Geoengineering Evaluation of Dammam Formation Rocks-Bahr Al-Najaf Depression-Middle of Iraq

Abstract


Introduction
The Dammam Formation is a geological formation found in Iraq's Bahr Al-Najaf Depression.It is a part of the Salman Platform, a huge structural structure that spans most of Iraq.The Dammam Formation, which is formed of recrystallized limestone with nummulite near the base, was identified by Bramkamp in Saudi Arabia in 1941.The formation is approximately 250 m thick.It was formed in a shallow maritime environment and runs along the Euphrates River from Al-Qaim to the Arabian Gulf, including Saudi Arabia, Kuwait, Bahrain, Qatar, Oman, and the United Arab Emirates (Jassim and Goff, 2006).The location is situated within the secondary Salman zone of the main remarkable Stable Shelf.
Limestone rocks are a common building material in Iraq.Raw stone is utilized in the construction of dwellings, residential units, and building facades, as well as a raw material for the cement industry (Ahmed, 2021;Ahmed et al., 2022).As well as the usage of ballast stone railways or utilized as a type of basis or under the basis of the roadways.Many researchers study the Dammam Formation in this area.The research region lies inside the administrative confines of the Najaf Governorate, within the Bahr Al-Najaf depression, which is 30 kilometers from southern Najaf City (Fig. 1).This work aims to study the physical, chemical, engineering, and mineralogy of limestone sediment rocks of the Dammam Fm. in the Najaf depression, in addition to its raw materials for Portland cement.

Geological Setting
Dammam Formation was formed in neritic to literal environments.It forms in the context of inner shelf lagoons and shoals and overlies the production of Rus deposits (Fig. 1; Tamar-Agha and Saleh, 2016).It is made up of limestone, marl, and dolomitic limestone and is typically found in the southwest of this study region (Al-Dabbas et al., 2013).The basin became significantly shallower and coastal in the Late Miocene in this research area.Fig. 2 depicts the stratigraphic column.

Tectonic and Structural Setting
According to Buday and Jassim (1987) divisions, the study area is located within the Stable Shelf within the Salman Zone which is characterized by its simple structures.The area is marked by NW-SE trending subsurface folds that are reflected on the surface as a series of elongated convex linear features associated with faults (Al-Atiya, 2006;Al-Turaihi et al., 2023).Abu-Jir fault is a normal fault where the eastern side is grabben, in addition to NE-SW transversal faults like Schbicha-Najaf-Badra, and Ruhaimawi-Hilla, (Jassim and Goff, 2006;Al-Turaihi et al., 2022).The Southern Desert is characterized by flat nature, very gentle due to almost horizontal beds towards Mesopotamian alluvial plains with a regional dip towards east and northeast (Ahmed, 2021;Hussein et al., 2023) Fig. 2. Stratigraphic section of the studied area after (Awadh and Al-Owaidi, 2021)

Materials and Methods
Fieldwork was conducted out in the research region on the limestone layer revealed at the Dammam Formation.The sample was carried out from one borehole.The coordinate of the borehole is 31°51'59.50"Nand 44°7'59.84"E.Ten samples were selected at Najaf Governorate.The laboratory work includes several laboratory tests for ten samples, these samples cover the study area including: • Physical tests: total density, porosity and water absorption.
• Chemical tests: These analyses are one of the basic analyses through which to determine the weight percent of oxides in limestone rocks and the loss on ignition (L.O.I.).• Engineering tests: Includes uniaxial compressive strength

Physical properties of rock
• Dry density Duggal (2008) defines density as the sample weight in relation to the entire volume (solid volume plus pore space volume).Total density is also known as the mass of volume unit, and it is affected by the mineral compounds, porosity ratio, and amount of fluid in the pores at the time of measurement.The density was determined using the equation and the conventional method (ASTM C568-03 1986; Ahmed et al., 2021). = (/( − )) × (1) Whereas: ρdry is Dry density (gm/ cm 3 ); ρw is the Density of water (gm/cm 3 ); Wd is Dry unit weight (gm); Wsub is the Weight of the submerged sample (gm); Wsat is Water saturated form weight (gm).The maximum value of dry density is 2.664 gm/cm 3 in sample No. S4, the minimum value 1.848 gm/cm 3 in sample No. S2 and the average 2.456 gm/cm 3 (Table 1).
The maximum value of porosity is 20 % at sample No. S4, the minimum value 5 % at sample No. S 2 and the average (10.8)% (Table 1).The quantity of porosity relies on the size and shape of the minerals that make up the rock, as well as the degree of grading.

-Water Absorption
The ability of a rock to attract water and fluids through its pores and among the grains is referred to as water absorption.The efficacy of the rock to absorb change as a result of the factors affecting porosity (Fatohi et al., 1990;Ahmed et al., 2021;Al-Sultani et al., 2023).The following formula can be used to calculate the percentage of water absorption:  =  −  (5)  =  / 100% (6) Which: WAsb is "water absorption (%); Wdry is "sample dry weight (g); Wsat is "sample weight saturated with water (g); Ww is "Weight of water in voids (g).
The maximum value of water absorption is 7.7 % in sample No. S6, the minimum value 0.29 % in sample No. S2 and the average 2.87 % (Table 1).The water absorption of the rock relies on the nature and size of the mineral grains of the same type of mineral groups.The stress on a rock is known as its compressive strength.Uniaxial compression strength is determined by continuous stress applied to the material to the material in the same directions until failure CaO ranged between 33.8 and 54.7% average 50.89%.The ratio of Al2O3 ranged between 0.11 and 1.31 % and average 0.508 % and the percentage of Fe2O ranged between 0.07 and 0.65 % and average 0.253% and the percentage of MgO ranged between 0.29 and 1.3 % and average 0.611%, the percentage of SO3 ranged between less 0.7 and 1.4% and average 0.07%, the percentage of L.O.I ranged between 20.21 and 43.23% and average 39.36%, the percentage of Na2O ranged between 0.02 and 0.08 % and average 0.0526 %, the percentage of K2O ranged between 0.01 and 0.048 % and average 0.066%.The percentage of Cl ranged between 0.03 and 0.14% and average 0.0751 % (Table 3).

Suitability as Raw Materials for Portland Cement
Cement is a soft substance that bonds things that hardens with the presence of water, acquiring cohesive and contiguous properties that allow it to bind the components of concrete together.Portland cement is one of the most important varieties of cement and the most extensively used in the world.Then, controlling the process of cement solidification, burning it to the temperature at which clinker is generated, and then grinding the cooled clinker produced by burning with gypsum, (Al-Ali, 2004;Ahmed, 2021;Alsaady and Alzubaydi, 2019;Al-Owaidi, 2021) When comparing the current study with the Duda (1985) classification (Table 4) for the Portland cement industry, the rocks of the study area are suitable for the Portland cement industry.

Conclusions
Weathering and erosion, as well as modification processes, affect the limestone rocks of the Dammam Formation, so that solution formed a large proportion of the cavity, increasing porosity and absorption rates while decreasing compressive strength values.
Based on the classification (Duda, 1985), the rocks of the Dammam Formation are suitable for use as a raw material for the manufacture of Portland cement.
The difference and variation in the values of the uniaxial compressive strength of the rocks for Dammam Formation is the effect of texture and digenesis processes such as compaction.
The study suggests evaluating and calculating the amount of limestone rock reserves accessible in the study area in order to determine their economic viability.

Table 1 .
Physical tests of limestone rocks for Dammam Formation

Table 3 .
Chemical tests for limestone rocks for Dammam Formation