Experimental Investigation of Wall Thickness Effect on Cold Joints in a Scaled Diaphragm Wall Model Using Fiber-Reinforced Self-Compacting Concrete

Abstract Concrete diaphragm walls are crucial structural components for permanent retaining systems and deep excavation support. The research examines how wall thickness and cold joints influence the deformation behavior of diaphragm walls. A small laboratory model with a rigidity that is comparable to the field model was used for this purpose. The scaled model was designed to preserve the relative stiffness of the field model; however, due to the slenderness of the specimens, conventional reinforcement could not be applied. Instead, polypropylene fibers were used as an effective alternative to enhance crack resistance and ensure structural integrity. Four-point bending tests were carried out under static loading conditions using a laboratory compression testing machine. The model sizes are (40, 60, 80, and 100 mm) in prismatic thickness and overall width and length (900 mm and 2600 mm), respectively. Additional tests on 60 mm walls with one and two cold joints, and on 100 mm walls with two cold joints, were compared against joint-free specimens to assess the influence of cold joints. The findings indicate that increasing wall thickness improves load-bearing capacity and reduces lateral deformation. For proposed specimens maximizing strength gains when aspect ratio ( thickness depth {{thickness} \over {depth}} ) increase form 1 40 to 1 30 {1 \over {40}}\,\,to\,\,{1 \over {30}} and for increasing from 1 60 to 1 40 {1 \over {60}}\,\,to\,\,{1 \over {40}} deflection decreases sharply. Specimens with aspect ratio of 1 40 {1 \over {40}} one and two joints reduced ultimate load by about 3% and 15%, respectively, while at 1 24 {1 \over {24}} two joints caused a 10% reduction. Thinner walls proved more flexible and thus more sensitive to joint-induced weaknesses.