C9The dynamic bearing capacity of a 15-inch -diameter bearing plate on dry sand without overburden was 90 percent higher than -he static bearing caoacity. Also, the dynamic bearing

00 mASA-13.018

Teljicl 277TdnclReport STATIC AND DYNAMIC PLATE-

CcC;**: i ::,:::.:..~i.*-*.e. BEARING TESTS ON DRY SAND

WITHOUT OVERBURDEN

14 Jnur 1964

U~. S. NAVAL CIVIL ENGINEERING LABORATORY

Port Hueneme, California

C9

STATIC AND DYNAMIC PLATE-BEARING TESTS ON CRY DASA-13.018

SAND WITHOUT OVERBURDFs,1

Y-F008-08-03-402

Type C

by -

Charles R. W1',4?

ABS*, xACT

- The NCEL atomic blast simulator is intended for testing beems, boom-column.connections, and other relatively narrow structural elements. This report describesthe successful aduptation of the simulator for providing dyrmmnic loads on a bearingplate on sand and presents some tentative results as a pre!;minary part of TaskY-F008-08-03-432, " Funuamental Behavior of Sails Uinder Time-Dependent Loads."The dynamic bearing capacity of a 15-inch -diameter bearing plate on dry sandwithout overburden was 90 percent higher than -he static bearing caoacity. Also,the dynamic bearing modulus was considerabiy higher than the static; e.g., 226 psiper inch dynamic versus 137.7 psi per inch static at 0.5 inch plate settlement.

This work sponse-red by the Defense Aiom~c Sujpport Agency

Quolified req.,,.t., may obtain opts .. this ,.g.,t from Mr'..Th,. Lobbetooy -. te*s comm.,,t on this ;. Q,, pahtmcuaiovly n this

pisults obtaine.d by theise iiha nit- ois o ,. nf- noton

INTRODUCTION

Increased knowledge of, the behavior of soils under dynamic loads of the typeproduced bv nuclear weapons is urgently needed by engineers engaged in disigningprotective structures. In addition to the utility of soil as a radiation shield, theeconomic and mechanical advantages of utilizing the strength of soil masses byplacing protective structures underground are being exploited. The backgroundof informoion regarding the dynamic strengths of soils and the behavior of structuresdynamically loaded in soil environments is gradually being enlarged, but the magni-tude of loads of interest is steadily increasing. This implies the need for stronger,more expensive structures. More precise information is needed to effect structurallyadequate, but economically feasible designs. Therefore, continued research isnecessary in the field of soil dynamics.

During the last decade, researchers have done a considerable amount oflaboratory experimentation with dynamically loaded soils. 1-5 These experimentshave included dynamic triaxial shear testing, studies of pressure-wave transmissionthrough soils in shock tubes, miniature bearing tests, and others. In the field, someopportunities have been affor-.ed to study soil behavior and soil-structure interactionunder ful:-scale co: Jitions dtiring nuclear weapons effects tests. Much vi luabieinformation has been developed by same of the laboratory research, but !aboratorystudies are hampered by the great difficulty of producing soil models which willsi.miulate the behavior of large soil masses under dyn-.-i c loads. The modelingdifficulty is not present in full-size experiments performed during weapons effectstests in the field, but other problems are there encountered. By evo mear -'of these ;s the expense involved in fu:l-sc'ile field test;" with !e.a 1-Oth,,r writers6 have pointed out the problems of ins',,eu.uet;;on, ncitrF-'-'oducihi-l ity of conditions, uncertainty of load magnitude, and infreq':ency of tes'ng witnwhich the reseurcher must conierd. The ultimate obstacle to fie!d testing is theban imposed from time to time on nuclear weapon detonations. The dynamicplate-bearing tests on soil which have bee and are being corducted by th.: NavalCivil Engireering Laboratory in the test pit of the NCEL atom'. last simul-3torhave ove-comt many of the difficulties mentioned above.

The dynamic bearing capacity experiments at NCEL are couidu..:.;J ur...-rTask Y-F008-08-03-402, "Fundamental Behavinr -f SoIs Under Time-DepencenLoads." Financial support for thcsx tests has been provided by the U. S. Defense

Atomic Support Agency thronh the Bureau of Yard: and Dccks, U. S. NarvyDeportmet. rhe e. perimontal work has been performed by the :oils and PavementsDIvision with the ossistnr.-d of the Structures Division. The task is j-rt of On overallobjective of providing infornation regarding soil-structure ;nteroctior, under dynaiaicloads.

This report describes tests which hav- I-- P mode on 15-inch-dinmeter and30-inch-diameter bearing plates on dry sand without ,.ver~urden. One purposeof these initial studies was to determine the degree of usefulness of the NCELatomic blast simulator for dynamic soil testing. A second purpose was to make apreliminary study of the dynamic bearing capacity of sand on a footing of substan-tial size without resorting to nuclear weapon .etoiations in the field. These first

experiments were not expected to yield Iiie desirable ultimate product of specificd.ta for structural designers. Nevertheless, the results of these pilot tests do permitsome tentative comparisons of static verus dynamic bearing behcvior of sand.

TEST PROGRAM

Background

The design of any engineering laboratory test intended to simulate fieldconditions is dictated by the prototype field event. Within bounds imposed byavailable test equipment, and by limitations in knowledge of the true characterof the field event, t!-. test is rr.-.de as realistic as possible. The NCEL plat.-bearing test program reported here was intended as a simulation of statically anddynamically loaded spread footings without overburden. It is realized that thebeha.ior of dynamically loaded footings on the surface of the earth is not ofprimary interest in the design of protective sructures. However, as a logicalby-procluct of evaluation of the blast simulator as a soil dynarrics testing device,the determination of surface footing be'lavior shou!d provide guidance F.rdesign of more realistic experiments to be corducted in the future.

Conventic'.al foundation loads are of a long-duratin, static rcture(exclusive of certain specialIzed loads imposed by rotating machinery, or loadsimposed upon parvenrient foundations by landing aircraft, surface vehicles, etc.).The bearing capacities of soils under these zonventional types o., loads have -ongbeen determined experimentally. Basically, the dererminatiGn involves the c.ppli-cation of static load increm ',rts to a bearing pk.te restinj on the soil. Se'vefentof the bearing pl c;, :,,su, euch load ;nr.re'nent is observed, and the succeed' 3load incrernent is added onliaffer the settlement has essentially topped. T%. i

is continued until cessation is dictated by on.e u t::,% following cr:.e to: (a) te.jpplied load . oxceeded by some preielected a-mount the desijn load later to be

2

placed upon the soil; Wb sett'-ment of the plate becomes exces5dve for Ote prototypestructire later to be ploccd upoin the srnil; or (c) the soil fails to suport the appliedload. Results of the lond-settlement test are plotted in graph form, ard from thegraph may be determined the failure load and modulus of subgrade reaction %values..This modulus is useful in predicting settleme... at loads less than failure. Us~ually,it is spoken of as the "k value" of the soil, and it has the units pounds per squareinch per inch of settlement. So common has this test become that reasonably accuratek values for many type; of soils at specified densities can be obtained from engineer-ing handbooks. Also, conservative estimates of bearing capacities for var'ous typesand conditions of soils have been tabulated. In addition, there are theoreticalmethods of computing conventional, or static, bearing capacity of continuous footings-Among the most frequently used of these are tlie Terzaghi formulas. Semiampiricaladaptations of these formulas hove been developed for various footing cotifigurations.That for a circular footing, suc~h as those of the experiments reported here, is asfol laws:

q .3cNc + v DfNq + 0.6y rN~

in which q d bearing capacity (load per onit area)

c = cohesion

v= soil unit weight

Df=depth of footing (or depth of overburden)

Nc, Nq, and N. are dimensionless bearing -capac ity factors whose magnitudesdepend upon the angle of internal frictlon, 0, of thc soil. Charts are avciLu:which disclose magnitudes of the beoriuig-capacty foclors for various aotn: ifriction for soils which are relatively loose and those which are relativel> dense.No :uch widely accepted forvnuans cre available to reveal the bearing capo:;tio-of soils loaded dynamically.

Some investigators have made, theoret;:al predictions of soi; kehavior undervarious assumed dynamic loads and have written extensve computer programsutilizing those theories. Usually, a highly ideclizad soil ;,i postuiated, ant: i.

behavior is analyzne b ying the pre.,;;i c] parameters of the idealized soil Todetermine the validity of the predictions, and to refine the theorericol ~cn..it 6s necessary to have some experimental d.3to o.ti;dfrom tests .i e.al soils

3

which have been loaded by real or simulated nucle-ir blast:. To provide such loadsfrequently and economically trr many research purposes, the atumic blc-t simulatorwas developed by NCEL. 6 Tne blast simulator was used to generate the dynamicload, ap lied during the P!ate-bearing experiments reported here.

Test Apparatus and Procedure

Blast Simulator. Reduced to its basic etement-, the blast simulator (Figure 1)consists of a test chamber beneath a cylindrical expansion chamber that contains aconcentricaliy placed firing tube. Primacord, an explosive fuse material, is deto-nated in the firing tube. Gases from the explosion are metered through hundreds ofsmall holes in the firing tube into the expans,)n chamber. From there, the gasespass through slots in the bottom of the expansion chamber into the test chamber,where they impose pressure upon the item being tested. The test chamber is formedby two flat steel plates (called "skirts") which etend downward from the bottomof the expansion chamber. The plates are paralleI, are 8 inches apart, and arewelded longitudinally along their upper edges to the bottom of the expansionchamber. An item to be tested is mounted in an appropriate manner between theskirts, where it is subjected to ths pressure of the gases of the primacord explosion.The rise-time ot the pressure, the duration of the peak pressure, and the characterof the pressure decay can be controlled. Beneath the blast simulator is a pit whichhas reinforced-concrete walls and floor. The pit is 9 feet by 10 feet in plan and12 feet deep.

Soil Placement A screened and dried river sand was used as the test soil(see Appendix A, Soil Pioperties). The sand was placed in the pit from a buttom-dump hopper through a chute similar to a transit-mix concrete chute. It wasspread uniformly in 2-foot-thick layers, and each layer was vibrated into placewith a Lazan oscillator mounted on an 18-ir-ch-square wooden plate. The oscillatorwas operated at 15 cycles per second with a force output of t 60 pounds. It wasmoved about the surface of each layer in a regulo: pattern which -ro.e :"-.of vibration, on all areas of the surfac.e of the lay-ar. Aiter vibrotio. O:- cer:.the density of the layer was measured in three places by tfe sand-cone. -. fiod.Folowing each ,se of !he pit for c bearing test, the sand was loosened by .,andshoveling to a depth of 16 to 18 inches and recompacted by operation of the Lazonoscillator upon the surface in the manner previously described.

Approximotely 45 tons of sand wererequired to fill the pir to the 9-rcotdepth. The time required to remove and recompact this cmount of sand fo- e~zhloading of the ba : ,.rtc was conX'.d-,Z proli.ttive. fi:r.efo. e, the pro. .nof post-test surface loosening and recompaction was adopted. I tas , -.. :..c" -strated previously8 that sand can e comFacted t'o !epths ef many Fr et by vibration.

4

Ur _ -

It was believed that the prog-n~m of post-test looie..ing and viLratory recan.poctionwould return the sand to v' derasity condition near that existing when the sand firstwas oloced in the pit onJ prcessed by vibration. Since the aoilabie method ofin-place density measurt~nent (modified sand cone) was net considiered very accurate(see Appendix A), density was not tr easure-* .;ier each recompaction. Rather, asystemtc rottno of sail recompaction was folowed rigorously to produce compa-rable initial conditions for 'Pcch test loadirg. The series of plate-bear.*n testsreported here actually was conducted during three different time periods in thetest pit. Each tiare, sand was placed in the pit and processed as desc-ibed above.The load-settlement chuiacteristics of the sand were determined on a 15-inch-diameter steel plate under static and dynamic loads. Additional dynamic loadtests were mode on a 30-inch-diameter plate. Soiai plates were 1 inch thick.

Figure 1. .atomic blast simulator with pit covers itn pia~-,

5

Dynamic Tests. In es-,ence, the oynamic plot,:--beari-~ tests were ..;ade byplacing sand to a depth of 9 tt et in the test pit catid dynamko-li1 ioadinrt a plateon the surface of the sar.:., utlizing farces generated in the blast s'iulatur. Pres-sures in the simnulator werc made to impinge upon a steel beam placed between +-t~skirts. Forces an the beam were trangyiitt' down to the plate on ihe sand mtrougha vertical steel column welded to the bottom center of the beam. The weight ofthe beam and column loading device was 915 pounes. Downward movement of theloading system (and hence ,ettlement of the loaded Fiate% was detected by a n.rmotion potentiomreter and by a mi-dtanical scriber traveling on a rotating cylinder(see Appendix 8, Instrum~nentation). The mechanical configuration of the load*ingsystem limited total settlement to approximately 6 inches. The gross lcad on theplate was detected by a compression load ce-I placed between the bottom of thecol1umn and the steel bearing plate on the sand. Figure 2 is a schematic view ofthe test arrangement. Lou~d and settlement information were recorded electronicallyagainst the samne time base' ir a recording oscillcgraph. Figure 3 is a facsimile ofone of the test osciliograms.

Static Tests. For conventional bearing tests, the soii preparation and plateplacement were the same as for the dynamic tests, except that a hydraulic jackwas placed between the plate and the load cell. Static loads were applied byjacking against the load cell, which transmitted the load through the loadingcolumn and load beam to react against the frame af the blast simulator. Setle-ments of the bearing plate were measured by dial-type mechanical strain gages.

RESU LTS

Bearing Capacity

The tests reported here produced Icad-settlament data of statir. plate-bearingtests on the 15- n ch -diameter plate, .:nd laad-ti.e and settlement-trn mc -

of dynamic plate-bearing tests on both 15-incL dirwtterer and i-,.'"-plate%. Various difficulties with the mountings and other -3ccessories .' 'he.potentiometers -.s' d for rmeasu:rinq plat; seltement made mosi of the ciec,oricsettlement-time records unusable. Figure 3 is a facsimile of one of the few testsmade after the difficulty was cor.cted. However, the electromechanical rotating-cylinder oscillogroph (described in Apper-:x B) functioned vet"! well and p.oducedgood records of settlement versus time. Unfortunately, the tirre boses of *h.. separaeelectronc load-measuring -tysem and the electrzmechu~ical serieleerl' s~ iirirqsystem were not .,nc.:.,..,zcd, and tht;e. -A*~ts i.wo be oatyz-i only in ter,;,. :.loading ioles, settlement ratis, and peak loads versus peak setti-mn. I'vT&.e!ists these values for the 15-inch and 30-inch p~o-us. Figure 4 t, c graph of PUK.jnit load c, e I 5-inch and 30-inc!. plates ve-iJs rate or plat'e .ettlem,nt.

6

Correlation lines were determined by 'he method of leas.' squares. The~e ;s aconsiderable amount of scatrer on the graph, but the tendency seems tc. be towarda faster rate of settlem.-.- for a given init load on the 30-;nch pk..,e. This reqiiresfuture experimental confhm-atior,.

Figure 5 shows three graphs of static ioad-settlement test.- on the 15-inchplate. The avetag ' lure load for the three tests was 7.4 !ons per s-,vore foot.T~t density of the s-.. :1 at tha times of these tests w..J approxii-.'ly 112.1 poundsper cub;: foot as measured by the mnodified sand-cone method (Appendix A). Theangle of iragrnal frietlon (Appendix A) was 43 degrees. Using these values andthe bearing-capacity factors from Reference 7, the bearing capacity mray beobtained by the Te.-zaghi bearing -capacity -.quc~ion for crcular footings:

q =, 1.3cN C+ yD f Nq + 0.6y rNy

Since cohesion, c, and overburden, represened by Df, are both zero, the first twoterms drop out, and the equation becomes

q O .6y rN

0,O60l12.1 lbft 3 (7. 5in.)( 240)( 1 ft3

1728 in.

70 7psi v 5tons p@7squ,;re friot

Cumparisan with the overagea experimental result indicates the Terz.:9-iequation gives a somewhat conservatixe. value. As indicated in Appendix A,there is some uticertainty about tP.r magnitude of the unit weioht of the sand atth- time of the experiment. Trial computc ~ons show that even- maximumpossible unit weight, the bearing caipac-ty as determined by the lorzaghi methodwill be less than the average experimental value.

7

8WF31

Fivur____ 2.Skmtcdarmo ym)cbci; etacneet

0.39..

0.51 in.

1.79 psi

130 psi-

0 psi

Figure 3. Facsimi~le ot dynamic becaring test oscillogmam (No. 2C'on 15-inch-diameter plate.

9

N 4) ONt G4 . "O.

% ..- kI" " i - q -' 9. -i R c i

c C;C

M, m~ V) i 4C,.4 C', 4C) 0

-4 *1 C4 --- NC.'

0 C4~u0 o o 00004 00000 CIS ; - " d ddS K Co m o4

41R R

41--.-"N u u.,I 10U1 It)1 T 000 000

o, o 0 p 4D4i.C . C, "0 -0 l0 0.4 -

10

V. C4'2'4,

4,

4'

______ ______ I. V Sa -

V 4'

~ ~. E~0

_____ _______ Vt ~ 4, -o

N I

* ~-o00 ~

______ lx00.I-~J

*0 -rE

~ a00 . -~

______ N5~ 4

I,~. V.(~9

4,

________ ________ ~('4 - N . -

(~~) 4atd VO p00~ 4~Vfl V.sV.UAQ ~

11

-2

cqa

122

Figure 6 is a graph of F'#zk dynamic unit loads on the 15-inch plate v'ersuscorresponding peak settlerments f the plate. The graph was obtained by plottingthe peak load and peak settlement values from each of eleven dynamic tests. Thepermanent settlement of the plate in most cases amounted tv 75 to 90 percent of thepeak settlement; but the peak settlement is -1 critical value in shelter design, andthat is the value chosen for Figure 6. The figure shows the peak dynamic unit loadcarried by the plate to be 196 psi, or 14.1 tons per square foot. This is nearly doublethe average static experimental value of 7.4 tons per square foot. Figures 7 and 8are photographs of the 30-inch plate before and after application of a dynamic lod.They illustrate the-punching type of action which was similar for all dynamic testsin this series.

Bearing Modulus

In addition to the bearing capacity, the beari.g modulus or k value also is ofinterest in shelter design. If means are available to predict load on a footing, thek value will give, some idea of the settlement to expect. Though these preliminaryexperiments were made on circular plates on the soil surface, the relative values ofk for static and dynamic loads are significant. Such values of the secant modulusat several amounts of settlement on the 15-inch plate are shown in Table II. Aswith the bearing capacity, the dynamic secant modulus values are considerablylarger than the static values.

Table " Compu.ison of Secant Bearing Moduli, k, of15-Inch-Diameter Plate Loaded Staticallyand Dynamically

Settlement Static k, Dynamic k,(in.) (p i/in.) (psi/"

0.25 160.3 ')96.0

0.50 137.7 226.00.75 126.0 184.0

1.00 108.0 15o.0

13

250

200

0

110

CL

12 3 4

Pooh SqttlO~wf of Plot. (in.)

Figure 6. Peak dynamic unlit load versus peak settlemnont of15- inch -diameter plate with no overburden.

14

Figure 7. 30-inch-diameter plate before application of load.

Figure 8. 3O-i.nch-diameter plate after applicationi of dynamic Imad.

15

Most of the results repe "ted here pertain to tie 15-inch plate. Te'-ts on the30-in:h plate were not ar. fru*tuI.. The relationship between appiied dyamic loadand plate settlement is not readily apparent from a graph of these d.ia for the largerplate. This may be explained in part by the details of the experimental procedure.Most soil mechanics texts contend that w 4i. footing is loaded the majo, iorrionof the soil-stress increase beneath the footing takes place in a zone extending fromthe soil surface to a depth uf 1-1/2 to 2 times the width of the footirG. In thatzone, an additional effect is an increase of soil density, or unit weight. Such adensity increite means that subsequent Ioadings will produce successively lesssettlement per unit of applied load on the footing. In conducting experiments todetermine the relationship of dynamic load to settlement, the cumulative effectsof the loads upon subsequent test settlements are undesirable. Preferably, eachtest loading should be made u-pon a soil mass which has had the same load historyas all others in the series. Time cmd cost precluded the provision of a new soilmass for each test in the series reported here. Consequently, the previouslydescribed program of surface loosening and recompaction followed each test load-ing. This repro.essing to a depth of 16 to 18 inches was somewhat effective forthe 15-inch plate, since a large percentage of the zone principally affecting theplate behavior mas returned to a density reasonably similar for all the tests. How-ever, the zone of significant density increase under a loaded 30-inch plate mightextend to a depth of 5 feet. Reprocessing the upper 18 inches would not besufficient. Such apparently was the coase, as may be seen in Figure 9, which -howsthe dynamic load versus settlement of the 30-inch plate. The number at each doaapo*nt indicates the chronological order of the tests. Those marked with a -ubscript$a: were not nade u.rinj the uime test period as the others. That is, the -%t I:;was emptied and refilled between tests marked "B" and "Ia." It is nominally truethat the pretest load history of point "la" was similar to that of point "1.0 Ths.envelope shown by the 6ashed lines on Figure 9 is an estimate of the range with;,,which a graph of dynamic load-settlement would fall if each test had been madeon sand previously not used for a test loading of a 30-inch plate. Being an -timate,the graph shown in Figure 9 is only of minor interest; but ;f the f- o;r r,. -is coorect, then the envelc.:e shows qualitatively tha: ;e :cl..omic k .-ihe atoeo,with increasing plate size. This may be seen in concept by cntparing Houres 6 and9. Such a relationship between s:oti. L value and plate size is well estoL!-.hC. 9

ASSESSMEl 'T OF TESTS

The objective of the -,,rk reported het w-s to oibtain saome preln, w,comporisons of static versus dynamic bearing behavior of sand while e",'!ua: .g theL'ost simulator as a soil-testing device. The rL...,"" of variables whch ultim.ulel-m,:.;t be investioated is very large. For this limited tial, they pu.posely were kept

16

-cop

to a minimum. Only one type o- soil was used, and attempth were made to maintainconstant soil density from t.st! to rest. Using dry sand circumvented tke necessity of

evaluating moisture effects. Two sizes of circular bearing plate were used. However,only the performance of the 15-inch plate hos been emphasized. Two types of load-ing were used. The static loading method was that which has tong been employed forbuilding-site investigations. The dynamic loads were :imple triangular pjises withsharp rise and exponential decay.

Included among the many factors which must be investigated are (1) the effectsof footing size, shape, rigidity, and inertia; (2) soil properties, including the marjni-tude .of the mass involved; and (3) load charact,!ristics, including inertial effects ofmasse. transmitting the loads. After evaluation of these effects, some of which arenow heing investigated at NCEI., the results will be compared and combined withthe work of others, and attempts will be made to f,mulate theoretical explanationsof footing behavior.

The blast simulator facilities at NCEL provide an opportunity to make soilsstudies in a larger volume of soil than can be utilized at most !aboratories. Thisalleviates, but does not eliminate, undesirable boundary effects. A closer studyof those boundary effects is a planned part of future experiments.

In general, the blast simulator worked very well as a loading dev'.* for thebearing plates. The magnitude of available dynamic load was ample for the size offooting which reasonay can be tested in the simulator pit. Difficulty was t-xperi-enced with some instrumentation mountings (Appendix B), but that difficulty itas beencorrected. A more serious problem was that of controlling the soil conditions.Pouring the soil into the pit through a chute created some grain-size segregation,

and undoubtedly contributed to nonuniform density dist:ibution. Some auxiliaryeffort is needed to perfect handling and placing techniques for the 40 to 50 cubicyards of soil used in these experiments. To this end, some auxiliary tests n1oc,-.- '

hnve been completed.1 0

With regard to a gain of vil dynamics information, severil comments -lay bemade. The numerical values deveioped in this preliminary study are useful primu~ilyfor indicating trends. In part, this is due to the probable errors in data from the30-inch-diameter plate tests assumed to iuv-, 6een caused by the cumulativeincreases in density at significant depthi beneath the plate. The .sts on the15-inch-diameter plate are more reliable. The li'isation in usefuiness of bot'isizes results From t'. ratu.. _r the exper'nicts; ;.c., the testT were loads G;isurface footings, a situation not widely encountered by designers nf pro... .i."str'ictures. The 15-inch plate tests do serve to sl-ow 4iat, under the soecificc.nditions of :'ie tests, the settlement wus much less under dynamc load than

17

under equal static load. Rise-times of .he dynan'c loo&l, on the pla..! were on theorder of 0.01 second, and ' -d durations were 3n the order c' 1.0 se'!und. Thena.'ural period of the sand itestimated to have been opproximot-ty O.C65 to 0.075second, based upon cxtensive vibratory compaction experiments made upon sord. 8

Even in dry sand, which reaches a state of equilibrium under a ;tat*callv loadedplate faster than othe.r soi~s, a dynamic load should not produce as much settlementas an equal static load unless the duration was ;evera' hundred times as lIng as thenatural period of the siou. Detonation of nuclear weapons does not produce loadsof such duradion. Furthermore, the inertia of the sail would tend to reduce settle-ment unde, vi dynamic load. Therefore, it is reasonable to ccnclude tf~ot compa'rativevalues of dynamic. versus static lood-scttlement d;sclosed by the tests reported herefor the 15-inch plate ore qualitntively similar to results that would be experiencedin the field under nuclear-detonation loads versus static loads.

250 _____- ____-

601

200 -_ _ _ _ _ _ _ _

61

Co _______ _____AOl ___

C

00 _______100-_ _ _____0__

50 _ _

012 3 a -

Figure 9. Peak dynamic unit inad versus peak setnement of30-inch-diameter plate with rio overburdeom.

18

-Mf

FINDINGS AND CONCLUSIONS

1. The NCEL blast simu!lor and test pit are useful for conducting -tatir anddynamic plate-bearing experiments on soil.

2. The dynamic bearing capacity under the 15-inch-diameter plate was approximately90 percent greater than the static bearing capacity; i.e., 14.1 versus 7.4 tons persquare foot.

3. The k voa!, for the dynamically loaded 15-inch plate was higher than for thestatically loaded 15-inch plate; e.g., at a settlement of 0.5 inch, the dynamick = 226 psi/inch and the static k = 137.7 psi/inch.

4. Though the results of tests on the 30-inch plate are questionable, the indicationsare that the dynamic k vales for the 30-inch pic-te are less than for the 15-inchplate. This parallels accepted knowledge of statically loaded plate behavior.

5. Again with, reservations about the 30-inch test results, the dynamic unit bearingcapacity of the 15-inch plate is greater thcn that of the 30-Inch plate. Ti.s alsoparallels accepted knowledge of statically loaded plate behavior.

FUTURE PLANS

The tests reported here were intended, in part, as preparation for moresophisticated experiments, reports of which wil! be forthcoming. The long-rangeplan for lynomic bearing capacity research under this task includes investigationsof the etfects of overburden, type of footing, and soil cohesiveness. The nextreport in the series will be concerned with a spread footing loaded statically anddynamically on dry sand while under various amounts of overburden. Followingthat will be studies of a wall or strip f-oting loaded statically and dynlarl.on dry sand while under various amoun.s of ove b,-rden. Forticului .nn,",)e placed upon tests of a strip footing having overbuiden on one side or,',', uswo,ld be the usual case for the footing of a buried structure.

rhe effects of soil cohesiveness may be studied experimentally or analytically.If Aone experimentally, the initial tests ptv;-b.ily will be made on sand whkb :asapparent cohesion caused by the introduction of moisture. It is toot yet cer t nwhether it will be physically and economically fe,,sible tn use a true clh ,;vi soiifor bearing capatc;, exper -," .rs in the N!CFL bl.la simulao: test pit. Hensc-analytical techniques may be employed, in conjunction with the reslt ; *e...,or, noricohesive dry sand, to estimate the effects of c ohesiveness.

19

!gil Z

In fuature tests ini the blast simulator test pit, the width of footing tested willbe limited to 12 or 15 inches. This wili permit repvzicessing the principc 'y affectedstrata while keeping the depth' of necessary reprocessing within reasonakie limrits.

Improved methods will, continue to be sought for placing soil in the test pitso that soil conditions will be uniform thrcr.p out. Also, better meth,:ds v4;ti besought to measure the true unit weight of the soil in place. For example, atechnique of sieving the soil into place is being evcluated for providing uniformdensity and nonsegregation of grain sizes. Nuclear soil clensity meters ore beingconsidered as a method of measuring density without disturbing the test soil.

ACKNOWLEDGMENTS

Aporeciation is exprogwd to those col~eagues who contributed valuablesuggestions during the conduct of this study. The following personnel of the Soi'sand Pavements Division of NCEL were employed at various times on the task:M. C. Chapman. R. Lorenzana, T. J. Garcia, and R. L Davis. C. J. Smith of theStructures Division also assisted. Special thanks are dcie to S. K. Takohashi ofthe Structures Division.

RE FERE NC ES

1. Massachusetts Institute of Technology, Department of Civil and Sanitat yEng~neering. The Be -qvior of ',oils Under Dynamic Loadings. Vol. 1 (August 1952),*Hydraulic Machine for Dynam ic Compression Tests." Vol. 2 (July 1953), 'InterimReport on Wave Propagation and Strain Rate Effect." Vol. 3 (August 1954), "FinalReport on Laboratory Studies." Cambridge, Massachusetts.

2. Walter E. Fisher. Experimental Studies of Dyr.3mically Loaded Footings on Sand.A report to the U. S. Army Engineer Y/citerways Evperiment Station uender ~No. DA-22-079-ENG-240. Univers.;y of ilinoi.-., Urbuna, IIi... J'j~v VdA

3. G eorge E. Trondafil dis. Analytical Study of Dynamic Btaring Ccpa(.ty ofr.,undations. A report to the Otfense Atomic Support Agency under ContractNo. DA-22-079-ENG-240, R&D Subproject No. 8S12-95-002. University ofll'.nrois, Urbana, Illinois, January 1961.

4. J. E. Roberts. "Small-Scale Footing Studies: A Revew of the Litc-,tilr*,"Appendix B to Pr-"rrirc.,, ":sign Stud,' a D,amic SolI Testing Loboiar~- i.A. report to the U. S. Air Force Special Weapons Center, Kirtland- Air F,. -eNew Mexico,.under Contract No. AF 29(601)-,9,&-,. Massochuset's Institute ofTechnology, fe"...bridge, Massachusett, July 196).

20

5. Narbey Khachaturian. Report on Survey of 1.1terature in Connection ;Ith theDynam ic, Bearing Capacity or Soils. A report to the U. S. Army Enginecr WaterwaysExperiment Station unde- Contract No. DA-22-079-ENG-240, R&L, SubprojectNo. 8-12-95-4X. University of Illinois, Urbane, Illinois, October 1959.

6. W. A. Show and J. R. Allgood. "An Atomic Blast Simulator," Proceedings ofthe Society for Experimental Stress Analysis, Vol. XVII, No. 1, 1959.

7. Karl Terzoghi and Ralph B. Peck. Soil Mechanics in Engineering Practice,John Wiley Z. Sons, New York, 1948.

8. California Institute of Technology. Vibruior, -Compaction of Sand. A reportsubmitted to the U. S. Naval Civil EngineerinT Laboratory under ContractNo. N~y-22271. Pasadena, California. January 1952.

9. Bureau of Yards and Docks. NAVDOCKS TP-Pw-4, Airfield Pavement.Washington, D). C., January 1953.

10. J. Nielsen. Technical Note N-520, Investigation of a Techniqu.e for PlacingSand irr the NCEL Blast Simuiator Pit. U. S. N1 aval Civil Engineering Laboratory,Port Hueneme, California, June 1963.

11]. Donald F. Griffin. USCEC Report 52- 101, In-Place Density Tests of tmontal.oBase Course Material Under Controlled Conditions. A report submitted to %~eU. S. Naval Civil Er.;neering laboratory under Contract No. NBy-3101.Engineering Center, University of Southern California, Los Angeles, June 1956.

21

*Appendix A

SOIL PROPERTIES

The send used for plate--beoring tests and certain other soil -structure*;nteraction experiments at NCEL is tak-!n fromt the bed of the Santa Clara Riverin V/entujra County, California. After being screenedJ and dried by the process,-.r,it is stored in indoor bunkers until placed in the NCEL blast sirtiujctoo test pit.Since the blast simulator is on ir'door facility, the sand has little contact withoutdoor atmosphere. Consequently, it remains quite dry throughout tht experi-ments. After severa; weeks in the test pit, '4e moisture content of the sand atthe end of any test period never reached 0.5 percent through absorption fromth.e atmosphere.

Several soporate shipments of sand have been, sampled f.om time to timeover a period if several years and found to hove remarkably constant grain-sizedistribut;on. That distribution is shown in the graph of Figure A-]. The maximumsize of the sand is 2.5 mm. The effective size is 0.21 mm, and the uniformitycoefficient is 3.

Auxiliary experiments have been mode with the NCEL test so.-d as port ofNCEL Task Y-F008-08-03-402 "Funidanmental Behavior of Soils Under T ime-De,,endent Loads." These have included determination of specific gravity, waterpermeablity, one-'"mensiom. I consolidation, and angle of internal frictizin. Someof these values ore listed in Table A-I.

Same difficulty was experienced in placing the sand uniformly in the testpit. Every effort was made to spread and compact the sand to e-homogenoeous grain-size distribution and a uniform density. Random thin strata of size-segi-egotedparticles were encountered during dins ity -meas.. rementtoperati--r's. lrnp-,placement tec~hniques are necessary.

In-ploca densty, or ur it weight, of the sand was mea~ured by a rn thodlsimilar to ASTM Designation D-1556-58T, "Density of Sail in Picce by theSand-Cone Method." Since the sand used for the bearing tests was dry, ;t wasimpossibi' to excavate a hole which wo.Ala retain it -ize and shape for voi jitedetermination with the sand-cone apparatus. It was necessary to modify thedensity -meos.ring apparatus to the extent of a~ding a cylindrikul prr '-tiorl tothe I -ttom of i,. plute u.j to &upsa ,~sn oe tt~ fte oat-ais shown itn Figure A-2. In use, the cylinder was inserted into the v.; n-'.conie-support plate was pressed dlownward unt.1 t!-e bottom surfince of the plarte

22

just contacted the soil. Sot #-hen -Nos excavated from within the cylinder. Thecavity thus formed was beckf~iled with- sand of known ur.*t weight using the sand-cone method mentioned previously. The ccibrated sand used for backfilling wasOttawa Sand, ASTM Designation C-i9-59. The unit weight of the test soi' inplace was catlculated using the weight of w:; exc-vated and the weght ofcalibrated sand used for backfil.

The volume of a cavity as determined by the mand-cone method is reasonablyaccurate.) I Aisc, the weight of soil removed for a density determination can bemeasured with great accuracy, However, the =iI was disturbed by the necessaryuse of the cylinder to support the cavity wail during excavation and volumemeasurement, This disturbance was considered great enough, in the tests reportedhere, to affect the density determination. The avercge density of the river sandupon which the NCEL plate-bearing tests were made w'as 109.1 pounds per cubicfoot. This value was determined by the modified sand-cone method just described.The maximum and minimum densitles of the river sand were found experimentallyto be 1 14.7 and 95.0 pounds per cub; z foot.

In another experiment at NCEL which has not yet been reported, sa nd waspl'iced 'n t'le bicst simulator test pit in a marnr sisnilor to that reported here forthe plare-6foring tests. In-place density was measured in the m-,nner reportedkere. In addition, a loog was kept of the weight of river sanid placed in the pit.Meastiremiint of the dimensions of that portion of the pit occupied by the sandpermitted cclcitlation of the volume and, hence, the density of the sand in place.rho se.'d-cane-cylnit: r rrethoo indicated the density to Le 113.1 )P~unds pe Icubic iuot. The weight log and volume measurement mathod reveaLtsd the densityto be 106,7 ;x"..nds per cubic foot. Of course, thime do aore insufficient top'-!v~deo correction factor to the pIate-bearirn,-te3., i"'s4 y '!ata. They dop"Vide frvidence of the directton of the error.

Knowledgze of the true density of tme :ind at the t;-! '.o:.- ~ swas not as qmportant as uniformity of th 6ensity hfr',m Aoze w~ place in 4ie pirand fromr test to test. As stated in tle ~oibody o; *s report, an attez-pt 'aachieve a homoganeous densty -afttrr. ivas n'cde h.y riqoros!y adhar~ng to asystematic pattern ofplacenient and vibation. 4CeTVWee te:ts, a routrne ofsurface loosening and revibration wzi o3ois'

For future tests requiring the ose of Icr. e .iokm~res of so! , hcei Ter , ethod;of placement and compaction or, rc~-a. 4!so ;--&e'd is a more reliablemethod o n-place .jensity maisu.reint.

23

Gcm~ Six* (mmn)

100 -q L%,r :''Ii! t 4

70 -- --

s- -- INI II

0

30 - - - - - - -

20 - - - -

10 - - - -- -

Mashes Pf Nas, U. S. SI-e.d

Figure A-1. Grain-size distribution of sand usedfor plate-bearing experimnents.

24

1111 W ". 1!, ri ,

Table A-I. Fundamental Physical P -operties of SoilUsed for Plate-Bearing Tests

Typ, of soil sand

Secant modulus of compression(consolidometer) at 50 psi:

at density =105.8 lb/ft3 6,500 psiat density = 1]11.9 l b/ft3 10,100 psi

Moisture content 0

Cohesion 0

Angle of internal friction43at density 1 1 l IIb/ft3

Specific gravity 2.62

Maximum grain size 2.5 mm

Effective size, 010 0.21 mm

Uniformity coefficient 3

Permeabilityat density = 95 lb/ft3 0.01'6 in./secat density = 105 lb/tt 3 0.0096 ii-..ec

25

11-i,'Edie

6-3/4 die

4-3/4*dio a

60.1 surfae

* -3/321 Wallo i Thiekna..

Figure A-2. Cross section of cylindrical wall support device usedfor sand-cone method of density determination indry sand.

26

SAppendix B

INSTRUMENTATION

Only two basic measurements were made d ring the conduct of the bearingtests - the load on the plate and the settlement of the plate. For the dynamictests, the load and settlement were recorded against a time base.

Plate settlement during static testing was detected by one of two methods.The first was the conventional use of mechanical strain dials. Four were used,and they were placed to detect vertical motion I inch from the edge of the plateon each of four radii 90 degrees apart. The other method of settlement measure--ent involved replacement of the strain dials by a Bourns Model 108 16-inch-strokelinear-motion potentiometer. It was connected to a four-arm bridge circuit. Aschematic of the circuit ig shown in Figure B-1. Motion of the plate, and hence ofthe potentiomet3r stem, caused an unbalance in the bridge. The unbalance wasmeasured with a Baldwin Type M SR-4 strain indicator. Precalibration of this systemagainst measured motion of the potentiometer stem permitted later computation ofthe plate settlement. The mechanical strain dials are quite satisfactory for statictests, but the potentiometer was used as a trial for planned future static tests inwhich strain dials will not be usable. The potentiometer functioned very well forthe static tests.

For the dynami te:ts, the strain dials naturally could not be used. initead,the 16-inch potentiometer was used in conjunction with the four-arm bridge.However, automatic recording of the dynamic settlement was necessary, and thiswas done with a bridge amplifier and recording osc'l!ograph. The electronicamplifying and recording equipment wi manufactured by ConsolidatedElectrodynamics Corporation (CEC). A CEC Type I-113B carrier amplifier-da CEC Type 7-323 galvanometer were used. This ampliF;--, with- c+i+a .K nX,*.jpply. is desigrated "System D" by the manufacturer, The -itst tests u,;;7zed aCEC Type 5-114 recording oscillograph. Later, this was replaced by a .ECType 5-119 osciltograph. This equ'pmnt is capable of monitoring dyncmicphenomena having frequencies up to 600 cycles per second, which is quite ade-quate for these experiments.

Considerable difficulty was experienced with potentiometer .wountingsduring the dynamic tests., These t"oblems were nr otrihutrible to the potec.iometer. The flexitii',y of the mountings and the mass-of the moving por! of • opotentiometer, though small, produced vibrations it +he settlement-measuringsystem. These vibrations obscured many of the oscillograms of plate settlement

27

• V

to the degree that they were unusable. (oward the end of the series of tests, thetrouble was corrected. The .tentiometer has worked well on , ther NCEL experi-ments not reported here ) A supplementary electromechonical dev-re was used inconiunction with the potentiometer to provide a settlement-time record in the eventof failure of the primary potentiometer sys.em. Because of the di;dic'Jlties mentionedearlier, the supplementary device actually become the primary means of measuringplate settlement. This supplementary device, whlc may be considered as a rotating-cylinder oscillograph, was developed by personnel of the. Structures Division, hICELIt consists of a spring-loaded pencil, and a paper-covered cylinder which rotates ata constant k..jwn speed to provide a time base. In use, the cylinder wvs so orientedthat the spring-loaded pencil, which was attached to the plate-bearing-test loadingmechanism, traveled parallel to the axis of the cylinder. The pencil scribed a mark,the excursion of which was equal to the settlement of the bearing plate. Rotationof the cylinder provided the time base from which rates of settlement were computed.This device was not coupled to the load-recordi.-g oscillograph, hence the time basesfor load and settlement were not synchronized. This precluded analysis of t6a dynamictest data in terms of load versus settlement at any particular instant of time. However,a study of maximum load versus maimum settlement was possible. Also, it was possibleto study load-time and settlement-time phenomena independently.

Static plate loads were measured with a Baldwin Type C SR-4 compression loadcell. The load cell was placed between the reacrion column and the hydraulic jackused to apply the load. The electronic output of the load cell was read on aBaldwin Type M SR-4 strain indicator. Th load cell was previously colibrated withthe Type M indicator in a 300-kip compmssion-testing machine.

Dynamic loads also were measured with a Baldwin Type C SR-4 load cell.For some of the tests, a 100-kip-capacity cell was used. For others, where dictatedby anticipated load, a 200-kip cell was used. During dynamic tests, the load cellwas operated through CEC "System D" equipment and recorded with the polentiometer-measured settlement data against the same time base in the recording o '-v,.

The load cells also were calibrated s.aticai!y with the "System p .. l priSA'

300-kip testing machine.

28

A-. Poftnt.0me:.r

39.5" 1 39.5kf2

30C

3001-

Fig're B-1. Schematic diograi" of potentiometer and L. oge circuitused to monitor bearirg-ploie settlement.

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34

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No. of TotelActivities Copes

I I CDR H. L.Murphry, ffe,m 211, Federal Office Building, Son Francisco

1 1 LCDR W. M. Bannister, CEC, US", Fleid Commend, Daises* Atomsic Support Agency,Sandia Bae, Albuquerque, N, M.

I 1 Major Robert Crawford, USAF, Air Fo,s Wepons Laboratory, Kirliont Air ForceBae, Albuquerque, N. M.

I 1 Orv. Johnt Balloch, Director., Operations Analysis, 26th Air Division, SAGE,e.coc k Field, Syracuse, N. Y.

I Mr. J. F. Toenini, A & E Devoloprn..t Division, Office of Civil Defense,Dvpertment of Defense, Washington, 0. C.

1 I LCOR C, R. Whipplo, CEC. USM, U. S. Novel Ordnance Laboroor, Whit* Oak, Md.

I 1 Or. W. E. Fisher, Air Fore. Weapons Lohorotory, Kirtland Air Force Bass,Albuquerque, N. M.

1 1 ~Mr. Everitt P. Bllzerd, Director, Neutren P'hysics, Oak Rid"e Natioal Labeoe",P.O0. beox X, Oak Rdge, Ternn.

1 1 LCOE T. Toshihera, CEC, USN, 0I. S. Novel Civi Engineering Laoarsy,Port Hueneme, Celif.

I 1 LT M. MacDonaeld, CEC, USH, U. S. Novel School. CEC Officers, Pert Muenem.,Cal if.

I 1 L ihrr, Engineering Department, Uni-earsity of California, 405 Hilgefd Avenue,Los agles

1 I Sandia Corperation, Bon 5g00. Albuquerque, N. M.

I 1 Rivers e,.d Harbor Library, Prineeten Uairersiry. Princeton, N. J.

I 1 Hed, Civil Engineering Deperneent, Carnegie Institute. of Technology, Scltenley Perk,Pittsburgh, Pa.

I Mr. G. M. Albright, Pannsoylvenie Stete University, College of Engi~.eering an.~Architec, *, 111111e10.7 Per, P.

1 1 Mr. A. F. Dill, Civil Engineering Mell, University of Illinois, Urben*, Ill.

1 I Dr. N.M. Newmaerk, Civil Englnoerng Hell, University of Illinois, Urbana, III.

1 1 Professor J1. Neils Thomepson. Civil Engineering Oporinsent, University of Teaxes,Austin, Tex.

I 1 mt. Fred Sauer, Physics Department, Stenford Reserch Institute, Menlo Perk, Cifi

1 1 Dr. T. H. Schiffeien, Armour Roseerer, f'eudsien of ll' .alv, I- - 1 4Toclinelogly Cente. Chicogo, 1ll.

I Dr. RobettV. Whitsnl escssv IsiueofTcv~ev eh~te es

I 1 Dr. Levvis V. Spencer, Ottewe University, Physics Department, Oyiwe, Kean.

1 I Mr. E. E. Slselowits, Protective Constructien, GSA Building, 19*6 end F Streets, N. .,Weshor.gton. 0. C.

I 1 Mr. Werner Webar, Nucleer ngnring Consultant, N. Y. State -il Defense CmsinP.O. Bern 7007, State offi c. uiding, Albany, N.Y.

I 1 Dr. Herold Brad., The Rend Cerporatien, 17u0 Mai., Street, Sante Menico, t7:1f.

I I Mr. R. 0. Cove-lough, berry Con-?els, Inc., 700 Pleasant Strest. Watertown. A,

35

~w

DISTRIBUTION LIST (Coned)

AMe. ofe TotalAciiis Copies

* I Mr. Kenneth '.~oBodre eer eprwe.11 ~t:." n.Bu.rlingeame, Calif.

1 1 Mr. Thames, Morrison, A 'oricorn Moc~li eand Fou.ndry Comepany, ?521 Nrrtt Nart:Avee. miles, 11.

1 I. Mik. Walter (runthor,The Mitra, Corporation. P.O. Bo. 208, Losing,e., Mess.

1 I) Mr. W. R. P ..ret - S112, Appliedf Experiments Divrision, Sandie ja ttn* Albirquerque., N.MI. C~ptaIo

1 I Mr. Lyndon Welch, Eberle IA. S..,h Associates, Inc~. 153 East Elizabeth Street,

I Professor Herbert M. Beach, Putblic HoealI Engineering, School of Public Health,* University of Minnesota, Mnneapolis, Minn.

1 Dr. Unrit P. White, Civil Engineering Deperwsenr., School of Engineering, University-of Masachusetts, Amherst, Mess.

I Dr. Rnbe~t . .Hanson, Deportmenttof Civil & Sanitary Engineering. MassachusettsInstitute of Technology, Cembris.t Mass.

1 1 Mr. Harold Horowitz, Butilding Research Institute, National Academy of Sciencs,2101 Constitution Aeeonu., NWV, Washington, 0. C.

1 1 Mr. Lukeo Voriwan . 5112, Applied Experiments Divrision, Sandia Corporation,.7Albuquertue, N.MI.

1 I. - Mr. Richard Park, Notional Acaedomy of Sciences, 2101 Constitution Aventie N. WWashington, 0. C.

11 Mr. Fredeorick A. Pamley, AlA Research Secretary. American Institute of Archoects,1735 New York Avnune, H. 0 Washington, 0. C.

1 I Prof. M. L. P. Go, Civet Engineering Deportmant Un-narssity of Howo-i, Honolulu,Howo,,

I 1 Dr. F. E sasay, Doeos Researc Beard, Department of Natronal Defense,Ottawa, (.ne04te

1 Dr. Robert Rapp, The Rend Coppoerilm, 1700 Main Stre.9, Satal Monica. Calif.

I 1 o~. Stephen B. W~toy, Program Oirer, Swery Research Canter, University of

Michigan, Ann Arbor, Meic..

I I Dr. Eric T. Clarke, Technical Operations, Inc., Burlington, Mess.

I Dr. A. B. Chilton, Civil Engm,nring Nell, U.. rsiry of Illinois, U.rban. ;!I.

1 Mrs. Shea Valley, CRTZS, A. I. Coes~br tfe.*ech Cente.r. Sedford. Mt..

I Professor J. T'. Hanley, Department of Civil Engineering, University of Mi~mneta.M-onopelis, Mint.

1 I Atest. Professor .1. Silverman, Departmentaof Chemical Ergineering, Universiry ofMsirylersd, Co~log. Pork, Md.

1 1 13,. F'. T. Mavis, Dean, College .1f oasring, Urer~es.y of fa.,ylarnd, CollegePark, Md.

1 1 .0. Raymond R. Fox, Associate Prefrisar oe Director, Pratecti'., CenstructiorCourses, The George Washington Unrsity, Wosh,nglti, D. C.

.16

DISTRI BUTION LIST (Cant I

No. of Total

I Director, U S, Army Envg-see Wotir-iys Expse.int Station. P. 0. Baix 631.Vicksb.,-j1. Mis, Air.- Mr. R. W. Cnn

I I Professlor F. E. Richort, Jr, Head, L).portmost of Civ p ErigineiernvUniversity of Michigan, Ann Arbor, Mich.

I Profess.r W. S. Housel, [lepoirtment of C-1i EngnrinIj Unisy ofMichigan, Ann ArbcIr Mich.

1 I Profess*r M. G. Spomi,j!.r, epr-siof Cmvil Enig.ieeing. Iowa StateUniversity, Iowa Cit, Iowit

1 I Profssoriii N. T. Dov,ssan, Department of CvIi Enigieering, Uniivrity

of Illinois, Urbana, I11.

I Professo., R. K. Bernharvd, Princeton University, Princeton, N. J..

I I Proffeszor F. J. Conveirso. California Institute of Technology, Pasadena,Calif.

1 I Professor 0. A. Sawyer. University of Florida, Gainesville, Fla.

1 I Professor G. A. Lisonoris. School af C-vl Engineering, Purdue Un-irsity.West Lafayette, Ind.

1 1 Dr. Norman W. McLeod, Imperial O.1 Co., Ltd.. Tworito. Can.

I I Mr. George, Triondofilidis, University of New Mexico, Air Farce ShockTube Foczlity. PO. Sox 1S8, University Station, Albuqerqiue, N. M.

I Mr. Jo~hn Le..s, DNfeiuset Atooaii Sup,i1 Ade)sI 0ep,rIieiit of Defense,

Washingto. D. C.I

37

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