ENGINEERING PERFORMANCE OF SELECTED PROPERTIES OF UMM AL-JAMAL BASALTIC ROCKS, NE JORDAN

The main objective of this research is to study the engineering properties of Umm Al-Jamal basalt rocks. The basaltic rocks in Jordan are mainly of Tertiary - Quaternary age. 
They occupy 18 % of Jordan. 
 Physical and mechanical tests were done on samples of basaltic rocks of Umm Al-Jamal. Umm Al-Jamal basalt has consisted of eight thickly basaltic flows with a total thickness up to 300m. It was concluded that the physical-mechanical properties of the studied samples significantly influenced by their textures and hence the rock textures can be used as a preliminary predictive tool for assessing the performance of basalt in relation to specific manners and classified as 3-4 class type. They are characterized by high-density values and exhibit very low absorption percentages which fit well with the classification schemes of the international and local specification.


INTRODUCTION
Harrat Al-Shaam spreads among Syria, Jordan and Saudi Arabia. It represents a giant basaltic field on the Arabian plate and occupies a total area of 50,000 km 2 (Coleman and McGuire, 1988;Al-Malabeh, 1994, Roobol et al., 2002, and Camp and Roobol, 1989. In Jordan, the segment of the Harrat is called Jordanian Harrat (Smadi et al., 2018) and covers 53 (1E), 2020: 44-54 45 an area of 12,000 km 2 , (Fig. 1). Chemical results of the basalt rocks in the Jordanian Harrrat (e.g., Barberi et al., 1979, Al-Malabeh, 1993 indicate that the rocks are mainly of alkali olivine types. The basalt rocks in Jordanian Harrat are mainly of Miocene to Holocene in age.

Fig. 1. Location map of Harrat Al-Shaam and the study area
Extensive amounts of basalts are occurring in Umm Al-Jamal. These basalts have been used by Greek, Roman-Byzantine and Islamic periods (Al-Malabeh, 2010 andAbu-Mahfouz et al., 2016). Huge cities are built of these materials they proved excellent ability and capacity to design. Moreover, they exhibit huge stability through the history (Rababeh et al., 2010).
The basalts are of Miocene to Holocene age (Fig. 2). They always reported in basaltic articles in general without any detailed physical and mechanical properties. The aim of the present study is to determine the engineering properties of these basaltic rocks.

STUDY AREA
The investigated area lies in the northeast parts of Jordan; within the Mafraq government, approximately 20 km northeast of Al-Mafraq city. The Umm Al-Jamal basalt is almost accessible through several asphaltic and track roads that already exist to connect several towns in the area. The Umm Al-Jamal lies in the eastern parts of the Jordanian Harrat, near the Jordanian-Syrian borders (Fig. 2). The elevation is about 800 m (a.m.s.l) and covers an area of about 10 km 2 . It was developed due to intermittent eruption from deep-seated faults in form of 5 successive basaltic pahoehoe flows with a total thickness of 50 m (Fig. 2).

MATERIALS AND METHODS
Ten representative samples were collected and studied for the purposes of engineering: physical and mechanical prosperities several tests are carried out at the Department of Civil Engineering at Jordan University for Science and Technology. The conducted tests are explained in the results. All these tests were conducted according to the specifications of (e.g., ASTM (2008), ISRM (1978) and IAEG (1986), the different tests and their references are listed in Tables (1 and 2).

Physical properties Tests
The experimental tests conducted on the samples show that the average values of specific gravity, apparent specific gravity and absorption (%) are: 2.73, 2.64 and 1.27%, respectively, (Table 3). These properties are varied slightly in the investigated samples which may be related to the presence of vesicles in cores. Porosity has an average of 1.46%, which related to class C of medium porous, based on the rock classification criterion given by Jumikis (1983). Specific gravity has moderaly positive correlations with the absorption where R 2 = 0.69 (Fig. 3a), a positive correlations with porosity, R 2 =0.65 (Fig. 3b) and a positive correlations with absorption R 2 =0.63 (Fig. 3c). These results do not show considerable similarity with the results obtained by Abu-Mahfouz et al. (2016). Specific gravity has positive correlations with unit weight gm/cm 3, R 2 =0.61 ( Fig. 3.d). Moreover, it is evident that the considerable dry unit weight with values between 2.58 and 2.67 gm/cm3. The high unit weight and medium porosity may be attributed to the crystalline nature of the rocks. The Umm Jamal is classified as a high ultrasonic wave velocity which gives an average of 4514 m/s (Table 3). Based on this criterion, set by the IAEG (1986), the tested samples lie in class 4. The correlation coefficient diagrams in the above-mentioned figures show that the density has a significant effect on absorption for the basalt rocks. Furthermore, since porosity is the major factor affecting absorption, This correlation indicates that the internal structures of basalt rocks in which micro-cracks and pores contribute significantly (Al-Malabeh and Al-Kharabsheh, 2002).

Mechanical Properties Tests
To measure the ability of basalt to withstand repeated impact loading, all samples were tested for calculating unconfined (uni-axial) compressive strength (UCS). The rocks have UCS that ranges between 98.5 and 106.9 (MPa) and averages 101.26 (MPa). The values were used to classify these rocks using Deere and Miller (1966) chart. All samples (Table 4)

Mechanical properties tests
To measure the ability of basalt to withstand repeated impact loading, all samples were tested for calculating unconfined (uni-axial) compressive strength (UCS). The rocks have UCS that ranges between 98.5 and 106.9 (MPa) and averages 101.26 (MPa). The obtained values were used to classify these rocks using Deere and Miller (1966) chart. All samples (Table 4) -Malabeh, 1996 andRababeh et al., 2010). Therefore, it is also recommended to take this study in consideration in any conservation at the Umm Al-Jaml archaeological city.

CONCLUSIONS
The following conclusions can be drawn from this study: 1. The Umm Al-Jamal basalts cover an area of about 10 km 2 . It was developed due to intermittent eruption from deep-seated faults in form of 5 successive basaltic pahoehoe flows with a total thickness of 50 m.
2. The Umm Al-Jamal basaltic rocks have relatively high bulk specific gravity (2.60-2.84), high apparent specific gravity (2.54-2.73), low absorption (%) (0.33-1.60 %) and high unit weight (2.58-2.67 gm/cm 3 ). This indicates the cohesive nature of the rocks. Porosity has an average of 1.46%, which relataled to class C of medium porous, based on rock classification criterion given by Jumikis (1983). The uniaxial strength (98.5-105.5 MPa) and tensile strength (9.5-10.9 MPa). Depends on the classification system suggested by Deere and Miller (1966), the rocks are classified as of medium strength rocks, class C. The results of slake durability indicate gigh durable. The calculated abration ratio of 100/500 shows ratio of 0.25% which is classified as medium strength, class C.
3. The basalt samples 100/500ified according to the IAEG (1986), as high ultrasonic wave velocity indicates that they are classified as class 4, which has an average of