Harald Klammler

Influence of Spatially Variable Side Friction on Single Drilled Shaft Resistance and LRFD Resistance Factors

Load and resistance factor design (LRFD) is a method that aims at meeting specified target reliabilities (probabilities of failure) of engineered systems. The present work focuses on ultimate side friction resistance for axial loads on single cylindrical drilled shaft foundations in the presence of spatially variable rock/soil strength. Core sample data are assumed to provide reliable information about local strength in terms of mean, coefficient of variation and spatial correlation structure (variogram) at a site. The geostatistical principle of support up-scaling is applied to quantify the reduction in variability between local strength and the average ultimate shaft side friction resistance without having to recur to lengthy stochastic finite difference/element simulations. Site and shaft specific LRFD resistance factors (Φ values) are given based on the assumption of lognormal load and resistance distributions and existing formulas recommended by the Federal Highway Administration. Results are efficiently represented in dimensionless charts for a wide range of target reliabilities, shaft dimensions, and geostatistical parameters including nested variograms of different types with geometric and/or zonal anisotropies. Field data of local rock strength is used to demonstrate the method and to evaluate the sensitivity of obtained resistance factors to potentially uncertain variogram parameters.

Analytical solutions for flow fields near continuous wall reactive barriers.

Permeable reactive barriers (PRBs) are widely applied for in-situ remediation of contaminant plumes transported by groundwater. Besides the goal of a sufficient contaminant remediation inside the reactive cell (residence time) the width of plume intercepted by a PRB is of critical concern. A 2-dimensional analytical approach is applied to determine the flow fields towards rectangular PRBs of the continuous wall (CW) configuration with and without impermeable side walls (but yet no funnel). The approach is based on the conformal mapping technique and assumes a homogeneous aquifer with a uniform ambient flow field. The hydraulic conductivity of the reactive material is furthermore assumed to exceed the conductivity of the aquifer by at least one order of magnitude as to neglect the hydraulic gradient across the reactor. The flow fields are analyzed regarding the widths and shapes of the respective capture zones as functions of the dimensions (aspect ratio) of the reactive cell and the ambient groundwater flow direction. Presented are an improved characterization of the advantages of impermeable side walls, a convenient approach to improved hydraulic design (including basic cost-optimization) and new concepts for monitoring CW PRBs. Water level data from a CW PRB at the Seneca Army Depot site, NY, are used for field demonstration.

A new device for characterizing fracture networks and measuring groundwater and contaminant fluxes in fractured rock aquifers

This paper presents the fundamental theory and laboratory test results on a new device that is deployed in boreholes in fractured rock aquifers to characterize vertical distributions of water and contaminant fluxes, aquifer hydraulic properties, and fracture network properties (e.g., active fracture density and orientation). The device, a fractured rock passive flux meter (FRPFM), consists of an inflatable core assembled with upper and lower packers that isolate the zone of interest from vertical gradients within the borehole. The outer layer of the core consists of an elastic fabric mesh equilibrated with a visible dye which is used to provide visual indications of active fractures and measures of fracture location, orientation, groundwater flux, and the direction of that flux. Beneath the outer layer is a permeable sorbent that is preloaded with known amounts of water soluble tracers which are eluted at rates proportional to groundwater flow. This sorbent also captures target contaminants present in intercepted groundwater. The mass of contaminant sorbed is used to quantify cumulative contaminant flux; whereas, the mass fractions of resident tracers lost are used to provide measures of water flux. In this paper, the FRPFM is bench tested over a range of fracture velocities (2–20 m/day) using a single fracture flow apparatus (fracture aperture = 0.5 mm). Test results show a discoloration in visible dye corresponding to the location of the active fracture. The geometry of the discoloration can be used to discern fracture orientation as well as direction and magnitude of flow in the fracture. Average contaminant fluxes were measured within 16% and water fluxes within 25% of known imposed fluxes.

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.

Effect of Passive Surface Water Flux Meter Design on Water and Solute Mass Flux Estimates

Standard methods for determining pollutant loads in streams typically require the collection of separate instantaneous measurements of water velocities and solute concentrations at discrete points in space and time. A recently developed device, the passive surface water flux meter (PSFM), has been introduced as an alternate method for the measurement of time-integrated surface water flux (velocity) and solute mass flux. This paper extends PSFM development by evaluating and comparing two PSFM designs in laboratory flumes, as well as reporting on initial steady-state field testing. The shape of the PSFM body determines the velocity with which water passes through the device, and different designs may thus be preferred for different applications. Experiments compared the accuracy of flux measurement by the previously introduced hydrofoil-shaped PSFM and nitrate-sorbing cartridge with that of a newly designed cylindrical-shaped PSFM and phosphate-sorbing cartridges. Testing was performed in a laboratory flume...

Capture flows of funnel-and-gate reactive barriers without gravel packs

Permeable reactive barriers (PRBs) are a passive in-situ technology, which is based on the interception and physical, chemical and/or biological remediation of a contaminant plume through installation of reactive material in an aquifer. Previous work of the authors includes analytical approaches in two dimensions (horizontal plane) based on the conformal mapping technique that allows for the determination of the groundwater flow fields and capture zones of PRBs of different types. Solutions assume that the permeability kr of the reactive material itself is high with respect to the surrounding aquifer permeability ka or that highly permeable gravel packs are present to equilibrate the hydraulic heads at the up and down-gradient faces of the reactor. Respective results include a simple relationship Q(R) between capture flow Q and reactor Darcian hydraulic resistance R. Based on the same technique, the present work gives an exact solution for funnel-and-gate (FG) and velocity equalization wall (VEW) PRBs without gravel packs for the particular case of kr = ka. Furthermore, a numerical finite difference study is performed to show that Q(R) is a good approximation (with errors in the 1% range of maximum capture flow Q(0)) for FG and VEW

Groundwater and contaminant travel time distributions near permeable reactive barriers

Permeable Reactive Barriers (PRBs) is a passive in-situ technology, which is based on the interception and remediation of a contaminant plume through installation of reactive material in an aquifer. Groundwater and contaminant travel times for a given location in the aquifer to or from the PRB are important parameters in PRB design and performance monitoring. The approach taken is two-dimensional in the horizontal plane and based on existing flow field solutions for a series of PRB configurations. Transport is considered purely advective with a possible retardation between groundwater and contamination. The aquifer is assumed homogeneous and a dimensionless travel time is introduced for arbitrary magnitudes of ambient groundwater flow, confined aquifer thickness and porosity as well as contaminant retardation. Travel time is expressed in a general form by an integral along curved stream lines in the physical plane and transformed into an integral along a straight stream line in the complex potential plane, where a simple numerical integration method is applied to generate maps of isochrones. Travel times are seen to be rather uniformly distributed within capture/release zones with minor effects of local low flow zones (stagnation points). Funnel-and-gate systems show a stronger lateral growth of capture/release zones at early times than other PRB types. Drain-andgate PRBs possess closed isochrones and are identified as transitional configurations between classic PRBs and pump-and-treat systems.

Evidence of rock matrix back-diffusion and abiotic dechlorination using a field testing approach

An in situ field demonstration was performed in fractured rock impacted with trichloroethene (TCE) and cis-1,2-dichloroethene (DCE) to assess the impacts of contaminant rebound after removing dissolved contaminants within hydraulically conductive fractures. Using a bedrock well pair spaced 2.4m apart, TCE and DCE were first flushed with water to create a decrease in dissolved contaminant concentrations. While hydraulically isolating the well pair from upgradient contaminant impacts, contaminant rebound then was observed between the well pair over 151days. The magnitude, but not trend, of TCE rebound was reasonably described by a matrix back-diffusion screening model that employed an effective diffusion coefficient and first-order abiotic TCE dechlorination rate constant that was based on bench-scale testing. Furthermore, a shift in the TCE:DCE ratio and carbon isotopic enrichment was observed during the rebound, suggesting that both biotic and abiotic dechlorination were occurring within the rock matrix. The isotopic data and back-diffusion model together served as a convincing argument that matrix back-diffusion was the mechanism responsible for the observed contaminant rebound. Results of this field demonstration highlight the importance and applicability of rock matrix parameters determined at the bench-scale, and suggest that carbon isotopic enrichment can be used as a line of evidence for abiotic dechlorination within rock matrices.

Modeling dynamic resilience in coupled technological-social systems subjected to stochastic disturbance regimes

Resilience of engineered systems is measured by the ability to anticipate, prepare for, recover, learn, and improve from an external disturbance regime that comprises of a series of chronic low-intensity and infrequent acute shocks, which disrupt functionality. Here, we present a new systems-level model for coupled technological systems, which provide functionality, and social systems in charge of management. Each system is characterized by a single, aggregated, dynamic state variable, namely (1) critical service deficit, representing services/functionality not provided by the technological system to match demands, and (2) adaptive capacity, representing total resources available to the managing/social institutions to maintain and repair critical services. These coupled systems are subjected to an external stochastic disturbance regime (Poisson shocks), and temporal perturbations in the two state variables are simulated. We use this “toy” model to simulate four hypothetical scenarios to illustrate likely coupled system temporal trajectories and shifts between a desirable (full service) and an undesirable (limited service) regime or complete system collapse (no service, no adaptive capacity). We also present several quantitative approaches to assess time series data and examine coupled systems dynamics. Resilience of the coupled systems for coping with and recovering from service losses is a dynamic property, contingent on system parameters that define the initial conditions before the shocks and recovery, and the frequency and magnitude of shocks.

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...