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Time Domain Reflectometry (TDR) technology has been widely used in areas such as agricultural science, soil science, and water resources for measuring soil volumetric water content and is beginning to be used in geotechnical engineering. Calibration relationships, which generally relate the soil volumetric water content to TDR measured dielectric constant, are critical for the accuracy of TDR measurements. For TDR technology to be useful for geotechnical engineering practice, the calibration relationship needs to be expressed in terms of gravimetric water content. Besides, geotechnical engineering deals with more compacted earth materials, where the effects of soil density on TDR calibration are significant. This paper introduces an improved TDR calibration relation that accounts for the density of soil skeleton while at the same time is simple in format. Application of this calibration relationship shows that it significantly reduces data scatter and achieves more accurate results than other existing calibration relationships.

This study extends the use of time domain reflectometry (TDR) in geotechnical engineering, a technique originally developed to locate faults in transmission lines. Different elements of the TDR technique are developed, including design of TDR probes, probe installation/test methodology, and relationships between TDR measured dielectric constant and water content of soil. A coaxial probe is developed that is used for measuring the dielectric constant of soil prepared in a cylindrical cell or compaction mold. A multiple-rod field probe is developed that modifies previously developed multiple-rod probes and extends their capability for measuring the in-place dielectric constant of soil. An analytical solution is developed to determine the sampling volume and spatial bias of the TDR measurement. The solution is extended to study the effect of soil disturbance and presence of air gaps due to probe insertion. Experimental results validate the solutions. New relationships are proposed between dielectric constant and water content to eliminate some of the limitations of the existing calibration relationships. Several possible applications of the developed probes, test methodology, and calibration equations for measuring water content and density of soil are illustrated.

Unusually strong ground motions at deep stiff clay sites in the East San Francisco Bay area during the 1989 Loma Prieta earthquake called for examination of the dynamic response of this clay deposit and characterization of its dynamic properties. In this paper, correlations of Old Bay clay dynamic properties with various soil parameters (e.g., plasticity, void ratio, magnitude and duration of confinement, consolidation stress history) are presented and compared with the existing database on cohesive soils. A special effort is made to evaluate the effects of sample disturbance on the laboratory measurement of dynamic properties of stiff cohesive soils. The laboratory measurement of low-strain shear modulus and damping ratios is adjusted by considering the aging of the Pleistocene era clay deposit. These adjustments, though effective, are not sufficient to account for the effects of structural disturbance. Shear modulus is reduced significantly by structural disturbance, but, surprisingly, the damping ratio is found to remain largely unaffected.

A new model is proposed that allows for more general boundary conditions at both the active and passive ends of resonant column apparatus, especially those incorporated within the resonant column/quasi-static torsional shear devices. The improved three-degree-of-freedom model can be used in order to obtain more accurate measurements of the dynamic properties of tested soils when the base and the reaction mass of the apparatus are not perfectly fixed. This becomes particularly important in the hybrid resonant column/quasistatic torsional shear apparatus where the load cell located below the bottom platen provides additional flexibility to the passive end and the inertia of the reaction mass of the Hardin-type oscillator is relatively small. The analysis confirmed that use of the model is particularly important if the natural frequency of the soil-apparatus system is close to that of the passive end or reaction system, and that the calculated modulus and damping values can be highly inaccurate if simplified boundary conditions are assumed. Such situations especially occur when very soft soils, very stiff soils, or rock specimens are tested. The solution was programmed in a spreadsheet where both the shear modulus (G) and the damping ratio (D) are established for a given set of measurements and apparatus constants. In order to obtain the necessary apparatus constants, calibration procedures are presented for a resonant column/quasi-static apparatus. Comparison of existing models and the new solution to the observed response for a rubber testing specimen showed that the three-degree-of-freedom assumption is more accurate in modelling the apparatus boundary conditions.

A two-degree-of-freedom model is proposed to study the effects of imperfect fixity at the active end of the spring-top resonant column apparatus. A computer program using the SYMPHONY spreadsheet is developed to calculate the dimensionless frequency, F, from which the modulus can be determined. It is found that the effect of reaction mass through the parameter, Tr; on dimensionless frequency, F, cannot be ignored if Tr

The liquid limit test is one of the most widely used tests in the soil engineering practice. Several properties, including mechanical properties (for example, compressive index), have correlations with the liquid limit. In this paper detailed investigations of the liquid limit of soil mixturs have been carried out using bentonite, kaolinite, sand (coarse grained, fine grained, rounded and angular shaped), and silts. Based on the results obtained, it has been shown that the liquid limits of soil mixtures are not governed by the linear law of mixtures. While the shape of the sand was not found to influence the liquid limit, the size of the sand particles had a definite influence. Liquid limit obtained by the cone method is lesser than the limit obtained by using the Casagrande apparatus. A good relationship exists between the results of these two methods. A procedure for obtaining the liquid limit of low plastic soil has been suggested.

An investigation was conducted to determine the variability of borehole shear test results obtained in testing soft and medium consistency marine clays. A statistical comparison of the results of stage tests obtained by different operators at two test depths at a research site is made. An additional comparison of the results obtained from stage tests and fresh shearing and a brief discussion of the linearity of both types of tests is also made. A short summary discussing the applicability of the results is also presented.

A series of unconsolidated undrained triaxial compression tests was carried out on specimens of reconstituted kaolin to determine the effects on modulus and strength of two different methods of sample storage after unloading. These results are compared with the values obtained when no unloading occurs, and when unloading is followed immediately by testing. It is seen that use of a simple sample compressor to restore the in-situ vertical effective stress in the specimen is very successful in reducing the deterioration of samples between unloading and testing.

Geotechnical centrifuges have been seen to date principally as research machines. A role is now suggested in which centrifuges of modest size and cost can contribute usefully to the education and training of geotechnical engineers in college laboratories. One such machine, which has been used in teaching for 15 years, is described, and examples of the results of a series of simple demonstrations are shown.

This technical note presents a new method to transport liquefiable soils from the investigation site to the laboratory. The development of this method resulted from research on liquefiable soils from the Imperial Valley, CA. This method is based upon the application of a slight vacuum on the pore water of the soil. The vacuum decreases the pore pressure, and therefore increases the effective confining stress. Sample recovery and integrity were compared with experiences of others. Comparisons were made in the sample quality after extrusion and sample preparation, as well as the variability of the test results. This method proved to be an improvement over previous techniques.

A standard accelerated weathering test using dimethyl sulfoxide (DMSO) was developed to simulate the chemical degradation of basaltic rock. The final development of the standard test involved a study of the interaction of DMSO with clay standards and an investigation of the test condition parameters affecting an existing DMSO test procedure. The weighted loss reported under the existing test procedure (similar to the sodium sulfate soundness test) was affected by the aggregate particle size, specimen mass, immersion time, and container geometry. In the recommended standard DMSO accelerated weathering test, aggregates in the particle size range of 2.4 to 4.8 mm are immersed in a container of DMSO for a period of five days. The mass loss determined by re-sieving the material on a 2.4-mm (No. 8) sieve after five days immersion provides a measure of durability. Immersion of basaltic aggregates in DMSO results in a greater breakdown owing to the type and concentration of ions contained in the rock matrix. Specifically, it was found that DMSO reacts with the cations held to the swelling clay minerals in the aggregate. The results from Atterberg limits tests indicate that DMSO substantially reduces the liquid limit for clays with high activities and increases the liquid limit for clays with low activities. The changes in the liquid limits were influenced by the interaction of DMSO with cations held on the surface of the clay mineral and the ability of DMSO to donate hydrogen ions.

The compressibility of a typical horticultural peat has been studied in the laboratory. Compressibility is an important factor in the processing of this material since volume governs the cost of shipping. The final reconstituted volume and the appearance of the peat after shipping must also be taken into account for marketing. Compression tests have been carried out on a horticultural peat from Newfoundland. Simple equations relating initial water content, relative volume change, and vertical applied pressure are proposed. A fluff factor has been defined, and it was found to decrease with the maximum applied pressure. Finally the results obtained in the laboratory are applied to storage and processing examples that are encountered in the horticultural peat industry.

The apparatus described in this technical note has several distinctive features. Seepage and force boundary conditions can be controlled separately and strictly. The stress of the specimen during the consolidation process can be controlled. The specimen can be controlled in a plane strain rate. The special structure of the internal and external drainage layer ensure that water flows freely in the seam. The device works without time suspension, so that the process of seepage and loading can be continuous.

A test system and procedures were developed to investigate ice forces on offshore structures with the technique of centrifugal modeling. The development progressed through four design stages associated with (1) the model container strong box, (2) the ice sheet formation system, (3) the model structure drive system, and (4) the instrumentation. The components were developed separately before incorporation into the final system. The test apparatus developed included an aluminum strong box with a motor driven model structure. The ice sheets were formed by prolonged application of vaporized liquid nitrogen. Temperatures, loads, and displacements were measured with thermistors, strain gages, and a linear variable differential transformer (LVDT), respectively. The test results indicate a relationship between ice thickness, temperature, and time may be used to create an ice sheet of predetermined thickness on the centrifuge. The test results from ice lateral load pile tests conducted with the system developed compare favorably with the results obtained by other investigators.

A finite strain consolidation test with a constant surcharge to determine the compressibility (e − σ′) and permeability (e − k) relationships of very soft clay is proposed. The method uses Gammarays and pore pressure transducers to measure density and pore pressure profiles, respectively, at various times of the test without hindering the consolidation process. The constant surcharge applied accentuates the changes in density and pore pressure profiles enabling them to be measured reliably. These profiles are then used to determine the compressibility and permeability of the soft clay. A test is carried out to extract these properties, which are used in a finite strain consolidation theory to predict the settlement, void ratio, and pore-pressure distributions of other tests done under different initial and boundary conditions. The predictions are found to agree well with the experimental data, thus suggesting that the properties determined are accurate.

The shortcomings of the conventional methods of determining the liquid limit using the Casagrande apparatus and the plastic limit by rolling soil balls by hand have led to the investigation of the fall cone (cone penetrometer) as an alternative. The use of the fall cone test to determine the liquid limit has long been adopted by several countries, but the proposal to use this test to determine the plastic limit as well, redefined on the basis of a strength criterion, is rather recent. In this paper the liquid and the plastic limits as determined by these two procedures for a number of natural soils and artificial soil mixtures are presented. A comparative and critical survey of experimental results involving the use of various cones to obtain consistency limits is also included.

The tiltmeter described consists of an electrolytic sensor (a glass jar containing an electrolyte and six electrodes) and a portable AC digital conductivity meter, which reads conductivity changes resulting from tilting deflections. The tiltmeter has a sensitivity of 2 to 8 min of arc/cmu (conductivity meter unit), with a measurement range of more than 45 deg. This tiltmeter measured earth flow subsurface movements reliably. It was easy to install and read.

The heat and moisture transfer characeristics of a silt from the Mackenzie River Valley have been determined in a laboratory investigation. A dual gamma-ray scanner was used to measure the changes in density and volumetric moisture content along the soil samples. The coefficients of soil-water diffusivity under isothermal conditions and under temperature gradients have been obtained. The development of a calibration curve for the analysis of gamma-ray readings has been described. The shortcomings of the procedures used for the measurement of transport coefficients have been discussed.

Over recent years, several geotechnical explorations in clay deposits have shown the flat dilatometer test (DMT) to provide reasonable estimates of in-situ overconsolidation ratio with depth. Why should the horizontal stress index (KD = initial contact pressure minus hydrostatic pressure normalized to the effective overburden stress) show an empirical trend with over consolidation ratio (OCR)? It is postulated that, since the closing pressure and contact pressures are nearly equal, the initial contact pressure in clay is an approximate measure of the total pore pressure induced during penetration of the dilatometer blade. Published data from a clay site tested by a special DMT having a pore-pressure sensor, as well as piezocone/dilatometer data from seven other sites, support this hypothesis. Since the pore-pressure response of clay is influenced by the in-situ OCR, the initial effective DMT contact pressure can be used to profile the stress history.

Procedures for measurement of percent compaction and several related practical issues are discussed. When measuring percent compaction, the “maximum” unit weight should be determined for each field unit weight test or nuclear unit weight measurement because minor differences in gradation and grain shape that are neither visually observable nor apparent from conventional gradation tests can have a significant effect on the “maximum” unit weight. A one-point compaction test should be performed as a minimum in most cases to reduce errors and the number of tests needed, to help focus on the soil type, and to help reduce conflicts with contractors. It would be very desirable to standardize on the use of only one compaction test for all types of construction control. Use of multiple compaction tests in specifications for various fill types causes confusion in practice without adding any complementary benefit. ASTM Test Method for Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 10-lb (4.54-kg) Rammer and 18-in. (457-mm) Drop (D 1557) is the test preferred by the author for controlling fill in dam embankments, building foundations, highways, and other fills and for establishing the degree of compaction of natural soils. Since the “maximum” unit weight is not a true maximum, it is suggested that the value measured with the selected standardized test be referred to as the index unit weight (IUW). Field unit weight tests for compaction control should be done within one layer, below surface disturbance, and in representative locations. Compaction test procedures for measurement of the index unit weight of clean sands and a discussion of the effects of grain breakage are presented.

Measurement of unsaturated soil volumes can be used to monitor drying shrinkage and allows calculation of the volumetric air content/moisture content relationship. From this relationship, the onset of significant desaturation can be established as a bound to the validity of conventional soil testing under saturated conditions and of conventional analysis procedures for the particular soil. Measurement of soil volumes over the full range of drying shrinkage is difficult because the soil is liquid at high-moisture contents, but changes to a deformed, cracked, unsaturated solid when dry. The method of volume measurement should be accurate and consistent, since it is used to calculate small changes in the small volumes of air present in the soil. Ideally, it should not stress the specimen or interfere with drying. Further, the method should be capable of distinguishing any volumes of air in exterior cracks or depressions in the soil surface. Finally, the method should be easily repeatable to enable progressive measurements of soil volume during the drying process. A simple, fast method of soil specimen volume measurement is described, based on measurement of displaced volumes of toluene in a pycnometer-like flask. It is compared with a method of calculating volumes from one-dimensional measurements of specimen length and moisture content during drying.

An expedient technique of reducing, significantly, membrane penetration errors and bedding errors at the platens is presented. This technique consists of coating the specimen/membrane and specimen/platen interfaces with a film of liquid rubber of appropriate thickness and properties. This film of liquid rubber is then squeezed into the interstices by a small seatting load/pressure before completion of curing. The effectiveness of this technique is demonstrated by a series of testing.

A servo-controlled cuboidal shear device with automatic data acquisition system is described. Provisions are made for pore-pressure measurements with specially designed “needle” piezometers. Complete stress-strain curves can be obtained with strains up to 20%. The application of servo-control in Ko consolidation and strain controlled loading is illustrated with flow charts and experimental data.

A comprehensive laboratory investigation was conducted to examine the compressive response of stiff cemented clays subjected to cement removal under stress. Results indicate that removal of cementation bonds in a stressed, stiff, cemented clay can cause a increase in soil volume, with the void ration increasing to the level of equilibrium for the uncemented state governed by the condition of the soil free of cementation bonds. (The authors attribute this increase to the latent physico-chemical behavior of the soil caused by restraint in the normal consolidation process.)

A triaxial system capable of very accurate automatic control of stress and strain paths is described. The apparatus consists of the ordinary triaxial apparatus available in our laboratory, connected through an analog/digital (A/D) converter to a microcomputer fitted with a feedback control unit. The operation of the system is discussed, and some typical test results of kaolin normally consolidated both isotropically and anisotropically over a wide stress range followed by the undrained triaxial compression are presented. These results show the range as well as the accuracy of the stress paths that are attainable with this system.

A simple method for classifying caliche with respect to excavatability is presented. The method is based on the results of a laboratory testing program from which two empirical equations were derived, one relating seismic velocity to size-corrected point load strength index, the other relating seismic velocity to a newly proposed parameter, the comminuted uniformity coefficient. The effect of carbonate content also was investigated, but no correlation between carbonate content and either point load strength or comminuted uniformity coefficient could be established. The excavatability of the caliche is determined from the seismic velocity by the empirical correlations between seismic velocity and ease of excavation established by excavation equipment manufacturers. The results of this study were applied successfully to a number of excavations in caliche in Tucson, AZ.

A large liquefaction tank used to prepare sand for laboratory testing required a 107-cm (42-in.) diameter filter. The filter was needed to separate the sand from water diffusers below, to facilitate a uniform upward flow of water, and to filter out undersired fines. The chosen design consisted of two geotextile fabrics sandwiched between a perforated plexiglass sheet and a steel grating. Selection of the geotextiles was based on the fabrics' porosities, permeabilities, and pore sizes. The system has been a success and has required no maintenance in over four years of usage.

The paper describes how the Swedish Geotechnical Institute (SGI) currently proceeds in the evaluation of shear strength in cohesive soils. Information is given on how different test results and empirical experience can be weighted and combined to give the best possible estimation of the shear strength properties in cohesive soils. The procedure described has evolved during the continuing work at SGI as research results and practical experience from the Institute as well as others have been obtained and taken into consideration.

Development of boundary friction forces is a common problem in testing of materials, such as rock and concrete. This article reports on experimentations with different friction reducing pads, aiming at diminishing the side friction effects in polyaxial tests. This appears technically possible by using special Teflon®-grease pads, with optimum lubrication achieved at high pressures. Ineffective lubrication can cause an apparent increase of strength and Young's modulus. The volumetric changes under polyaxial stress states appear relatively little affected by boundary friction, contrary to the partial volume changes of ΔV2 and ΔV3.

A new simple shear device capable of measuring a complete set of stresses during simple shear deformation is described. This simple shear device tests a cuboidal specimen whose lateral sides are surrounded by a rubber membrane reinforced by a stack of Teflon® coated aluminum plates. One of the aluminum plates is used as a transducer to determine the lateral stresses on planes normal and parallel to the direction of shearing. A load cell located around the middle of the top boundary provides data to deduce the normal and shear stresses as well as the pore-water pressures. A sample set of results are presented to illustrate some of the advantages of this new simple shear device. The advantages include the ease of specimen preparation, the determination of the stress invariants, the pore-water pressures at the center of the sample, and the rotation of the principal axes of strain and stresses on a routine basis.

A large-capacity water balloon aparatus has been developed specifically for measuring the in-situ density of compacted high-way trench backfill. In operation water is expelled from a calibrated 6-L reservoir to displace a rubber membrane. A dual-valve system enables larger volumes to be measured by repeated filling of the reservoir. The apparatus is simple, robust, and inexpensive, and has been used to measure hole volumes up to 30 L, with depths up to 0.8 m. It is much smaller and more easily handled that previous medium capacity apparatuses. Proving trials have shown that the apparatus can reliably determine hole volumes to an accuracy of +0/−0.6%, which is a significant improvement over the performance of the standard small volume equipment.

While there exist many types of mechanical tests for use on geosynthetics, most seem to be more suitable for one type of system or another. This paper focuses on a test which may have widespread applicability to assess the strength of all types of geosynthetics. It is the forcing of a 50-mm (2.0-in.) diameter plunger through a horizontally fixed geosynthetic of 150-mm (6.0-in.) diameter. Such dimensions are common to the California bearing ratio (CBR) test apparatus used in assessing soil strength for road subgrades. In actuality, the test is not a puncture test, but is an axisymmetric strength test and should be considered as such. The unsupported geosynthetic is indeed in a state of tension. The stress conditions are well defined, which allow for stress and strain to be calculated and compared to the actual value as obtained in a plane strain (wide width) tension test. This approach has been followed in this study wherein a wide range of geosynthetics (geotextiles, geomembranes, geonets, and geocomposites) have been tested for CBR (puncture) strength and then calculations performed to determine stress and strain. These calculated values were then compared to those obtained in wide width tests. Results are interesting in that the average values of percent variation between wide width tensile strength and CBR calculated tensile strength for those geosynthetics tested are as follows: (1) geotextiles ±12%, (2) geomembranes ±33%, (3) geonets ±17%, and (4) geocomposites ±10%. It is felt that this type of test (which is basically an index test) is helpful in a number of situations, not the least of which is in assessing strength changes before and after exposure of various geosynthetic materials to chemical or biological incubation.