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PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Investigation for Optimizing the Location of Contraction-Expansion Joints in a Concrete Canal Lining
H. Ahmadi, H. Rahimi and J. Abdollahi
Department of Water Engineering, University of Tehran, Iran
H. Ahmadi, H. Rahimi, J. Abdollahi, "Investigation for Optimizing the Location of Contraction-Expansion Joints in a Concrete Canal Lining", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 230, 2007. doi:10.4203/ccp.86.230
Keywords: finite elements, concrete lining, irrigation canal, contraction-expansion joint.
Typical side slopes for designing canals with a concrete lining are 1:1 and 1:1.5. French  recommends that, for slopes steeper than 1:0.7, exerting pressure forces from the surrounding soil must also be taken into account.
Finite element analysis was used to perform numerical computations and the Plaxis software was used for this purpose. A Mohr-Coloumb model was selected as the constitutive model and unstructured six node triangular elements were used for the analysis. To investigate and model the behaviour of concrete lining panels, its behaviour was assumed to be elasto-plastic. The required data input for the stress-strain governing equations and soil properties were taken from USBR and DIN classifying system respectively [2,3,4]. Since the elasticity modulus has the largest range of variation (from 2,000 to almost 100,000 KPa) and also the Poisson's coefficient plays a primary role in the stress strain equations, their values were first set equal to 2000KPa and 0.2 respectively and finally a sensitivity analysis was performed to investigate the effect of various values of these parameters on the results obtained.
The distribution of bending moments acting on the rigid concrete lining of canals is such that the lower regions of the lining experience maximum values of bending moments. In a full capacity conveyance case the maximum value of bending moments are exerted upon central parts of the canal bed lining and also the maximum value of bending moments acting upon side lining occurs at a depth of approximately one-third of the total canal depth from the bed.
The patterns of distributions of moments acting upon the lining can be observed as a function of canal depth and width, various side slopes and operating conditions. For the cases of full capacity conveyance and inverse seepage, the moments acting upon lining is much larger than the bearing capacity of a 20cm thick lining. Any increase in bed width to canal depth ratio will cause an increase in associated moments, being greater for larger bed width to canal depth ratios.
In the case of full capacity conveyance at the and end of construction, larger bending moments occur for steeper sidewalls. However the opposite occurs for the case of inverse seepage. This can be helpful in conditions where the conveying canal is going to be designed in terrains with a high groundwater table. The most critical operating conditions are directly related to canal dimensions
In order to decrease the magnitude of bending moments, construction and contraction joints may be placed in locations such that in addition to their common task, they are able to reduce bending moments by large amounts. For canals less than 4m deep, the risk of rupture of lining can be minimized by providing a longitudinal joint in a depth equal to one-third of the total canal depth from the bed. For deeper canals, in addition to these joints, joints must also be provided where the canal bed and sidewall lining coincide and in the centre of the canal bed lining.
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