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NASA CONTRACTOR REPORT 159199

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DEPARTMENT OF C I V I L ENGINEERING SCHOOL OF ENGINEERING OLD DOMINION UNIVERSITY NORFOLK VIRGINIA

N80- 15299

S O I L ANALYSES AND ELmLUATIONS

DYNAMICS RESEARCH F A C I L I T Y FOR

AIRCRAFT CRASH TESTS ._-

BY

Robert Y. K. Cheng

,T THE IMPACT

TWO FULL-SCALE

Final Report For the period May 24-August 31, 1977

Prepared f o r t h e National Aeronautics and Space Administration Langley Research Center Hampton, Virginia

Under Master Contract Agreement NASI-14193 Task Authorization No. 36 Robert G. Thornson, Technical Monitor Structures and Dynamics Division

December 1977

https://ntrs.nasa.gov/search.jsp?R=19800007040 2020-04-28T03:19:04+00:00Z

DEPPSTMENT OF CIVIL ENGINEERING SCHOOL OF ENGINEERING OLD DOMINION UNIVERSITY NORFOLK, VIRGINIA

S O I L ANALYSES AND EVALUATIGNS A T THE IMPACT

DYNAMICS RESEARCH F A C I L I T Y FCR TWO FULL-SCALE

A I R C R A F T CRASH T E S T S

BY

Robert Y. K. Cheng

Final Report For the period May 24-August 31, 1977

Prepared f o r t h e National Aeronautics and Space Administration Langley Research Center Xampton, Virginia

Under Master Contract Agreement NASI-14193 Task Authorization No. 36 Robert G. Thomson, Technical Monitor Structures and Dynamics Division

Sxjmitted by t h z O l d Dominion University Research Norfolk, Virginia 23508

December 1977

Foundation

TABLE OF CONTENTS

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . SOIL TEST BED . . . . . . . . . . . . . . . . . . . . . . LABORATORY AND FIELD MEASUREMENT METHODS . . . . . . . .

Soil Classification Using Grain Size Analysis . . . Moisture Content Determination . . . . . . . . . . . Moisture Density Determination . . . . . . . . . . . Field Density Determination . . . . . . . . . . . . The California Bearing Ratio (CBR) . . . . . . . . . Airfield Cone Penetrometer Measurement for S o i l Strength . . . . . . . . . . . . . . . . . . . . .

SOIL ANALYSES AND RECOMMENDATIONS . . . . . . . . . . . . CONSTRUCTION OF TEST BEDS . . . . . . . . . . . . . . . .

Test Bed 1 . . . . . . . . . . . . . . . . . . . . . Test Bed 2 . . . . . . . . . . . . . . . . . . . . .

FIELD MEASUREMENTS . . . . . . . . . . . . . . . . . . . CRASH TEST RESULTS . . . . . . . . . . . . . . . . . . .

T e s t 1 . . . . . . . . . . . . . . . . . . . . . . . Test2 . . . . . . . . . . . . . . . . . . . . . . .

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . . . . . . . . . .

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LIST OF TABLES

Table Page

1 CBR, mois ture c o n t e n t , and d ry d e n s i t y measurements 15

2 Measured A i r f i e l d Index (AI! values f o r tes t bed 1 . 1 6

3 Measured A i r f i e l d Index (AI) values for test bed 2 . 1 8

LIST OF FIGURES

Fiqure

1 F u l l - s c a l e a i r c r a f t crash-test technique . . . . . . 2 Grain s i z e d i s t r i b u t i o n curve . . . . . . . . . . . 3 Moisture d e n s i t y r e l a t i o n s h i p . . . . . . . . . . . 4 Schematic of CBR f i e l d test . . . . I . . . . . . . 5 Schematic of a i r f i e l d cone penetrometer . . . . . . 6 CBR and mois ture c o n t e n t r e l a t i o n s h i p . . . . . . . 7 A i r f i e l d Index and CBR r e l a t i o n s h i p . . . . . . . . 8 R e l a t i v e so i l e l e v a t i o n of test beds . . . . . . . . 9 CBB a long t h e f l i g h t p a t h . . . . . . . . . . . . .

1 0 V a r i a t i o n of A i r f i e l d Index number w i t h depth a long t h e f l i g h t p a t h between grid points G1 and G 6 . . .

11. Var ia t ion of mois ture c o n t e n t and c?ry d e n s i t y &long the f l i g h t pa th between g r i d p o i n t s G2 apd G5 . . .

12. C r a t e r and s o i l p r o f i l e a long f l i g h t pa th c r e a t e d by c r a s h test 1 . . . . . . . . . . . . . . . . .

13. C r a t e r and soil p r o f i l e a long f l i g h t p a t h created by c r a s h tes t 2 . . . . . . . . . . . . . . . . . .

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SOIL ANALYSES AND EVALUATIONS AT THE IMPACT DYNAMICS RESEARCH

FACILITY FOR TWO FULL-SCALE AiRCRAFT CRASH TESTS

BY

Robert Y. K. Cheng’

SUMMARY

An icvestigatioc to determine the aircraft structural crash behavior and occupant survivability fo r aircraft crashes on a soil surface was conducted at the Im?act Dynamics and Research Facility at NASA Langley 2esearch Center. This repcrt contains the results of placement, compaction, and maintenance of two soil test beds, and a description of the crators forined by the aircraft after each test.

INTRODUCTION

Currently, the Impact Dynamics and Research Facility at NASA

Langley Research Center is conducting a series of aircraft free- flight-crash test programs. Under controlled flight conditions, real aircraft are crashed on concrete surfaces to study the crash characteristics of the aircraft. Descriptions of the test facility and the crash safety program are given in references 1 and 2 .

In furthering the knowledge of structural crash behavior and occupant survivability, two real aircraft were crashed on a soil surface. This is the first attempt in the teat program to crash aircraft on a yielding surface such as soils. A high-winged and a low-winged single-engine aircraft were crashed on a soil sur- face at a velocity of 13.4 m/s with a pitch acgle of -30’.

’ Professor, Department of Civil Engineering, School of Engineering, Old Dominion University, Norfolk, Virginia 23508 .

The purpose of this study is to identify and classify the soils used in the two crash tests and to develop criteria for placement, compaction, and maintenance of the soil bed.

LIST OF SYMBOLS

G = specific gravity of soil-solid particles

S = degree of saturation

w = moisture content

Wd = weight of dry soils

= weight of water wW

y = wet unit weight of soils

- - 'd dry unit weight of soils

SOIL TEST BED

Figure 1 shows the test facility with the soil test bed. The test bed was approximately 12.1 m (40 ft) wide, 24.4 m (80 ft) long and 1.2 m ( 4 ft) high and was built on top of a concrete pad. With a depth of 1.2 m, the test bed would simulate an actual field condition. As the soils were purchased in advance, the selection of an appropriate soil strength was of prime importance. Using the criteria of crash tests on a ploughed field, the test bed was prepa-ed f o r a CBR (California Bearing Ratio) strength of four. The CBR number is used to rate the performance of soils primarily for use as bases beneath pavements of roads and airfields. A s o i l strength of CBR 4 is rated as poor to fair by the Unified Soil Classification System. The soils would be sufficiently firm to support the load of a light pneumatic-tired tractor and soft enough for the aircraft to sink into the soils during the crash.

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LABORATORY AND FIELD MEASUREMENT METHODS

Laboratory tests were performed to provide necessary infor- mation for construction of the test bed. Field tests were performed to monitor construction of the test bed to satisfy the specified conditions and to establish the soil bed properties. Whenever possible, similar testing procedures were used for tests in the laboratory and in the field.

S ~ i l Classification Using Grain Size Analysis

The so i l s acquired by NASA are typical top soils commonly classified for agricultural purposes as loam. The soils contain a significant amount of organic matter consisting of roots and decayed vegetation. The organic content of soils is expressed as a percentage of the total dry weight of soils. matter can absorb moisture and is so much lighter than the mineral soil particles, a small amount of organic matter will decrease the density and increase the moisture content of soils, To perform the tests effectively, the soil sample used in the laboratory was processed to remove a l l visible forms of twigs and roocs. The organic content of the soils used f o r the labora- tory tests was one percent, whereas the organic content of s o i l s in the field was nine percent. The substantial variation in organic content between the soils would influence the guidelines for construction of the test bed.

Since organic

The gradation curve was determined by sieve analysis. The curve presented in figure 2 shows the range of particle size for three samples taken at various locations. The maximum size par- ticle is less than 2 mm (passing No. 10-sieve size), and less than 6 percent (by weight) of the particles are smaller than 0 . 0 7 4 mm (passing No. 200-sieve size). The No. 200-sieve size i s about the smallest particle visible to the naked eye. Using the Unified Soil Classification System, the soil is classified as a

nonplastic sand-silt mixture (SM s o i l s ) .

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Moisture Content Determination

The moisture content was determined in the laboratory by the standard oven-dry method. The moisture content expressed as a percentage is determined by

The oven-dry procedure is time consuming and will not be expedient for field measurements where rapid determination of moisture content is desired. The moisture content was also determined on the same soil sample by the speedy moisture tester. The tester measures the moisture content by gauging the pressure of acetylene gas generated when calcium carbide reacts with the moisture in 2 small soil sample. The maximum variation of moisture content between the oven-dry method and the speedy moisture tester method is 0.5 percent. The speedy moisture method was adopted for monitoring the proper moisture content for construction just prior to the aircraft crash-test.

Moisture Density Determination

The moisture-density tests were performed in accordance with ASTM specification D698-70, Method B. The soils were thoroughly mixed in a mixer and were compacted in a mold 15.2 cm (6 in.) in diameter by 11.6 cm ( 4 . 5 8 4 in.) high in 3 equal layers. Each layer was compacted by 56 uniformly distributed blows with a 2.5 kg (5.5 lb) hammer free-falling 3 0 . 5 cm (12 in.). The 15.2 cm diameter will permit both CBR and Airfield Index (AI) penetration resistance tests on the same specimen. The main emphasis for con- ducting the moisture-density tests is to establish the relationship between the CBR number and the moisture content, whereas the normal objective for the moisture-density test is to establish the maximum dry density for a given compaction effort. The maximum dry density usually becomes the compaction job standard for the soils. Figure 3 shows the results of the test.

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Field Density Determination

The density at the surface of the test bed was measured by the Field Density Sampler designed by the Corps of Engineers. It consists of a 7.6 cm ( 3 in.) diameter by 7.1 cm ( 2 13/16 in.) long cylinder which is driven into the ground with a 4 . 5 kg (10 lb) driving hammer. The cylinder is then removed carefully from the ground to prevent disturbing the soil sample within the cylinder. Excess so i l s are trimmed off the cylinder, and the cylinder is then immediately weighed; the wet density can be readily computed. the soils in the cylinder are also used to determine the moisture content. The dry density of the soil sample is determined by

Some of

The California Bearing Ratio (CBR) Test For Soil Strength

The CBR test measures the relative quality of subgrade, subbase, and base soils for pavements of roads and airfields. The CBR number was used as a measure of soil strength for studies of aircraft operation on s o i l runways as given in reference 3 . The test is a plate bearing test intended to measure the soil's resistance to small indentation prior to reaching the ultimate shear strength. The bearing plate is a cylindrical piston 4.95 cm (1.95 in.) in diameter. Annular weights 4.5 kg (10 lb) or more are placed around the piston. The test can be performed on any flat surface.

In the laboratory, the piston was driven into the so i l s previously compacted in a compaction mold by a compression machine geared to a strain-rate of 0.127 cm/min (0.05 in./min). For all field tests the piston was driven into the so i l s by a screwjack reacting against a counterweight suyported by a crane, and the loads were measured by a proving ring (see figure 4). ?he deflections were measured by a dial gage referenced to the soils from a fixed s tee l beam. Readings of load versus penetration were taken at eacn 0.063 cm (0.025 in.) of penetration to include the penetration value of 0.508 cm (0.200 in.) and then at each

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0.254 cm (0.1 in.) thereafter until the penetration reached 1.27 cm (0.5 in.). errors due to improper seating of the piston on the soils. pressure at 0.254 cm (0.1 in.) deflection is compared to that supported bl a typical well-graded crushed gravel which is assigned a CBR number of 100 (equivalent to supporting a pressure of 6895 kN/m2 or 1000 psi). The CBR number is expressed as a percentage. performed in accordance with ASTM specification D1883-67.

The pressure-deflection curve was plotted to reflect The

A l l the CBR tests were

Airfield Cone Penetrometer Measurement for Soil Strength

The cone penetrometer measures the penetration resistance of soils as it is gradually forced into the so i l s . The pene- tration resistance is a measure of the shear strength of the s o i l s . As the penetration resistance will vary according to the size and shape of the penetrometer and the type of soils, the pene- trometer measures the relative shear strength of soils, and it is necessary to correlate the penetrometer measurements with other types of strength measurements. However, the cone pene- trometer provides an efficient and rapid method for measuring the relative soil strength and, more importantly, the variation of soil strength with depth. Penetrometer measurements were used to monitor the uniformity of soil strength of the test bed.

The airfield cone penetrometer is a hand-operated device with a 30’ cone having a 1.29 cm2 (0.2 in2) base area as shown in figure 5. The penetrat!.on resistance is measured by a spring which is calibrated in terms of the Airfield Index (AI) number. One AI number equals a force of 4 4 N (10 lb). The AI readings are made at 5.08 cm ( 2 i n . ) intervals UF to a depth of 45.7 cm (18 in.). However, if the AI readings at any depth exceeded AI of 15 (660N or 1 5 0 lb), the test was discontinued and the penetrometer was considered to have been driven to refusal. For field measurements, the operator forced the penetrometer into the soil at a slow uniform rate calling out each 5.08 cm ( 2 in.) of penetration. An observer would then recorc! the AI number at each command. Because of the large quantity of roots present in the soils, the penetratim tests required repetition on many occasions. In the laboratory, the AI number of the first 5.08 cm

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( 2 in.) was determined on the soils in the compaction mold, since the height of the sample was 11.4 cm ( 4 . 5 in.). Two tests were performed on each compacted sample immediately following the CBR test.

SOIL ANALYSES AND RECOMMENDATIONS

Figure 3 represents the data for all tests for the moisture content-density relationship. The data also include a modified compaction effort using 25 blows for each layer instead of the standard 56 blows for each layer of compaction. The degree of saturation is larger than 95 percent at a moisture content of 12 percent. Consequently, at moisture contents greater than 12 percent the compaction effort has a small influence on the moisture- density relationship, whereas at moisture contents less than 12 percent the compaction effort has a larger influence.

Figure 6 presents the data for all tests for CBR versus moisture content. As in the case for the moisture content-density relationship, the compaction effort has a small influence on the CBR number when the moisture content is greater than 12 percent. Furthermore, a significant amount of scatter is apparent in the data when the moisture content is less than 12 percent. These tests indicate that to obtain a soil test bed of CBR4 the mois- ture content of the soils should be 12 percent or higher.

The correlation between the airfield cone penetration resis- tance from 0 to 5.08 cm ( 2 in.) depth and the CBR strength tests in the laboratory is shown in figure 7 using AI and CBR numbers. For CBR of eight or less, the data showed good correlation between the AI and CBR numbers. The relationship may be approximated to be linear. A significant amount of scatter is apparent in the data at higher values of CBR.

Based on the laboratory investigations, the following guide- lines were established for the construction and maintenance of the soil test bed:

1. That the moisture content of the soils be maintained at 12 percent or higher during compaction in order to obtain a soil strength CBR of 4 ;

2 . T h a t l i g h t pneumat ic - t i red tractors be used f o r compacting t h e s o i l s . Good un i fo rmi ty of d e n s i t y can be ob ta ined s i n c e t h e

deg ree of s a t u r a t i o n would be g r e a t e r t han 95 p e r c e n t so t h a t a moderate v a r i a t i o n i n compaction e f f o r t would n o t s i g n i f i c a n t l y change t h e CBR number of t h e so i l s ; and

3 . T h a t a i r f i e l d cone penet rometer measurements be used t o provide a r a p i d method f o r moni tor ing t h e un i fo rmi ty of s o i l s t r e n g t h a t v a r i o u s l o c a t i o n s of t h e t e s t bed and depth .

CONSTRUCTION OF TEST BEDS

T e s t Bed 1

N o s p e c i a l e f f o r t could be made t o monitor and c o n t r o l t h e

moi s tu re e m t e n t of %he soils f o r c o n s t r u c t i o n of t e s t bed 1. The so i l s were p laced on t h e c o n c r e t e s l a b by dump t r u c k s and t h e n s p r e a d by a l i g h t bu l ldoze r and a pneumat ic - t i red grader. Wherever p o s s i b l e l a r g e r o o t s and twigs were removed by combing t3e s u r f a c e w i t h r akes towed by l i g h t pneumatic t r a c t o r s . The s o i l s were sp read t o less than 1 5 . 2 c m ( 6 i n . ) . and compacted i n p l a c e by a box-grader towed by

a l i g h t pneumatic t r a c t o r . The combination of t h e pressure of t h e

box-grader and t i r e - p r e s s u r e of t h e t r a c t o r served t o compact t h e s o i l s . S p e c i a l e f f o r t was made t o avoid load ing t h e s o i l bed w i t h

heavy dump t r u c k s . the s o i l bed t o t h e proper e l e v a t i o n .

Rakes and box-graders were a l s o used t o dress

Once c o n s t r u c t e d t h e t e s t bed w a s p r o t e c t e d from exposure t o t h e

sun and r a i n by cover ing it w i t h p l a s t i c sheets . The p l a s t i c sheets prevented t h e l o s s of moi s tu re i n t h e s o i l s by evapora t ion . Where

a d d i t i o n a l mo i s tu re w a s r e q u i r e d , water was sprayed on t h e surface wi th hoses . T h i s procedure served t o p reven t t h e s u r f a c e from d r y i n g wi thout a p p r e c i a b l y changing t h e moi s tu re c o n t e n t of s o i l s below t h e

s u r f ace .

P r i o r t o t h e c r a s h t e s t , e l e v a t i o n r e a d i n g s a t t h e t o p of t h e

soil bed were made by su rveyor s . E l e v a t i o n s a t one-meter squa re

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g r i d s are g iven i n f i g u r e 8.

a t g r id p o i n t G1. 1 . 3 m ( 4 . 4 ft:. A q"nt le s l o p of 1:30 ( t r a n s v e r s e l y from t h e f l i g h t p a t h ) pe rmi t t ed adequate s u r f a c e r u n o f f .

The planned impact t a r g e t w a s l o c a t e d The d e p t h crf s o i l a t t h o c e n t e r i s apFroximately

T e s t Bed 2

A major p o r t i o n 02 the tes t bed was l e z t i n t a c t a f t e r t h e - f i r s t c r a s h tes t . A s t r i p about 4 . 9 m (1-6 f t ) wide and 4 6 CK ( 1 8 i n . ) deep a c r o s s t h e wid th of t h e tes t bed a t t h e a i r c r a f t impact p o i n t was removed. The excavated s o i l s were raked aga in to remove a d d i t i o n a l roo ts and twigs. F i e l d measurements of moi s tu re c o n t e n t by t h e speedy method i n d i c a t e d m o i s t u r e c o n t e n t s v a r y i n g between 14 and 1 6 pe rcen t . The moi s tu re c o n t e n t was a c c e p t a b l e , and no a u d i t i o n of water no r f u r t h z r d ry ing of t h e s o i l s w a s necessary . A s mentioned ear l ie r i n t h e r e p o r t , a h i g h e r o r g a n i c c o n t e n t i n t h e f i e i d s a n p l e would i n c r e a s e t h e moi s tu re c o n t e n t i n t h e soil.

The soils w e r e compacted and leveled by t h e box-grader. P l a s t i c , sheets w e r e p laced over t h e impact area whenever p o s s i b l e u n t i l t h e t i m e o f t h e crash tes:. The e l e v a t i o n s zt one-meter squa re g r i d s are givei: i n f i g u r e 9.

mate ly 1 . 2 m (4.1 ft-). The d e p t h of s o i l s a t t h e c e n t e r was approxi -

FIELD MEASUREMENTS

A l l f i e l d measurements for e s t a b l i s h i n g t h e soil p r o p e r t i e s were made one day b e f o r e t h e c r a s h a t t h e g r i d p o i n t s i n t h e v i c i n i t y of t h e t a r g e t area. The t a r g e t p o i n t is l o c a t e d a t g r i d p o i n t G l . The f i e l d measurement program inc luded t h e followincj tes ts :

1. CBR measurement,

2 . A i r f i e l d cone penetrometer measurement a f t e r c ra sh t e s t a t t h e impact a r e a ,

3 . Densi ty measurement by f i e l d d e n s i t y sampler , and

4. Moisture c o n t e n t measurement by speedy mois ture t e s t e r .

Table 1 shows t h e C B R , mois ture c o n t e n t , anu d r y d e n s i t y a t v a r i o u s g r i d p o i n t s . For c r a s h t e s t 1, because of o b s t r u c t i o n s

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at the target area, 11 CBR tests were performed cnly at the southern half of the test bed. Although there was substantial variation o€ CBR from 0 . 9 to 10 percsnt in the target area, the postcrash test indicated that the zone of soils significant to the crash test was along the flight path, which is along line G shown in figure 8. Taking the average of the CBR along line G ,

the average CBR for the test bed is 3.5 for crash test 1 as shown in figure 9.

With no obstructions at the target area, 18 CBR tests were performed. The grid pattern for the CBR tests was based on the low winged aircraft used in crash test 2. The average CBR along the flight path (line G) for crash test 2 is 3.4 (see figur,? 91,

which indicated that the CBR strength were similar for both test beds.

Tables 2 and 3 show the AI numbers of the airfield cone pene- trometer measurements for crash tests 1 and 2 respectively. The average value of the AI numter is the mean average of the AI reiidings from 0 to 40.7 cm (16 in.) depth. Variation of the AI number along the flight path (line 2) is shown in figure 10. Variation between the 2 AI test bed averages is 10 percent.

The density and moisture measurements for test bed 2 were taken essentially along the flight path line, and the results are given in table 1. The measurements were taken from ssmples at 2.5 cm (1 in.) below the surface. The moisture content varied from 13.3 to 16.3 percent with an average value of 14.5 percent. The dry density varied from 1474 kg/rn3 (92 lb/ft3) to 1586 k g j m 3

(99 lb/ft3! with an average value of 1586 kg/m3 (96 lb/ft3i as chown in figure 11. The moistc.re contents from the field measurements were higher thzn those predicted by laboratory studies for the corresponding CBR of 3.5 (see figure 6) because the field soil samples contained more organic contents.

In s m a i y , the results of the field measurements indicated that the desired soil properties were attained and that the s o i l ?roperties for both test beds vex2 similar and relatively uniform dlong the flight path.

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CRASH TEST RESULTS

T e s t 1

A high-winged s ingle-engine a i r c ra f t was used i n tk,a c r a s h test. During t h e c r a s h , t h e f r o n t p a r t of t h e f u s e l a g e , which con ta ined t h e engine , p e n e t r a t e d i n t o t h e scils, heavir.9 and

s p l a s h i n g s o i l s i n t h e d i r e c t i o n o f t h e f l i g h t pa th . w i t h o t h e r high-speed photographs t aken du r ing t h e c r a s h , t h e

crater formed by t h e f u s e l a g e w a s cons ide rab ly sha l lower , i n d i c a t i n g t h a t a s u b s t a n t i a l amount of loose s o i l s had f a l l e n back i n t o t h e crarer. Due t o r a i n y weather, t h e 2ostcrash test s o i l measurements were made t w o days a f t e r t h e test. Although t h e c ra sned area w a s p r o t e c t e d by p l a s t i c s h e e t s , seepage of w a t e r had damaged the con tour s of t h e crater and a l tsred t h e

moi s tu re c o n t e n t . F igu re 1 2 shows t h e p l a n view af t h e crater and t h e s o i l p r o f i l e a long t h e f l i g h t p a t h a t t h e c e n t e r of t h e crater. The crater w a s about 1 m (3.3 ft) wide by 3.5 m (11.5 f t )

long. The l e n g t h of t h e crater i n d i c a t e d t h e approximate d i s t a n c e s t ravel led by t h e a i r c ra f t upon impact w i t h t h e so i l s . number a t t he c e n t e r of t h e area c o n t a c t e d by t h e nose g e a r v a r i e d from 1 t o 1 . 5 f o r t h e first 1 0 c m ( 4 i n . ) of p e n e t r a t i o n . It appeared t h a t t h e f a i l u r e zone of t h e so i l extended 10 c m ( 4 i n . ) below t h e s u r f a c e . A number of A I measurements w e r e made a t t h e crater, b u t t h e r e s u l t s w e r e t o o scattered t o permi t any i n t e r p r e t a t i o n t o e s t a b l i s h t h e dep th of p e n e t r a t i o n of t h e

f u s e l a s e .

I n comparison

The A I

T e s t 2

A low-winged s ingle-engine a i r c ra f t w a s used i n t h e crash test . So i l measurements were c a r r i e d o u t i m r s d i a t e l y fo l lowing the crash tes t . F igu re 13 shows t h e p l a n view of t h e crater and t h e s o i l p r o f i l e a long t h e flight p a t h a t t h e c e n t e r of t h e crater . A s i n t h e case w i t h t e s t 1, a cer ta in amount of loose

s o i l s f e l l back i n t o t h e crater . The c r a t e r was about 1 m ( 3 . 3 ft : wide by 1 .5 m ( 5 f t ) long.

11

The a c t u a l f l i g h t p a t h occurred between l i n e s G and H. A i r -

f i e l d p e n e t r a t i o n r e s i s t a n c e s were made a long t h e c e n t e r l i n e of t h e crater. The average AI number v a r i e d from 1.5 t o 2.0 f o r t h e first 15 c m (6 i n . ) of p e n e t r a t i o n . The AI number i n c r e a s e d t o three or h igher below t h i s depth. The l o w AI number i n d i c a t e d t h a t loose so i l s which were formed by either t h e accumulation of the loose soils f a l l e n i n t o t h e crater or t h e h igh ly d i s t u r b e d ~

soils caused by shear f a i l u r e . P e n e t r a t i o n r e s i s t a n c e measure- ments w e r e also tnade a t t h e g r i d p o i n t s surrounding t h e crater. The r e s u l t s d i d n o t show any s i g n i f i c a n t changes from t h o s e t aken p r i o r t o t h e tests.

I n an a t tempt t o trace t h e so i l displacement i n t h e impact zone, t h i r t y 2.5 m (1 i n . ) d iameter steel b a l l s w e r e p laced a t depths 1 5 cm (6 i n . ) and 30 cm ( 1 2 i n . ) i n a cross p a t t e r n . The balls were p a i n t e d whi te and numbered. A f t e r t h e c r a s h tes t , t h e s e b a l l s were Located by a metal d e t e c t o r . The displacement of each ball w a s determined from t h e i n i t i a l and f i n a l p o s i t i o n s of the ball. Unfor tuna te ly , the a c t u a l f l i g h t p a t h occurred about 50 c m ( 2 0 i n . ) sou th of t h e planned f l i g h t pa th . Only two of t h e steel b a l l s w e r e d i s p l a c e d , as shown in f i g u r e 13.

CONCLUSIONS

Tile fol lowing conclus ions were made on t h e b a s i s of soil tests and s t u d i e s f o r t h e two c r a s h tests:

1. Laboratory tests of t h e s a n d - s i l t soils (SM) es tab l i shed t h e CBR-moisture con ten t r e l a t i o n s h i p and t h e AI-CBR r e l a t i o n s h i p . These r e l a t i o n s h i p s provided s u f f i c i e n t g u i d e l i n e s fo r c o n s t r u c t i n g t h e t e s t bed.

2 . The s o i l p r o p e r t i e s a long t h e f l i g h t p a t h fo r both tes t beds were s imilar . The CBR's for t es t beds 1 and 2 &re 3 . 5 and 3 . 4 r e s p e c t i v e l y for s u r f a c e f i e l d readings . The average AI number for tes t beds 1 and 2 a r e 5 .3 and 4 . 8 r e s p e c t i v e l y f o r a depth of 40 .6 c m ( 1 6 i n . ) . The

average moisture con ten t f o r test Sed 2 t aken a t 2 . 5 c m

12

(1 in.) below the surface varied from 13.3 to 16.3 per- cent with an average of 14.5 percent. The dry density varied between 1 4 7 4 kg/m3 (92 lb/ft3) and 1586 kg/m3 (99 lb/ft3) with an average of 1538 kg/m3(96 lb/ft3).

3. Based on the length of the crater formed after the crash, the fuselage was stopped by the soils after it had travelled 3.5 m (11.5 ft) and 1.5 m (5 ft), respectively, from the point of impact for tests 1 and 2. No conclusive observations could be made on the depth of penetration by the fuselage due ~a insufficient information.

4. Based on penetration measurements, the crater was formed mostly by shearing and removal of the soils as the fuselage Ploughed through the so i l s . the crater and its immediate vicinity would be indicated by high penetration resistance.

Any compaction of the soil within

5. Buried steel balls can be used to trace the soil displace- ment between the initial and final positicns for the crash test. However, a significant number of balls must be used over a wide area if one desires a detailed plot of the displacement field.

13

XFERENCES

1. Vaughan, V.L.; and Alfaro-Bou, E.: Impact Dynamics Research

F a c i l i t y f o r F u l l - s c a l e Ai rcraf t Crash Test ing. NASA TN 0-8179,

A p r i l 1976.

2. Tnomson, R.G.: Gene ra l A v i a t i o n Crash S a f e t y Program a t Langley

Zesearch C e n t e r , t h e Proceedings o f A i r c r a f t S a f e t y and -

Opera t ing Problems. NASA SP-416, October 1976.

3. Crenshaw, B.M.; Bu t t e rwor th , C.K.; and T r u e s d a l e , W.B.:

A i r c r a f t Landing Gear Dynamic Loads from Opera t ion on Clay

and Sandy Soil. AFFDL-TR-69-51, U.S. A i r Fo rce , February

1971.

14

Table 1. CBR, moisture content , and dry d e n s i t y measurements.

T e s t Bed 1 T e s t Bed 2

Moisture Dry CBR Content Density

% % kg/m3 - T e s t Bed Location CBR

% - c4

D4

E4

F3

F4

F5

G1

G2

G3

G4

G5

H1

II 2

H3

H4

H5

I1

I 3

I4

I5

I7

5 4

K4

3.3 - - 4.8 - -

- - 1.8

- - 4.9

2.5 13.8 1570

4 . 5 - - 14.4

16.3

13.9

13.3

4.0 2.2 - 1474

1522

15815

1570

6.2 3.2

4.6 2.9

2.9

0.9 3 . 9

3.5

5.0

5.0 2.9

2.1

3.0

3.9

15.5

- 1538

- 10.0

3 . 6

3.9 - - 0. a 2.7

2 . 4

3 . 4

w u- .

0 rl

v

- m

m

m

m

d

N w

m W

I

a0

Q)

P

W

Ln

W

9

m w

(u

W

W

fi

m

P

u)

W

r-

N

L n w

N

m

Ln

m

P

m

W

W

N

N

0 W

m m

P

P

W

P

W

Ln

9

In

ri c

hl

W

In

P

W

UP

P

co

\D

N

(\I

C3

16

A

5 a, 5 I d 0 r: 0 u

d

v

a a, .Q

cr cn a, 4J

k 0

rcI

cn a, 7 rl m >

H h

4

X aJ a E: H

v

2 a, -4 u4 k -4 4

$ k 7 m 4 a, x

N

Q) 1 P a E-r

a, rn m k a,

2 d

W

Q3

a0

w

m

w

r-

co

m

W u

d

w

ul

0)

m

9.

W

I-

In

m

0 u

I-

m

m

w

W

W

In

9.

N

4 z

W

W

W

I-

o)

a,

a,

F

In

9

m z

N

I-

m

W

W

W

0 d

0 t-i

m

W

4 H

d

I-

a0

F

W

r-

0 rl

0)

W

v1

N H

OD

W

d rl

0 rl

m

W

9.

m

m

9.

m H

0

v1

o)

II

W

-3

W

m

m

m

P H

1 7

N

19

19

m In

IT

0

In

m IT

0

W

0

h . In

m . m

W

hl

W

0

w

* W

I

hl

W

m m

rl

IT

rl

W

m r- m m In rl rl

0 rl

Fr) 0) W m m W a) P

(v

a al

.Q

4J m al c,

k 0

ICC

m al 5 d

s h

H 4

X Q) a c

Y

H

2 a, *rl ICI k

* I+

4 a al k 7 rn m

. m

al 4 A a B

m m 03 h m m m m P m W QJ W

m m m In W 03 P W P P W 03 W c)

P \o W m In In r- P v In 03 W

m In In \o In m P P W W r-

In In \D P In v W W v

d 5 r- m m m W m W In m hl .ri

d rl

N m m m N N r 4 m m 7 N/ In

m m N v

rD W

m z n

Ul a v w In w r\J G-l

m cu v G-l

Ln G-l

rl U

N 13

m u -3 u In

W

18

m m

m

[c

W

W

r-

W

ul

w

w z

N

m

In

In

-3

03

I-

W

ul

(u

In 3:

d

In

Ln

W

W

W

In

W

m

In b

19

I 1 1

1 I I I I I I I I I I 1 I I I I I I I

o v1 ffl o

a k U

L, lu a k u k -4 a ffl rl a U m I

rl d 7 E

20

U.S. Standard S ieve Numbers

100

80

60

40

20

0 10 1 0.1

Grain S i z e , mm 0.01

F i g u r e 2 . G r a i n s i z e d i s t r i b u t i o n curve.

21

k k a , Q ) P l a

0 0

A / dp 0 0 / VI Y

v) a -4 0 O r - > '

'- I Cho In m II

CI]

0

0

0 0

0 0

0 m d

0 N rl

0 hl

m d

0 d

In

0

2 2

0

F i g u r e 4 . Schematic of CBR f i e l d test,.

Screwjack

2 3

Q) 0

m

H I / m c -4 k a

a 0 co X P) a c

.ri 1 w

Q) E 0 0

a

c u CI]

5

m

E 3 F -4 Err

2 4

1

0 0

0

0

I I I 1 0 I I

0 m

In cv

0 cv

ln r!

0 d

In

25

k k Y a l a a

0 0

0 0

0

0

0

0 0

0 ri

00

2 6

d OD m

In m m

03 o! Pl

a 0

P

rl rl

-3

0 rl

P

In 0

w

m o!

m

I- o! m

N 0

c 0 ri

P

r- rl

P

0 N

Q

aD rl

P

m 3

d

w 0

0

I- O

0

m .-I

t

r- .-I

Q

m N

v

N N

0

OD m cn 0 0 0

0 Q w

a CI rl 0 0 d

9 d P

0 N m ri ri 4

9 w P

m p. hl d ri N

P 9. d

0 N P N N N

P QL w

9 QL VI cv N N

Q v b

Q 9 0 N cy N

w Q Q

P 0 Q

o! 0

w

r- d

w

P N

w

J) N

w

q N

P

9 N

Q

\o o!

m

P 0 v

P 4

Q

r- ry

Q

P N

P

w N

Q

m N

v

0 n

3 ri v o!

m m

m m m o!

m m

0 m 0 a q m

m ro 0 s Q Q

9 e C v cp

. n - .

27

0

# . !x m u

0

0 1 2 3 4 T e s t Bed 1

5 6

0

0 --------------

Average 0

0

0

I I I I 1 i

0 1 2 3 4 5 6 Distance Along F l i g h t P a t h , m

Test Be2 2

r’igure 9 . CBR alonc, t h e f l i g h t p a t h .

0 Average value of each depth I Range 10

Average k

G 0 2 4 6 a 10 12 14 16

Test Bed 1, m

8

k

- 4 4

2

Average value of each depth

Range

T

c 2 4 6 8 10 12 14 16 Depth of Penetration, in.

Test Bed 2

Average

Figure 1 0 . V a r i a t i o n o f A i r f i e l d I n d e x number with depth alona the flight p a t h between grid points G 1 and G 6 .

29

0

” 15 a,

k 3

$ 14 0 z -4

13

- 73---------

0 -

1 1 i I I J

0 1 2 3 4 5 6

1600 r i m

I E \ tr X I -

1500 -4 u) C aJ n

0 0

--------.-- 0 Average

0

& * 1 4 0 0 [ I I I I I 1

0 1 2 3 4 5 6 Distance Along Flight Pa th , m

Figure 11. Variatiox? of mois ture content and ciry density along t h e f l i g h t p a t h between grid points rJ2 and G 5 .

30

G -4 4 a -4 H

(a) Crater Outline

direction 0 1 1 L i

m I I I I J

- O I

E a, .-I -4 w

b

k

m k

-10

2 -20 0 1 u

Pretest soil surface -

-

~ ~ ~~

6 5 4 3 2 1 0

Grid Line Identification

(b) Soil Profile Along Flight Path

Figure 12. Cra te r and soil profile alonq flight path created by crash test 1.

31

2 Displacement of steel b a l l

Nose g e a r impact p o i n t f Ac-1 Impact

d i r e c t i o n

0 1

I m

I 1 I 1 6 5 4 3 2

Grid L i a e I d e g t i f i c a t i o n

( a ) Cra.ter O u t l i n e

1

Pretest s o i l s u r f a c e ,u 2 , 1 ,

0 -

-10 -

6 5 4 3

(b) S o i l F r o f i l e Along F l i g h t P a t h

F i g u r e 1 3 . Crater and s o i l p r o f i l e a long f l i g h t p a t h c r e a t e 2 by crash t e s t 2 .

3 2