Development, experimental validation, and applications of 3D hydro-mechanical concrete fracture models for structural safety evaluation and rehabilitation of concrete hydraulic structures subjected to floods and earthquakes

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Existing concrete gravity, arch dams, and gated spillways are expected to sustain damage in the event of extreme events such as floods and earthquakes inducing concrete cracking raising major concerns to maintain structural stability. The objectives of the proposed research program are (i) to develop innovative 3D hydro-mechanical modelling methodologies to quantify the safety of concrete dams and spillways considering cracking and uplift pressures (diagnostic aspects), (ii) to determine experimentally mass concrete constitutive parameters to model joints/cracks (validation aspects), and (iii) to study the effectiveness of actions to repair/strengthen cracked dams by grouting drainage, and added steel elements (rehabilitation aspects). Effective and innovative assessment / rehabilitation strategies of concrete hydraulic structures will permit substantial saving on costly remedial work. The proposed research program is divided into two projects: Project 1 –3D Stability Evaluation and Rehabilitation of Cracked Concrete Gravity Dams and Spillway piers using fiber elements: Existing gravity hydraulic structures (dam, spillway, intake) are complex structures with limited ductility that are sensitive to lateral seismic excitations that have often been ignored in the past. We will pursue the development a novel robust and computationally efficient 3D coupled nonlinear hydro-mechanical model using (a) strength of material, (b) beam-column theory combined with (c) 2D sectional finite element analyses to account for axial-flexure-shear-torsion interactions leading to a "hydro-mechanical" fiber element suitable for static and seismic safety assessment. Sectional properties will be integrated along the element to form the mass and the stiffness matrices to be assembled with other elements to represent the complete structure. Failure criteria will be considered for the flexural and shear strengths that could be mobilised within the context of hydraulic structures. Cracking along lift joints (or arbitrary planes) will be modelled including water penetration in cracks. Detailed 3D FE analyses will be used to validate the proposed macro-element (fiber element) approach directed towards robust and efficient industrial applications. A particular attention will be given to the following aspects that have not been extensively studied in the past, (i) simultaneous 3D cracking along multiple planes, (ii) stability of cracked components in the presence of uplift pressures and limited, old steel reinforcement, (iii) consideration of phases of construction (presence of shear key, initial stress-strain condition before repair), (iv) application of post-tensioning, steel or concrete jacketing to reinforce weak piers. Project 2 -Strengthening of Cracked Dam by Cement Grouting and Drainage: Grouting is used to restore water tightness and reduce uplift pressures in cracked dams. However, the post-grouted stress-strain state and the gains in tensile and shear strengths are very difficult to quantify. No work has been reported on mechanical strength of grouted mass concrete cracks subjected to different load paths representative of in situ conditions. The safety assessment of grouted dam will be tackled by (a) development of a novel hydro-mechanical finite element model with drainage in a multi-physic problem coupling different hydraulic and mechanical meshes in the presence of drains in the dam body (re drilled after grouting), and (b) 3D innovative experimental testing of grouted mass concrete blocks to validate constitutive models for grouted cracks. Special adhesive (gap)-friction grout finite element will be developed. Case studies will be performed on cracked arch dams.