Preliminary Report On Measurement Of Soil Stresses Caused By An Underground Explosion

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To: Carole Lojek, SNL/NM Date: Kelley Peters, IT Corporation t61From: Subject: Department 9311 Archive Search of Luke Vortman Files During aninterview with ADS 1334 Technical Staff, Mr. Luke Vortman stated that his document-feles are housed in Department 9311 under the custody of Mr. Al Chabai, 9311. On Tuesday morning, December 21, 1993, Terry Cooper and Kelley Peters, IT Corporation, met Mr. Al Chabai, 9311, to review Mr. Vortman's files. There are 16 filing cabinets in the Department 9311 Archives containing documents and correspondence accumulated by Mr. Vortman. The files are extremely well-organized which facilitated the records search by IT personnel. The following indicate the contents of each cabinet searched: 1) University of California Radiation Laboratory, Livermore, California Technical Documents; Operation Plowshare information 2) Meteor impact crater technical papers; Operation Plowshare information; and 3) Technical papers on Projects Chariot, Churchill, Schooner, Gondola, Lost Creek, Essex, and Sphere; Nevada Test Site (NTS) cratering data; Waterways 4) Proceedings of Nuclear Weapons Effects Conferences; instrumentation procedures; Non-SNL/NM cratering studies 5) Ground motion study documents; Department of the Army Technical Manuals on Explosives and instrumentation 6) Defense Nuclear Agency reports; NTS signal processing and ground motion 7) Technical Papers on NTS Operations Upshot-Knothole, Teapot, Plumbbob, Hardtack, Danny Boy, and Sun Beam Johnie Boy 10) USGS Technical Letters - NTS and Alaska 12) NTS Technical Documents; Sandia Technical Documents 13) NTS and Alaska Technical Reports 14) NTS and Alaska Technical Reports 15) USGS Topographic Maps; Blume Reports (Seismic Effects of Blasts at NTS)

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The majority of the documents in the files do not pertain to Sandia test activities. Documents authored by Mr. Vortman were located in Cabinet #12. These are the same reports requested from the Environmental Programs Records Center, therefore, IT staff did not make copies of these documents: 1T staff obtained copies of the following as a result .of the Department 1) Memo from M. Merritt to L.J. Heilman listing report titles authored by potential ADS 1334 interviewees. These documents should be requested from the Environmental Programs Records Center. 2) "Preliminary Report on Measurement of Soil Stresses Caused by an potential interviewee. When Mr. Perrett is contacted, ask if this report is related to any test activities at Sandia. 3) Drawing No. BI-RB-25, Basic Information Boundary and Ownership, 1954.

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PRELIMINARY REPORT ON MEASUREMENT OF SOIL STRESSES CAUSED BY AN erial contains information affecting the of the Unite ge Laws, Title 18, U.S.C., Secs. 7 revelation of which o an unauthorized person is by This document is the property of Sandia Corporation and.ls only loaned' to the recipient Et must be returned to the Sandia Corporation Documents Room upon request or when no longer needed.,,... ky authority ot, -gERICILZTI Mwshsdbyi 7 VrAN DIA CORPORATION

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PRELIMINARY REPORT ON MEASUREMENT OF SOIL STRESSES CAUSED BY AN The significance of any measurement of subsurface soil pressures induced by blast loading depends, at least for general engineering purposes and for analysis of the stress condition in the soil mass, upon the extent to which the state of stress can be defined in terms of direction, as well as magnitude and time. Such measurements require that the instruments be directionally responsive. All soils are elasto-plastic media -- the emphasis varying between elasticity and plasticity with the type and condition of the soil. These characteristics indicate that soils develop and support shear stresses when subject to mechanical loading. It is possible, therefore, to describe fully the state of stress in a soil mass in terms of either the distribution of normal and shear stresses or the distribution of the principal stresses. The . latter stresses have, by definition, such orientation that shear stresses vanish in the principal planes which are normal to the principal stresses. No instruments have been developed for measuring shear stresses in soils satisfactorily. Consequently the state of stress, may be fully determined if directionally responsive instruments for measuring normal stress are employed with such orientation that the magnitude and direction of the principal stresses at a specific point in the soil mass may be derived from the measurements. Tests were made as a part of an HE test program to determine tlieasibility of measure ments which would yield data suitable for derivation of principal stress magnitudes and directions. Data for these tests, made in connection with the BE-land HE-3 shots, were recorded on several available channels of the Stanford Research Institute (SRI) blast line instrumentation This preliminary report describes the procedures followed in placing the gauges and analysis of the data and indicates the type and reliability of the results which can be e?cpected from such measurements. Only the data from the HE-3 test are discussed in detail. The HE-1 data were not considered suitable for analysis because of serious ringing of the gauges-- a condition which was partially remedied prior to the HE-3 test.

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The instruments used for stress-component measurements were Carlson-Wiancko earth-pressure gauges of 0-15-psi range. These gauges respond to pressures normal to the circular face plate and are insensitive to shears and accelerations within their working range. The relatively long protruding transducer housing at the rear of the CarlsonWiancko gauges makes them less suitable for measurement of stresses developed within the soil mass than for measuring stresses exerted by soil on structures. Nevertheless, gauges of this type were used for the HE tests because they were available and the errors introduced by the geometry of the gauges were not considered sufficient to affect adversely the significance of the results for determining feasibility of stress-component measurements. The techniques and methods of gauge placement and data analysis which have been used successfully by the Corps of Engineers for studies of static stress distribution in soils were adapted for dynamic stress-component measurement. An initial assumption of radial symmetry of the ground shock wave was made to simplify the installation and interpretation of data.. The limited number of gauges and recording channels available also indicated advisability of limitation to a plane-stress condition. Instrumentation for determining stress distribution at a point in a radial plane passing through the charge center required the placement of the gauges in such orientation with respect to the charge that the data would be applicable to one of the normal stress rosette equations such as the 45°-90° equation for plane Placement of Gauges One station at a radial distance of 58.8 feet from the center of the charge was instrumented for stress-component measurements adjacent to the SRI blast line for the HE-3 test. Four gauges were placed at a depth of 5 feet below the ground surface in a trench excavated perpendicular to the radial plane. The gauges were spaced 3 feet apart, the one nearest the SRI blast line instruments being 15 feet clockwise from the centerline of the blast line. Fig. 1 shows four gauges in place in the trench. The gauge at the top of the picture was placed to respond to the horizontal-radial component of stress, sch, and was nearest the blast-line instrumentation. The second gauge from the top was placed to respond to the verticalstress component, cr v; the third gauge responded to the radial-stress component directed downward away from the charge at 45 ° from horizontal, c 45 (away); the fouftfr gauge responded to the radial component directed downward toward the charge at 45 0 -from horizontal, a-45 (toward). The photograph was taken after conclusion of the test and shows the gauges following excavation for their recovery. Each gauge was placed in the trench after calibration on its assigned recorder channel. The gauges were carefully oriented and bedded in moist compacted sand tamped to a density slightly greater than the natural density of the surrounding soil. Moist soil was hand-tamped .around and over the gauges to a depth of about 1 foot. The remainder of the bacicfill was dry random material compacted with a pneumatic tamper in 8-in. lifts to a density approximately equal to that of the surrounding material. The cables were carried through shallow trenches to the recording shelter, the first hundred or more feet of trench being loosely backfilled to minimize cable damage from fall-out material.

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soil stress components Methods of Analysis The basic data derived from the stress-component gauges consisted of oscillograph records of the time-pressure response of each gauge. Tracings of these records, converted to uniform time and pressure scales, are presented in Fig. 2. The record from an 'oil bag' pressure gauge, which was a part of the SRI blast-line instrumentation at the same radial distance from the explosive, is included for comparison with the stress-component records. This gauge consisted of a pressure-sensitive Wiancko transducer placed in a neoprene bag filled air-free with oil. It was placed 5 feet below the surface in the bottom of a 6-in, diameter hole filled with drillers mud. There is evidence of some ringing or natural-frequency oscillation of the gauge in each of the stress-component records. This effect was relatively minor in the horizontal and vertical component records, but was of considerable magnitude in the two 45 ° component traces after the initial positive phase. Average curves were drawn, as shown in Fig. 2, through the recorded oscillations to give a reasonable approximation of the incident pressure function. The pressures indicated by these smoothed curves were read at 10-msec intervals from 0.03 to 0.20 sec after detonation of the explosive. These data were used to compute principal stress magnitudes and directions and maximum shear stresses at each 10-msec interval. The 45 (3 - 90° rosette equations from which the principal stresses in a plane can be derived require knowledge of three normal stress components in the plane -- two mutually perpendicular and the third displaced 45 ° from each. These same data are applicable to graphic analysis by Mohr's stress circle. The measured stresses included a second 45 ° component

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(downward away from zero) Fig. 2. -- Measured soil stress components (HE-3 test)

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UNCLASSIFIEDprimarily for checking the instantaneous stress equilibrium, which requires that the sum of orthogonal stress pairs (vertical-horizontal and two 45 components) be equal. Both the rosette equations and Mohr's stress circle used for derivation of principal-stresses and other parameters are dependent only on equilibrium. and continuity of stresses. Therefore the question of the degree to which elasticity and plasticity of the soil affect the propagation of the stresses is irrelevant to this phase of the study. The rosette equations given by Taylor * in his discussion of earth-stress distribution provide a means for defining the state of stress within a medium independent of shearing stresses since they permit derivation of the principal stresses from certain measured normal stress components. These equations are important to the present problem since no practical instrument has been developed for measuring shear stresses in soils. The three' equations given by Taylor are: The 0- 's represent normal stresses, and the subscripts define the directions of the stresses; 1 represents the major and 3 the minor principal stress direction; h, v, and 45 represent the horizontal, vertical, and 45° stress-component directions as measured. The angle 0 represents orientation of the major principal stress with respect to a horizontal datum. The intermediate principal stress, a_2, is defined here. as the transverse or tangential component but is assumed to be negligible in this case. Measurements of the tangential stress component under static loading conditions have shown that when the stress condition is symmetrical, the tangential component of the stress is negligibly small .t The soil mechanics convention of representing compressive stresses as positive is used in this analysis. The maximum shear stress was also determined from the algebraic relation between it and the principal stresses for each 10-msec interval. The equation used was where T max is the maximum shear stress. The principal stresses, their orientation with respect to a horizontal datum, and the maximum shear stress may be derived graphically from data of the typetained in the stress-component measurements by means of Mohr's stress circle. Mohr's stress circle for plane stress is based on the fact that the locus of the points representing the stress conditiOns on all planes through a point in a medium is a circle in an orthogonal coordinate system in which abscissae are normal stresses and ordinates are shear stresses. The axis of abscissae is a diameter of the circle, and by definition of principal stresses, the major and minor values of these parameters are at the two intersections of the circle with the axis of Taylor, Donald W., Soil Mechanics Fact Finding Survey, Progress Report, Waterways Experiment Station, Vicksburg, Mississippi, April 1947, p 279 1-investigation of Pressures and Deflections for Flexible Pavements; Report No. 1 - Homogeneous Clayey-Silt Test Section, Technical Memorandum 3-323, Waterways Experiment Station, Vicksburg, Mississippi, March 1951 •

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absciSsae, where the shear stress is zero. The radius of e cle is equal to half the difference of the major and minor principal stresses. The center of the circle falls on the axis of abscissae at a distance from the ordinate axis equal to half the sum of the major a-nd minor principal stresses. The maximum shear stress is numerically equal to the radius of the circle and is associated with a normal stress equal to half the sum of the principal stresses. Each point on the circle describes the associated normal and shear stresses which act on a plane whose direction with respect to the major principal plane is given by the angle between the axis of abscissae and a line joining the point to the major principal stress point. All these relations express graphically the same thing that the previously quoted equations express algeConstruction of a Mohr stress circle for analysis of stress-component data such as that obtained in the HE-3 test follows the pattern described below and illustrated in Fig. 3. The data consist of the measured normal stresses at a specific instant at a point in the soil mass. The measured stresses act normal to planes which pass through the point in the soil mass and which are perpendicular to the radial plane containing the center of the explosive and the measurement point. The graphic representation of the measured normal stresses consists of three are parallel to the ordinate axis. The points on these lines which represent the true stress condition are initially unknown in the absence of shear stress data. If, for purposes of construction, the .plane of the graph is chosen to represent the radial plane in the soil mass, some point on the graph will correspond to the origin of stress planes (the measurement point in the soil). The trace of the vertical plane on which 0- h was measured will be the line on the graph representing all , and the origin of stress planes will fall on that line. For convenience the position of this point is fixed arbitrarily, and the position of the axis of abscissae is left temporarily indeterminate. Two other lines, corresponding in direction to the traces of the planes on which v v and a- 45 were measured, are plotted through the origin of planes and the intersection of these …