Influence of degree of saturation on soil nail pull-out resistance in compacted completely decomposed granite fill

Abstract

The nail–soil interface shear strength is a key parameter in the design and stability assessment of soil nailing systems. A number of factors will influence the nail–soil interface shear strength. Among these factors, the degree of saturation (S r ) of the soil is an important one especially for permanent soil nail structures. To study the influence of S r on soil nail pull-out shear resistance, a series of laboratory pull-out tests have been conducted on soil nails in compacted completely decomposed granite (CDG) fill prepared to different S r . The tests were conducted using two specially designed pull-out boxes (with same specifications). In the near-saturated tests, a high S r (about 98%) was achieved using two special features of the apparatus: a waterproof front cap and back-water pressure pipes at the bottom of the pull-out box. Test results showed that the nail–soil shearing plane migrated outwards into the soil when the S r of the soil increased. Also, peak pull-out strengths of soil nails were strongly influenced by the S r of the soil. Among the tested S r , the highest values of peak pull-out shear strength were obtained at S r values between 50% and 75%.