Donald E. Yule

Microgravity investigations of foundation conditions

A microgravity investigation was conducted in the upstream and downstream switchyards of the Wilson Dam powerplant, Florence, Alabama. The objective of the survey was the detection in the switchyard foundations of subsurface cavities or other anomalous conditions that could threaten the stability of the switchyard structures. The survey consisted of 288 gravity stations in the downstream switchyard and 347 stations in the upstream switchyard. Significant anomalous areas in the switchyards were selected on the basis of residual gravity anomaly maps. These results were prioritized and used to guide an exploratory drilling program to investigate the cause of the anomalies. Highest-priority boring location recommendations were in negative gravity anomaly areas, since negative anomalies could be caused by actual cavities or low-density zones that might represent incipient cavity formation. Remaining boring locations were in positive anomaly areas for verification purposes. The results of the borings confirm the presence of cavities and soft zones indicative of cavity formation.

Applied geophysical techniques to evaluate earth dams and foundations

Mill Creek Dam, near Walla Walla, Washington has experienced anomalous seepage since its first filling in 1941. Various attempts to abate and control the seepage, including construction of a concrete wall, have not been completely successful. Construction of the cutoff wall reduced the seepage by about 30 percent, from 33 cubic feet per second to 22 cubic feet per second, and downstream saturated farmland was reduced by 56 percent. However, there are indications of increased seepage pressures in a conglomerate formation in the right abutment. A comprehensive, integrated geophysics investigation of the right abutment area of the dam was conducted to detect and map anomalous conditions and assist in the evaluation of remedial measures. The geophysics program consisted of microgravity, ground penetrating radar, seismic reflection, electromagnetic conductivity, and electrical resistivity surveying. Results of the program indicate anomalous conditions extending from the reservoir area through the right abutment. The aspects of the program planning leading to technique selection and field procedures are emphasized, as well as the role of different geophysical techniques in defining the nature of anomalous condition.

Remote Sensing and Monitoring of Earthen Flood-Control Structures

Abstract : The purpose of this study was to identify and review technologies that are applicable in locating weaknesses and poor performance within flood-control structures from extreme loading events. The focus of this study was to assess current technologies and state-of-practice techniques involving remote sensing, testing, and real-time monitoring of earthen structures. Advancements in satellite and sensor technology combined with high-speed internet and telecommunication capabilities and smart decision-making software permits real-time monitoring of earthen flood-control structures such as dams and levees. Technologies evaluated included both active and passive sensing methods. These technologies included satellite, airborne, and ground-based sensor systems to identify surface and subsurface characteristics of the watershed, as well as point sensors typically embedded in hydraulic structures to monitor the health of the structure. Point sensors typically record water loading, soil pore pressures, soil movements, and other important properties to evaluate global stability of the water control structure. Geophysical-based methods are typically used in mapping, monitoring, and detection of subsurface stratigraphy, seepage, and any changes in subsurface conditions through time within flood-control structures and their foundations.

Ground motion and air overpressure study

A seismic attenuation and air overpressure study was conducted to determine the attenuation of explosion induced ground motions and air overpressures as a function of distance from shallow subsurface detonated charges, and to derive parameters to predict blast effects at distances beyond the ordinance disposal facility boundary. A total of 210 explosive shots were monitored producing 2048 time histories of ground motions recorded in the vertical, radial, and transverse directions, in addition to recording air overpressures. The data were analyzed for peak particle velocities and peak air overpressures, then plotted versus scaled range. A best fit line was determined for the data to give average, 95% non-exceedance, and upper bound predictive equations which can be used in the disposal operations to avoid damage to adjacent structures.

Foundation investigation for dynamic response analysis of radar support structure

Results of a foundation investigation for the dynamic loading of a radar tower are presented. Geophysical tests comprised of surface refraction and borehole seismic tests were performed. Results from geotechnical in situ tests, which included plate bearing tests, are also presented. The elastic properties, Young’ s modulus, Poisson’ s ratio, shear modulus and constrained modulus were determined as a function of depth for the foundation soils. These properties are necessary to design a stable foundation that will experience dynamic loading. Foundation materials encountered at this site were coral sands silts and gravels to a depth of 60 ft. The upper 14 ft of foundation soils are a hydraulically placed sand fill. The shear modulus ran es from 7.7x(103) psi at 93 the surface to 22x(10 ) psi at the bottom of t e 5 profile. Youn

Foundation investigation of a poer plant switchyard using microgravity

s modulus shows a range of 22x(10 ) psi to 66x(10 ) psi. Poisson’ s ratio varies from 0.40 for unsaturated to 0.49 for saturated soil. A method was presented to estimate moduli under the expected load from present unloaded in situ moduli values using the K2 parameter. An estimate of the moduli for the expected foundation load was presented for the upper 30 ft of the foundation. A comparison of the plate bearing test and seismic derive 4 Young’ s modul s Y shows good agreement, 123x(10 ) psi and 78x(10 ) psi, respectively.

Analytical and Data Processing Techniques for Interpretation of Geophysical Survey Data with Special Application to Cavity Detection.

A microgravity survey consisting of 347 stations was conducted in the upstream switchyard of a dam powerplant. The objective of the survey was the detection of subsurface cavities or other anomalous conditions which could threaten the integrity of the switchyard structures. six anomalous areas were identified on the gravity anomaly map and ranked for their interpreted significance. From these results nine boring locations were selected to investigate the cause of the anomalies. This paper presents details of the field survey, data processing, interpretations, and recommended drilling locations for subsurface investigation.