Editorial
Volume 20, Issue 77 , January 2020
Original Article
yaser hoseini; Peyman Varjavand; Javad Ramezani Moghaddam; Mohammad Reza Nikpour
Abstract
Analysis of flow behavior of water in labyrinth channels is difficult because of micro-characteristics of the emitter. So use numerical models that has been tested in experimental conditions can be used in the hydraulic analysis of drip Emitters. In this study Fluent software was used to simulating flow ...
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Analysis of flow behavior of water in labyrinth channels is difficult because of micro-characteristics of the emitter. So use numerical models that has been tested in experimental conditions can be used in the hydraulic analysis of drip Emitters. In this study Fluent software was used to simulating flow in labyrinth channels of Type Stripe emitter and the relation between pressure and rate of discharge under 3 pressure levels (4, 5 and 6 mH2O) is determined. For turbulent flow, in addition of Navier-Stokes Equations that was used in the laminar model, also the simplified equations of the standard k-ε model were used. Also, meshing was done by GAMBIT software and for this purpose, four-sided meshes were used. Results showed that. The model has not been able to model the discharge from the droplet in laminar and turbulent conditions, and the estimated output by the Fluent model for various pressures and laminar and turbulent conditions were calculated respectively 23 and 25 percent more than examining test. So that in laminar and turbulent flow in pressures of 4, 5, 6 m the difference between model and test, were 0.28, 0.23, 0.2 and 0.27, 0.23, 0.19 lit. hr-1 respectively. The results show upper estimations in all pressure by the model, which indicates that upper estimations increase with increasing applied pressure.
Original Article
Hamid Kianmehr; Saeed Reza Khodashenas; Mohammad Rostami
Abstract
Introduction
A side sluice gate is an underflow and metering diversion device set into the side of a channel with the purpose of allowing part of the liquid to spill through the side. Review of the literature shows that in spite of the importance of the side sluice gate, little attention has been given ...
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Introduction
A side sluice gate is an underflow and metering diversion device set into the side of a channel with the purpose of allowing part of the liquid to spill through the side. Review of the literature shows that in spite of the importance of the side sluice gate, little attention has been given to studying the behaviour of flow through this device. The available published works on side sluice gates found are those of Panda (1981), Swamee et al. (1993) and Ghodsian (2003). They related the discharge coefficient of the side sluice gate to depth of flow and gate opening. For this purpose, the side sluice gates, since flow control devices, are widely used in the irrigation channels to divert flow from a main channel to a secondary channel. The main purpose of present study was to determine the water surface profile, gate opening, and flow discharge through the sharp-crested rectangular side sluice gates in a subcritical flow regime in free and submerged flow conditions. This study also provides some approaches to differentiate the free or submerged flow conditions. For this purpose, two approaches of solving spatially varied flow equation in a sub-critical flow regime and the direct solution of the discharge equation of the side sluice gates in determining the flow characteristics of the side sluice gates was experimentally investigated.
Methodology
The first approach (Solving the Spatially Varied Flow Equation)
The general differential equation of spatially varied flow along a side sluice gate with decreasing discharge is:
(1)
To determine the variation of flow discharge during the side sluice gate, the functional relationship for discharge equation must be defined. The velocity at each height V of the gate opening section is obtained as follows:
(2)
Considering the discharge dQ passing through an elementary strip of length dx along the side sluice gate (Fig. 2c), the discharge per unit length of the side sluice gate is given by:
(3)
Swamee et al. (1993) and Gill (1987) considered the following relationships for determining the flow discharge per unit length of side sluice gates, which is the simplified version of Eq. 3.
(4)
(Swamee et al. (1993) )
(5)
(Gill (1987) )
By inserting the Eqs. 3, 4, and 5 in Eq. 1, the governing differential equations were obtained in these types of flows in different conditions.
The second approach (direct solution of the side sluice gate discharge equation)
In this approach, assuming that the flow discharge variation along the sluice gate is constant and equal to the upstream water depth y1, the equations for determining the flow discharge through the side sluice gate (Eq.. 3, 4, and 5) are re-written as follows:
(6)
(Present Research)
(7)
(Swamee et al. (1993) )
(8)
(Gill (1987) )
Experimental Setup
The experiments of the present study were carried out on a physical model with a width of 1.5 m, a length of 17 m, and the depth of 0.8 m. In order to intake water, a branch channel with a width of 0.6 m and a length of 2.5 m in a distance of 8 m from the beginning of the main channel was used. In this study, the experiments were performed for a sluice gate with three different openings of 2, 4, and 7 cm with the width of 60 cm in two free and submerged flow conditions.
Results and Discussion
In order to determine the discharge coefficient of the side sluice gate, the first step was to study the variations of the specific energy and water surface profile along the side sluice gate. Then, by choosing the best relationship for determining the flow discharge of the side sluice gate, the two approaches of solving the equation of the spatially varied flow and direct solution of the side sluice gate discharge equation were examined. . Further, some approaches are presented to differentiate the free or submerged flow conditions, some fitting equations are given in order to estimate the discharge coefficient using various non-dimensional variables and step-by-step consideration of their effect.
Conclusions
In this study, the central axis of the main channel was introduced as a measuring axis in side sluice gates. Comparison of experimental profiles and those obtained from the solution of the differential equation governing the spatially varied flow indicates the proper agreement between experimental results and numerical solutions. In addition, by examining the results of solving the spatially varied flow equation, Gill (1987) ’s equation was selected as the best equation for determining the flow discharge through side sluice gates, due to the simplicity and high precision. By examining the discharge coefficient in two mentioned
approaches, it was found that the discharge coefficient obtained from the direct solution of the discharge equation is well consistent with the solution of the spatially varied flow equation. Next, some approaches are presented to differentiate the free or submerged flow conditions. It was found that the discharge coefficient of the side sluice gate in the free flow conditions depends on the ratio of the flow depth to the side sluice gate opening and upstream Froude number, and in submerged flow conditions depends on ratio of the flow depth to the tail-water depth at branch channel and the ratio of the flow depth to the side sluice gate opening.
Original Article
Milad Kheiry Ghojeh Biglou; Alireza Pilpayeh
Abstract
Introduction
The cost of dam construction is very high. A lot of dams are broken due to the water passing through dam crest. The most important factor which causes this is, insufficient spillway capacity. The aim of present study was investigating optimal height and length for Ogee-Crested spillway ...
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Introduction
The cost of dam construction is very high. A lot of dams are broken due to the water passing through dam crest. The most important factor which causes this is, insufficient spillway capacity. The aim of present study was investigating optimal height and length for Ogee-Crested spillway because such height and length minimizes the cost of spillway construction. In order to determine objective function, the spillway length variations were considered in the range of 10 to 30 m and the flood return period was estimated in the range of 1000 to 10,000 years. Optimization was done with using genetic algorithm in MATLAB software environment. In fact, the aim of this study was investigating the effect of height and length of spillway on the cost of spillway construction, therefore, Analytical relationships presented with using regression model. The main function of Ogee-Crested spillway is providing ideal conditions for passing designed flood from upstream to downstream. Bagatur & Onen in 2016, used gene expression planning (GEP) models as an alternative approach to predicting appearance features and spillway design coefficients and therefore, proposed new relationship, for Ogee-Crested spillway. It was found that GEP is much better than regression model for predicting Ogee-Crested spillway characteristics. Haghbin in 2015 proposed that using multi-objective genetic algorithm can optimize spillway geometrical dimensions. The results of this study provide the appropriate height and length for the spillway.
Methodology
The question of this research is, what is the appropriate height and length for the Ogee-Crested spillway of Ballarood Dam? In this study, the Ballarood Reservoir Dam was selected as a case study and genetic algorithm process was used for optimizing this issue. First, objective function was coded and then, this function was added to the MATLAB software. In order to provide Spillway cost function, spillway length variations were considered within the range of 10 to 30 m. In modeling with using genetic algorithm method, first, the length component was divided into discrete data which included integer numbers from 10 to 30.
K
eeping in view each optimization problem has its decision variables, constraints, and objective function. The decision variables of this present study, namely the Ballarood Dam spillway decision variables, included height (P), length (L), and flood return period (T). The models derived from algorithm modeled with using regression, and their meaningful level was obtained.
Results and Discussion
In this study, after determining objective function and choosing suitable operators, optimization was done with using genetic algorithm; the most appropriate response was reported as problem answer.
Considering the maximum design load (Hd = 50.50 m) and (T = 10000 years), the optimum dimensions and costs were obtained by function: The optimal spillway length and height was was found to be 14.4 m and 47.31 m respectively.
It needs to be mentioned that the designed Ballarood Dam spillway is 20 meters in length. With optimization by genetic algorithm, this length was reduced to 14.4 meters. Comparison of the results showed that if this amount of spillway had been applied during construction of the dam, it could have saved up to 28% on project implementation economically. The output value for the spillway height in this study was 31.47 m and the operational value for the height was 47.7 m. Comparison of these two data indicates 34% higher altitude allocation for the margin of confidence.
Conclusions
One of the goals of this study was reducing costs. Keeping this in mind, the operational cost for the spillway length and height respectively were 31% and 28% more than designed values, with reduction of spillway length and height, operational costs was greatly reduced. The other goal of this study was optimizing dimensions of spillway but according to the principles of genetic algorithm, we could not achieve to 100% of this goal. In the other words, the genetic algorithm determines the optimal dimensions but it does not determine the best answer. According to this fact, we can find other optimal dimensions for this problem, which is possible by adding more constraints to the problem. The genetic algorithm has some weaknesses, which include: Extremely high sensitivity to the population size and mutation operators which imposes high costs on the whole project in high reliability dam construction projects. Therefore, we recommend in future dam construction studies the scholars take into consideration the issue of benefits and costs future projects along with consideration of and also the high factor of safety in dam construction projects.
Original Article
S. Mohammad Hassan Saeidi; Majid Rahimpour; Mohammad Zounemat-Kermani; Mohamad Reza Madadi
Abstract
Introduction Piano key weir (PKW) is a hydraulic structure that can be installed at dams and canals for regulating the flow surface and discharge. The main feature of this weir is the ability to pass a large flow of water over a small head. Regarding its geometrical properties, this weir is classified ...
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Introduction Piano key weir (PKW) is a hydraulic structure that can be installed at dams and canals for regulating the flow surface and discharge. The main feature of this weir is the ability to pass a large flow of water over a small head. Regarding its geometrical properties, this weir is classified into four types of A, B, C and D. PKW with symmetrical upstream and downstream overhangs is classified as Type A, one with only upstream overhangs as Type B, one with only downstream overhangs as Type C, and one without overhangs as Type D. Despite various studies on piano key weirs (some of which were mentioned in the text), the flow behaiviour over these structures is very complex, unpredictable and three-dimensional. So further laboratory investigations on PKWs are needed. In the present study, the effect of the width of the inlet and outlet keys on the hydraulic characteristics of these weirs is investigated. In addition, the occurrence of undular flow on these types of weirs is reported for the first time. To achieve the aims of this study, more than 300 experiments were conducted at a laboratory flume. Methodology The experimental tests of this research were conducted in the hydraulic & water structures laboratory of Shahid Bahonar University of Kerman, on a laboratory flume with 8 m length, 80 cm width and 60 cm height, having glass walls and metal bottom. The flow discharge was adjusted in a range of 5 to 60 liters per second by a valve. In total, 16 physical models of PKW-A and PKW-D weirs were constructed to investigate the effect of width of inlet and outlet keys on the hydraulic characteristics of flow over such weirs. Seven discharges were tested for each model of weirs, and experiments were repeated three times for each discharge. Results and Discussion The results demonstrated that at low water loads (Ht <3cm), both types of weirs have almost the same performance. But as the water load increases, the performance of PKW-A weir deviates from the type PKW-D weir, i.e. it was able to pass larger discharges for an identical flow head. The superiority of PKW-A weir was more evident in small inlet-to-outlet ratios of keys. For low flow heads, the performance of weirs with different Wi/Wo ratios in terms of discharge capacity is almost similar. Anderson and Tullis (2013) found similar results in their experiments. At higher flow heads, the PKW-A1.66, compared to other models, had the largest discharge capacity in same flow heads, indicating its better performance. At maximum flow head (5.5cm), this weir was able to discharge 52 liters per second, which is 24% more than PKW-A0.6 weir. Similar trend exists for D-type piano key weirs. It was observed that undular flow is formed on D-type piano key weirs. Although, this phenomenon was previously observed on rectangular broad-crested weirs (Chanson, 1976; Madadi et al, 2013), but for the piano key weirs, this is the first report on formation of undular weir flow above D-type PKW. Conclusions According to the results of this study, the ratio of the width of the inlet keys to the width of the outlet keys is a very effective parameter in the discharge capacity of the piano key weirs, and the presence of a forehead can also play a role in enhancing the performance of the weir. Also, the results indicated that for a given head, not only the A-type PKW has more discharge capacity comparing to D-type weir, but also due to its special geometry, the undular flow phenomenon cannot be formed above such weir. Furthermore, the PKW weir with inlet to outlet key width ratio of 1.66 demonstrated 30% higher performance comparing to the other investigated models.
Original Article
Fatemeh Tayyebi; M. Bi Jan Khan; Hadi Ramezani Etedali
Abstract
Introduction
Water distribution uniformity is a key in pressurized irrigation systems. Pressure fluctuations due to topographical changes, local and frictional head losses, and different water uses are anticipated. Any mechanical device with the ability to keep an almost constant flow delivery being ...
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Introduction
Water distribution uniformity is a key in pressurized irrigation systems. Pressure fluctuations due to topographical changes, local and frictional head losses, and different water uses are anticipated. Any mechanical device with the ability to keep an almost constant flow delivery being irrespective of the pressure fluctuations is of great practical importance. In this regard, a flow control valve is a useful tool. A flow control valve is a mechanical choked orifice plate structure including a float-spring mechanism inserted in an ordinary orifice (Zhang and Wang 2015). Such a valve is not yet produced commercially.
In this study, the effect of the spring elasticity mainly due to spring fatigue is investigated experimentally on the valve performance. Also, the changes in the installing location of the float, when the valve is in rest condition, may affect its performance. To quantify this effect a detailed experimental plan was performed.
Methodology
This study presents an experimental approach for testing the effects of the spring fatigue and spring installation location on the performance of the discharge control valve. In this regard, an experimental model was constructed at Imam Khomeini Intentional University, IKIU. It consists of a centrifugal pump, a motor drive to adjust the pump’s rotational speed, and a Rosemont digital pressure gauge. The flow rate was measured by a calibrated Venturi meter. Two design discharges of 0.4 and 0.6 l/s were considered and the valves were fabricated based on the design guidelines available at Rezazadeh et al. (2019).
In order to quantify the valve performance PI index was used (Atashparvar et al., 2019).
(1)
in which, DPID and DNID are the total/sumation of the positive and negetive discharge deviations from the design value respectively.
Results and Discussion
According to the experimental curves of valves’ discharge variations, PI values were calculated to identify the effects of the spring fatigue and inappropriate valve assembly (Fig. 1 and Fig. 2). The results indicated that, if the distance of the float to the orifice location, b, varies in the ranges of 0.5£b(mm) £4.3 and 2.75£b(mm) £5 for Q=0.4 and 0.6 l/s respectively, the valve performance is affected marginally (Fig. 1). It is found that for the design discharge values of 0.4 and 0.6 l/s the spring elasticity can decrease no more than 3% and 6% respectively (Fig. 2).
Fig. 1- PI-values of changing the distances of the float of MCOP
Fig. 2- PI-values of changing the MCOP’s spring elasticities
Conclusions
Water distribution uniformity is a key in pressurized irrigation systems. In this regard, flow control valve is a useful tool. The control valve studied in this investigation, consists of a float moving into an orifice of a given diameter. The mechanism makes it possible to have a semi constant flow rate being irrespective to the pressure fluctuations. The design criteria of the valve were proposed in 2015. It is not
yet produced in commercial scale. Discharge control valve can be used in tape irrigation systems. Spring fatigue and inappropriate assembly can affect the valve performance. In this study, the effect of these parameters on the performance of the control valve are investigated experimentally. The results indicated that, if the distance of the float to the orifice location, b, and the spring elasticity, K, are considered 82% and 15% greater than their design values, the valve performance is affected less than 5%. Spring elasticity variations due to the spring fatigue can affect the valve performance significantly. It is found that, for the design discharge values of 0.4 and 0.6 l/s the spring elasticity can decrease no more than 3% and 6% respectively.
Original Article
Soroush Esmaeili Zadeh; Babak Lashkara-Ara
Abstract
Introduction
Formation of air-entraining vortices in an intake leads to unsteady flow and cause problems such as vibration in hydro mechanical equipment, abnormal noises, severe fluctuations in local pressures and exacerbated cavitation conditions (Chen & Chen, 2015). As stated by (Sarkardeh, 2017) ...
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Introduction
Formation of air-entraining vortices in an intake leads to unsteady flow and cause problems such as vibration in hydro mechanical equipment, abnormal noises, severe fluctuations in local pressures and exacerbated cavitation conditions (Chen & Chen, 2015). As stated by (Sarkardeh, 2017) the stronger vortex the greater will be its negative effects on intake performance. There have been many studies on the critical submerged depth and vortex formation in intakes. (Kocabas & Yildirim, 2002) investigated the effect of rotational flow on the critical submerged depth in intakes and found that the vortex formation with the air-core vortex and the critical submerged depth was significantly dependent on the approach flow conditions and the inlet geometry. Therefore, a separate case study should be undertaken to address any structure with a particular geometry. In this paper, the effect of flow rate deviation due to the use of a deflector on a vertical intake was investigated. In this paper, also the variation of submerged depth, Froude number, vortex type, and critical submerged depth was discussed.
Methodology
In this study, different scenarios were created by varying the deflector angle from 3 to 11 degrees. In order to measure the discharge rate, the flow passes an electromagnetic flow meter with a full-scale accuracy of ±0.2%. A depth gauge with an accuracy of ±0.05 mm was used to measure the water head on the intake crest. Given that the critical submerged depth is in agreement with the nature of the type 4 vortex (Naderi & Gaskin, 2018). Therefore, in experiments with the observation of type 4 vortex, the critical submerged depth was determined. Then, according to the dimensional analysis and the results of the last experiments, the key factors affecting the critical submerged depth, including deflector angle (α) and Froude number (Fr) were identified. The range of variation of the tested parameters included in deflector angle (α) of 3, 7 and 11 degrees, the discharge of 2 to 26 liter/s and the Froude number of 0.3 to 3.9.
Results and Discussion
After processing experimental observations, the trend of the rating curve changes, the relative submerged depth versus the Froude number, as well as the vortex type were evaluated. The results showed that the flow with a higher deviation angle α has a steeper rating curve. In other words, the angle α has a direct effect on the spherical sink surface sector, so that by increasing the angle α, the effective cross-sectional area of the flow decreases, resulting in a reduced spherical sink surface sector, and leading to a weak performance of the intake. This caused water to be stored in the reservoir for low discharges. According to the experimental observations at a fixed Froude number, the greater the angle α, the lower the relative submerged depth. To be more precise, the deflector inside the intake, in turn, compresses the air-core vortex and moves it upstream, thereby creating weak vortices and reducing the amount of rotation of the flow on the crest, thus it was observed that with increasing the angle α at a constant Froude number, less relative submersion depth was required. On the other hand, decreasing the angle of α causes the vortex core to be emitted outward, so more rotation was needed to maintain this vortex. Therefore, in this situation, the intake at a constant Froude number requires a greater relative submersed depth.
Conclusions
The results of this study showed that the use of a deflector in the vertical intake, in addition to reducing the critical submerged depth, weakens the formation of a vortex, stabilizes reservoir water level changes, and prevents unsteady flow conditions. The results also revealed that an increase in deviation angle α and consequently the Froude number, allowed the vortex compression effect to impose the greatest impact on the relative submerged depth (S/Di).
Acknowledgement
We are grateful to Jundi-Shapur University of Technology and for funding of present project allowing access to the hydraulic and river engineering laboratory of the Department of Civil Engineering.
Original Article
Reza Bahramlou; Ghasem Asadian; saeed gohari; Ali Ghadami Firouzabadi
Abstract
Introduction
Conveyance and Water distribution irrigation canals are hydraulic structures that transport water supplied from sources such as diversion dams for drinking, agricultural, industry or other purposes. These canals are usually lined by materials such as: concrete, stone with sand cement mortar, ...
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Introduction
Conveyance and Water distribution irrigation canals are hydraulic structures that transport water supplied from sources such as diversion dams for drinking, agricultural, industry or other purposes. These canals are usually lined by materials such as: concrete, stone with sand cement mortar, asphalt, to prevent water seepage losses along the flow path. Concrete lining that is used in irrigation canals is an unreinforced concrete with a thickness of 5 to 10 cm. Basic requirements of good hardened concrete are: satisfactory compressive strength and sufficient durability (Aba, 2005). After the implementation of each engineering structure, it is necessary to evaluate the project to determine the optimal performance and quality of implementation. Evaluation of the quality of irrigation canal linings is often carried out by the destructive and costly method of coring and carried out various experiments in the laboratory. Although destructive method yields relatively exact and straightforward results from the desired parameters, it also has some side problems that are sometimes difficult to recover. The problems of destructive test (DT) method with coring and destructive method are associated with damage of project, high cost, need the expert group and equipment, time-consuming and sometimes stoppage of project operation. Non-destructive testing (NDT) methods can be used to prevent these complications. Electrical, ultrasonic and Schmidt hammer tests are among non-destructive testing. Nowadays, non-destructive testing of concrete has an effective and practical function in the repair of concrete structures. Non-destructive testing of concrete by providing data on various existing structures allows experts to judge and decide on the performance, needs and methods of repair and restoration of concrete structures. The indicator of evaluation of the quality of concrete lining in irrigation canals in different environmental conditions is the same as the other structures based on the amount of compressive strength (Anon., 2014). The failure of hardened concrete due to repeated cycles of thawing- freezing in cold air in hydraulic structures (such as irrigation canals that
can absorb water and saturated) is more probable than other concrete structures (Ramazanianpour and Shahnazari, 1988).
Methodology
In this study, in order to establish a relationship between non-destructive testing (NDT) of Schmidt's Hammer number with destructive testing (DT) of compressive strength and water absorption parameters, 13 sections from 3 main conveyance canals were studied in Nahre Shaban irrigation network in Nahavand City. At all sections, non-destructive testing of Schmidt's Hammer accomplished for determining the rebound number, then from the same points, 12 and totally 156 cores were provided from 3 canals. Next relationship between rebound numbers (RN) with each of the parameters of laboratory experiments on the linings was investigated. The study area in this study was 6 km from the main canal of the irrigation network of Nahre Shaban in 3 sections of Ghaleqabad, Shaban and Jahanabad in Nahavand City. This canal is divided by diversion dam of Sha'ban with height of 3.5 m which was constructed in a section with coordinates of (X = 262862, Y= 3775625) during 1985 and 2001. Table 1 presents the characteristics of the main canal at the location of the Ghaleh Ghobad river section on the Shaban network. The coordinates of each section of the canal intended for coring were determined using GPS; these coordinates are presented for the 13 points in the selected canals in Table 2.
Table 1- Geometrical and hydraulic properties of studied canal in Nahavand plain
Network name
Canal length
(m)
Lining material
Cross section type
Discharge
(lit/s)
Land area
(hac.)
Geometrical properties
Bed
(m)
Depth
(m)
Side slope
Shaban river
5000
Situ concrete
trapezoidal
3000
2700
1.4
1.5
1:1
Table 2. Position and coordinates of canal sections for destructive and non-destructive experiments
Coordinates (UTM)
Canal Code.
Local canal name
Y
X
3775681
263046
GH1
Ghaleh Ghobad
3776121
262772
GH2
3776737
262411
NSH1
Shaban river
3777241
262299
NSH2
3777606
262335
NSH3
3778060
262086
NSH4
3778201
261471
NSH5
3779031
261256
JNA1
Jahan abad
3779369
261431
JNA2
3779687
261967
JNA3
3779580
262107
JNA4
3779758
261656
JNA5
3779865
261828
JNA6
Results and Discussion
Based on the results obtained, Schmidt hammer number and compressive strength values have direct relationship with correlation coefficient of 86%. Also, the Schmitt Hammer and initial, boiled and capillary water have a reverse power relationship with a correlation coefficient of 72, 70 and 71 percent respectively. Considering these relationships with proper correlation, it is possible to estimate the durability parameters in through the non-destructive testing of the Schmidt hammer at the site. There is a direct relationship between the initial and boiled water absorption, with a correlation coefficient above 95%. Therefore, boiled water absorption capacity of cores, w hich requires more than 3 days, can be determined from the results of initial water absorption. There is an inverse relationship with grade of 3 with a correlation coefficient above 96% between boiled water absorption and compressive strength of cores.
Conclusions
Between Schmidt hammer number and compressive strength values in concrete-lined irrigation canals are a direct relationship with correlation coefficient of 86%. So it is possible to estimate the durability parameters of irrigation canal linings in through the non-destructive testing of the Schmidt hammer number at the site.
Original Article
Danesh Sattari; Masoud Hajialilue Bonab; akbar arabpour javadi
Abstract
Introduction The stability of unsaturated slopes during rainfall is an important natural hazard. Past studies have shown that slope failures generally occur during or after rainfall. A review of past studies shows that instability of natural or excavated slopes for infrastructure construction occurs ...
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Introduction The stability of unsaturated slopes during rainfall is an important natural hazard. Past studies have shown that slope failures generally occur during or after rainfall. A review of past studies shows that instability of natural or excavated slopes for infrastructure construction occurs mainly during or after rainfall. Due to rainfall infiltration into unsaturated soil, the apparent cohesion and shear strength provided by matrix suction reduces d, resulting in slope instability. Library studies for this research, revealed that in recent years, extensive studies have been conducted on the rainfall infiltration in unsaturated slopes and their effect on shear strength and stability. But much of the research has been on high-intensity rainfall over a short period of time, however, some instability of slopes occurs during long-term rainfall or after rainfall. In addition to field research and physical modeling, numerical methods have also been developed to solve complex problems of unsaturated soils within the framework of various scientific theories in recent years. In this paper, in addition to considering the results of previous studies, the stability of the excavated soils with multiple berms has been investigated by considering transient fluid-mechanical coupled analysis. Khodafarinn Irrigation network is one of the largest water resources development projects in northwestern Iran. The length of its main canal is 144 km. According to the topography of the project area, excavations were required to construct the main canal and its structures. The stability of the slopes created by excavation is of great importance for canal construction and operation. One of the critical slopes created along the main canal is in the trench created at the site of the Golmali cut and cover which was selected as a case study. Methodology FLAC 2D is one of the most applicable geotechnical software based on the FDM and complex LAC 2D is one of the most applicable geotechnical software based on the FDM and complex geotechnical problems can be modeled by using FISH. The general framework of the study is that geometrical characteristics and materials parameters of the slope were first extracted using in situ and laboratory tests and then the average monthly rainfall was obtained from the meteorological station statistics. Then, transient fluid-mechanical coupled analysis was prepared for rainfall infiltration and deformation analysis using TPFlow. As a result of the analysis, pore water pressure, degree of saturation and deformation were calculated and according to results, the stability of slope was evaluated by using the shear strength reduction method. Filter paper test and RETC code were used to extract the SWRC and HCF of unsaturated soil parameters by Van-Genuchten model. Table.1 shows the parameters used in the analysis. Table 1-Parameters of slope material for numerical analysis γsat G C Ks ϕ θs θr α n KN/m3 MPa Pa m/s Deg. - - - - 19.1 100 8340 1.42E-06 27.4 0.453 0.05 1.282 1.585 Based on the available meteorological data, the average annual rainfall and monthly values of rainfall were extracted for the study area. In order to reach initial conditions in terms of water content and degree of saturation, average annual rainfall (288 mm) was applied to the slope for six months. Then, the most critical time limit for performing the task in terms of rainfall was selected from monthly values of rainfall for the 4 critical months (March-June) Fig. 1. Results and Discussion Fig. 1 shows the changes in the factor of safety during the four months of rainfall. According to the results, the FOS was 1.72 at the end of the initial condition and after applying four-month rainfalls, it was reduced to less than 1 and as result failure occurs. By finding the trend of its changes, it can be concluded that, when the FOS was reached less than the unit after about 80 days and the slope became unstable. In other words, with the passage of time and the increased rainfall infiltration at higher depths, after about 80 days, the complete slope failure started from the slope claw. Figure 16- Factor of safety and rainfall history for the 4 month Conclutions 1) Due to very low permeability and high suction at a low saturation ratio, the behavior of unsaturated excavated slopes in fine-grained soil is relatively complex compared to coarse-grained soil slopes. 2) In fine-grained soil slopes, pore water pressure and degree of saturation increase nonlinearly with increasing rainfall duration. However, the increase rate and the trend of increase was different from studies for high-intensity short duration rainfalls, The increase was faster at the slope surface but with increasing depth, water infiltration rate and consequently changes in pore water pressure will take longer time. 3) The factor of safety decreases with the time of rainfall and after about 80 days, the instability of the slope begins and the reason for its prolongation can be attributed to the low permeability of the slope material. Therefore, for relatively low permeability soil slopes such as those in fine-grained soils, long-duration rainfall is more effective than high-intensity but low-duration rainfall. 4) According to the results of previous studies conducted on high-intensity rainfall on slope stability in fine-grained slopes, high intensity and low duration rainfalls cannot infiltrate due to low permeability of materials and moves in the form of runoff at the slope surface and their stability should be examined for moderate to long-duration rainfall if necessary.
