The volume-mass properties of an unsaturated soil can change significantly with changes in negative pore-water pressure (i.e., soil suction). Changes in the soil properties are hysteretic with respect to drying and wetting; however, it is commonly considered adequate to first focus on the drying behavior as a “reference behavior” and then estimate the effect of hysteresis. Unsaturated soils analysis can be based on two unsaturated soil tests readily performed in a geotechnical laboratory. These are: i.) the gravimetric water content versus soil suction test, and ii.) the shrinkage curve test. In addition to data reduction, calculations for subsequent unsaturated soil property functions, USPFs, (e.g., permeability function, water storage function, shear strength function, etc.), are substantial and time-consuming. The reported research study shows that a series of Spreadsheet templates can be used to greatly expedient and ease the calculation of other remaining volume-mass versus soil suction relations as well as other physical properties related to unsaturated soil property functions. The calculations involve: i.) integration, ii.) differentiation and iii.) regression analyses to best-fit published equations for unsaturated soils behavior. Estimation of the magnitude of hysteresis between drying and wetting can also be incorporated. The calculated USPFs can then be imported to numerical modeling software and used to model soil behavior of a saturated-unsaturated soil continuum.

The solution to the problem of beams and plates on an elastic foundation has been attempted in the past using various subgrade models developed by many researchers, one of the pioneers being Winkler. Most recently, a new calibrated and more advanced multifaceted continuum foundation model has been presented by Worku without neglecting any stress, strain, or deformation component in the continuum unlike previously proposed models.

The study of interaction between a plate and an elastic medium has useful applications in geotechnical engineering. This research investigates the use of a generalized continuum subgrade model of Worku for analyzing circular plates resting on an elastic foundation. The approach employed is both analytical and numerical. In the analytical work, the governing differential equations of an axisymmetric circular plate on a homogeneous elastic foundation has been formulated that incorporates Winkler and Pasternak-type subgrade models. Closed form particular solutions have been presented for different loading conditions of small and large circular plates after obtaining a general solution of the differential equations. A math solving software (i.e. Mathematica) is used to compute the deflections and internal actions in a spreadsheet program due to the complexity of the functions. In the numerical study a FEM based software (i.e. PLAXIS 2D) is used to calibrate the analyzed circular plate using the presented models by seeking adequate agreements with the FE outputs. At last, numerical examples are solved using these models and compared with PLAXIS 2D for small and large radii circular plates of some loading conditions. From the plots of the outputs, it is observed that the generalized models of Worku are suitable and more appropriate than classical models to analyze circular plates on elastic foundations.

Keywords: Continuum subgrade model, Circular plate, FEM, Mathematica and PLAXIS software.

The shear strengths of in situ large-scale rockfill are key parameters required in stability analysis of structures made of rockfills. These materials contain a wide range of particles from fine particles as fine as silt to coarse particles as large as boulders. Doing laboratory test using a full scale rockfill and respecting the minimum required ratio between specimen size to the maximum particle size, dmax, specified by divers standard is very difficult and overly expensive if not impossible. To overcome this difficulty scaling down techniques were proposed by excluding the over-size particles in sample preparing. The most popular scaling down techniques are scalping, parallel, replacement, and quadratic methods. Among theme, parallel method has gained popularity over the years and largely used. In this paper, the four scaling down techniques are reviewed along with some available experimental results. The reliability of these methods used to extrapolate the shear strength of in situ large scale rockfill is reviewed, analyzed and discussed.

Two main elements of earth pressure – vertical and lateral – must be considered in the design of structures such as tunnels and retaining walls, and during deep excavations. While vertical pressure is easy to determine by direct measurement, or calculated if the depth and material characteristics of the overburden are known, lateral earth pressure is difficult to measure accurately. Risks of unknown or inaccurately estimated lateral earth pressure include soil movement and wall collapse, which can lead to personal injury, and equipment and infrastructure damage, therefore knowledge of the lateral earth pressure is vital for sound infrastructure design and long term integrity. Vertical pressure can be converted to lateral pressure with the empirical coefficient K0, defined by Terzaghy as the coefficient of earth pressure at rest. The accepted theoretical approaches to estimate K0 are based on the Rankine and Coulomb theories; however, both make assumptions and often cannot be considered as accurate. There are several known laboratory tests for K0 determination, most of them requiring complicated and sometime cumbersome equipment. A new method for determining K0 was developed in the GHD Geotechnical Laboratory. A series of drained K0 tests were performed on saturated soil using standard triaxial equipment with some minor modifications. The objectives of this paper are to describe the experimental equipment and present and discuss the obtained results.

The strength-deformation-pore pressure characteristics of saturated clay under consolidated undrained (CU) triaxial compression are highly dependent on the applied strain rate. An increase in strain rate causes an increase in undrained peak strength, reflecting the viscous plastic behaviour of the material. Based on the theory of critical state plasticity, the increase in undrained peak strength due to the increase in strain rate could be modelled by an apparent increase in overconsolidation pressure or ratio (OCR). Since the OCR controls the loci of the yield surface or function, the yield surface becomes non-stationary (dynamic) and rate-dependent. Based on the strain rate dependency among the undrained peak strength, OCR and dynamic yield surface, this paper develops an interpretation technique to correlate the undrained strength parameters measured in CU tests with the Hvorslev drained strength parameters. The drained strength parameters are rate-dependent (viscous) cohesion and rate-independent (intrinsic) true friction angle. Data of CU tests on resedimented Boston blue clay will be processed and analyzed using the proposed interpretation technique.

An extensive laboratory testing program was carried out for recent transit expansion projects in the Toronto area. The testing included routine characterization index testing - moisture content, grain size distribution, Atterberg Limits and unit weights - and a suite of advanced testing consisting of approximately 181 triaxial compression test sets (in the order of about 540 specimens) to define the strength properties (friction angle, φ’, and the cohesion, c’) of the soils for use in design. In this paper, we present a summary of the characterization and triaxial compression results, classified using the physical properties of the TTC Soil Groups.
Two different sampling methods were used to obtain triaxial test samples conventional PQ coring and the faster Sonic coring method. A comparison of the results indicates that the sampling method (PQ or Sonic) had minimal impact on friction angle results, with the Sonic soil samples generally indicating a slightly lower friction angle when compared to those soil samples obtained using PQ methods.
A review of strength parameters recommended for various new developments and transit infrastructure improvement projects was carried out and compared to the results obtained from the triaxial compression testing. Based on this review it appears that geotechnical design engineers may be underestimating the strength of the soils in the Greater Toronto Area favouring to use more conservative values for friction angle and cohesion.