SOME STRENGTH TESTS ON THE

GABBROIC ROCKS FROM THE

NORTH HATTA AREA, UNITED

ARAB EMIRATES

Hasan Arman, Mohamed El Tokhi and Bahaa Eldin Mahmoud Amin

United Arab Emirates University

The Third International Forum for Industrial Rocks & Mining, Expo, Emirates

of Fujairah, United Arab Emirate30 March- 1April, 2015

Outline of the Presentation

INTRODUCTION

GEOLOGICAL SETTING

FIELD & LABORATORY STUDIES

RESULTS

CONCLUSIONS & DISCUSSION

ACKNOWLEDGEMENTS

INTRODUCTION

The study area is located in North Hatta Shear

Zone, at the border between the United Arab

Emirates and Oman.

It is about 95 km north of Al-Ain city and 60 km

southeast of Dubai.

It is located between longitude 24°50'N - 24°60'N

and latitude 55°60'E - 56°17'E (Figure 1).

INTRODUCTION

Figure 1. Simplified

geologic map for the study

area

INTRODUCTION

The geological features of the proposed region was

restudied through the available literature and field

observations.

During the study, sample locations were identified and

marked on the map (see Figure 1).

INTRODUCTION

Number of rock samples having different size of at

least 0.30x0.30x0.30 m were collected from selected

sample locations and taken to the laboratory.

Those rock samples were used to prepare rock samples

for different strength types. These are:

o The unconfined compressive strength (UCS),

o Brazilian strength (BRS),

o Point load strength index (PLSI) and

o Schmidt hammer hardness (SHH)

INTRODUCTION

Those tests were carried out either on the selected rock

block samples or core samples according to suggested

standards.

The main objective of this study is to investigate and

report the strength properties of the gabbroic rocks,

which are important parameters in geology and

engineering applications on/and in rock mass, from North

Hatta area, through in-situ and experimental studies and

discuss their probable influences as foundation and

construction materials.

GEOLOGICAL SETTING

Field observation revealed that the rock units exposed in

the Hatta zone structurally below the Semail ophiolite,

include platform slope carbonates (Sumeini Group), base

of slope re-deposited sediments (Hamrat Dom Group),

and more distal, deep-sea sediments (Hawasina),

volcanics and metamorphic rocks of the ophiolite sole

(Haybi Complex).

GEOLOGICAL SETTING

Moreover, Wadi (valley) Hatta consists of highly

deformed imbricate thrust sheets, (allochthonous unit)

which are intact and unconformably overlained by

Maastrichtian sedimentary cover in Jabel (mountain) Al-

Rouda.

The rocks of Hatta area consist predominantly of mafic

and ultramafic rocks, which are considered as units of the

ophiolitic succession.

GEOLOGICAL SETTING

Hatta area comprises of highly deformed imbricated

thrust sheets of ultramafic rocks.

The ophiolite complex dominates the area around Wadi

Hatta as are relatively continuous belt covering more

than 2/3 area.

Mafic and ultramafic rocks are considered as the major

units of the ophiolitic succession represented by

peridotites, pyroxenites and gabbros (see Figure 1).

Figure 1. Simplified

geologic map for the study

area

GEOLOGICAL SETTING

GEOLOGICAL SETTING

The gabbroic rocks in the study area form rugged

mountains and rest with tectonic contact against the

underlying mantle sequence.

They occur as faulted blocks to the east and north of

the study area being bounded to the NE and NW by

thrust faults, which have emplaced them over tectonized

peridotite.

The gabbros comprise troctolite, olivine gabbro,

gabbronorite, and normal gabbros.

FIELD & LABORATORY STUDIES

Number of Schmidt hammer hardness tests were

performed in-situ (approimately1000 readings).

About 40-rock block samples, at least 0.30x0.30x0.30 m

in size, were collected from the field, and were used to

prepare rock samples for different strength tests.

FIELD & LABORATORY STUDIES

o The unconfined compressive strength (UCS),

o Brazilian strength (BRS),

o point load strength index (PLSI) and

o Schmidt hammer hardness (SHH)

Those tests were carried out either on the selected rock

block samples or core samples according to suggested

standards.

FIELD & LABORATORY STUDIES

FIELD & LABORATORY STUDIES

FIELD & LABORATORY STUDIES

FIELD & LABORATORY STUDIES

FIELD & LABORATORY STUDIES

All UCS test specimens had a length of diameter ratio of

approximately 2:1.

Both samples ends of the test specimen were kept

perpendicular to the long axis as possible as (ASTM

D4543, 04.02, 1986).

The ASTM standard was used to define UCS of rock

samples (30 core samples) and a constant loading rate

was applied to the test specimen (ASTM D2938, 04.08,

1995).

In general, diagonal shear failure was commonly

observed.

FIELD & LABORATORY STUDIES

The ITS test samples (37 circular cylinder samples) were

accomplished with reference to procedure described by

Bieniawski and Hawkes (1978) and tested following to

the ISRM procedure (ISRM Suggested methods, 1981).

The PLI tests (24 core samples) were performed following

the procedure described by ASTM (ASTM D5731, 04.0.,

1995).

FIELD & LABORATORY STUDIES

The SHH of the gabbroic rocks was defined by the rock

hammer test (about 1000 readings in the field and 300

readings in the laboratory). The testing procedure as

recommended by ASTM was followed (ASTM D5873,

04.08., 1996).

RESULTS

UCS

(MPa)

ITS

(MPa)

PLI

(MPa)

SHH

Field Test Laboratory Tests

Min. 115 5 5 14 34

Max. 340 19 18 49 49

Mean 209 9 11 36 43

SD*54 3 3 7 3

CONCLUSIONS & DISCUSSION

The UCS of gabbroic rocks in the study area ranges

from high to very high strength with most being high

strength according to Deere and Miller, 1966 .

The ITS was determined by Brazilian and point load

index tests. The strength value obtained by Brazilian

test were more or less same to the strength value

obtained with the point load index test.

The SHH test exhibits quite scattering. This may be due

to rock surface roughness characteristics.

CONCLUSIONS & DISCUSSION

The strength properties of the Gabbroic rocks are

important parameters in geology and engineering

applications on/and in rock mass.

Nevertheless, generalizing the mechanical properties of

the gabbroic rocks is unreliable due to changes in their

structure, texture and even mineralogical composition.

Therefore, engineers should take extreme precaution

when they use these values in foundation design and as

construction materials.

This research was financially supported by the Research

Affairs at the UAE University under a contract

#COS/122/156. The authors grateful to the

Department of Geology for encouragements and

support, which led to finalize this research work.

ACKNOWLEDGEMENTS

Thanks

The Third International Forum for Industrial Rocks & Mining, Expo, Emirates of Fujairah, United Arab Emirate,

30 March- 1April, 2015