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The paper presents hydrogeologic properties for a leaky till-mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K' = 7.2 x [10.sup.-9] m/s, transmissivity T' = 2.3 x [10.sup.-8] [m.sup.2]/s, and storativity S' = 2.7 x [10.sup.-4], and for the underlying fractured bedrock aquifer: T = 6.5 x [10.sup.-6] [m.sup.2]/s with an average fracture aperture of 46 µm and hydraulic conductivity [K.sub.f] = 1.3 x [10.sup.-3] m/s. These results should describe similar unweathered coarse-grained till-mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations. Key words: aquifer, fractured bedrock, till, transmissivity, hydraulic conductivity. Le present article decrit les proprietes hydrogeologiques d'un systeme aquifere rocheux fracture, presentant des fuites et recouvert d'un till, en se basant sur des essais geophysiques et hydrauliques realises sur le site d'un drumlin, dans le nord-est du Massachusetts, aux Etats-Unis. Ce site comporte un aquifere rocheux fracture recouvert d'un aquitard de till de 30 m d'epaisseur, non altere et compose de grains grossiers. Les parametres hydrauliques en regime permanent a l'echelle decennale ont peu varie jusqu'a ce qu'on commence a effectuer des pompages saisonniers a des fins d'irrigation au cours des dernieres annees, ce qui a entraine une baisse importante annuelle du niveau de l'aquifere et l'apparition de fuites provenant du till recouvrant ce dernier. Des series de donnees sur la charge hydraulique sont recueillies a courts intervalles dans des puits de surveillance pour enregistrer la reponse hydraulique de l'aquifere au pompage aux fins d'irrigation. Ces donnees, associes aux resultats des essais d'injection et de purge realises a echelle reduite dans les puits de surveillance, permettent de caracteriser le comportement hydrogeologique de ce systeme hydrologique souterrain. L'enregistrement chronologique de donnees dans les puits fores dans le substratum a confirme la presence de nombreuses fractures oU se produisent des ecoulements. L'analyse en continu et a taille reelle de la reponse de l'aquifere rocheux fracture au pompage aux fins d'irrigation genere des valeurs de transmissivite qui concordent avec celles obtenues lors des essais de purge effectues a echelle reduite et sur une courte duree. La faible conductivite hydraulique du till influe beaucoup sur la reduction du niveau de l'aquifere rocheux fracture. Les valeurs ajustees issues de l'ensemble des series de donnees et des analyses aboutissent aux proprietes suivantes, qui caracterisent le till non altere de 30 m d'epaisseur : conductivite hydraulique K' = 7,2 x [10.sup.-9] m/s; transmissivite T' = 2,3 x [10.sup.-8] [m.sup.2]/s; et coefficient d'emmagasinement S' = 2,7 x [10.sup.-4]. Les proprietes caracterisant l'aquifere rocheux fracture sous-jacent sont les suivantes : T = 6,5 x [10.sup.-6] [m.sup.2]/s; ouverture moyenne de fracture de 46 µm; et conductivite hydraulique de fracture [K.sub.f] = 1,3 x [10.sup.-3] m/s. Ces resultats devraient pouvoir decrire des systemes aquiferes rocheux fractures similaires, recouverts d'un till non altere compose de grains grossiers, et servir de donnees utiles aux analyses preliminaires effectuees avant n'importe quelle etude propre a un site particulier. [Traduit par la Redaction] Mots-cles: aquifere, substratum fracture, till, transmissivite, conductivite hydraulique., Introduction Pleistocene tills are wide spread in the Northern Hemisphere and, along with other glacial deposits, are often parts of major groundwater systems (Stephenson et al. 1988). Due to their [...]

The undrained remolded shear strength of soft clays is of importance in geosystem design, particularly for offshore structures. Common methods to estimate remolded shear strength, such as correlations with cone penetration data, direct measurement with an in situ field vane shear device, and laboratory measurements, produce varied results and can be particularly costly and time consuming. Full-flow penetrometers (T-bar and Ball) provide an alternative rapid method to estimate remolded shear strength and soil sensitivity through remolding soil by repeated cycling of the penetrometer up and down over a given depth interval. The cyclic penetration resistance degradation curve inherently contains information regarding remolded strength and sensitivity. The objective of this paper is to assess the ability of full-flow penetrometers to predict remolded strength and soil sensitivity, and to develop a suite of predictive correlations in which these properties can be estimated in the absence of complementary laboratory or in situ test data. To accomplish this, full-flow penetration profiles and cyclic tests were performed at five well characterized soft clay sites, which together represent the broad range of soils in which the penetrometers will be often used. A previously developed model for the reduction in penetration resistance with cycling is modified to predict the entire degradation curve, including the remolded penetration resistance using only measurements obtained during initial penetrometer penetration and extraction. Using field vane shear strength as the reference measurement, correlations are developed to predict soil sensitivity and remolded shear strength based solely on full-flow penetrometer data, which is particularly useful in site investigation programs where site specific data are not yet available or are sparse. Finally, the usefulness of these relationships is demonstrated by implementing them for two additional soft clay sites. DOI: 10.1061/(ASCE)GT.1943-5606.0000037 CE Database subject headings: In situ tests; Drainage soft soils; Clays; Sediments.

While improvements in equipment and sampling methods have enabled collection of better quality samples of soft clays for more reliable engineering design and performance prediction, current sample quality assessment methods typically require destructive laboratory testing performed long after samples are taken. This paper describes a nondestructive technique for sample quality assessment of soft clays using shear wave velocity. A portable bender element device was used to measure shear wave velocity ([V.sub.vh]) in the field immediately following collection of Sherbrooke block, tube, and split spoon samples of Boston blue clay. [V.sub.vh] values were compared to in situ values from seismic piezocone ([V.sub.SCPTU]) tests. The ratio [V.sub.vh]/[V.sub.SCPTU] was compared with results from a conventional, laboratory-based assessment method. Results indicate a consistent correlation between laboratory-based methods and the [V.sub.vh]/[V.sub.SCPTU] ratio, which ranges from [V.sub.vh]/[V.sub.SCPTU]=0.77 for the block samples to 0.28 for split spoon samples. The portable bender element device and nondestructive assessment technique offer the potential for field quality assessment and allow for real time adjustments to sampling techniques and/or more effective selection of samples for laboratory testing. DOI: 10.1061/(ASCE)1090-0241(2007)133:4(424) CE Database subject headings: Clays; Soil sampling; Velocity; Nondestructive tests; Laboratory tests; Shear waves.

We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and underdamped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 X [10.sup.-3] m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as much as 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction., Introduction Existing Slug Test Theory Slug tests provide a rapid and economical estimate of aquifer hydraulic conductivity (Butler 1998) and a substantial literature interprets the data. Hvorslev (1951) and Bouwer [...]

The foundation soil of an offshore Arctic gravity structure is subjected to complex loading conditions. In addition to radial shear stresses induced by the weight of a structure, large horizontal shear forces from ice loads can produce large rotations and even reversal in the direction of horizontal shear stresses acting on soil elements within the foundation soil. The Multidirectional Direct Simple Shear (MDSS) apparatus was developed to simulate, at the element level, these star of stress. The MDSS first consolidates a circular specimen under both a vertical stress ([[Sigma][prime].sub.vc]) and a horizontal shear stress ([[Tau].sub.hc] = [[Tau].sub.1]; setdown conditions). The specimen is then sheared undrained by applying a second independent horizontal shear stress ([[Tau].sub.2]; ice loading) at an angle [Theta] relative to the horizontal shear stress [[Tau].sub.1]. The experimental program of MDSS and Geonor Direct Simple Shear tests on normally consolidated Boston Blue Clay used [[Tau].sub.hc] = [[Tau].sub.1] = 0.2[[Sigma][prime].sub.vc] and varied [Theta] in 30 [degrees] increments from zero (shear in the same direction) to 180 [degrees] (shear in the opposite direction). The peak undrained resistance decreased almost twofold from [Theta] = 0 [degrees] to [Theta] = 120 [degrees], and the deformation behavior varied from very brittle at low [Theta] angles to becoming ductile at higher angles. These dramatic changes in foundation response are an important design issue.

This paper presents results of a laboratory investigation of the influence of the nonuniform stresses imposed by the Geonor direct simple-shear (DSS) apparatus on measured stress-strain behavior. The investigation concentrated on the influence of the apparatus on the measured strain-softening behavior of cohesive soils during constant volume (undrained) shear. Special DSS tests were conducted on an elastic material and cohesive soils at varying overconsolidation ratios. The experimental results clearly indicate that the nonuniformity of stresses imposed by the device during undrained shear causes a decrease in the vertical effective stress with increasing shear strain. This in turn causes a reduction in the measured horizontal shear resistance at large strains. The device-induced 'unloading' probably has relatively little effect on measured peak strengths in [K.sub.o] consolidated-undrained DSS tests but certainly contributes to the pronounced strain softening typically

This paper investigates predictive capabilities of the effective stress soil model MIT-E3 (described in a companion paper) through detailed comparisons with laboratory test data for Boston blue clay (BBC). The main focus of these evaluations is predictions of anisotropic stress-strain behavior using data from two special laboratory shear devices: the directional shear cell (DSC), and the multidirectional direct simple shear apparatus (MDSS). Input parameters are first estimated from standard types of laboratory data, including one-dimensional (K(sub 0)) compression and undrained triaxial shear tests. The DSC is a plane strain apparatus with the additional capability of controlling principal stress directions during shear. Measurements in this device include undrained shear tests with principal stress rotations at OCR = 1, and with fixed stress direction but different principal stress orientation at OCR = 4. The MIT-E3 model describes accurately the observed variations in undrained shear strength and stress-strain behavior in tests at OCR = 1, but is notably less reliable at OCR = 4. The MDSS has the same dimensions and boundary conditions as the Geonor simple shear apparatus, but can apply horizontal shear stresses in two independent directions. Measurements in the MDSS apparatus demonstrate the anisotropic properties of BBC at OCR = 1 induced by consolidation under an applied shear stress. MIT-E3 predictions are in excellent agreement with measured variations in peak shear resistance and prepeak stress-strain response.

The spatial variability of soil properties in situ is often modeled by trend surfaces and residual variations about trend. With the advent of computer-aided design, statistical procedures are now routinely applied to trend and residual estimation. A maximum likelihood (ML) technique is presented for simultaneously estimating spatial trends, measurement noise, and the autocovariance structure of residuals about spatial trends. This technique has more favorable statistical properties than traditional procedures, and these properties have an important practical advantage in that they lend themselves to incorporation in computerized data-analysis systems. Simulation experiments are used to verify small-sample-size properties of ML estimation and to draw conclusions on optimal boring layouts. The experiments show that analytical asymptotic properties of maximum likelihood estimators are approached even at the modest sample sizes common in geotechnical site investigations. Field vane strengths from a site-exploration program are analyzed using the maximum likelihood technique and comparisons are made with results obtained using traditional moment estimators.