Showing papers in "Geotechnical Testing Journal in 1998"

Effects of non-plastic fines on minimum and maximum void ratios of sand

Abstract: The behavior of sand is affected by the content of nonplastic fine particles. How and to what degree the fines content affects the minimum and maximum void ratios has been studied in detail. A review is presented of previous theoretical and experimental studies of minimum and maximum void ratios of single spherical grains, packings of spheres of several discrete sizes, as well as optimum grain-size ratios to produce maximum densities. A systematic experimental study is performed of the variation of minimum and maximum void ratios with contents of fines for sands with smoothly varying particle size curves and a large variety of size distributions. It is shown that the fines content plays an important role in determining the sand structure and the consequent minimum and maximum void ratios. It is indicated how the fines content and sand structure affects the compressibility and the static liquefaction potential of the sand.

Analysis of Bender Element Tests

Abstract: A study is presented of potential errors in, and methods of interpreting, the results of cantilever-type, piezoceramic bender element tests for measuring the shear wave velocity of laboratory soil specimens. Interpretations based on the first direct arrival in the output signal are often masked by near-field effects and may be difficult to define reliably. Interpretations based on characteristic points or cross-correlation between the input and output signals are shown to be theoretically incorrect in most cases because of: (1) the effects of wave interference at the boundaries; (2) the phase lag between the physical wave forms and the measured electrical signals; and (3) non-one-dimensional wave travel and near-field effects. Interpretations based on the second arrival in the output signal are theoretically subject to errors from non-one-dimensional wave travel and near-field effects. Differences in Vs values obtained by the different interpretation methods are illustrated analytically and experimentally.

The measurement of stiffness anisotropy in clays with bender element tests in the triaxial apparatus

Abstract: The paper presents the results of a program of research investigating the effectiveness of bender elements when used in conjunction with the triaxial apparatus for measuring the anisotropy of small strain stiffness of fine-grained soils. Tests were carried out on both intact and reconstituted samples of London clay and on kaolin up to high stresses. The paper shows that the transverse isotropy of small-strain stiffness that commonly occurs in many soils because of a one-dimensional loading history can be fully investigated in the conventional triaxial apparatus and that London clay is an example of such a soil. The stress-induced component of anisotropy was found to be very small for axi-symmetric loading conditions common to both the appartus and the in situ state of these soils. In contrast, the inherent or structural anisotropy was much more significant and is shown to be a variable factor resulting from the plastic strain history and is not related to its natural structure. Consequently, inherent anisotropy is reversible, but the rate of change is very slow when a new regime of stresses is imposed. Inherent anisotropy of the very small strain stiffness also persists long after the plastic strains of the soil have become oriented toward the new stresses.

Experience with the Use of Methylcellulose as a Viscous Pore Fluid in Centrifuge Models

Abstract: In geotechnical modeling, the use of a pore fluid having viscosity greater than that of water is a well-established method of satisfying the scaling laws relating to movement of pore fluid through the soil during dynamic loading events. This has often been achieved with either silicone oil or mixtures of water and glycerol. However, there are a number of inherent drawbacks and difficulties in using silicone oil in particular, and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has been used recently with success. This paper presents test data documenting the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration. The relative performance of the fluid is illustrated with data from two centrifuge model tests, one with pure water as the pore fluid and one with an HPMC solution having viscosity ten times that of water.

Experience with the use of methylcellulose as a viscous pore fluid in centrifuge models. technical note

Abstract: Pore fluids having viscosity greater than water are sometimes used in geotechnical centrifuge model tests to more accurately satisfy the scaling laws relating to movement of pore fluid through the soil when modeling dynamic loading events This is frequently done using either silicone oil or mixtures of water and glycerol There are some drawbacks in using silicone oil and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has recently come into use The authors present test data showing the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration The relative performance of the fluid is illustrated with pore pressure dissipation data from two centrifuge model tests involving earthquake simulations One test was done with pure water as the pore fluid and the other test was done with an HPMC solution having viscosity ten times that of water

Mechanism controlling the shrinkage limit of soils

Abstract: Based on the results from an extensive experimental program involving a number of natural soils as well as pure clays with extreme clay mineral types, namely kaolinite and montmorillonite, as the principal clay minerals, a hypothesis explaining the mechanisms controlling the shrinkage limit has been proposed. The shrinkage limit of a natural soil has been shown to be primarily a result of the packing phenomenon, which in turn is governed by the grain-size distribution of the soil; the shrinkage limit of pure clays appears to be affected by the fabric also. Even though clay-sized particles play an important role in the shrinkage phenomenon, there is an optimum clay content at which the shrinkage limit of a soil can become minimum. It has been further illustrated that the shrinkage limit is not at all related to the plasticity characteristics of the soil. As the factors governing the shrinkage limit are entirely different from those controlling the swelling of soils, the shrinkage limit cannot indicate the swelling behavior of the soil.

Application of bender elements in measuring Gmax of sand under K0 condition

Abstract: A new application of bender elements to measure the small strain shear modulus of sand in multiple shear planes under anisotropic loading is developed. The tests were conducted in a specially designed oedometer with the side of the ring smoothed by a Teflon sheet. The soil used in the tests is clean angular pool filter sand. The effects of size of bender elements on the results of shear wave velocity measurement are discussed. Shear modulus in four different shear planes during a loading-unloading cycle is presented. The results of experiments are compared with the Hardin-Blanford equation on Gmax, which shows good agreement. The influence of side friction of the oedometer is investigated.

Influence of viscous fluids on properties of sand

Abstract: The time scale for dynamic events differs from that for consolidation events if the same soil and pore fluid as in the prototype are used in a model test. In order to satisfy the scaling relationship for dynamic centrifuge tests, viscous fluids such as silicone oil or glycerin-water mixtures have been used as the pore fluid. The use of a pore fluid with higher viscosity will significantly reduce the permeability of a soil, making it possible to achieve the same time scale. However, the use of viscous fluids may also affect the mechanical properties of soils such as strength and stress-strain relationship. This paper presents results of permeability tests and triaxial tests on two types of sands over a range of void ratios. It is found that using a glycerin-water mixture as the pore fluid has little effect on the strength and stress-strain relationship of Ottawa sand No. 40. For tests with both silicon oil and glycerin-water mixture as permeants, coefficients of permeability are inversely proportional to the viscosity. However, at small hydraulic gradients, it was observed that the highly viscous fluids can cause clogging of flow in sand, especially for silicone oil in dense sand. It is recommended that when a viscous fluid is used in a centrifuge test, it is desirable to conduct a sequence of laboratory tests to make sure there is no unexpected influence on the properties of a soil.

Development of an Accelerated Creep Testing Procedure for Geosynthetics, Part II: Analysis

Abstract: A procedure for extrapolating creep strains to longer time intervals was developed The procedure was based on applying time-shift factors to creep strain curves at elevated temperatures to establish a master strain curve for longer time intervals The procedure was applied to creep test results on high density polyethylene (HDPE) geogrid tested at creep loads up to 40% of its maximum tensile strength Tmax and at temperatures up to 72°C (160°F) Temperature creep curves of 1000-h tests were shifted along the log-time scale to create 10 000-h master strain curves at each loading level The established master curves were compared with experimental results of 10 000-h creep tests at room temperature and at the same loading levels The shift factors were then applied to the creep curves to predict creep response for a duration of more than 100 000-h (about two cycles shift on the log-time scale from the initial 1000-h tests) The analysis demonstrated the applicability of applying shift factors to elevated-temperature creep test results to predict the response at longer times for this type of geogrid The analysis was applicable to creep loads up to 40% Tmax The procedure, however, did not accurately estimate creep response at higher loading levels and temperatures where accelerated creep failure occurred

Evaluation of True Cν and Instantaneous Cν, and Isolation of Secondary Consolidation

Abstract: It is shown that the presence of a distinct straight line in the initial portion of settlement versus the square root of time plot indicates that soil follows theoretical behavior and that there is no initial and secondary compression in the straight line portion. If the coefficient of consolidation, c v , is determined using the data of only this portion, it can be regarded as the true c v . Secondary consolidation essentially starts after 60% consolidation and runs superposed over the primary consolidation. Its effect is to gradually decrease c v so that at every instant of time it is a new Terzaghian soil with a new c v and other consolidation parameters. Characteristics of linear and semi-log plots of U versus U, where U is the degree of consolidation and U is the theoretical velocity, are used for determining true c v and instantaneous c v , and for isolation of secondary consolidation from the experimental consolidation curve.

Particle size analysis of lime-treated marine clays

Abstract: Lime is commonly used to improve the engineering behavior of marine clay. But there is a need to investigate the lime-attributed changes in a particulate system in a marine environment. Lime columns 50 mm in diameter and 500 mm in length were installed in test tanks 600 mm in diameter at a depth of 550 mm, while lime injection was attempted in a test tank, 1000 by 1000 by 750 mm. The present investigation deals with experimental work carried out in the laboratory using lime column and lime injection techniques to stabilize an Indian marine clay in a salt water environment. Different inorganic additives were used with lime as column filler material to study the effect of lime-attributed changes occurring in the particle growth of soil systems. Grain-size distribution tests and SEM technique were carried out to study the lime-induced changes on the constituent particles. The test results indicate that there is an increase in the size of clay particles towards silt or fine sand fraction due to lime treatment. The formation of aggregates due to lime-soil reactions can be seen in the micrographs of different lime-treated soil systems, and the same has been confirmed using the SEM technique.

Methods for predicting shale durability in the field

Abstract: Durability of shales and other weak rock is an important parameter describing the material's susceptibility to breakdown upon exposure to water or during construction work. While laboratory methods have been developed to measure durability, no correlations between laboratory results and simple field tests have been determined. The results of this study show that certain field parameters can predict slake durability with acceptable accuracy. The recommended field tests, in order of desirability, are slake index, jar slake, hammer rebound, and NGI “Q” value. Single variable and multiple variable linear regression equations are given, including equations conservatively modified so that 95% of the slake durability values are underpredicted.

Development of an axisymmetric field simulator for cone penetration tests in sand

Abstract: The calibration chamber has been an important research tool in establishing interpretation procedures for cone penetration tests (CPTs) in sand. A new simulator system capable of simulating axisymmetric field conditions has been developed. This system is an improvement over conventional calibration chambers and enables CPTs to be calibrated under minimal boundary effects. The new simulator consists of a stack of 20 rings to house the sand specimen. These rings are lined with an inflatable silicone rubber membrane on the inside. The boundary expansion and stress are measured and individually controlled, respectively, at each ring level during the CPT. The soil from physical boundary to infinity is simulated using a nonlinear cavity expansion curve derived from a lateral compression test on the specimen. Results from a series of CPTs show that, at relative densities of approximately 80%, the cone tip resistance values agree within 4% as the diameter ratio of the physical specimen over cone varies from 18 to 22. This paper describes the unique features of this field simulator, presents available CPT data performed in the simulator, and discusses its implications on future calibration tests.

Assessment of damage to geomembrane liners by shredded scrap tires

Abstract: This paper presents the results of a field and laboratory study performed to assess damage to the geomembrane liner caused by using shredded scrap tires as a leachate drainage layer material in landfills. The field testing was performed to assess the damage that occurred to the geomembrane liner during construction and included nine tests conducted with different combinations of tire chip size and thickness, both with a geotextile and without a geotextile overlying the geomembrane, and under different loading conditions. The laboratory testing was performed to characterize the shredded tires, particularly their size distribution, hydraulic conductivity, compressibility, and chemical resistance. The laboratory testing also included performing simulation testing to determine the extent of damage that occurs to the geomembrane liner by the shredded tires under long-term waste-loading conditions. The damage that occurred to the geomembrane liners in both field tests and simulated laboratory tests was determined by visual observations as well as by conducting multi-axial tension tests, wide strip tension tests, and water vapor transmission tests on the exhumed geomembrane samples. Based on these results, a 0.46-m (18-in.)-thick layer of secondary shred tire chips, with an average size of 7.6 cm, placed over a 543-g/m2 (16-oz/yd2) geotextile installed over a geomembrane liner using low-ground-pressure (

Centrifuge Testing of Vertically Loaded Battered Pile Groups in Sand

Abstract: In order to develop a coupled bridge superstructure-foundation finite element code (FLPIER) that is capable of modeling both plumb and battered pile groups, a series of centrifuge tests on battered pile groups was conducted at the University of Florida. This paper reports the results of such tests on vertically loaded fully instrumented 3 by 3 and 4 by 4 battered pile groups in loose to medium sands. These tests simulated 0.43 m wide by 13.7 m long square piles founded in loose (D sub r = 36%) and medium dense (D sub r = 55%) sands at three diameter spacing. The axial load and shear in each pile were measured during the tests. Numerical analysis was also carried out to predict the battered pile behavior using FLPIER. The results showed that the vertical capacity of a battered pile group was slightly larger than that of a corresponding plumb pile group. The shear forces and bending moments in battered piles induced by design vertical loads were approximately one third of the ultimate lateral capacity.

Model Tests for Uplift Resistance of Piles in Sand

Abstract: An experimental program using large model piles in sand was conducted to study the shaft resistance behavior of piles subject to uplift loads. Model single pipe piles of different diameters (45 to 178 mm) were subjected to static uplift loading to failure. The piles, which had an embedded length of about 1.7 to 2 m, were installed in a large test pit (3 by 3 by 3 m) by three different methods (driving, jacking, and a reference undisturbed method with negligible lateral displacement) to assess the influence of method of installation on shaft resistance. The tests were performed in two initial densities of a sand (loose and dense). The experimental results were analyzed statistically. The results show that the initial sand density and the method of pile installation are the most significant factors that affect uplift capacity. Installation methods that cause less disturbance give higher uplift capacity. Unit shaft resistance could be reduced as much as by half depending on the method of pile installation relative to the undisturbed method. The displacement at the ultimate uplift load is in the range of 5 to 12.5 mm and independent of soil type and pile diameter, but depends on method of pile installation.

Commentary on Marchetti Flat Dilatometer Correlations in Soils

Abstract: This paper provides commentary on the many uses of the flat dilatometer test (DMT) developed by Marchetti in 1975. The test has been used as a simple but repeatable means of obtaining information about a wide variety of soil properties and parameters. It is an expedient indexing tool for site stratification and evaluation of soil properties. The test is used to analyze soils primarily in North America, Europe, and Southeast Asia. The initial statistical trends were based on data from only eleven natural soils found primarily in Italy. Even so, the original empirical correlations have proved useful in obtaining approximate parameters for geotechnical analysis and design. A number of comparative studies, modified relationships, and new correlations have since become available in foreign soils, and several of these are reviewed in the present paper. The possibility of adopting generalized expressions for data reduction and the interpretation of soil properties is explored, particularly for evaluating the lateral stress coefficient, K sub 0, in clays from the dilatometer index K sub D. The test is useful for determining soil type, classification, and consistency for clays, silts, and sands. It provides information about stress history, undrained shear strength, shear modulus, consolidation, and pore water pressure to name just a few of the many soil parameters determined by the test.

Measurement of the contact angle of water on geotextile fibers

Abstract: The contact angle of water on geotextile fibers significantly influences capillary behavior. Measurements of the dynamic contact angle of tap water on geotextile fibers are reported for two geotextiles, as received from the manufacturer and after they had been treated (cleaned). There is considerable hysteresis between advancing and receding contact angles, as expected. Fibers from one geotextile have significantly lower contact angle cosines than the other, indicating that it is less wettable. The cleaning of geotextiles resulted in significant reduction in the advancing contact angles of fibers from one of the geotextiles but not the other. The heights of water capillary rise in strips of the geotextiles were also measured. Results showed that the contact angle measurements are helpful; but, information on pore sizes is also needed to predict capillary behavior.

Interpretation of Lateral Statnamic Load Test Results

Abstract: The Statnamic device has been used to test piles in the lateral direction. This paper describes a dynamic analysis approach for the prediction of the static lateral behavior of piles using the results of the Statnamic lateral test. The objectives of this analysis are twofold: to simulate the pile head displacement-time history observed during the test using the measured load time history at the pile head and varying the soil parameters along the pile shaft until a satisfactory match is achieved and to predict the static lateral load-deflection curve of the pile using the soil parameters established through the matching process. The dynamic analysis was used to analyze some Statnamic lateral tests, and satisfactory agreement between the computed and measured displacement-time histories was achieved. The predictions of the proposed approach in the given case studies were in good agreement with the static lateral load test results. The results obtained thus far suggest that the Statnamic lateral test and the described model are successful in the prediction of the lateral load-deflection behavior of piles. Both the Statnamic lateral test and the one-dimensional analysis are simple, fast, and inexpensive, and the approach promises to be very useful in the prediction of the lateral load-deflection behavior of foundations.

Theoretical Evaluation of the Transient Response of Constant Head and Constant Flow-Rate Permeability Tests

Abstract: A theoretical analysis is presented that compares the response characteristics of the constant head and the constant flow-rate (flow pump) laboratory techniques for quantifying the hydraulic properties of geologic materials having permeabilities less than 10−10 m/s. Rigorous analytical solutions that describe the transient distributions of hydraulic gradient within a specimen are developed, and equations are derived for each method. Expressions simulating the inflow and outflow rates across the specimen boundaries during a constant-head permeability test are also presented. These solutions illustrate the advantages and disadvantages of each method, including insights into measurement accuracy and the validity of using Darcy's law under certain conditions. The resulting observations offer practical considerations in the selection of an appropriate laboratory test method for the reliable measurement of permeability in low-permeability geologic materials.

Experimental modeling of the shaft capacity of grouted driven piles

Abstract: Pile foundations are widely used in compressible soils such as calcareous sediments. However, the friction capacity of driven piles in such soils tends to be very low, owing to severe reduction of the normal effective stresses at the pile-soil interface during installation of the pile, caused by densification of the soil. The shaft capacity may be increased by injection of grout along the pile-soil interface, referred to as “grouted driven pile” construction. A new apparatus for testing such a type of pile has been developed at the University of Western Australia. In this paper, the design of the apparatus and associated model piles are described, along with the grouting technique. Limitations of early versions of the apparatus and difficulties with grouting at small scale are discussed, and recommended solutions are presented. Results of tests performed on specimens of calcareous soils that were artificially cemented in order to reproduce typical in situ strengths are also presented.

Evaluation of Surface-Related Phenomena Using Sedimentation Tests

Abstract: This study attempts to evaluate the specific surface of fine-grained geomaterials using data collected during simple sedimentation tests. It is assumed that cation exchange processes affect clay layer spacing without leading to complete physical separation, that is no delamination. Based on an idealized parallel structure model, an analytical formulation of the problem is presented. The sedimentation tests are used to assess the sensitivity of clay-water systems to environmental changes. The parallel structure assumption is used as the basis for a simple framework to analyze the data from the sedimentation tests. The slope of the relationship between the final sediment volume and the ionic concentration, plotted on a log-log scale, is related to the specific surface, the double layer thickness, and to the specific gravity. A new parameter, the reactivity coefficient, where the reactivity coefficient equals the product of the specific surface, the double layer thickness, the specific gravity, and the mass density of water, is introduced to help identification of reactive clay-water systems. High values of the reactivity coefficient identify systems that are sensitive to changes in pore fluid characteristics. An experimental procedure is suggested to acquire relevant sedimentation parameters. Data collected during sedimentation tests of kaolinite, bentonite, and disaggregated Pierre shale, Macos shale, a Queenston shale are used to verify the model. Agreement between experimental data and the model suggests that this simple technique can be used to identify reactive shales in the field. Other applications arise in tailing pond modeling, drilling mud management, and clay liner reliability assessment.

A new apparatus for measuring oxygen diffusion and water retention in soils

Abstract: A new apparatus developed for measuring the diffusion of oxygen, or any gas, through a soil sample is described. The apparatus uses nitrogen pressure to change a soil sample's degree of saturation and can therefore minimize the effects of structural changes due to remixing and packing. As a consequence, some innovative methods are employed to simulate oxygen concentration versus time data obtained with the apparatus. A one-dimensional semianalytic diffusion model is used to back-calculate diffusion coefficients based on laboratory data. Results for a local silt and a sand are presented to illustrate the utility of the apparatus. The apparatus is shown to perform well and provide gas diffusion coefficients similar to those reported by other researchers. The major advantage of the apparatus over other published methods lies in the fact that both the soil-water characteristic curve and oxygen diffusion coefficient at any degree of saturation can be obtained on the same soil sample in a single suite of tests. These two parameters are required for several geotechnical and geoenvironmental engineering designs involving unsaturated soils, such as the use of soil covers for mitigating acid drainage in sulfide-bearing mine waste.

Analysis of consolidation data by a non-graphical matching method

Abstract: Conventionally the laboratory time-compression data from an odometer test are analyzed by graphical methods. This involves the determination of initial compression, delta(i), total primary consolidation, delta(100), and coefficient of consolidation, C-v. The advent of computer-controlled data-logging systems calls for adoption of non-graphical techniques for analysis of consolidation test data. In this Technical Note a non-graphical matching method is proposed for analyzing the time-compression data. The values of delta(i), delta(100), and C-v can be obtained by direct matching with the theory. The computed time-compression curve for this C-v value matches very well with the experimental data in the primary consolidation phase. The proposed method is also applicable to consolidation under conditions of radial drainage. The method will be very useful if the data are collected through computer-driven data-logging systems

The Application of Computer-Assisted Tomography in the Analysis of Fracture Geometry

Abstract: An experimental study was conducted to investigate the surface characteristics of an oil sand fracture. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tension test. A computer-assisted tomography scanning analysis was performed to determine the fracture geometry. The fracture was shown to be a variable aperture system that would have significant effects of the permeability of the fracture. The aperture distributions of the fractures were found to follow a log-normal distribution, similar to that of previously studied rock fractures.

Evaluation Tests for Colloidal Silica for Use in Grouting Applications

Abstract: Colloidal silica (CS) is a low-viscosity chemical grout that can be injected to form an impermeable barrier in the subsurface. Such a barrier was proposed to be placed under a disused unlined retention basin at the Savannah River site. Specifications for the CS grout were included in the bid package, including performance tests. The product must meet requirements of low viscosity, low permeability when gelled, and controllable gel time both in vitro and in situ. Bidders submitted samples for evaluation, and this paper describes the tests that were conducted and presents typical results. Gel time in soil was assessed by injection tests in packed-soil columns and the monitoring of gelling in the columns. Injection tests were designed to ensure that grout injection would not be impeded by rapid gellation caused by contact with soil. The requirement was that the injection pressure during 2 h of injection be less than 2.5 times as great as the injection pressure without gelling. Gelling of the grout in the soil columns was monitored by repeated falling-head tests that showed that mobility decreased to zero during the prescribed time for gelling in situ.

Effects of Test Duration and Specimen Length on Diffusion Testing of Unconfined Specimens

Abstract: Effective diffusion coefficients, D*, of chloride and zinc diffusing in saturated, unconfined specimens of a compacted sandclay mixture are measured for three specimen lengths, L (2.91, 5.83, and 11.60 cm) and three test durations (7, 14, and 21 days). For a specimen length of 2.91 cm, both the chloride and zinc D* values tend to decrease with increasing test duration, possibly due to the measurement of concentration-dependent D* values. For a 14-day test duration, no consistent trend in D* with specimen length is observed, but the overall effect of specimen length on D* is minor relative to the range of measured D* values. A 21-day test duration provides the best correlation between the D* values based on reservoir concentrations, D*Res, and the D* values based on soil concentrations, D*Soil, for chloride for a given test regardless of the specimen length. The effect of test duration on the correlation between D*Res and D*Soil for zinc is minor based on the relatively narrow range of measured zinc D* values. The observed effects of specimen length on the correlation between D*Res and D*Soil for a given test are consistent with the more uniform final porosity distributions in the shorter specimens and the contrasting effects of the non-linear distributions in porosity and dry density that become less significant as the specimen length increases.

Compaction curves on volume basis

Abstract: The compaction curves of soils are generally expressed in terms of dry density and water content. While this representation serves well to compare the efficiency of compaction of different soils whose specific gravities lie in a narrow range (2.6 to 2.7), it fails for materials of varying specific gravities. It has been shown that for fly ashes with a wide range of specific gravities the degree of compaction of different fly ashes cannot be compared from conventional compaction parameters. Compaction curves expressed on a volume basis, viz., volume of solids per unit volume of compacted sample or porosity or void ratio and volume of water per unit volume of solids, can better serve to explain the compaction. Further, it has been shown that for fly ashes of different specific gravities only compaction parameters expressed on a volume basis can be interrelated.

T Chart to Evaluate Consolidation Test Results

Abstract: Using Terzaghi's degree of consolidation, U, and the time factor, T, relationship, if M-U1 and M-U2 (M-U1 not equal M-U2) are slopes of the U-root T curve at any two time factors T-U1 and T-U2, then it can be shown that a unique relationship exists between T-U2/T-U1, M-U1/M-U2, and TU, (or TU2), and knowing any two of these, the third can be uniquely determined. A chart, called the T chart, has been plotted using these three variables for quickly determining T and U at any experimental time, t, to determine the coefficient of consolidation, c(v), corrected zero settlement, delta(o), and ultimate primary settlement, delta(100). The chart can be used even in those cases where settlement and time, at the instant of load increment, are not known.

Design and performance of soil-pile-slip test apparatus for tension piles

Abstract: The T-Z method is the common method available to estimate load-displacement behavior of tension piles. Obtaining accurate T-Z curves from laboratory tests has a vital role in better estimation of pile behavior. The available apparatus used to obtain laboratory T-Z curves (Coyle and Sulaiman 1967) suffers from a set of limitations. A soil-pile-slip test apparatus has been designed at the University of Nottingham (UK) to obtain better T-Z curves for tension piles. This paper presents the design details and the testing procedure of the soil-pile-slip test apparatus. A set of T-Z curves obtained using this apparatus is analyzed, which provides insight into the mechanism of soil-pile-slip dilation near the pile surface.