Study on the Rapid Drawdown and Its Effect on Portal Subsidence of Heybat Sultan Twin Tunnels in Kurdistan-Iraq

The excavation of tunnels below the water table causes variations in the hydraulic level, pore pressure and effective stresses. In this regard, rapid drawdown is considered as a destructive phenomenon as to the change in the flow regime which has mostly been studied for the reservoirs of embankment dams. The rapid drawdown occurred at the upstream shell of the dam gives rise to increase in the pore pressure at the upstream shell. This is as a result of the incompliance between the water loss inside the shell and the reservoir water level. Hence, it would be more likely to have instability and sliding at the upstream slope on account of decrease in the effective stress. Lack of sufficient studies performed on this matter in tunnelling projects on the one hand and the knowledge on the most important parameter for decreasing the destructive effects of this phenomenon on the other hand necessitates performing further studies on this matter. To this end, the reasons for the occurrence as well as the affecting parameters were studied by modelling the large subsidence of the inlet portal of Heybat Sultan twin tunnels located in Kurdistan-Iraq making use of the variations of the groundwater boundary conditions under Phase2 code. The modelling results depict the importance of the drawdown rate and the permeability coefficient of the surrounding rock mass. In the interim, the rapid loss in the hydraulic gradient caused by the drainage of a considerable volume of precipitations into the tunnels led to the rapid decrease in the pore pressure and increase in the effective stresses up to total stress. This has resulted in the consolidation settlement in the tunnel portal

Structural behaviour of reinforced concrete beams containing a novel lightweight aggregate

This paper reports the results of an experimental investigation into the structural behaviour of reinforced concrete beams incorporating a novel EPS-based lightweight aggregate (LWA) called stabilised polystyrene (SPS) aggregate. Four concrete mixtures with water to cement (W/C) ratio of 0.8 were used. The replacement levels of natural aggregate by SPS were 0%, 30%, 60% and 100%. The volume ratio to manufacture SPS aggregate was 8:1:1 (80% waste EPS: 10% cement: 10% clay). A total of 24 beams were cast and tested at 28-day age. Three types of tension reinforcement were used: 2 bars, 3 bars and 2 bars + shear links. There were no compression bars at the top for all beams. Four point-loading flexural tests were conducted up to failure. In general, it can be observed that the structural behaviour of SPS concrete beams is similar to that of other types of lightweight aggregate concretes used around the world.Iraqi government-Kurdistan regio

Concrete Capillarity under Different Curing Conditions Produced in Kurdistan-Iraq

This study discussed the effect of the curing condition on the capillary water absorption of concrete incorporating the locally available materials. The compressive strength and ultrasonic pulse velocity (UPV) as part of mechanical and durability properties of concrete were also investigated. The engineering properties were conducted on concrete under three different curing conditions at different curing ages of 2 days, 7 days and 28 days. The three different curing conditions were water curing, dry curing and gunny-covered curing. According to the results obtained, the concrete under water curing condition demonstrated a lower capillary water absorption (CWA) at 2 and 7 days ages and the concrete under gunny-covered condition demonstrated lower CWA at 28 days of age, compared with the other curing conditions. It is interesting to see that the compressive strength (38 MPa) of concrete was almost the same at 28 days age under the gunny-covered and water curing conditions

Combined Effects of Densified Polystyrene and Unprocessed Fly Ash on Concrete Engineering Properties

The present study evaluated the combined effects of two types of waste materials of expanded polystyrene (EPS) and unprocessed fly ash (FA) on different properties of concrete. A novel recycling technique of densifying waste EPS is used to produce a novel lightweight aggregate (LWA). This new technique has solved the problem of segregation in concrete by coating EPS particles with a natural binder of clay and cement. Nine different concrete mixtures with a water to cement ratio of 0.8 were used. The densified EPS and unprocessed FA were partially replaced with natural aggregate and Portland cement, respectively. The engineering properties, including workability, density, compressive strength, ultrasonic pulse velocity (UPV), and water absorption (WA) were investigated at different curing times. According to the experimental results, there is a decrease in compressive strength and UPV with increasing this novel LWA content in concrete. However, by using a suitable mix design, the utilisation of these two waste materials in concrete using an appropriate recycling technique is possible

Sustainable Concrete in the Construction Industry of Kurdistan-Iraq through Self-Curing

The improper curing of concrete can seriously affect its hardened properties. However, a large quantity of water is required to cure concrete after casting. Water is a valuable resource and its availability is posing a particular challenge in the Middle East including the Kurdistan region of Iraq. Self-curing concrete may be considered a novel curing method in that the water inside the concrete mix is retained so that hydration can continue without the supply of additional water after casting. Therefore, the aim of this study was to include a self-curing agent, named Polyethylene glycol-400 (PEG-400), as one of the concrete mix constituents in order to save water that is normally required after casting. Six concrete mixes were cast with a constant W/C ratio of 0.5; two of them were ordinary concrete mixes whereas the other mixes contained 0.5%, 1%, 1.5%, and 2% of PEG-400 by weight of cement. All concrete ingredients, except the PEG-400, were provided locally. Three different curing regimes were employed: air curing under ambient laboratory conditions, water curing, and self-curing using different dosages of PEG-400. Testing included compressive strength, ultrasonic pulse velocity (UPV), and water absorption. The results showed that 1% of PEG-400 is the optimum dosage to be used for self-cured concrete

Effect of Varying Steel Fiber Content on Strength and Permeability Characteristics of High Strength Concrete with Micro Silica

For the efficient and durable design of concrete, the role of fiber-reinforcements with mineral admixtures needs to be properly investigated considering various factors such as contents of fibers and potential supplementary cementitious material. Interactive effects of fibers and mineral admixtures are also needed to be appropriately studied. In this paper, properties of concrete were investigated with individual and combined incorporation of steel fiber (SF) and micro-silica (MS). SF was used at six different levels i.e., low fiber volume (0.05% and 0.1%), medium fiber volume (0.25% and 0.5%) and high fiber volume (1% and 2%). Each volume fraction of SF was investigated with 0%, 5% and 10% MS as by volume of binder. All concrete mixtures were assessed based on the results of important mechanical and permeability tests. The results revealed that varying fiber dosage showed mixed effects on the compressive (compressive strength and elastic modulus) and permeability (water absorption and chloride ion penetration) properties of concrete. Generally, low to medium volume fractions of fibers were useful in advancing the compressive strength and elastic modulus of concrete, whereas high fiber fractions showed detrimental effects on compressive strength and permeability resistance. The addition of MS with SF is not only beneficial to boost the strength properties, but it also improves the interaction between fibers and binder matrix. MS minimizes the negative effects of high fiber doses on the properties of concrete