required for reliability-based serviceability limit state design.
121 citations
TL;DR: An optical fiber strain-sensing technique, on the basis of Brillouin optical time domain reflectometry (BOTDR), was used to monitor the performance of a secant pile wall subjected to multiple props during construction of an adjacent basement in London.
Abstract: An optical fiber strain-sensing technique, on the basis of Brillouin optical time domain reflectometry (BOTDR), was used to monitor the performance of a secant pile wall subjected to multiple props during construction of an adjacent basement in London. Details of the installation of sensors and data processing are described. Distributed strain profiles were obtained by deriving strain measurements from optical fibers installed on opposite sides of the pile to allow monitoring of both axial and lateral movements along the pile. Methods for analyzing the thermal strain and temperature compensation are also presented. Measurements obtained from the BOTDR were found to be in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed.
114 citations
TL;DR: In this article, a transparent soil model is used to investigate the surface settlement profile induced by shield tunneling, and the distribution of soil deformation within the soil mass near the tunnel.
Abstract: Ground movements induced by shallow tunnels affect the safety of nearby underground and aboveground structures. Therefore, the reliable prediction of these movements is important. A transparent soil model is used to investigate not only the surface settlement profile induced by shield tunneling, but also the distribution of soil deformation within the soil mass near the tunnel. The observed surface settlements are consistent with the normal probability curve commonly used for predicting settlement, with only the inflection points or trough width parameters somewhat different. The measured data are consistent with field measurements in that the trough width parameter is independent of the volume loss and linearly proportional to the tunnel depth. An analysis of the displacement field inside the transparent soil models indicates that the subsurface settlement trough at different depths can be approximated by a normal probability curve; and the horizontal displacement can be expressed by the trough width parameter and the volume loss, at the point at which maximum horizontal displacement occurs at the point of inflection. Additionally, the measurements indicate that subsurface ground movements can be in excess of the observed surface settlement, which can adversely affect underground utilities.
TL;DR: In this article, geosynthetic clay liners were exhumed from composite barriers, i.e., geomembrane over GCL in final covers at four sites after 4.7 to 6.7 years to evaluate the in-service condition.
Abstract: Geosynthetic clay liners GCLs were exhumed from composite barriers, i.e., geomembrane over GCL in final covers at four sites after 4.7 to 6.7 years to evaluate the in-service condition. Monovalent bound cations were replaced by divalent cations in all GCLs, with near complete exchange at two-thirds of the sampling locations. Hydraulic conductivity was measured using two dilute solutions commonly used as permeant water: standard water SW, 0.01M CaCl2 solution and type II deionized water DW. Hydraulic conduc- tivities to SW varied over four orders of magnitude, whereas identical specimens i.e., from same sample had hydraulic conductivities to DW consistently 310 10 m /s. Higher hydraulic conductivities and sensitivity to permeant water did not correspond directly to the amount of cation exchange. Exhumed GCLs with higher gravimetric higher water contents 50% exhibited a gel structure indicative of osmotic hydration and had lower hydraulic conductivities to both SW and DW, regardless of the amount of sodium Na replaced by divalent cations. These GCLs with higher water contents were placed on subgrade having water content in excess of optimum water content standard Proctor. Conditions that promote rapid hydration and osmotic swell in a GCL are recommended to ensure that a GCL in a composite barrier maintains low hydraulic conductivity 510 11 m /s, even if the native Na is ultimately replaced by divalent cations. Subgrade with water contentoptimum water content is recommended. DOI: 10.1061/ASCEGT.1943-5606.0000407 CE Database subject headings: Geosynthetics; Clay liners; Landfills; Hydraulic conductivity; Barriers; Composite materials; Water content. Author keywords: Geosynthetic clay liner; Landfill; Final cover; Hydraulic conductivity; Cation exchange; Hydration; Osmotic swell; Crystalline swell; Preferential flow.
TL;DR: In this paper, a probabilistic analysis of the face stability of a tunnel driven by a compressed-air pressurized shield is presented, where the collocation-based stochastic response surface methodology (CSRSM) is used.
Abstract: A probabilistic analysis of the face stability of a tunnel driven by a compressed-air pressurized shield is presented. The collocation-based stochastic response surface methodology (CSRSM) is used. The deterministic model employed in the probabilistic analysis is analytical. A translational multiblock collapse mechanism in the framework of the kinematic theorem of limit analysis forms the basis of the analysis. The soil friction angle and cohesion are considered as random variables. CSRSM was first validated by the comparison of the results obtained from the original analytical deterministic model. Then, the influence of the probabilistic characteristics of the uncertain variables was studied. Contrary to the correlation between c and phi and the coefficients of variation of these variables, which have a significant effect on the variability of the critical collapse pressure, the nonnormality of the distributions of the random variables was shown not to have a considerable effect on the distribution of the output.
TL;DR: In this paper, an in situ air-injection test that aims to examine the effectiveness of the air injection to desaturate ground and the validity of observation techniques to monitor the evolution of the unsaturated zone is described.
Abstract: Desaturation of ground by air injection attracts considerable attention in recent years as an innovative technique for a liquefaction countermeasure Several research programs were conducted in laboratories regarding the related topics This paper describes an in situ air-injection test that aims to examine the effectiveness of the air injection to desaturate ground and the validity of observation techniques to monitor the evolution of the unsaturated zone In the test, air was injected from an air injector deployed in a targeted saturated-sand layer at a depth of 6 m Observations revealed that the air-flow rate increased linearly with increasing air-injection pressure and the desaturated zone was generated within 4 m from the injection point A 3-dimensional electric resistivity tomography technique was effective for evaluation of the desaturated zone The degree of saturation of the in situ soil was observed by using high quality undisturbed samples obtained by the ground freezing method The degree of
TL;DR: In this paper, the authors present field measurements and back analysis of two different cemented paste backfill (CPB) cases and show that these two cases demonstrate considerably different consolidation behaviors, which in turn influence critical design and management aspects such as applied barricade stresses and choice of an appropriate curing technique for laboratory control specimens.
Abstract: Over the past decade there has been increasing use of "paste" for backfilling of mined-out voids ("stopes") in underground mines. Paste backfill is generated from full stream tailings and is almost always placed underground with cement. This paper presents field measurements and back analysis of two different cemented paste backfill (CPB) cases. Using the collected data and subsequent back analysis, the writers show that these two cases demonstrate considerably different consolidation behaviors, which in turn influence critical design and management aspects such as applied barricade stresses and choice of an appropriate curing technique for laboratory control specimens. The paper presents pore pressure and total stress monitoring data gathered from two different CPBs during the deposition process. Both filling cases are modeled using Minefill-2D, which is a finite-element (FE) model capable of fully coupling the time-dependent processes of fill accretion, consolidation, cement hydration, and stress arching. Input parameters for the model are obtained from independent laboratory tests. Comparison between measured values and those calculated based on laboratory measurements verifies that, in general, the model provides a good representation of the process. However, there are some significant difficulties relating to modeling a three-dimensional stope with a two-dimensional plane-strain FE program, and some ways of accounting for these difficulties are explored. The model is then used to extrapolate the measured results to investigate the influence of varying filling rate, cement content, and number of drawpoints on critical design aspects.
TL;DR: In this article, a series of centrifuge model tests of the lateral response of a fixed-head single pile in soft clay is reported, and both monotonic and cyclic episodes of loading are described, with varying amplitude and with intervening periods of reconsolidation.
Abstract: A series of centrifuge model tests of the lateral response of a fixed-head single pile in soft clay is reported. Both monotonic and cyclic episodes of loading are described, with varying amplitude and with intervening periods of reconsolidation. The soil conditions are characterized by cyclic T-bar penetrometer tests. The ultimate capacity under monotonic load for virgin and for postcyclic conditions was found to be comparable with calculations based on existing design methods, including theoretical plasticity solutions and empirical methods. The lateral stiffness was observed to degrade with cycles, with the rate of degradation being greater for larger cycles. The degradation pattern has been tentatively linked to the cyclic T-bar response, by considering the ‘damage’ associated with the cumulative displacement and remolding, in each case. This approach provides a consistent interpretation of the tests. Although episodes of pile movement and soil remolding led to a reduction in lateral resistance, interv...
TL;DR: In this article, a new empirical criterion for assessing the potential of internal erosion and suffusion of granular soils is presented, based on the porosities influenced by the particle size distribution and the degree of compaction.
Abstract: This study presents a new empirical criterion for assessing the potential of internal erosion and suffusion of granular soils. This method considers the bimodal structure of a soil having a primary coarse fabric and loose finer particles based on the porosities influenced by the particle size distribution and the degree of compaction. By comparing the representative particle size of a loose finer fraction with the controlling constriction size of a primary coarse fabric, a distinct boundary between internally stable and unstable soils with respect to internal erosion may be found.
TL;DR: In this paper, a load-controlled laboratory model test and their numerical simulations are presented for floating stone column group foundations placed in slurry deposited clayey soil beds with known effective stress states, such as area ratio, length of columns, relative density, and moisture content of column material.
Abstract: Fully drained, load-controlled laboratory model tests and their numerical simulations are presented. The tests were performed on adequately instrumented, small scale physical models of floating stone column group foundations placed in slurry deposited clayey soil beds with known effective stress states. Effect of various group foundation parameters, such as area ratio, length of columns, relative density, and moisture content of the column material is evaluated. The numerical analyses consist of three-dimensional, elastoplastic, finite-element analyses of the model foundation. In the analyses, the clayey soil behavior is represented by the modified Cam-clay model, and the stone column and mat are represented by the elastic, fully plastic Mohr-Coulomb constitutive relationship. The finite-element analysis was successful in predicting the model test results with reasonable accuracy. The results are presented in nondimensional form. The major foundation parameters affecting the group response were identified...
TL;DR: The feasibility of using GFRP soil nails for slope stabilization is evaluated in this article, where two field-scale pullout tests were performed at a slope site using fiberbragg grating sensors, strain gauges, linear variable displacement transformers (LVDTs), and a load cell were used to measure axial strain distributions and pullout force-displacement relationships during testing.
Abstract: Glass fiber–reinforced polymer (GFRP) materials provide practical solutions to corrosion and site-maneuvering problems for civil infrastructures using conventional steel bars as reinforcements In this study, the feasibility of using GFRP soil nails for slope stabilization is evaluated The GFRP soil nail system consists of a GFRP pipe installed by the double-grouting technique Two field-scale pullout tests were performed at a slope site Fiber Bragg grating (FBG) sensors, strain gauges, linear variable displacement transformers (LVDTs), and a load cell were used to measure axial strain distributions and pullout force-displacement relationships during testing The pullout test results of steel soil nails at another slope site are also presented for comparison It is proven that the load transfer mechanisms of GFRP and steel soil nails have certain difference Based on these test results, a simplified model using a hyperbolic shear stress-strain relationship was developed to describe the pullout performance of the GFRP soil nail A parametric study was conducted using this model to study some factors affecting the pullout behavior of GFRP soil nails, including nail diameter, shear resistance of soil-grout interface, and ratio of interface shear coefficient to the Young’s modulus of the nail The results indicate that the GFRP soil nail may exhibit excessive pullout displacement and thus a lower allowable pullout resistance than with the steel soil nail
TL;DR: In this article, the authors developed a more general reliability-based design approach for drilled shafts that formulates the design process as an expanded reliability problem in which Monte Carlo simulations MCS are used in the design.
Abstract: This paper develops a more general reliability-based design approach for drilled shafts that formulates the design process as an expanded reliability problem in which Monte Carlo simulations MCS are used in the design. Basic design parameters, such as the shaft diameter B and depth D, are formulated as discrete uniform random variables. Then the design process becomes one in which failure probabilities are developed for various combinations of B and D i.e., conditional probability pFailureB,D and are compared with a target probability of failure pT. Equations are derived for this expanded reliability-based design RBD E approach, and criteria are established for the minimum number of MCS samples to ensure a desired level of accuracy. Its usefulness is illustrated using a drilled shaft design example. This RBD E approach has the following advantages: 1 it gives results that agree well with current RBD designs, but it improves the resolutions of the designs; 2 it offers design engineers insight into how the expected design performance level changes as B and D change; 3 it gives design engineers the ability to adjust pT, without additional calculation effort, to accommodate specific needs of a particular project; and 4 it is transparent and "visible" to design engineers who are given the flexibility to include uncertainties deemed appropriate. Finally, the effects of uncertainties in the at-rest horizontal soil stress coefficient K0 and allowable displacement ya are illustrated using this approach.
TL;DR: In this paper, high capacity tensiometers and capacitance relative humidity sensors were used to quantify the water-retention behavior of geosynthetic clay liners (GCLs).
Abstract: The hydration and subsequent hydraulic performance of geosynthetic clay liners (GCLs) depend on the water-retention curve (WRC) of the GCL. Because of the inherent difficulty in obtaining the WRC for these materials, limited data exists regarding the WRCs of GCLs in the literature. In this study, high-capacity tensiometers and capacitance relative humidity sensors were used to quantify the water-retention behavior of GCLs for four different GCL products that vary both in materials (woven and nonwoven geotextiles) and in fabrication detail (thermal treatment and needle-punching). The water-retention behavior was investigated under wetting and drying paths; we present results in terms of gravimetric and volumetric moisture content and bulk GCL void ratio. The WRCs of the different GCL products showed significant variation among wetting and drying curves, indicating that both needle-punching and thermal treatment have a significant effect on the swelling behavior of the GCL and its WRC. Theoretical equations...
TL;DR: In this article, the authors describe an experimental investigation designed to assess the impact of pile end condition on the capacity of piles installed in soft clay. But the authors do not consider the effect of the type of soil plugging.
Abstract: This paper describes an experimental investigation designed to assess the impact of pile end condition on the capacity of piles installed in soft clay. A series of field tests are described in which instrumented open-ended and closed-ended model piles were jacked into soft clay. The radial stresses, pore pressures, and load distribution were recorded throughout installation, equalization, and load-testing. Although the total stress and pore pressure developed during installation were related to the degree of soil plugging, the radial effective stress that controls the shaft resistance was shown to be independent of the mode of penetration. The long-term shaft capacity of the open-ended pile was closely comparable to that developed by closed-ended piles, suggesting a limited influence of end condition on the fully equalized shaft resistance. In contrast to the shaft resistance, the base capacity was highly dependent on the degree of plugging.
TL;DR: In this paper, the authors developed a rational and practical methodology to determine both clay mineralogy distribution and dominant clay mineral in a soil by using three measured chemical soil properties and their analyses.
Abstract: Stabilization design guidelines based on soil plasticity properties have certain limitations. Soils of similar plasticity properties can contain different dominant clay minerals, and hence, their engineering behavior can be different when stabilized with the same chemical additive and dosage. It is essential to modify stabilizer design guidelines by including clay mineralogy of the soil and its interactions with chemical additives used. Chemical properties of a soil including cation exchange capacity (CEC), specific surface area (SSA) and total potassium (TP) are dependent on clay mineral constituents, and an attempt is made in this study to develop a rational and practical methodology to determine both clay mineralogy distribution and dominant clay mineral in a soil by using three measured chemical soil properties and their analyses. This approach has been evaluated by determining and evaluating clay minerals present in artificial and natural clayey soils of known and unknown clay mineralogy. A total of twenty natural and six artificial soils were considered and used in the chemical analyses. Test results and subsequent analyses including the development of artificial neural network (ANN) based models are evaluated and described in this paper.
TL;DR: In this paper, the influence of the amount of lime, porosity, and voids/lime ratio on the initial shear modulus (G0) and unconfined compressive strength (qu) of a lime-treated clay-ey sandy soil was quantified.
Abstract: Lime treatment is an attractive technique for soil improvement in the construction of rail tracks and pavement layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as in the case of soil-cement technology, where the voids/cement ratio is shown to be a key parameter for the estimation of both strength and stiffness. The present study, therefore, was aimed at quantifying the influence of the amount of lime, porosity, and voids/lime ratio on the initial shear modulus (G0) and unconfined compressive strength (qu) of a lime-treated clayey sandy soil. From the results of unconfined compression tests and bender elements measurements, it was shown, for the soil-lime mixtures investigated, that the voids/lime ratio is an appropriate parameter to assess both initial stiffness and unconfined compressive strength. Also, a unique G0/qu versus voids/lime ratio relationship was established linking the soil-lime mi...
TL;DR: In this article, the authors used numerical modeling techniques to better understand multiplate circular anchor foundation behavior in clay soils, and established a practical design framework for multiplate anchor foundations to replace existing semi-empirical design methods.
Abstract: In recent years, the use of helical anchors has expanded beyond their traditional use in the electrical power industry. The advantages of rapid installation and immediate loading capability have resulted in their being used in more traditional civil engineering infrastructure applications. Unfortunately, our current understanding of these anchors is unsatisfactory, and the underlying theoretical framework adopted by engineers has proven to be largely inappropriate and inadequate. A better understanding of helical anchor behavior will lead to increased confidence in design, a wider acceptance as a foundation alternative, and more economic and safer designs. The primary aim of this research is to use numerical modeling techniques to better understand multiplate circular anchor foundation behavior in clay soils. A practical design framework for multiplate anchor foundations will be established to replace existing semiempirical design methods that are inadequate and have been found to be excessively under- or...
TL;DR: In this paper, the authors presented new experimental results on a silica sand to validate the concept known as threshold α, below which the cyclic strength of sand increases with α and above which it decreases with α, with α representing the sustained shear stress level.
Abstract: The existence of initial shear stress can have a significant effect on the cyclic strength or liquefaction potential of sand. This effect is not yet fully understood because of a lack of convergence and consistency in the existing data and interpretations, leading to great uncertainty in quantifying the effect for practical applications. This paper presents new experimental results on a silica sand to validate the concept known as threshold α, below which the cyclic strength of sand increases with α and above which the cyclic strength decreases with α (with α representing the sustained shear stress level). On the basis of a series of monotonic loading tests on the same sand, and in the framework of critical state soil mechanics, it is further confirmed that threshold α can be well related to a state parameter in the void ratio-mean effective stress plane and thereby a unified and consistent interpretation can be established. A new platform is proposed on which the relationship between cyclic strength and ...
TL;DR: In this paper, the authors performed triaxial compression tests on crushed coral sand from nearstatic strain rates to very high strain rates (up to approximately 1,800%/s).
Abstract: Drained triaxial compression tests on crushed coral sand were performed from near-static strain rates to very high strain rates (up to approximately 1,800%/s). Experiments were performed on dry, vacuum-confined axisymmetric specimens at two different confining pressures (98 and 350 kPa) and two different densities (Dr approximately 36 and 60%). A gravity drop weight loading system was used to generate high strain rates. High-speed film photographs of the specimen were taken through the flat sides of a square triaxial cell. By using digital image analysis techniques, strains were locally measured near the center of the specimen to obtain the most uniform assessment. Stress-strain relationships are presented. The following effects were observed with increasing strain rates: the elastoplastic stiffness increased significantly; the failure shear strength increased moderately; the axial strain at peak stress decreased significantly; and volumetric strains became more dilatant. Unusual behavior was observed at ...
Journal Article•
TL;DR: In this article, the results of 167 full-scale field load tests were used to examine several issues related to the load-displacement behavior of footings in cohesionless soils under axial compression loading, including (1) method to interpret the failure load from the loadsettlement curves; correlations among interpreted loads and settlements; and (3) generalized load-settlement behavior.
Abstract: The results of 167 full-scale field load tests were used to examine several issues related to the load-displacement behavior of footings in cohesionless soils under axial compression loading, including (1) method to interpret the “failure load” from the load-settlement curves; (2) correlations among interpreted loads and settlements; and (3) generalized load-settlement behavior. The L1 - L2 method was found to be more appropriate than the “tangent intersection” and “10% of the footing width” methods for interpreting the failure load. The interpreted loads and displacements indicate that footing load-settlement behavior is less elastic and more nonlinear than that of drilled foundations. The results show that the footing behavior will be beyond the elastic limit for designs where a traditional factor of safety between 2 and 3 is used. A normalized curve was developed by approximating the load-settlement curve for each load test in the database by hyperbolic fitting, and the uncertainty in this curve was qu...
TL;DR: In this article, a parametric study was performed to quantify the loss in anchor embedment during keying in terms of the anchor geometry, soil properties, loading eccentricity, and inclination.
Abstract: The loss in anchor embedment during keying, as it rotates to become normal to the cable load, reduces the uplift capacity of anchors in normally consolidated clay. The keying behavior of plate anchors has been studied previously by using centrifuge and field model tests. In this paper, a large deformation finite-element approach incorporating frequent mesh regeneration and allowing for evolution of the anchor-chain profile, was developed to simulate the keying process of rectangular and strip plate anchors. A parametric study was undertaken to quantify the loss in anchor embedment during keying in terms of the anchor geometry, soil properties, loading eccentricity, and inclination. The embedment loss decreased dramatically with increasing loading eccentricity and decreasing chain angle at the mudline to the horizontal. The loss in anchor embedment during keying increased as the local soil strength increased relative to the weight of the anchor, up to a limit determined by the eccentricity of loading. In c...
TL;DR: In this paper, the ground deformation during a pneumatic caisson construction in Shanghai soft ground was evaluated using a finite-element program, and the accuracy and reliability of the proposed model were verified.
Abstract: Characterized by unmanned excavation and remote controlling, the new pneumatic caisson (NPC) method has advantages in deep excavation such as deep shield tunnel shafts and some underground construction close to the existing structures or facilities. When adopted in urban areas, it is very important to control the ground deformation during a caisson construction. For this purpose, field measurements of ground deformation were conducted during a tunnel shaft construction in Shanghai soft ground, in which the NPC method was used. On the basis of the particular construction procedure of a pneumatic caisson, one kinematic mechanical model was proposed for evaluating the influence of NPC construction on the surrounding strata. This model was incorporated into a finite-element (FE) program. By comparing the FE-predicted results of the proposed model and the field measurements, the accuracy and reliability of this model were verified.