Effect of Secondary Impacts on SPT Rod Energy and Sampler Penetration

This paper explores the standard penetration test (SPT) hammer-anvil behavior and investigates the effect of secondary impact on SPT energy and sampler penetration. It is observed that the hammer-anvil behavior after the impact depends on the characteristics of the wave reflected from the sampler. The type-I secondary impact, which is dominant for N<25, is induced due to the rapid downward movement of the anvil and the recontact of the following hammer on the rebounding anvil. The maximum energy calculated by integrating force and velocity (EFV) is achieved immediately after the occurrence of the type-I secondary impact and an additional sampler penetration is triggered by the type-I secondary impact. The type-II secondary impact, which is dominant for N>50, is produced by the restrike of the pushed-up hammer on the resting anvil. The type-II secondary impact causes only recoverable anvil deformation and does not contribute to the maximum EFV energy. For N-values of 25–50, both or either types of secondary impacts happen. As N-value increases, the type-I secondary impact fade away progressively and the type-II secondary impact becomes more distinctive.     

Drop and Energy Characteristics of a Rotating Spray-Plate Sprinkler

A laboratory investigation was conducted to measure wetted radii and drop sizes and to estimate the energy characteristics of a rotating spray-plate sprinkler. Maximum wetted radii were positively related to increasing sprinkler elevation above an irrigated surface and increasing nozzle pressure. Nozzle diameter had a minimal effect on drop size, but nozzle pressure had a significant inverse influence. Energy parameters were calculated for sprinkler operational scenarios. Average kinetic energies over sprinkler-wetted areas were inversely related to nozzle pressure and the square of nozzle pressure. Rapidly and slowly rotating spray plate sprinklers had similar time-averaged specific power distributions. However, the rapidly rotating sprinklers had continuous rotational distribution patterns in space with relatively low peak specific power values that corresponded to natural rainfall intensities of about 20 mm/h. Slowly rotating sprinklers had discontinuous spatial distribution patterns with very high peak values that corresponded to natural rainfall intensities of about 200 mm/h.     

Correcting Liquefaction Resistance for Aged Sands Using Measured to Estimated Velocity Ratio

Factors for correcting liquefaction resistance for aged sands using ratios of measured to estimated shear-wave velocity (MEVR) are derived in this paper. Estimated values of shear-wave velocity (VS) are computed for 91 penetration resistance-VS data pairs using previously published relationships. Linear regression is performed on values of MEVR and corresponding average age. Age of the sand layer is taken as the time between VS measurements and initial deposition or last critical disturbance. It is found that MEVR increases by a factor of about 0.08 per log cycle of time, and time equals about 6?years on average when MEVR equals 1 for the recommended penetration resistance-VS relationships. The resulting regression equation is combined with the strength gain equation reported by Hayati et al. 2008 in “Proc., Geotechnical Earthquake Engineering and Soil Dynamics IV,” to produce a MEVR versus deposit resistance correction relationship. This new corrective relationship is applied to create liquefaction resistance curves based on VS, standard penetration test blow count, and cone tip resistance for sands of various ages (or MEVRs). Because age of natural soil deposits is usually difficult to accurately determine, MEVR appears to be a promising alternative.     

Prediction of Soil Properties from the Concepts of Energy Transfer in Dynamic Penetration Tests

Results from dynamic penetration tests are traditionally interpreted on the basis of empirical correlations, this being a frequent criticism to these tests. An alternative rational method of interpretation is proposed in this paper from which the energy delivered to the composition of rods is used to calculate a dynamic force that represents the reaction of the soil to the penetration of the sampler (Fd). Interpretation of soil properties both in sand and clay is based on this calculated dynamic force from which the internal friction angle and the undrained shear strength can be estimated. This is achieved from a simple combination of limit equilibrium analysis and cavity expansion theory. Case studies gathered from the Brazilian experience are reported in this paper to illustrate the applicability of the proposed approach.     

锤砧锤模联接方式的改造

介绍了锤钻锤模改造前后的使用状况和经济效益比较，认为新型配合适用于冷拔无缝钢管的生产条件     

Hydraulics of Stacked Drop Manholes

This paper presents the results of an experimental investigation on flows inside stacked drop manholes (SDM). An SDM consists of two identical rectangular or square manhole chambers stacked together at an elevation difference. SDMs for different conditions were assessed on their ability to dissipate the energy of the approaching flow and their suitability to perform adequately under different flow conditions. Flow regimes were classified based on the inflow conditions and geometry of the structure in the first chamber and downstream outflows in the second chamber. An analysis based on the integral momentum equation was developed to estimate pool depths and energy losses under critical flow conditions. A fully surcharged stage with inflow and outflow pipes running full was also tested and velocity profiles were measured at a horizontal center plane to the opening connecting both shafts. Additionally, air flow rates were measured to assess the air demand into a large-height SDM.     

Evaluating the Constrained Modulus and Collapsibility of Loess from Standard Penetration Test

Argentinean loess has mechanical properties highly dependent on moisture content. Sand and silt particles jointed by clay bridges and precipitated salts form macropores which undergo high volume decrease when loaded or wetted. The constrained deformation modulus is an important parameter for the assessment of settlement and to characterize loessical formations. This work analyzes experimental results obtained in double-oedometer test and standard penetration tests (SPT) performed in silty loess. Typical behaviors observed in double-oedometer test are related to the decrease of soil modulus, collapsibility, cementation, and presence of disseminated cementing nodules. Correlations between the constrained modulus, collapsibility, and the blow count from SPT are presented. The influence of disseminated nodules, moisture content, and collapsed soil structure on the constrained modulus and collapsibility of loess is highlighted.     

Effect of Penetration Rate on Penetrometer Resistance in Clay

This paper discusses the effects of penetration rate on the penetration resistance in soft clay for various shaped penetrometers (cone, T-bar, ball, and plate) and for T-bars with different aspect ratios. Constant rate (“normal”) and variable rate (“twitch”) penetration tests, where the penetration rate was successively halved over eight steps with the penetrometer advanced by one or two diameters in each step, were undertaken in the beam centrifuge at the University of Western Australia. The tests were conducted on samples reconstituted from clay collected from the Burswood site in Western Australia. The twitch tests showed higher penetration resistance than the corresponding normal tests after the penetration rate had been reduced by a factor of 16 due to cumulative effects of partial consolidation. The penetration rate at which the resistance started to increase due to partial consolidation was used to estimate the consolidation coefficient, cv, of the reconstituted clay. The interpreted cv values were similar to values estimated from other consolidation data, both in the centrifuge and from laboratory Rowe cell and constant rate of strain consolidation tests. In addition, results from in situ twitch tests at the Burswood site were examined to evaluate viscous effects on the penetration resistance.     

Undrained Anisotropic Monotonic Behavior of Sand from In Situ Tests

A procedure for estimating the undrained stress-strain behavior of sand from drained self-boring pressuremeter and seismic piezocone penetration tests is proposed in this paper. The procedure offers an inexpensive alternative to laboratory testing and avoids the uncertainty of the empirical methods based on index measurements such as the Standard Penetration Test blow count and the tip resistance in a Piezocone Penetration Test (CPTU). To check its validity, the proposed procedure was used to infer the undrained triaxial stress-strain curves and the results were compared with laboratory triaxial tests on undisturbed samples. The undrained limit equilibrium stability of a dike was also assessed using the inferred stress-strain behavior to illustrate the usefulness of the procedure. The result of the stability analysis was found to be in qualitative agreement with the observed performance of the dike during a recent field experiment attempting to trigger static liquefaction.     

Computation of Cavity Expansion Pressure and Penetration Resistance in Sands

A cavity expansion-based theory for calculation of cone penetration resistance qc in sand is presented. The theory includes a completely new analysis to obtain cone resistance from cavity limit pressure. In order to more clearly link the proposed theory with the classical cavity expansion theories, which were based on linear elastic, perfectly plastic soil response, linear equivalent values of Young's modulus, Poisson’s ratio and friction and dilatancy angles are given in charts as a function of relative density, stress state, and critical-state friction angle. These linear-equivalent values may be used in the classical theories to obtain very good estimates of cavity pressure. A much simpler way to estimate qc—based on direct reading from charts in terms of relative density, stress state, and critical-state friction angle—is also proposed. Finally, a single equation obtained by regression of qc on relative density and stress state for a range of values of critical-state friction angle is also proposed. Examples illustrate the different ways of calculating cone resistance and interpreting cone penetration test results.     

Numerical Parametric Study of Piezocone Penetration Test in Clays

This paper presents a numerical model for the simulation of the piezocone penetration test that is used to carry out a parametric study of the piezocone penetration test in cohesive soils. The piezocone penetration is numerically simulated using an axisymmetric elasto-plastic large deformation finite-element analysis code. The numerical simulation is accomplished in two stages. First, the piezocone is expanded radially from an initial small radius (0.1ro) to the piezocone radius, ro, at the specified depth. Second, the continuous penetration of the piezocone is simulated by applying incremental vertical displacements of the nodes representing the piezocone boundary. The constraint approach is used to model the soil-piezocone interface friction. The Mohr-Coulomb frictional criterion is used to define the sliding potential of the nodes. The main objective of this paper is to present the numerical model and to investigate the effect of the lateral and vertical stresses and the overconsolidation ratio on the cone tip resistance and the developed excess pore pressure around the piezocone. The variation of the horizontal and vertical hydraulic conductivity coefficients on the developed spatial excess pore pressure and its dissipation are also investigated. The results of the numerical study are also compared with the miniature piezocone penetration tests in cohesive soil specimens conducted at the Louisiana State University Calibration Chamber. Results of this study are in good agreement with the measured values.     

Unit Skin Friction from the Standard Penetration Test Supplemented with the Measurement of Torque

The standard penetration test (SPT) supplemented with the measurement of torque (SPT-T) may be used to obtain a direct measurement of unit skin friction (fs) between the sampler and the surrounding soil. The test is performed after the standard SPT procedure and does not compromise conventional SPT results. In order to perform the SPT-T, the split-barrel sampler is rotated after driving the ASTM specified distance and the maximum torque is measured using a calibrated torque wrench or transducer mounted to the top of the drill string. The measured torque is used along with the known geometry of the split-barrel sampler to determine a value of unit skin friction. SPT-T test results at 12 sites are presented. The results also show that the unit skin friction values obtained from the SPT-T generally correlate well with SPT N60 values. The results may be valuable for making preliminary estimates of unit skin friction for driven piles and provide some rationale for reported correlations between N60 and skin friction from piles.     

Influence of Penetration Rate on Penetrometer Resistance

Penetration resistance in fine-grained soils varies with the rate of penetration. Considering undrained behavior as a reference, as the rate of penetration is reduced, soil resistance increases because of the effects of partial consolidation and soil strengthening immediately ahead of the probe. Many penetration tests have been performed under different rates of penetration to identify the range of drainage characteristics of the soils used, correlating these conditions with laboratory interpretations and in situ tests. A backbone curve relates the variation of the normalized point resistance with the normalized rate of penetration. This work presents an analytical approach to the backbone curve equation used to fit test data. In addition, this paper presents a set of centrifuge tests with variable penetration rates performed with a soil classified as silty tailings, which has different geotechnical behavior from most of the soils used by previous researchers.     

Strength Measurement for Near-Seabed Surface Soft Soil Using Manually Operated Miniature Full-Flow Penetrometer

A manually operated penetrometer (DMS) fitted with cylindrical (T-bar) and ball penetrometer tips was developed for measuring the profiles of undisturbed and remolded undrained shear strength within box-core samples. This paper summarizes the findings of a series of miniature penetrometer tests and vane shear tests that were carried out on reconstituted clay from a local site in Western Australia. The aim of the tests was to evaluate the potential of the DMS in characterizing the shear strength of seabed surficial sediments. It was found that the DMS gave essentially identical T-bar and ball penetration resistances but these were up to 17% lower than the net cone resistance. From the comparison between the T-bar and ball penetration resistance and the shear strengths measured from vane shear tests, average N factors of 11 and 14 were obtained for intact and fully remolded conditions, respectively. The test results suggest that the DMS is a reliable and efficient means of obtaining intact and remolded shear strength profiles.     

Hydraulics of Circular Drop Manholes

Circular drop manholes are widely employed in steep urban drainage systems. Drop manholes may lead to poor hydraulic conditions if their energy dissipation is inadequate. The dominant hydraulic features of drop manholes depend on the flow regimes, characterized in terms of the dimensionless impact parameter. Depending on the latter parameter, the energy dissipation can vary within large limits, affecting thereby the downstream flow features. Also, the water pool depth inside the manhole and the air entrainment have been studied in terms of both the hydraulic and geometric parameters. Moreover, the conditions for which a drop manhole generates flow choking at its inlet or outlet have been investigated. Empirical equations for practical manhole design are provided. The importance of suitable manhole aeration is highlighted.     

Determination of Hydraulic Conductivity Using Piezocone Penetration Test

An elastoplastic, finite-strain, coupled theory of mixtures in an updated Lagrangian reference frame is applied to the piezocone penetration test to estimate the hydraulic conductivity of the soil via analysis of the steady-state excess pore pressure generated during piezocone penetration. The results of this approach were compared with piezocone penetration test data. It showed that reliable hydraulic conductivities can be estimated conveniently without performing pore pressure dissipation tests. This study also shows that the change in the dimensionless excess pore pressure (excess pore pressure is normalized by the effective overburden pressure) at the cone tip is almost constant when the dimensionless hydraulic conductivity (hydraulic conductivity is normalized by the penetration speed and cone radius, hereafter called DLHC) is less than 10?7 or greater than 10?4. It is also shown that the drainage condition around the cone tip is close to a fully undrained condition when the DLHC of the soil is less than 10?7, while it is close to a fully drained condition when the DLHC of the soil is greater than 10?4.     

Effect of Penetration Rate on Cone Penetration Resistance in Saturated Clayey Soils

In this paper, the effects of penetration rate on cone resistance in saturated clayey soils are investigated. Shear strength rate effects in clayey soils are related to two physical processes: the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained. Special focus is placed on this second effect. Cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber, and the resulting data were analyzed. The field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table. Additionally, tests with both cone and flat-tip penetrometers in sand-clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained. A series of flexible-wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation, which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained. A correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests.