Operation Hardtack, April - October 1958, Project 1.4, Physical Characteristics of Craters from Wear - Surface Nuclear Detonations (Deleted)

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Physical Characteristics of Craters From Headquarters Field Command Defense Atomic Support Agency Sandia Base, Albuquerque, New Mexico This is an extract of WT-1609, which RESTRICTED DATA as of this date. Extract version prepared for: DEFENSE NUCLEAR AGENCY Approved for public release;

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Project 1.4 - PHYSICAL CHARACTERISTICS OF CRATERS U.S. Army Engineer Research & Development Labs Fort Belvoir, VA Headquarters Field Command May 10, 1960 Sandia Base, Albuquerque, New Mexico Approved for public release; unlimited distribution” This report has had the classified information removed and has been republished in unclassified form for public release. This work was performed by Kaman Tempo under contract DNAo01-83-C-0286 with the close cooperation of the Classification Management Division of the Defense Nuclear Agency. The objective of this project was to measure and correlate with existing data the physical characteristics of craters (radius, depth, lip height and width, throwout, and permanent verticl ground-surface displacement surrounding the crater) resulting from near-surface nuclear detonations. Do ,:::;, 1473 EOITION or tN0v6SIS0DsOLgTE UNCLASSIFIED

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This report has had classified material removed in order to make the information available on an unclassified, open publication basis, to any interested parties. This effort to declassify this report has been accomplished specifically to support the Department of Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies of the low levels of radiation received by some individuals during the atmospheric nuclear test program by making as much information as possible available to all interested parties. The material which has been deleted is all currently classified as Restricted Data or Formerly Restricted Data under the provision of the Atomic Energy Act of 1954, (as amended) or is National Security Information. This report has been reproduced directly from available copies of the original material. The locations from which material has been deleted is generally obvious by the spacings and “holes” in the text. Thus the context of the material deleted is identified to assist the reader in the-determination of whether the deleted information is germane to his study. It is the belief of the individuals who have-participated in preparing this report by deleting the classified material and of the Defense Nuclear Agency that the report accurately portrays the contents of the original and that the deleted material is of little or no significance to studies into the amounts or types of radiation received by any individuals during the atmospheric nuclear test program.

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This report presents the final results of one of theprojects participating in the military-effect programs of Operation Hardtack. Overall information about this and the other military-effect projects can be obtained from WT -1660, the “Summary Report of the Commander, Task Unit 3.” This technical summary includes: (1) tables listing each detonation with its yield, tYPe, environment, meteorological conditions, etc. ; (2) maps showing shot locations; (3) discussions of results by programs; (4) summaries of objectives, procedures, results, etc. , for all projects; and (5) a listing of project reports for the military-effect programs. .

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The objective of this project was to measure and correlate with existing data the physical characteristics of craters (radius, depth, lip height and width, throwout, and permanent vertical ground-surface displacement surrounding the crater) resulting from near- surface nuclear Primary participation was on Shots Koa, Cactus, and Fig, the only land-surface bursts of Operation Hardtack. Dimensions of the craters were determined by topographic, lead-line, and aerial- stereographic surveys. Secondary participation included fathometer surveys of barge shots Linden, Oak, Yellowwood, Butternut, and Holly. When the crater dimensions of the above shots were compared to adjusted dimensions taken from the crater curves of TM 23-200 it was found that Shot Cactus and Shot Fig crater data compared favorably, but the Shot Koa crater dimensions were enlarged because the device was em@aced in a water tank. The barge-shot craters were larger than values calculated from

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The author wishes to acknowledge the assistance in the planning and execution of this project bers of the Special Projects Branch, ERDL, Fort Belvoir, Virginia; the Chief and members of Program 1; and to Projects 1.7 and 1.8 for transient displacement and pressure measurements. The author would also like to thank PFC D. Carpenter for his assistance in the preparation of art work.

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Site Yvonne Drilling Log, Station 181.03- ----------- ----------------- 19 Site Helen Drilling Log, Station 180.01 ---------------- --------------19 Site Irene Drilling Log, Station 180.03 ------------------ ------------DO

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1 Crater r%diusversus hetght of burst, scaled tolkt --------------------- 10 2 Crater depth versus height of burst, scaled tol ~---------------------- 11 5 Depression marker, Station 170 ---------------------------------- 17 6 Depression marker, Station 171- ------------------------ ‘-------- 17 9 Shot Cactus preshot aerial photograph ------------------------ ‘----- 23 11 Shot Cactus postshot aerial photograph ------------------------- ‘--- 24 17 Shot fiapostshot aerial photograph ------------------------ ‘------ 27 19 Shot Koa crater profile, Radii land 4-------------- ---------------- 28 21 Shot Koa crater profile, &dii3and 6------------------------------ 29 34 Crater depth versus yield, barge shots ----------------------------- 39

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PHYSICAL CHARACTEWS77C’S of CRATERS from NEAR -SURFACE NUCLEAR DETONATIONS The objectives of this project were to (1) measure the physical characteristics of the apparent craters and lips from near-surface nuclear detonations; (2) compare ~d correlate the data so obtained with those already available in order to more firmly establish the capability of predicting craters from surface-burst weapons; and (3) document the crater lip, throwout, and permanent vertical ground surface displacement surrounding the apparent craters. In the last several years, the increased interest in cratering as a primary damage mechanism has resulted in a need for data to improve crater-prediction techniques, particularly for surface detonations. Craters from twelve nuclear detonations in the EPG were documented during Operations Greenhouse, Ivy, Castle, and Redwing (References 1, 2, 3, and 4). Results have been analyzed and used in the prediction curve with factors given in TM 23-200 (Reference 5, Figures Figures 1 and 2 of this report contain a summary of scaled crater data from past EPG operations as well as cratertng curves taken from TM 23-200. The data show considerable scatter - which is due primarily to variation in soil structure of the islands, washing action of waves generated by the shots, and washing action by tidal effects. .TM 23-200 suggests multiplication factors be used in conjunction with the TM dry- NTS-soil curves to account for these environmental conditions. In the theory section of this report, results from past EPG craters are compared with TM 23-200 by the use of factors. In past operations, unusual weapon-tamping configuration has influenced the crater size (References 4 and 6). It would be impossible to assign crater adjustment factors for the many possible types of weapon-tamping configurations. One configuration that has not been fully evaluated is that in which a large water tank encloses a device, i. e. , Shot Seminole, Operation Redwing (Reference 4). This configuration became important to this operation because Shot Koa had a similar tamping configuration. The crater formed from Shot Seminole was larger than expected, and this was attributed to the water enclosure. It was expected that Shot Koa would give additional information on this effect. Reliable data on crater lip dimensions have been limited to a few high explosive cratering series and three nuclear craters. Lip dimensions for these shots have been taken from smoothed, average profiles representing actual lips of rough and irregular shapes. Several methods of predicting lip height are given in test literature; TM 23-200 indicates that the crater lip height is onefourth of the crater depth, while other sources indicate scaling by fractional powers of the yield (Reference 7). Predictions of lip width have included areas large enough to contain all the large At the present time predictions of crater dimensions are based largely on empirical curves derived for the most part from data from high explosive charges supplemented by a few nuclear

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detonations at the NTS and the EPG. These shots, however, were fired under a wide range of conditions; for example, variations of soil type, moisture content, and height or depth of burst (HOB). This complicated the correlation and enabled numerous curves to be drawn to f it plotted points without a sufficient number of points under one condition tomake a statistical analysts or to determine and understand deviations. A need, therefore, existed to collect all shot data and if possible reduce them to a standard condition, (i. e., soil, yield, and height of burst). In order to reduce existing data to a standard condition it is recognized that many assumptions will have to be made ~d in many cases arbitrary factors used, especially on the data from the EPG. Much of this could be eliminated by high-explosive testing. Through a series of small highexplosive tests i.n homogeneous ~ils it might be possible to isolate certain soil properties

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such as strength, saturation, and void ratio and to determine effects of these parameters on In the absence of more refined testing, and for the purpose of more closely relating EPG data in this report, the following assumptions and factoring systems will be used. The assumed standard conditions are: (1) homogeneous dry sandy soil; (2) zero height of burst; i.e., the center of gravity of the charge at the ground surface with the lower part of the charge in full contact with the cratering medium; (3) spherical ctige; and (4) l-kt yield. . Scaling for crater radius is based on cube root scaling; i. e., the radius varies directly as the cube root of the yield (or charge weight) This is a straight line with a slope of one third when plotted on log paper; i. e. , log R = log A + 1/3log W with A the intercept for a yield of 1 kt at the surface. Although deviations from cube root scaling may exist for variations in yield and height of burst, cube root scaing is assumed to hold for al wteri~s (sand, cky, rock), conditions of materials (saturation, compaction), and heights of burst, then only the intercept (A) will be changed with a change in materhls or height of burst, ~d a family of lines which are p~allel to the standard line will exist. lt becomes necessary to introduce factors by which the intercept (A) can be modified in order to reduce all data to the standard line: Thus R = /(Fl, F2,--Fn) AW’. Since the precise nature of the function is not known, it will be assumed as R = F, F2-- FnA WM. There remains the problem of finding the variables, defining them with known tests and relating them to the crater radius. It is assumed that the values of these factors can be determined independently of each other.

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Since no new high-explosive test data are available for determining these variables, TM 23-200 and past test data will be used as a guide. These variables are defined in the TM by three gross factgrs as follows: Soil Type Factors Granite or Sandstone 0.8 The above factors may be a guide to the limits by which craters are affected by these variables. If a more detailed analysis of the soil is made other variables such as void ratio, soil fracture in the crater vicinity, and degree of confinement can be used toward a greater accuracy in crater prediction. Until further determinations are made as to stintird soil conditions, the dry soil curve as given in TM 23-200 shall serve as the standard curve, and the value of A shall be taken as 64 With the exception of height of burst, energy containment, and washing, all variables are directly concerned with soil properties. The HOB factor, F,, is determined from the standard dry soil curve contained in TM 23-200. This curve, Figure 1, shows a change in crater radius as the burst position of the device varies from the ground surface. A factor for any scaled height of burst is found by determining the . factor needed to adjust the crater radius to that of a surface burst. The accuracy of such factors would depend upon the accuracy of the TM 23-200 curve and scaling. Adjusting and tom- . paring of craters with scaled height of burst above 20 feet by means of HOB factors is not considered necessary since these craters are only shallow ground depressions. The Fz factor may be denoted as a strength factor and-is probably related to the strength of the soil in compression and shear. The relationship should be sought in terms of the unconfined compressive strength since the appropriate degree of confinement is not constant, sand cannot be tested for compression in an unconf~ed condition, therefore, it- shall be given a strength factor of one. The upper limit, then, for the Fz factor is 1.0. The lower limit would be the value for hard rock, which for granite, as given in the TM, is approximately 0.8. The F3 factor accounts for degree of saturation. (The degree of saturation is the percentage of voids which are filled with water and ranges from 0.0 for a dry sand to 100.0 for a completely saturated soil. ) Since dry sand is the standard having a value of 1,0 the lower limit would be 1.0. The upper limit, representing complete saturation, will vary for sand or clay type soils but to be consistent with TM 23-200 a value of 1.5 will be used. The F, factor is for washing and ranges from 1.0 to 1.33 for saturated sand. Clay type soils are expected to be affected to a lesser degree by washing, and rock is expected to be affected to a stilllesser degree. It is recognized that craters at the EPG have been subjected to different degrees of washing as evidenced by the existence of crater lips for some craters. An attempt will be made to assign factors for (1) complete washing to craters with no lips, (2) partial washing to craters where evidence of lip exists, and (3) no washing for craters with lips that are land Another factor, F5, energy containment, can be entered into the equation. This factor will be a correction for the degree of containment of the nuclear device which results in the directing of more or less energy into the ground. This is a significant factor since data from two contained surface shots (Shots Seminole and Koa) in the E PG area indicate a considerable increase in crater dimensions with some form of tamping. A number of variables such as density and thickness of containment material, weapon design, and placement all enter into the determination of this factor. It is probable that each detonation of this nature must be analyzed Another factor, F~, can be inserted for inhomogeneities that are relatively distant in comparison to the close-in phenomena. That is, this inhomogeneity factor is a correction for such

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changes in the media as interfaces and cavities. Here again each shot must be studied individually. This factor has more effect on crater depth and profile than radius according to data from a high-explosive test, Reference 8. The above analysis has been for the determination of crater radius. Crater depth, it iS felt, is a function of the …