Iraqi Geological

Abstract


Introduction
A dam is a barrier that restricts surface stream water and rainwater. Reservoirs created by dams suppress floods and provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Moreover, a dam must retain water, have enough safety against sliding, and adjust to terrain deformations without too much cracking in service (Romana, 2003b).
The Rock Mass Rating geomechanics classification was originally proposed by (Bieniawski, 1973) for use in tunnels, slopes, and foundations. The use of Rock Mass Rating has been very diverse extremely frequent in underground works, very scarce in slopes, and almost nil in dam foundations, which is why Romana (2003a) suggested Dam Mass Rating Which is a new classification for use in dam foundations, as an adaptation of Rock Mass Rating, due to the difficult effective use of RMR for the dam foundation.
Foundation conditions depend upon the geological character and thickness of the strata which are to carry the weight of the dam, their inclination, permeability, and relation to underlying strata, existing faults, and fissures, the case study focuses on the assessment of the foundations rocks at the proposed Makhol Dam site using different Classification systems that mentioned above.
The primary aim is focusing on the using Rock Mass Rating (RMR), Dam Mass Rating (DMR), and Geological Strength Index (GSI) systems in determining the characteristics of the different rock masses (rock mass units) under the dam foundation, and also assessment their suitability for different dam types From the above mentioned GSI system in conjunction with the Hoek-Brown failure criterion, the mechanical properties of the rock masses (compressive strength, tensile strength, deformation modulus, shear strength parameters including the friction angle (Ø), and cohesion (c)) were then estimated by RocLab programme.

Location of the Study Area
The study area is located in the northeastern part of Salah -Aladdin Governorate, and the northwestern part of Kirkuk Governorate and lies between latitudes 35° 16΄ 23˝ N & 35° 16΄ 49˝ N and longitudes 43° 41΄ 95˝ E & 43° 44΄ 38˝ E (Fig. 1).

Geology of the Study Area
The geological situation of the study area, which includes the geomorphology, stratigraphy, and structure of the area, is one of the most important aspects that have a clear impact on the ground in the construction of dams and reservoirs.
The dam lies in a geologically complex area, with two anticline folds. They are a Makhol anticline parallel to the western side of the Tigris Rivera and a Khanugah anticline on the eastern side. The anticline fold is parallel to the left shoulder of the river as in Fig. 2.
The outcrops Formations at the site of the dam are Fatha and Ingana Formations, as well as Quaternary deposits as in Figure 2, which aged from the Middle to Late Miocene (Fouad, 2002).

Geology and Foundation Condition
The main purpose of constructing a good foundation for the dam is to lessen the deformation caused by the dam's weight, increase the bedrock's compressive strength, and prevent seepage under the dam and erosion that may follow seepage. (Tallberg and Karlsson, 2011)

Right Bank
The Foundations of this site are the Fatah Formation rocks, these layers are inclined at about 18°-40° to the northeast and consist mainly of a succession of marl, gypsum, and limestone rocks of varying thicknesses (Fig. 3). Significant fracturing of these rocks, fracture, and Karstification are also observed, and the outposts of this Formation are candidates for engineering problems as in Fig. 4, so special treatments are placed in the design. 0

Left bank
The surface of the land on this site is covered by river sediments that are consisting of sandy gravel with small percentages of silt and clay, these deposits are thick and are between 5-12 m. the sediments cover most parts of the Injana Formation, as in Fig. 5, which overlaps with sandstone rock. An outcrop of sandstone layers' rocks can be seen on the left bank of the Tigris River (Fig. 6).

Materials and Methods
Fieldwork, which succeeded in phase one of desk work, advanced from preliminary field investigation to detailed field investigation. During this phase, the rock mass units were determined along the dam axis, for lithological and structural measurement, and detailed engineering geological investigation was done for each of the weathering grade, discontinuity attitudes, spacing, and conditions of discontinuities and groundwater condition, which they are required in the computation of the Rock Mass Rating, Dam Mass Rating, and Geological Strength Index values.

Rock Mass Rating (RMR)
Rock Mass Rating, also known as Geomechanics Classification System, was originally proposed by Bieniawaki in 1973 for use in tunnels, slopes, and foundations. However, it has gone through several evolutions through the years (1974, 1975, 1976, and 1989), Rock mass rating uses six different parameters that can be determined in the field as follows:

Unconfined Compressive Strength (UCS)
The intact rock strength is an important parameter in the rock mass and dam mass ratings. The strength of the intact rock material should be obtained from rock cores by site conditions. It can be evaluated indirectly using the point load test or directly by the unconfined compression test. Deere et al. (1967) created the idea of the RQD to measure the quality of the rock using drill cores. RQD is the percentage of complete core fragments longer than 100 mm in the total length of the drill run RQD = ≥ 10 * 100%.

Rock Quality Designation (RQD)
(1) RQD can be calculated from the number of joints (discontinuities) per unit volume (Jv) in the absence of cores. For rock masses devoid of clay-free, a relationship used to transform Jv into RQD is (Palmstrom,1982) as follows  (2) Where Jv is the volumetric joint count or the total number of joints per cubic meter. Palmstrom

Spacing of Discontinuity
The space between neighboring discontinuities in the same set is perpendicular to one another (ISRM, 1978). The mean value was used to determine the distance between various joint sets. The measurement was performed using a power tape.

Condition of Discontinuities
The descriptions of discontinuity surface roughness and coating materials are generally weighed towards the smoothest weakest discontinuity. According to the Rock Mass Rating system, their conditions include their persistence, surface roughness, aperture, infilling (gouge) material, and weathering state.

Groundwater Condition
Groundwater has an effect on the disposal of the rock mass, which Its effect varies with the rock state when it is (dry, humid, or saturated) and the water hurts the properties of the rock and when it is dry, the groundwater coefficient is high (Bieniawski, 1989).

Orientation of Discontinuities
The orientation of discontinuities relative to an excavated face can influence the rock mass's behavior. For this reason, (Bieniawski,1989) recommends adjusting the sum of the first five rating numbers to account for favorable or unfavorable orientations. (Romana, 2003a & b) a new Geomechanics classification system, known as Dam Mass Rating, as an adaptation of Rock Mass Rating, giving guidelines for several practical aspects of dam engineering and the appraisal of dam foundation.

Dam Mass Rating (DMR)
The DMR of the rock mass was computed as per Romana (2003b), where a relationship has been suggested: DMRSTA = RMRBD (1989) Where: DMRSTA = Dam Mass Rating related to the dam foundation stability RMRBD = Basic Dry RMR CF = Geometric Correction Factor RSTA = Rating of the adjusting factor for dam stability. When the dip direction of the significant joint is not almost parallel to the downstream-upstream direction of the dam axis, the danger of sliding diminishes due to the geometrical difficulties to slide. It is possible to take account of this effect by multiplying the rating of the adjusting factor for dam stability RSTA, by a geometric correction factor CF: CF is calculated as: Where: αd = upstream-downstream direction of the dam axis αj = dip direction of the significant discontinuity (here it is the bedding planes). Once, the DMRSTA is computed, a correlation between the value of DMRSTA and the degree of safety of the dam against sliding is suggested as a rule of thumb as in Table 1. It is desirable to gather data on the RMR value of dam foundations. Some simple guidelines can be tentatively proposed for dam foundation excavation and consolidation grouting (Romana, 2003a), as in Table 2. (+) minimum (desirable) Two cases are dangerous for the normal behavior of a concrete dam: if Em varies widely across the dam foundation, or if Ec/ Em reaches certain values (Ec being the deformation modulus of concrete). Rocha (1975and 1976) (In Romana,2003a,2003band 2004 established the most followed rule for dams, as in Table 3.  Table 4 displays the various ranges of DMRDEF about the various ranges of potential issues in the dam as a result of the differences in deformability between the dam and its foundation.

Geological Strength Index (GSI)
The Geological Strength Index (GSI), was introduced by Hoek (1994), (Hoek et al. 1995), and Hoek and Brown (1997) to overcome the deficiencies in Bieniawski's RMR for very poor-quality rock masses. The GSI system estimates the reduction in rock mass strength for different geological conditions as identified by field observations. The rock mass characterization is based on the visual impression of the rock structure, in terms of blackness, and the surface condition of the discontinuities indicated by joint roughness and alteration (Hoek, 1994).
The final rating, called RMR76, can then be used to estimate the value of GSI (Hoek et al., 1995) as follows: For RMR76 < 18 Bieniawski's (1976) classification cannot be used to estimate GSI. The minimum value which can be obtained for the RMR89 classifications is 23. The estimated RMR can be used to estimate the value of GSI as follows:

Results and Discussion
It was noticed in the field that the thirteen (13) different rock mass units comprised along the Makhul dam axis, the characterization of rock mass units are shown in Table 5 The RMR, DMR, and GSI were computed for all thirteen rock mass units. RMRBD was obtained with considering the rock mass completely dry, as in Table 6. CF was calculated from equation no.5, which taking into account the direction of the significant discontinuity (here bedding planes) that have an attitude 038/15, 034/7.5, and the downstream direction of the dam axis which is 147. whereas the Geological Strength Index were estimated for Marl, and Claystone rock masses, from Hoek and Marinos (2000) chart, and Limestone, Gypsum, and Sandstone from Hamasur (2009) chart, the results are shown in Table 6. The RocLab software was also used to find the mechanical properties (cohesion, friction angle, tensile strength, compressive strength, global strength, and deformation modulus) of the rock mass, as in Figure 7 for unit no.1 as in the example. The program was also applied to all the rock mass units in the study area, and the summary of these six parameters is shown in Table 7. After finishing the rock mass classification systems RMR, DMR, and GSI and determining the mechanical properties of the rock mass by the Hoek-Brown criterion using the RocLab program, the rock mass units were evaluated as follows: • Assessing every rock mass unit for the dam's safety against sliding after filling the reservoir, "Fill dams or Gravity dams" are used to prevent horizontal sliding; this is dependent on each unit's DMRSTA, as stated in Table 8. • Evaluating all rock mass units for the necessity of foundation excavation and consolidation grouting in the case of construction of different dams (Gravity dams, Rockfill dams, and earthfill dams), which depends on the RMRBD(1989) value, then comparing this value with the Table 2 and the results are shown in Table 9. • When evaluating all rock mass units for the impact of Ec / Em on the projected Makhol Gravity (CVC, RCC) or Hardfill dams behaviors, Ec / Em value demonstrates its influence on the dam and the severity of issues. The outcomes of this assessment are displayed in Table 10 and were determined by comparing Em values with Table 3. • Determining the type of deformability problems as described in Table 11 by evaluating all rock mass units for the deformability problems, which depend on the DMRDEF value of each unit, and comparing this value with Table 4.   (Romana,2003a Where: RMR = Rock Mass Rating (the sum of the rating of the six parameters).
RMR (1976 or 1989) = Rock Mass Rating related to the year of that version. DMR = Dam Mass Rating. RMRB = Basic RMR, with no adjusting factor for joint orientation. RMRBD (1976) = Basic dry RMR (the addition of the first four parameters of RMRB (1976) plus 10. RMRBD (1989) = Basic dry RMR (the addition of the first four parameters of RMRB (1989) plus 15. DMRSTA = DMR related to dam stability. DMRDEF = RMR related to relative deformability, with WR (water rating) = 5, and no adjusting for discontinuity orientation. 40 52 * Rating of the average spacing of all discontinuities………. (Beiniwaski, 2011) **In DMR → Water rating (WR) = 5 when water pressure ratio (ru) = 0.25 (Romana,2003a Where: RMR = Rock Mass Rating (the sum of the rating of the six parameters).
RMR (1976 or 1989) = Rock Mass Rating related to the year of that version. DMR = Dam Mass Rating. RMRB = Basic RMR, with no adjusting factor for joint orientation. RMRBD (1976) = Basic dry RMR (the addition of the first four parameters of RMRB (1976) plus 10. RMRBD (1989) = Basic dry RMR (the addition of the first four parameters of RMRB (1989) plus 15. DMRSTA = DMR related to dam stability. DMRDEF = RMR related to relative deformability, with WR (water rating) = 5, and no adjusting for discontinuity orientation. 52.2 52.3 50 * Rating of the average spacing of all discontinuities………. (Beiniwaski, 2011) **In DMR → Water rating (WR) = 5 when water pressure ratio (r u ) = 0.25 (Romana,2003a Where: RMR = Rock Mass Rating (the sum of the rating of the six parameters).
*DMRDEF (RMR related to deformability = RMRBD (1976) -5), the values of DMRDEF are from Table 6. ** Em (Deformation modulus of the rock mass), according to " Romana, 2003a", if RMRBD > 60 or DMRDEF > 55 the Em = 2RMR -100 was used, and if RMRBD < 60 or DMRDEF < 55 the Em =10 (RMR-10)/40 was used (Note: Here RMR = DMRDEF). ***Ec / Em and its guidelines are based on Table 3. ****CVC = Conventional vibrated concrete dam (Gravity dam, having Ec = 30 GPa). *****RCC = Roller compacted concrete dam (Gravity dam, having Ec = 20 GPa). ******Hardfill dam (having Ec = 10 GPa). ■The same guidelines for the Gravity dam were also used for hardfill due to the lack of guidelines for the Hardfill dam. Note about abbreviations: Neg.= Negligible L.im= Low importance, Imp. = Important, Som.= Some, Non. = None. • The DMRDEF (RMR related to relative deformability) values range between 27-65.3, which indicates some -serious deformability problems on the right sides of unit 3, there are also some problems on the left side and to a lesser extent. The degree of problems decreases whenever the dam type changes from CVC to RCC and from RCC to Hardfill dam and this conclusion is observed in Table 11.