Geotechnical Properties Evaluation of Selected Reservoir Sediments in Samarra Barrage and Wind Dam, Iraq

Abstract


Introduction
Sediment pollution is an important environmental problem all over the world Reservoir.sedimentation has detrimental effects on dams in two ways: first, by reducing functional storage, which changes the dam's benefit-to-cost ratio, and second, by decreasing the dams' capacity for flood routing, which increases flooding risks for both the dam and downstream.As a result, taking the sedimentation problem seriously during the initial stages of design is essential to examining the anticipated accumulation of sediments and allowing adequate storage.Generally, rock weathering and erosion produce reservoir sediments, which are transported by the alluvial process and deposited in dam reservoirs (Adongo et al., 2020).In Iraq, many studies are conducted in engineering traits field.(Al-Samarrai, 2014;Al-Zubaidi and Alamar, 2016;Mutashar, 2007).All these researches deal with sedimentary and geotechnical harvesting, geotechnical Properties and geotechnical analysis of sediments in Iraq.These methods depend on sediment and metal characteristics (e.g., grain size fractions, and physical and chemical properties.The main objectives of the current study are a detailed analysis of sediments and evaluate the physical, mechanical and chemical properties of sediments in Samarra Barrage and Wind dam, Iraq.

Location of the Study Area
The research region is located in the Salah al-Din (Samarra barrage) and Diyala (Wind dam), which are home to small dams with sedimentation issues in their reservoirs owing to a lack of dredging and disinfection activities (Figs. 1 and 2).The fieldwork stage involved conducting many reconnaissance trips to identify the geological characteristics surrounding the dam locations and a field tour of each dam selected for the research to determine the nature of the work performed by each component of the barrier.Different parts of the reservoir were sampled, where the number of sites was 3 stations for each dam using Cree mechanical type IHC1600, IHC5514 (Fig. 3).Geologically, In the Samarra Barrage, the waters of the reservoir flooded part of the river terraces that were deposited during the Quaternary era, which represent the shoulders of the Tigris River before starting the construction of the dam and its surroundings in its present condition, which consist of gravel deposits.The Quaternary period sediments cover more than 90% of the area of the dam site.The other formations are the Upper Miocene Formation and the Mukdadiya Formation at the age of (Pliocence) (Buday, 1980) (Fig. 4) Fig. 4 The geological map of the site of the samarra dam (Sissakian and Fouad, 2015).
The Mukdadiyah Formation in the wind reservoir area is considered the oldest, represented by the layers of the Injana Formation as for the right side of the river course, there are Quaternary period sediments represented by river terraces, which consist of silt interspersed with lenses of pebbles and sand, and polygenetic deposits on the right side of the river, which are recent sediments that fill the low places in the study area.They are incoherent and are located in a narrow flood plain that does not exceed tens of meters along the course of the river.These sediments are submerged at the beginning of the height of the levels in the reservoir and after the flood plains are inundated (Buday, 1980)

Physical and Engineering Tests
The moisture content of the soil are affected by two factors are sub-surface water level, which changes with the fluctuation of the water levels of the river adjacent to the bank; The second influencing factor is the type of soil, either composed of coarse sediments such as sand with high permeability and low porosity, in which water retention is low, or vice versa in fine grains soils such as clay and silt; where it recorded the range moisture content (W%) which was between 8.5 to 10.16 percent in the Samarra barrage to 16.3 and 18.6 %percent in the wind dam.As for the specific gravity (Gs)، which is affected by the type of sediments and the extent of their compactness and convergence when forming the soil, as is the case in examining the weight of the dry and wet unit volume, where the specific weight was recorded values between (2.66 -2.68) in the Samarra barrage and between (2.71 -2.76) in the Wind Dam.The result s of the grain size analysis shows the silt percentage is higher than the clay and sand percentage.The value of silt percentage is between 46.10-56.3%,The clay percentage is between 19.8-19.30%,and the importance of sand percentage is 22.7-34.70%at the Samarra barrage.while the value of silt percentage is between54.7-61.85%,The clay percentage is between 30.5-38%, and the importance of sand percentage is 0.15-14.8%at the Wind dam.Another important characteristic that depends on the moisture content and soil type is the Atterberg limits.The range percentage of the liquid limit is 20.3-21.9%in Samarra barrage and 36.6-40% in Wind dam, because of the moisture content of soil is low, and fine grain size of soil.While the range of the Plasticity Index is 2.4 -2.6 % in Samarra barrage (10.5-5 1 ) % in Wind dam. as shown in Table 1 and Figs. 6, 7 and 8.The shear strength for the undisturbed samples relatively decreased because of the remolding process.This phenomenon is called sensitivity, which is the ratio between the shear of the undisturbed soil to that of the disturbed soil.The direct shear results of soil shown in Table 3. the results of the cohesion force (C) and the internal friction angle have a range value of the cohesion force of 15-53 kPa in the Samarra barrage and 40-60 kPa in the Wind dam.Additionally, the Wind dam's range value for the angle of internal friction is 20-24 °, while the Samarra barrage's range value is 17-38 °.Some sites have high values of C because of the high amount of clay and silt.Consolidation and the results were Compression index that the range value of the index was 0.180-0.210for the Samarra Barrage and 0.246-0.251for the Wind because the soil has a high percentage of clay, which is characterized by its ability to compress, and the lowest value of the Compressive Index, because the soil has a low percentage of clay, which is characterized by being highly compressible.(Cr) Swelling index the range value was0.0102-0.0117 in the Samarra Barrage and 0.0566-0.076 in the Wind.This may be due to the soil containing some clay minerals that have the ability to swell, also Primary void ratio (eo) the highest ratio was 0.760-0.780 in Samarra Barrage.While it ranged between 0.652-0.667 in the Wind dam due to the sediments' high percentage of clay, which is known for its high porosity and ability to contain connected voids, and the lowest initial void ratio due to the soil's relatively low percentage of clay, which is known for its high porosity and ability to contain gaps.The range value of Pre-consolidation pressure (Pc), was 215-250 kPa in the Samarra barrage and 31-65 kPa in the Wind dam.This means that the soil contains a high percentage of clay or has been affected by previous loads that caused the consolidation, and the lowest value of Pre-consolidation pressure (Pc) , because the soil contains a low percentage of clay or the soil may not have been previous loads that caused its consolidation; And the initial consolidation pressure (Po),it is Primary consolidation pressure , the range value of Po was 51.6-55.76kPa in the Samarra barrage and 23.98 and 24.64 kPa in the Wind dam.Due to the increase in the density of the soil layers above the sample, due to the increase in depth effect of lithostatic pressure above the sample, and the lowest value of Po due to the low density of the soil layers above the sample.These factors are very important indices to assess the ability of the clay sediment and predict their consolidation settlement (Figs.11 and 12), (Table 2).

Chemical Analysis
The findings of chemical analysis are crucial for evaluating sediments because the ratio of sulfate, gypsum, and organic matter impacts the composition of the soil and its cohesiveness, which is inversely correlated with the soil's Bearing Capacity.Gypsum decreases the soil's Strength, increases the soil's moisture, and increases the likelihood of gypsum swelling in the ground.These effects modify the soil's composition or, in some instances, drive the establishment and bases results of the chemical examination of silt samples.shows in Samarra barrage, pH, Total dissolved salts, Organic material, a sulphate content, chlorites, gypsum, as shown in Table 3.

Mineralogical Test
X-ray diffraction analysis of sediment samples revealed the presence of clay minerals and non-clay minerals (Major, 1999), including quartz, calcite, dolomite, gypsum, albite, montmorillonite, chlorite, illite, vermiculite, and kaolinite, as in    the less the number of particles in the unit size, thus decreasing the strength of cohesion.The value of resistance to cohesion is affected by the type of soil; the more clay content in the soil the higher is cohesion.The Ø° varies between 17° and 38° in Samarra dam, and between 20° and 40° at the Wind Dam which decreases with the increase of the PI.It is clearly affected by the percentage of clay materials, where it decreases with the increase of clay materials.It is also influenced by the value of soil compaction.The low value of this angle, which is below the ideal limit of the required values, is due to the presence of clay minerals such as illite and chlorite, which help to slip and reduce resistance during shear.According to the results of the consolidation test, the soil's non-swelling sediments ranged between 0.0102-0.0117 in the Samarra barrage and between 0.0566-0.0761at the Wind dam site.These results have been used to determine the cause of the samples' lack of swelling minerals.Similarly, the extracted Directory values compression index results show that the soil's high compression and values ranged between 0.180-0.210at the Samarra dam site whereas 0.246-0.251at the Wind Dam .These types of sediments are liable to settlement and consolidation.• Chemical analysis indicate that the sediments of the study location were bare, with only a tiny amount of organic material that did not alter the engineering qualities.The high percentage of gypsum in the foundation concrete at the Wind Dam, A site A is a favorable feature affecting the sediments' engineering characteristics.At the same time, total dissolved salts in all samples are more than (0.5 percent) and have a detrimental influence on the concrete.• The X-ray analysis of sediments at the research locations revealed non-clay minerals such as quartz, carbonate minerals (calcite, dolomite), and gypsum, as well as clay minerals including chlorite, Illite, kaolinite, montmorillonite, and vermiculite.And the clay minerals that pose engineering issues (montmorillonite and Illite) are present in minute quantities -archaeological.

Fig. 2 .
Fig. 2. Location map of the Wind Dam

Fig. 3
Fig.3 Images for study area represent field investigations stage A, B, C, D.
Fig. 5.The geological map of the site of the wind dam

Fig. 9 .
Fig. 9. Direct shear tests; A, B, and C sites in Samarra barrage

Fig. 10 Fig . 11 .
Fig. 10 Direct shear test A, B, and C sites in Wind dam

Fig. 13 .
Fig.13.X-ray test the in the Samarra barrage

Table 1 .
Results of the physical tests in the study sites.

Table 2 .
Results of the engineering test in the study sites.

Table 3 .
The chemical analysis in the study sites.

Table 4 .
The percentages of clay minerals and non-clay minerals in the study sites.