Estimation the Q-Value and some Mechanics Parameters of Fifth Caves in a Haditha Area to Determine their Suitability for Underground Storage

Abstract


Introduction
At present time , the underground storage caves of various materials in the rocks are the main method used in different countries , such as construction of large water secured underground oil storage caves in a coastal regions.underground storage is undoubtedly a project of economic importance.there Several advantages in construction cost, environmental protection and operating safety have been reported.The rock-carrying theory, published by Terzaghi (1946) is the first reference of the rock mass classification system being used for engineering purposes.Since then, a lot of systems have been created., for example.the Rock Quality, Designation system, (RQD) (Deere, 1962), the Rock Mass-Rating, (RMR) system (Bieniawski, 1984) the Norwegian Geotechnical Institute Qsystem (Q) (Barton et al., 1974), the Rock Structure Rating, system (RSR) (Whickham et al., 1972), the Geological, Strength Index (GSI) (Hoek and Edwin, 1997) and the New Austrian Tunneling Method, (NATM), (Dhawan et al., 1982) to enhance techniques used when designing structural support systemsThe Qsystem is a favoured alternative technique for classifying rock masses in underground storage projects.Between 1971 and1974, the NGI developed the Q-system (Barton et al., 1974).There has been a significant advancement in support philosophy and technology in underground excavations since the introduction of the Q-system in 1974.Numerous novel rock bolt varieties have been developed.and the advancement of fiber reinforce technology, has altered the support procedure in many ways.The use of sprayed concrete has become more popular recently due to demands for a better level of safety, even for good quality rock masses.Sprayed concrete reinforced ribs have largely replaced cast concrete structures.The system was first put into use in 1974, and two changes to the support chart were made and announced at the conference.
Based on 1050 samples, largely from Norwegian underground excavations, Grimstad and Barton (1993) carried out a detailed update in 1993.In order to update the model in 2002,were used more than 900 new samples from underground excavations in Norway, Switzerland, and India .Additionally, (Grimstad et al., 2002) carried out analytical research on the thickness, spacing, and reinforcement of reinforced ribs of sprayed concrete (RRS) as a function of load and rock mass quality.

Location and Topography of the research Area
The studied area is located between 33º 52ˉ -34º 30ˉ north latitude and 41º 58ˉ -42º 48ˉeast longitude at the Haditha area in western Iraq, which forms a part of Western Desert.The physiographic height of the Western Desert increases from east to west, defining its regional morphology.The region is located in Al-Hammada, which is located east of the Iraq-Jordan border (Hamza, 1997).
Carbonate fragments cover the whole surface.The exposed bedrock has disintegrated, resulting in the pieces zone.Carbonate beds make up the zone.The valleys are trending northeast, shallow, and have a rippled shape (Jassim and Goff, 2006).

Geological Setting of the Studied Area
The formations' stratigraphic sequence in the upper Euphrates valley consist of formations namely ; Sheikh Alas, Azkand, and Anah Formations are covered by a layer of basal conglomerate, followed by the Euphrates Formation, and finally the Fatha Formation appears at the end of the rock sequence, entirely covering the Euphrates Formation (Al-Ghreri, 2007) (Fig. 1) The Euphrates Formation includes massive sinkholes and caverns within carbonate rocks.The Euphrates Formation is the sequence's most widespread formation.Consists Two supplementary type sections were described Wady Chabbab, 39 km west of Anah, and Wady Rabi, 20 km west of Husaiba, The first section represents the lower and middle units with a thickness of 110 meters.The upper unit of the formation is represented by the second section, which is 25 m thick.The combined section comprises of the following: • Lower unit: 20 metres thick consists of basal conglomerater and cobbles of limestone sourced from the underlying Oligocene Anah Formation, then 10 metres of recrystallized fossiliferous limestone that grades into coralline limestone.• Middle unit consists of : 90 metres of hard ,pseudo-oolitic limestone beds and fossiliferous limestone.• The upper unit: is 25 metres thick composed of thin layers of shelly, recrystallized limestone or shelly oolitic limestone with of soft, fossiliferous blue green marl .(Jassim and Goff, 2006).cavitation is a common occurrence in several locations of reserch area .The dissolution of limestone or gypsum creates Caves.the main type caves and sinkholes, which are developed in different shapes and sizes.The problem of sinkholes, which makes it one of the geological hazard is when the forms are developed under the ground.If they are not recognized and located, then they will certainly cause serious harm to any engineering structure built on top of it.The rock-slabbing factory in Haqlaniyah is an excellent example (Sissakian et al., 2005).
Large caverns develop in gypsum layers of the Fatha Formation and carbonate rock of the Euphrates Formation in the southern part of Al-Jezira, along the left bank of the Euphrates River.The study includes a study of five caverns in a Haditha area (Fig. 2).Q-values can be determined in a variety of ways, including subterranean excavations, on the surface, or by core logging.Underground geological mapping yields the most accurate results.Each of the six parameters is calculated separately.based on a description found in the Table 1.The Q-value ranges from 0.001 to 1000.Please keep in mind that extreme parameter combinations might result in slightly higher and slightly lower numbers.In such unusual circumstances, 0.001 and 1000, respectively, can be used to determine support (Norwegian Geotechnical Institute, 2015) 2.1.1.Rock Quality Designation ( RQD ) Deere (1963) defined RQD and intended it to be used as a basic categorization system for rock mass stability.The RQD percentage value is also the RQD rating for the Q system.When RQD is less than 10%, a minimum value of 10 should be used to evaluate Q in a poor rock mass.(Table 1).
In the absence of rock cores, the RQD may be calculated using the volumetric joint count (Jv) from Eq 3 Palmstrom proposed the following new relationship between RQD and Jv: RQD=110 -2.5 Jv (2) where Jv denotes the number of joints in1m 3 Volumetric joint count/ is a measure for the number of joints intersecting a volume of rock mass, as expressed by the following equation (Palmström, 2005).
(3) Where S1, S2 and S3 are the average distances between joint sets.Nr represents the number of random joints.

Joint Set Number (Jn)
The joint geometry determines the size and shape of the blocks within a mass of rock.Within a joint set, joints will be roughly parallel to one another and have a consistent joint spacing.Random joints are those that do not appear in a predictable pattern or have a spacing of many meters.
Random joints are those that do not exist systematically or have a spacing of several metres.However, the effect of spacing is heavily dependent on the span or height of the underground opening.If more than one joint from a joint set appears in the underground opening, it affects stability and should be considered a joint set.The number of joint sets and the number of Jn are not the same (Norwegian Geotechnical Institute , 2015).

Joint Roughness Number and Joint Alteration Number (Jr and Ja)
Joint Roughness Number and Joint Alteration Number are both numbers that describe how rough a joint is (Jr and Ja).Roughness and degree of alteration of joint walls or infill materials are represented by the parameters Jr and Ja in Table ( 1), respectively.For the zone's clay-filled discontinuity or weakest critical joint set, the parameters Jr and Ja should be obtained.When determining Q from Eq. 1, one should consider the value of a second, less favourably oriented joint set or discontinuity because it may be more significant if the joint set or discontinuity with the lowest value of is oriented advantageously for stability (Singh and Goel, 2011).

Joint Water Reduction Factor (Jw)
Joint water has the potential to soften or remove the mineral infill, reducing friction on the joint planes.The typical load on the joint walls may be lessened by water pressure, make the blocks more susceptible to shearing (Norwegian Geotechnical Institute , 2015).
The parameter (Jw) is a measure of water pressure that represents the previously specified groundwater condition.This parameter's rating values are shown in the (Table 1).

Stress Reduction Factor (SRF)
SRF refers to the relationship between stress and rock strength in the surroundings of an underground opening.Slabbing, deformation, spalling, squeezing, dilatancy and block release are all examples of stress effects in an underground opening.However, some time may pass before the stress phenomena are visible.
SRF may be determined from the relationship between the rock's uniaxial compressive strength (σc) and the main primary stress (σ1), or the relationship between the greatest tangential stress (σθ) and, (σc) in large rock by measuring both the stresses in and the strength of the rock mass.. SRF may be determined during the design phase of an underground excavation using overburden and topographic factors, as well as general experiences from the same geological and geographical location (Norwegian Geotechnical Institute , 2015).

Other Parameters of Rock Mechanics
There are some important parameters that should be taken into consideration when rock is fractured.These are the fracture hardness, Young's modulus, and Poisson's ratio (Anderson, 1995).The rock mechanics parameters, such as cohesion, tensile strength andfriction angle , are thus frequently not well understood or simple to measure.Direct measurements of these variables necessitate time-consuming, costly field tests, and the results' accuracy is occasionally questioned.Since they are required input parameters for various kinds of numerical analyses, it is imperative to obtain accurate values for these parameters for any analysis that takes deformations into account.There are several studies on the connections between Q Values and tensile strength, angles of cohesion, Poisson's ratio, and the deformation coefficient, which are all very helpful for Initial estimation for projects involving underground storage when field parameters are difficult to obtain .
Table 1.Description and ratings for the input parameters of the Q-system (Barton et al., 1974;Barton, 2002).
These parameters were calculated according to the following equations (4) (5) (cp) cohesive strength , (ϕp)frictional strength (Barton, 2008).For determining the equivalent tunnel dimension (De) for self-supporting and unsupported tunnels (Barton et al., 1974) .presented the following equation.(6) In similar dimensions, the height of the wall is used for wall support and the span or diameter is used to analyse roof support.Table 9 shows the excavation support ratios (ESRs) for a range of underground excavations.
Modulus of deformation varies greatly, with horizontal deformation occurring more frequently than vertical deformation.However, using the following relationship, a mean value of modulus of deformation, may be calculated (Barton, 2008).(7) This relationship is similar with Bieniawski (1978) and Serafim and Pereira (1983) (Table 9).The following empirical association for ultimate support pressure was discovered by Barton et al. (1974) and(1975) when he plotted the support capacity of 200 underground holes against the rock mass quality (Q).

Rock Mass Quality (Q system)
To determine the support pressure for both the roof and the wall, the values of Q were computed for all of the rock unites .In the following step, the average Q value for each cave was determined.Depending on the value of Q , other parameters were calculated ((cp) cohesive strength , (ϕp)frictional strength, Unsupported Span, Estimation OF Support Pressure) Tables (2,3&4)

Estimated Support Recommendations
The Q system is used to determine the appropriate supports for the caves, (Tables 6 & 7).The support estimate chart has evaluated the Q-values as well as other required parameters (cave height and excavation support ratio).(Figure 3).This method is used to support the ceiling, while supporting the walls, we multiply the Q value by certain values based on the table (5) then we use the chart.The support chart is most useful for underground openings and caves' crowns and springlines.For high and intermediate Q values (Q > 0.1), the amount of support on the walls is often lower.The height of the walls must be utilised instead of the span when the Q -system is used for wall support.Table 8 shows how the real Q value is changed.The number produced following this conversion is then used to estimate suitable wall support using the chart in Fig 3.  (Barton, 2008).

Total Area and Total Volume
The total area was calculated by dividing the cave into parts and projecting the dimensions of each part onto a graph paper.The different dimensions were communicated with each other and through the scale of the drawing, the total area was identified, and the total volume was calculated by multiplying the area of each part of the cave by the height (Table 15).

Discussion
Based on the above study, the results show that first Cave has a value of 8.34, second Cave 8.59, third Cave 8.54, forth Cave 8.89, and fifth Cave 8.50.These are the results of the kyu system all fall into the fair class.This indicates that the caves are currently stable, but need support, based on Fig. 2.
The support estimated by the Q-System for the Ceilings and walls of both Cave 1 and Cave 2 isfalls in category 3, which contain, Systematic bolting, bre reinforced sprayed concrete, 5-6 cm, B+Sfr, as for the other caves, they fall into category 1 and are unsupported or spot bolting.But bolt spacing and bolt length are different for ceilings and walls, as in Tables 7 & 8 The portion of the rock mass that necessitates shotcrete, mesh, or concrete support is its cohesive strength (cp).The frictional strength (ϕp), also known as the angle of internal friction, reflects the portion of the rock mass that needs bolting.He continued by saying that while rock masses with low (pϕ) values require more rock bolts, rock masses with low( cp )values require more shotcrete (Singh and Goel, 2011).
The values of the internal friction angle range from 48.5 to 56 degrees, and this indicates that there is no need for more bolts, while the cohesion values range from 1.47 to 2.18 MPa, as the low value is in the fifth cave, which needs more from shotcrete, especially in the first and second layers of the cave.It is possible to create safe and unsupported pan (De) in this rocky layer with dimensions ranging from 4.67 to 4.79 meters in all directions.
The value of the deformation modulus of the rock mass ranged from 13.01 to 14.85 MPa, as for the support pressure values, they ranged from 0.02 to 0.04 MPa, as shown in the table (9).From the above results and from field studies, caves can be used for underground storage operations, but not for all materials, as they can be used for solid materials, as well as they can be used by placing steel, plastic or concrete tanks in them.This is because the caverns are close to the surface of the earth and are not found at sufficient depths to enable them to store various hydrocarbons.It can also be used in the form of small warehouses because these places are characterized by conditions that differ from the surface conditions in terms of temperature, as they help to provide a sustainable environment due to the use of energy in them and therefore the lack of harmful substances emitted to the atmosphere.
The total size of these caves is as follows: first Cave has a value of 3640.4 m 3 , second Cave 14791.25 m3, third Cave 2250 m3, forth Cave 940 m3, and fifth Cave 4115 m3 .table8.The basal conglomerate layer has a key role in the formation of caves, because most caves are located within or near this layer.Therefore, this layer can be exploited to create man-made caves and exploit them for various underground purposes, as this layer is about 3-4 meters thick and is located between the Euphrates formation and the Anah formation, which are composed of limestone.

Conclusions
• The types of rocks are limestone and chalky limestone.
• According to the Q-system, the rock masse quality classifying in the fair rock category.
• The average dimensions of the subsurface openings that do not require support range from 4.45 to 4.69 meters.• Caves can be used for underground storage operations, but not for all materials, as they can be used for solid materials, as well as they can be used by placing steel, plastic or concrete tanks in them, because of the high porosity and permeability, as well as the proximity of caves to the surface of the earth • The basal conglomerate layer has a key role in the formation of caves, because most caves are located within or near this layer.

Table 3 .
(Jv), (RQD), and average spacing of all discontinuity measures taken from joint sets in the rock mas for five caves

Table 4 .
Rating of the rock mass parameters and value of the Q-system for rock mass in five caves

Table 5 .
Conversion of real Q values to adjusted Q values for wall support design (Norwegian Geotechnical Institute, 2015)

Table 6 .
Values of Excavation Support Ratio

Table 7 .
Permanent support recommendations for the roof based on Q and values.

Table 8 .
Permanent support recommendations for walls based on QW and values.

Table 9 .
Calculated values cp,ϕp ,Ph ,Pv ,SPAN and Ed of rock mass

Table 10 .
Results of the total volume and total area of the caves