Michael McVay

Measured and Predicted Response of a New Jetted and Grouted Precast Pile with Membranes in Cohesionless Soils

AbstractWith increased urbanization, deep foundation (bridges, signage, walls, etc.) selection is moving toward the minimization of disturbance and installation time, as well as addressing quality control and assurance issues. Unfortunately, many types of deep foundations involve noise and vibration during installation (e.g., driven piles) or integrity and reduced resistance issues (e.g., drilled shafts, both conventional and post grouted tip, continuous flight auger piles). This paper presents a new foundation type, a jetted and grouted precast pile, which uses the advantages of several proven deep foundation installation techniques. The installation of the new pile is comprised of three distinct phases: (1) pressurized water-jetting of a precast pile into the ground; (2) side grouting of the pile; and (3) tip grouting. The pile has two separate side grouting zones, each with its own grout delivery system. Each grout zone is covered with a semirigid membrane, which results in radial expansion of the soil...

Approximate up-scaling of geo-spatial variables applied to deep foundation design

We present a series of simple approximate methods for up-scaling the cumulative distribution function of spatially correlated variables by using an effective number n e of independent variables. Methods are based on the property of distribution permanence of the gamma and inverse Gaussian distributions under averaging, bootstrap sampling and expansions about the normal and gamma distributions. A stochastic simulation study is used to validate each method, and simple parameters are defined to identify respective ranges of applicability. A practical example is presented where core sample rock strength data are up-scaled to shaft size for probabilistic (risk-based) deep foundation design. Supplemental material is available online.

Experimental Group Behavior of Grouted Deep Foundations

Post-grouting of deep foundations following installation is a proven technique for enhancing axial resistance. The grouting is performed either below the tip of the foundation only (e.g., post-tip-grouted drilled shafts) or at both the side and the tip (e.g., jetted, side, and tip-grouted precast piles). The interaction of such foundations in group placement is currently unknown. This research focused on the group behavior of post-tip-grouted drilled shafts and jetted, side, and tip-grouted piles at a center-to-center spacing of three times the pile/shaft diameter. The study revealed that the post-tip-grouted drilled shafts acted independently within the group (i.e., negligible group interaction), whereas jetted, side, and tip-grouted piles behaved as a block under axial loading. It was determined that side grouting of a foundation prior to tip grouting significantly increases the grout pressure developed during tip grouting and helps in the formation of a tip grout bulb via a spherical cavity expansion process. Thus, the side and tip grouting of adjacent foundations within a group increases the confining stress and relative density of the soil mass within the group, resulting in block behavior under top-down loading. In contrast, tip-only grouted foundations showed little if any increase in radial stress and radial soil displacement, resulting in minimal improvement of the soil stiffness between shafts; as a result there was no block behavior and a negligible group effect at the tip.

Construction material properties of slag from the high temperature arc gasification of municipal solid waste

Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m(3)) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self cementing character which supports the elevated LBR results. Preliminary material characterization of the HTAG slag establishes potential for beneficial use; larger and longer term studies focusing on the materials possibility for swelling and performance at the field scale level are needed.

Evaluation of Drilled Shaft Capacity Using Embedded Sensors and Statnamic Testing

AbstractThis paper presents an application of the embedded data collector (EDC) approach using strain and acceleration measurements at the top and bottom of a pile (drilled shaft) during dynamic loading (Statnamic) for estimation of static side and tip resistance. For assessment of the skin friction, wave propagation along the pile was modeled as a one-dimensional (1D) wave equation with nonlinear static skin friction and viscous damping. The soil–pile system was divided into segments, and each segment was characterized with independent multilinear skin friction. The skin friction of each segment was determined by least-squares fitting of computed particle velocities to the measured data at the top and bottom of the pile. For assessment of the tip resistance, the pile tip was modeled as a single—degree-of-freedom nonlinear system. A nonlinear stiffness–displacement relationship was determined by balancing force and energy from inertia, damping, and stiffness against the measured tip data. The technique wa...

Influence of Spatially Variable Side Friction and Collocated Data on Single and Multiple Shaft Resistances

AbstractReliability-based design, such as LRFD, aims at meeting desired probability of failure levels for engineered structures. The present work attempts to contribute to this field by analyzing the influence of spatially variable soil/rock strength on the axial resistance uncertainty of single and multiple shafts in group layouts. This includes spatial variability over the individual shaft surfaces, effects of limited data, random measurement errors, and workmanship. A possible correlation between boring data inside or near the footprint of a foundation and the foundation itself is considered. In a geostatistical approach, spatial averaging (upscaling) and a degenerate case of ordinary kriging are applied to develop variance reduction charts and design equations for a series of foundation group layouts (single, double, triple, and quadruple). For the potential situation of an unknown horizontal correlation range at a site, the worst case scenarios are identified and demonstrated in an example problem. R...

Seismic Waveform Tomography at Test Site with Open Chimneys

An application of two-dimensional time-domain waveform tomography to map the extent of open chimneys at a variable karstic limestone site is presented. The seismic surface wave fields were measured next to three open chimneys and inverted with a full-waveform inversion technique, which was based on a finite-difference solution of two-dimensional elastic wave equations and the Gauss–Newton inversion method. Both the compression wave (P-wave) and shear wave (S-wave) velocities were inverted independently and simultaneously to increase the credibility of the characterized profiles. The waveform analysis successfully profiled embedded low-velocity zones and highly laterally and vertically variable limestone. The inverted results are consistent with the known open chimneys observed from the ground surface. The Poissons ratio determined from the inverted P-wave and S-wave velocities is consistent with soil types: high values of 0.3 to 0.5 for silt and clay and low values of 0.1 to 0.2 for limestone. Results show that the full-waveform inversion technique is applicable to both shallow and deep foundation design in which soil stratigraphy and variability are important. The technique is also computationally practical, because the results were all achieved in about 3 h of computer time on a standard laptop computer.

Study of Laboratory Compaction System Variance Using an Automatic Proctor Calibration Device

AbstractThis paper describes the development of a portable dynamic energy calibrator (PDEC) for mechanical Proctor compaction machines along with an analysis of system variance on a silty sand’s (A-2-4) dry unit weights. The PDEC measures a rammer’s kinetic energy delivered to the sample and the compressive energy retained in the sample. The monitoring system uses a photoelectric gate and impact force sensor attached to the machine. When the rammer mass is included, the system’s impedance can be calculated. Next, 30 Florida Department of Transportation (FDOT)-approved machines throughout the state were tested, and summary statistics (i.e.,xa0mean, standard deviation, and so on) of the kinetic and compressive energies of the machines were found. Scatter plots of hammer kinetic energy along with sample energies allowed for identification of poorly functioning machines (e.g.,xa0low-impact energies or variations in mold support). Finally, a series of blind modified compaction tests were performed on A-2-4 soil at...

A Practical LRFD Design Method for Deep Foundations Using Side Friction and End Bearing

One of the uncertainty components in Load and Resistance Factor Design (LRFD) stems from spatial variability in design parameters, such as local soil / rock strength or modulus. A solution is presented for uncertainty propagation of effective rock mass modulus through O’Neill’s (non-linear) equations for drilled shaft settlement in intermediate geomaterials. Associated tip resistance is combined with side friction resistance (fully mobilized) of one or more geological layers to form total ultimate shaft resistance with respective uncertainty. Based on this, a graphical iteration chart (existing for side friction in a single layer without end bearing) is generalized to find shaft length as a function of given reliability (probability of failure), factored design load and site conditions. Results are demonstrated by a practical example.