Hoop stiffness and its reduction factor of diaphragm wall panels for circular excavation

Since the joints between diaphragm wall panels lead to reduction of hoop stiffness in circular excavation, it is necessary to propose a method to quantitatively evaluate the hoop stiffness correction coefficient α. The stress-strain curves of joints are first measured through the mechanical experiments on specimens containing joints and then compared to those of intact concrete cubes, separately considering the two typical locations for diaphragm wall panels with milling joint, in panels and between panels. For reliability purpose, the intact concrete cubes and specimens containing joints are both produced with concrete and slurry applied from a construction site. Then, the trilinear function is introduced to best fit the measured stress-strain curves, thus the formula for the stiffness correction coefficient α is proposed and subsequently applied to a real case analysis. The results show that the value of the stiffness correction coefficient α mainly depends on the average length of panel, the width of joints as well as the stiffness of joints and concrete. The value of α ranges between 0.485~0.514 in case of low hoop stress, and turns into a rise when the hoop stress exceeds 7.37 MPa, and reaches 0.545~0.581 when it rises up to 11 MPa. Further, the calculated results based on α obtained in the site tests indicate that it is efficient when considering the effect of joints by just taking α into account when the hoop stress stays at a low level, but the nonlinear stiffness of joints should be considered when the stress is high. In conclusion, an approach for quantitatively evaluating the hoop stiffness correction coefficient α is proposed and can be further applied for engineering application purpose.