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BUREAU OF MINGOLOGY AN 3

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RECORD

BMR Record 1981/25

ROAD GRAVEL INVESTIGATION, BLOCK 64,

TENNANT, ACT

by

G.F. Sparksman

The information contained in this report has been obtained by the Bureau of Mineral Resources, Geology and Geophysics aspart of the policy of the Australian Government to assist in the exploration and development of mineral resources. It may not be -published in any form or used in a company prospectus or statement without the permission in writing of the Director.

BMR Record 1981/25

ROAD GRAVEL INVESTIGATION, BLOCK 64,

TENNANT, ACT

by

G.P. Sparksman

CONTENTS

Page

ABSTRACT

INTRODUCTION^ 1

FIELD INVESTIGATION

SAMPLE ANALYSIS

ALTERNATIVE SOURCES OF MATERIAL^ 2

CONCLUSIONS^ 2

REFERENCES^ 3

TABLE I. SUMMARY OF TEST DATA^ 4

FIGURES

1. LOCALITY MAP

2. LOCATION OF GRAVEL PIT AND BACKHOE TRENCHES

3. PARTICLE SIZE DISTRIBUTION CHART

4. PLASTICITY CHART

APPENDIX I. BACKHOE TRENCH PROFILES

ABSTRACT

Investigation of gravel pit on Block 64, Tennent, ACT by means

of trenching in described. The material - extremely weathered granodiorite -

proved to be too highly plastic for use on unsealed roads. EaLlier reports

of alternative sources of non-plastic gravel in the district are listed.

INTRODUCTION

Late in 1980, the Department of Capital Territory requested

BMR to investigate a disused gravel pit on Block 64, Tennent, ACT.

The purpose of the investigation was to determine the suitability of the

gravel for use on rural roads in the southern part of the ACT. About

1000 m3 per annum is required. The pit is located 9 km from Tharwa,

along the Naas Road and adjacent to the Gudgenby River, (Figs 1 and 2).

FIELD INVESTIGATION

Six backhoe trenches were excavated on 9 December 1980, and

samples were collected from various depths within the trenches and the

gravel pit. Twenty samples were collected, of which twelve were analysed.

Trench profiles are shown in Appendix 1. The gravel consists of in-situ

weathered granodiorite, moderately weathered to a depth of 2.5 - 3.0 m.

The possible working area for a gravel pit is shown in Figure 2. The

reserves of gravel in this area, using a working depth to 2.5 m, are 150, 000

m3

.

SAMPLE ANALYSIS

Testing of samples was undertaken in March 1981. Tests were

carried out according to procedures set out in Australian Standard 1289.

(Standards Association of Australia, 1977). These tests were Grain Size

Analysis, Liquid Limit, Plasticity Index and Linear Shrinkage.

The results of these tests are shown in Figures 3 and 4, and

Table 1 is a summary of the test data. Figure 3 shows graphs of the particle

size of samples. All samples tested lie within the limits specified by the

Department of Housing and Construction for unsealed pavements. All

samples have a low degree of uniformity; samples 1,5, 6, 8 and 11 have

-2-

high plasticity, while samples 2, 3, 4,^7, 9, 10 and 12 have medium plasti-

city. (Table 1).

The Department of Housing and Construction's specifications for

unsealed pavements are: Liquid Limit should not exceed 35%; Plasticity

Index (P.I.) should be between 2% and 10%, and even a less exacting

specification would require a P.I. between 10% and 16%. All the samples

tested, except one, do not conform to these specifications. The one sample

which does conform to even the less exacting specifications, no 7, had a

slightly coarser grain size in the fine sand section.

The gravel, because of its high plasticity is unsuitable for use

on unsealed pavements.

ALTERNATIVE SOURCES OF MATERIAL

There are two locations on the Naas Road just north of the

investigated site, where reserves of non-plastic gravel have been proved

in previous BMR investigations (Hansen, 1970; Bishop, 1973). These

locations are: Grid Reference 6087-2084, Michelago 1:50 000 sheet, where

there is about 100 000 m3 of non-plastic granitic slopewash; and Grid

Reference 6092-2088, Michelago 1:50 000 sheet, where there is about

--26 000 m3 of non-plastic, in-situ weathered granite.

CONCLUSIONS

I.^The material from the investigated pit is too highly plastic

for the proposed use on unsealed roads.

2.^There are alternative sources of non-plastic gravel in the area.

Fis. 1 LOCALITY MAP

148° 50'

•

HALL

V

149°10'

7

4).■ t'A^.--/COTTER

/^-,,..',..- DAM

,.

35 ° 20'

Ma Area Investigated

1.11 Built up Area

-7-- Railway

Highway

Principal Road

^Secondary Road

Vehicle Track

-^Territorial Boundary

• Township

(

CORIM ' DAM

See Fig 2NAAs

I^\7"--/

`.!`,^-aco^_\

az •_cr

"S5°40'

(

12^16^20 Kilometres0^4^81

16/155-16/38Record 1 '81/25

Fi9ure 2 Location of 9r~vel pit and backhoe trenche,

-- ---

M~ 2~~O-+'-+I~I~'~b~-------4----------s~A-o--------~--------~IO~ M~TRcS

__ -:::: TO

¥ ~ >IrIi#1s Rei Il_ -----\:-,)

I \

RFFER£NCE

........ -...... ---I I ---

ROQaI s~led ROQd unsealed

81 oc k bo .... nolary

Grovel pit

Trench) sQrtlple no.

River- , perenn'lCtI Creek, intermittent Area of fDssible

'llJarry; oul-lined +0 calc u late reserves .

- - ---- ----- - ---

C ontol.l" intervQ1 25" Metres

£iJure 3 PARTICLE SIZE DISTRIBUTION CHART

8.S. 51 £ VE

2 -+ 6 \0 20

PARTICLE SIZE -MICRON I CLAY SILT

FINE 1 MEDIUM I COARSE FINE Ru.ord 19&1/25

N-1 3' • 1" - 1 1_ 4 '2

PARTICLE SIZE -MILLIMETRE SA NO GRAVEL

IMED/UM I COARSE FINE IMEOIUM I co ARSE

6" 3G"

16111i~-1& 40 UI/lf(NJ/U

lCOBBLES BOULDERs

)< lu o :z

>­I-

bO

50

4-0

30

10

LOW

. _- --- - - --- ----_._ - -

MEC 'UM

i0 3

q V 0 12-

/ l(

HI GH PLA STICITY /'" V

~ V

b' y

0 ,/ // ~

0 b

fb ~ /

71 ._ -- _._ ---_.- ------- - --- - - - - -

o

Rcccord 1961/26

I O · :J. 0 30 4-0

L I QUID

Fi9ure 4- PLASTICITY CHART

50 LIMIT

-- - - - - - -- -- --- . . _- ------ - - _ . - --- - --- - - -

60 70 8'0 qO 100

16/1 SS-16/ 4.1

3

REFERENCES

BISHOP, I.D., 1973 - Gravel for rural roads - seismic refraction surveys

near Tharwa and Williamsdale, A.C.T. Bureau of Mineral Resources,

Australia - Record 1973/40.

HANSEN, R.J., 1970 - Gravel for rural roads, Naas Road, Tharwa area.

Bureau of Mineral Resources, Australia - unpublished report.

STANDARDS ASSOCIATION OF AUSTRALIA, 1977 - Methods of testing soils for

engineering purposes. Australian Standard 1289.

4

TABLE 1. Summary Of Test Data

Sample No.^ 1^2^3^4^5^6^7^8^9^10^11^12

Location (Q, Quarry Wall;^Q^Q^T6^T6 T4^T4^T3 T3 T3 T2 T2 T2T, Trench)

Depth (m)

3

0.7 1.5 0.5 1.4 0.5 1.4 0.2 0.6 1.1 0.3 0.6 1.3

Passing^ INCH sieve/8

% 99 99 100 99 100 99 99 100 99 92 90 92

3 n/16

% 82 72 84 80 97 82 92 81 88 69 73 60

Passing BSS No^7 (2.41 mm) % 56 38 51 45 76 40 65 45 51 39 46 3714^(1.20 mm) % 41 22 32 26 56 21 48 27 29 25 30 2025^(^.60 mm) 7. 31 14 22 16 41 12 38 17 18 16 20 1336 (^.42 mm) % 27 11 19 13 35 10 34 13 15 13 16 1052 (^.29 mm) % 24 9 16 11 29 8 29 10 12 10 13 8100^(^.15 mm) % 19 6 12 8 21 6 23 6 9 7 8 6200 (^.076mm) % 15 4 10 5 16 4 17 4 6 5 6 4

-200 % 15 4 9 5 15 4 16 4 6 5 6 4

Uniformity Coefficient 11 30 12 8 12 15 14 17 12(U=d60

/d10 )

Passing No 36 BSS Material

Liquid Limit % 65 41 44 43 53 56 31 53 40 48 63 38

Plastic Limit % 26 22 22 20 23 24 23 24 20 22 25 20

Plasticity Index % 39 19 22 23 30 32 8 29 20 26 38 18

Linear Shrinkage % 14 11 12 12 12 13 4 11 10 12 12 9

APPENDIX 1

Trench^1

Backhoe trench profiles (depths in metres)

Trench 4

0^- 0.3 Topsoil 0 - 0.1 Topsoil

0.3 - 0.4 Brown silty sand 0.1 - 0.25 Sandy silt

0.4 - 0.5 Brown-yeflow mottled silt . 0.25 - 0.8 EW granodiorite

0.5 -^1.3 HW to MW granodiorite 0.8 -^1.4 HW grabodiorite

1.3 - 1414 granodiorite 1.4 - MW granodiorite

Trench 2 Trench 5

0 -0.15 Topsoil 0 - 0.2 Sandy topsoil

0.15 -.0.4 Light brown gravelly sand 0.2 - 0.35 Silty gravel

0.4 - 0.65 Dark brown-yellow silty clay 0.35 -^1.0 EW granodiorite

0.65 -^1.4 HW granodiorite 1.0 -^1.5 HW granodiorite

1.4 - MW granodiorite 1.5 - MW granodiorite

Trench 3 Trench 6

0 - 0.2 Sandy topsoil 0 - 0.15 Sandy topsoil

0.2 - 0.4 Silty gravel 0.15 - 0.4 Silty gravel

0.4 - 0.8 EW granodiorite 0.4 - 0.6 EW granodiorite

0.8 -^1.5 HW granodiorite 0.6 -^1.4 HW granodiorite

1.5 - MW granodiorite 1.4 - MW granodiorite

Reference

MW = Moderately Weathered: rock is discoloured and noticeably weakened;N-size drill core generally cannot be broken by hand across the rock fabr -

HW = Highly Weathered: rock is discoloured and weakened; N-size drill corecan generally be broken by hand across the rock fabric.

EW = Extremely Weathered: rock is decomposed to a soil, but the originalrock fabric is mostly preserved.