Most of rubber engineering components endure cyclic loading during their service, and a nonzero mean stress during cyclic loading may cause an accumulation of strain which is known as ratchetting phenomenon. In order to study the ratcheting effect of rubber, a series of uniaxial ratchetting experiments were conducted on vulcanized natural rubber (NR). The effects of cyclic stress amplitude, mean stress and their histories on ratchetting behavior were studied, respectively. The uniaxial ratchetting behavior of natural rubber depends greatly on the stress amplitude and mean stress. The ratchetting strain rate greatly increases with the stress amplitude or mean stress increased. Experimental results reveal that the rubber material exhibits a strong memory of the previous high loading history, and such memory plays a significant role on the subsequent ratchetting. The ratchetting behaviors of the rubber exhibit little sensitive to the applied cyclic stress rate except for the initial strain. POLYM. ENG. SCI., 48:191–197, 2008. © 2007 Society of Plastics Engineers

The conventional support forms of foundation pit retaining piles include single-row piles, double-row piles, anchor-row piles, and so on. The double-row pile supporting structure is widely used in the deep foundation pit supporting the engineering of wharves, bridges, subways, tunnels, and high-rise and super-high-rise buildings. This study on double-row pile supporting structures mainly focuses on four aspects: (1) The influence of dimension parameters, such as pile diameter and pile length, and engineering parameters, such as pile spacing and row spacing, on the deformation control of a double-row pile structure and the stability control of foundation pits; (2) Influence of the soil arch effect on the stress and deformation of the double-row pile supporting structure; (3) Study on the deformation characteristics and rules of the components and the whole structure of the double-row pile supporting structure; (4) Study on the calculation model of pile-soil interactions. Based on the above four aspects, this paper summarizes the latest research status of the existing double-row pile supporting structure and its stress and deformation characteristics. The deformation characteristics and calculation model of the pile-soil interaction of double-row piles are reviewed and evaluated. Finally, the problems and deficiencies in the research on double-row pile support are summarized. These results provide a reference for future research on the double-row pile supporting structure of the foundation pit and the numerical analysis and calculation model and lay a solid foundation for further development of the theory.