Shotcrete tunnel linings with steel ribs: Stress redistribution due to creep and shrinkage effects

摘要

To study the time-dependent behaviour of sprayed concrete linings coupled to steel ribs, an accurate monitoring system was developed in an experimental tunnel including strain gauges, pressure cells, incremental extensometers and topographic controls. The significant delayed deformation under almost constant load, reaching 5–6 times the initial elastic strain, and the stress redistribution from shotcrete to steel ribs, loaded up to four times their initial value in a few weeks, were the most interesting results due to creep and shrinkage effects. The elastic modulus and the creep deformation of shotcrete with different dosages of accelerators were investigated, based on the in situ data readings and through specific laboratory tests on samples collected at site. Using creep parameters from the experimental evidence, a simplified calculation approach, based on the linear algebraic Age-Adjusted Effective Modulus Method (AAEMM), was developed in order to simulate the stress and strain variations over time. A comparison with the creep parameters by CEB-FIP Model Code 1990 for ordinary concretes was also carried out.