During pipe jacking, the pressure transfer ring, also referred to as pressure compensation ring, compensates any unevenness of the pipe face and guarantees a full load transmission between adjacent pipe segments. Of course, specific requirements apply for pressure transfer rings, such as a high compressive strength, certain elastic deformation characteristics and a low lateral strain.
In this paper pressure transfer rings made of various materials and their relevant characteristics will be presented and compared to each other. Particular attention is drawn on newly developed Elastic Pressure Transfer Rings (Elastischer Druck-Ausgleichs-Ring; EDAR) consisting of styrene-butadiene rubber (SBR). This material is characterized by its elastic behavior at high strength.
As part of the testing program in the laboratories of the Ruhr-University, EDAR-sections of four different types of reinforced layers were analyzed in order to assess the effects of possibly occurring shear tensile stresses. The aim of the trials was to determine the load-deformation behavior of the elastic pressure transfer ring on one hand and the appropriate modulus of elasticity on the other hand. Furthermore, the development of the compressive and the shear tensile stresses along the pipe face were evaluated. Tests with a pressure transfer ring of a nominal diameter of 1600 mm at full-scale were also conducted. For that reason, a testing machine with a maximum force of 20.000 kN was used in the laboratories of t Ruhr-University in Bochum.
For a further evaluation of the testing results, the EDA-rings were used for a pipe jacking project conducted by the Emschergenossenschaft. For the reinforced concrete pipe jacking of a nominal diameter of 1600 mm, which had a total length of 828 m and where the alignment had the shape of a S-curve, three elastic pressure transfer rings (EDAR) were installed instead of wooden pressure transfer rings made from OSB.
The measurements showed that the deformation-behavior of the EDA-rings was mainly in the elastic range. This is a significant advantage compared to wooden transfer rings which usually exhibit permanent plastic deformation behavior. Furthermore, the pipe faces of all removed pipes showed no cracks or other abnormalities. Because of the knowledge which was gained throughout these inquiries further practical applications of EDA-rings will be possible.