Cracking, uplifting and displacement of concrete canal lining would increase loss of water, decrease conveyance efficiency and produce tremendous economical damages to irrigation projects. This may be greatly due to high uplift pressure under concrete lining in areas where the groundwater level is high. Thus, provision of a filter-drainage system in such conditions is vital. In recent years, application of synthetic drainage materials in the form of geocomposite, as a replacement for conventional granular drainage materials have been considered. In the present study, performance of geocomposite as a filter-drainage material under concrete canal lining has been investigated in a laboratory model. The results of the investigations showed that a geocomposite layer of sufficient thickness is able to successfully reduce uplift pressure under the canal lining. As the weight of the concrete lining may itself cause some deformations and reduction in the thickness of geocomposite layer, such effect was also investigated. The results showed that weight of concrete lining would reduce the thickness of drainage layer, causing a substantial reduction between 2 to 8 percent in drainage capacity. Therefore, it was concluded that the effect of overburden pressure caused by the weight of lining must be considered when application of synthetic drainage layers is considered.

1. Introduction: Unreinforced concrete canals are one type of sensitive and important water conveyance structures. Whereas these structures are inevitably constructed on different types of soils, investigation of geotechnical issues related to the interaction of soil and concrete lining is important for reducing damages to the canals. These damages in the hydraulic canals are observed in the forms of cracking in the concrete lining and their large displacement.

Using a finite element numerical model, the amount of coverage bending moment into concrete linings of irrigation canals were examined; based on minimum bending anchored into the concrete panels, the optimum structural dimensions of a trapezoidal canal were extracted. This study showed that the optimal size depends on the side slope and to the depth of the canal such that for canal depths greater than 4 meters, the optimal ratio of the depth of the canal to the width of bed is between 1 to 1.5. For canals with a 1:1 side slope, this ratio is around 1.5 and it is reducing by decreasing the amount of side slope, as for a canal with side slope equal to 1:2, the optimum ratio of depth of canal to width of bed approaching to one. This study also showed that the increasing of soil elasticity modulus has essential role in reducing of the amount of the anchored bending moments of concrete lining. In addition, the amount of acting anchor on the concrete cover has a direct relation to the canal side slope.

Design of a minimum cost canal section involves minimization of the sum of costs per unit length of the canal, subject to uniform flow condition. These costs are included with costs related to covering every meter of channel length, the cost per cubic meter earthworks and costs associated with water loss (including seepage and evaporation losses) as the objective function is considered in this study. Seepage and evaporation are forms of water loss in an irrigation canal, while the seepage loss depends on the canal geometry and evaporation loss is proportional to the area of free surface. In this study, the main constraint equation is Manning’s Formula. In addition, the minimum permissible velocity and Froud’s number are used for optimizing design canal as subsidiary constraints. In this study the Optimization algorithm based on directly search is used and a computer program in MATLAB was developed to solve the above mentioned equations. Feasibility simplex and optimal design to minimize costs of per unit of length of canal is improving with obtained non-dimension carves from results. Studies comparing results with other researchers, can be seen the effect of further constraints and earthworks and cover costs related to the final dimensions of the channel.

In this research, the reasons of failures in concrete linings in Shabankareh irrigation project were studied. In this context, a detailed field survey was performed and all concerning technical reports were studied. In the second stage, several test pits were dug along the canal embankment and soil samples were taken from different depths. All samples were tested for their chemical, physical and mechanical properties. The results of grain size analysis and Atterberg Limits tests showed that most samples werer coarse grained soils with classification of GP, GM, GP-GM and SM according to USCS standards. The results of Pin Hole tests showed that some samples were of medium to highly dispersive type. The results of the chemical tests indicated that the gypsum content of the soils varied from 2 to 70 percent. Based on the overall results of the field and laboratory investigations, the main causes of the damages to the lining were related to geotechnical properties of the foundation soil. Also, it was concluded that the existence of gypsum particles in the bed materials was mainly responsible for the failures. Finally it was observed that Gypsiferrous soil layers under the lining were easily dissolved and eroded by seepage flow and surface runoff and cavities were formed extensively, which in turn caused lack of support of the concrete slabs, and general failure of the lining.

There are various methods for the analysis of the interactional behavior of the surrounding land, using the lining structure which is the most common method of deigning lining structure tools for the static loads by using the hyper static methods. In recent years, there has been a question that depicts whether this method provides the best results in designing the tunnel structure or not. Due to the nonlinear behavior of the earth surrounding the lining structure, utilizing the lining method could lead to conservative results in the design. If it is possible to somehow find the forces caused by the real behavior of the land surrounding the lining structure influencing the structure and conduct the design based on them, more optimal results would be obtained. This study is based on the actual behavior of the land surrounding the lining structure and the displacement of the structure caused by forces with linear behavior in the static design according to the non-linear behavior of the land around the tunnel structure. The behavior is modeled using the non-linear programs and the forces affecting the lining of the structure will be inference. Also there is a case study based on this method in which the soil interaction with the tunnel analysis and designing the lining structure was first performed and eventually the obtained results were compared with the hyper static method. In this paper, analysis of maintenance system with lower thicknesses considering land-shield, indicated that applying the reinforced concrete with 40cm thickness has the potential to tolerate the applied load but lining with 45cm thickness is capable of tolerating the loads of design and it can be concluded that applying the simulation method combined with the soil and structure besides considering the nonlinear behavior of the soil leads to more economical results in a project.

Damage of canal concrete lining is one of the common problems in irrigation and drainage network projects. Results of several Studies show that swelling of unsaturated expansive soils usually led to theses damages. In recent paper, this phenomenon is studied by physical modeling. In this paper two different ways are studied to control and reduce the effect of swelling soil on canal lining. The first way is the optimization of number and location of joints on canal linig and the second is the investigation of the effect of canal wall slope on soil-lining interaction behavior. For this purpose the irrigation and drainage network of Tabriz plain canal that is under construction on expansive soil is selected as a refrence for geometric properties of canal section. The physical models are constructed as small scale (1/10) in laboratory and two techniques is used in tests: PIV method and instrumentation. By using of PIV method displacement vetors, volumetric countours and magnitude of them in bed soil are obtained and drawn. In addition the results of physical modelings show the effect of joints to control and distribute of expansive soil-canal lining interaction forces. In the other hand the strain gauges recorded data show that the relative displacement of panels and destructive bending moments of lining are decreased by considering joints on location of maximum internal forces in the canal section. Also it is inferred that the variation of canal wall slope is not an effective way to reduce the lining damages.

For the purpose of protection of canal bed against erosion and to prevent seepage from the bottom or side of a canal, different types of impermeable linings are used, which may face to several problems including damages due to uplift pressure while water table is high. Thus, it is necessary to provide a drainage system under hard lining of the canal to release the water pressure especially at the end of operation season, when canal is empty. The drainage system is included a layer of drainage material (made of aggregate or geosynthetics) and outlet.In this paper the assessment of geocompsite application as layer of drainage in the bottom and side of the canal is considered. The conclusion from the laboratory investigation and numerical model results (SEEP/3D), it is concluded that synthetic drain- filter (included two layer of geotextile and a layer of geonet in the middle) can be appropriate replacing for grain drain- filter, if technical characteristic for chose and design drain- filter to be noticed. Also, the placing drain –filter in side of the canal has no effect in increasing drainage system efficiency so it is not necessary to use of drain-filter in side of the canals. In additional the application of numerical model based on finite element for assessment, chose thickness and installation position of this material as drain – filter is recommendation.

The main objective of this research was to find the stable side slope of irrigation canals, considering type of subgrade materials as well as canal depth. For this purpose two methods of limit equilibrium and finite element methods were used for stability analysis. In respect to the geotechnical properties of subgrade materials, the Unified Soil Classification System as well as the technical properties of each soil group such as cohesion, angle of internal friction and unit weight was used based on the recommendations given in the literature. To consider operation conditions, three cases namely: steady seepage, rapid drawdown and end of construction of canal were taken in to consideration. The results of investigation showed that stability of side slopes in canals is a function of type of subgrade material in respect to its cohesiveness, operation conditions and depth. In non-cohesive materials, the safety factor is not related to the canal depth and is normally less. Based on the mentioned functions safety factor of side slopes of canals with depth up to 8 meters were calculated. For non-cohesive soils stable slopes were about 1:0.6 and for cohesive soils it was determinate around 1:3.