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 (Sr) of the soil is an important one especially for permanent soil nail structures. To study the influence of Sron 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 Sr. The tests were conducted using two specially designed pull-out boxes (with same specifications). In the near-saturated tests, a high Sr(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 Srof the soil increased. Also, peak pull-out strengths of soil nails were strongly influenced by the Srof the soil. Among the tested Sr, the highest values of peak pull-out shear strength were obtained at Srvalues between 50% and 75%.