Cemented soil-soil interface shear strength evaluation I: Size effect and characteristic experimental size quantization

The shear strength of cemented soil-soil interface is affected by the size effect of experimental sample. With the advancing density of urban underground space and the wide application of grouting reinforcement for adjacent underground structures, the inaccurate interface strength results due to size effects are receiving increasing attention. This study conducted different scaled interface shear tests and numerical simulation to evaluate the influence of size effect on the cemented soil-soil shear strength. In large scale interface shear experiments, the shear stress increased with the accumulation of shear displacement in two stages and finally stabilized at interface shear strength. But in small scale direct shear tests, interface shear stress dropped after reaching a much higher interface shear strength. With the increasing of sample size, the interface shear strength gradually reduced to a stable value. This relation was analyzed and the characteristic sample size for interface unaffected by size effect was determined, which, for cuboid sample, is 300 mm. The relation of the cemented soil-soil interface shear strength from commonly used direct shear sample and sample with characteristics size was concluded by a series of comparative experiments. By analyzing the failure properties of cemented soil-soil agglutinate layer and the displacement pattern of material grains, the internal mechanism of size effect on cemented soil-soil interface were proposed. The conclusions can advance the accurate acquisition of cemented soil-soil interface, provide references to the unification of research achievements with different sample size, and give recommendations to the standard interface shear experimental method in the future. • Analyzed the influence of size effect on cemented soil-soil interface shear strength. • Proposed standard sample size for cemented soil-soil interface shear test. • Different failure pattern of agglutinate layer causes the size effect.