Experimental study on the coefficient of sandy gravel under different loading conditions

To study the coefficient of earth pressure at rest () for the sandy gravel, a new large-size test apparatus with the diameter of 400 mm and height of 400 mm is developed. This apparatus can be used for test of sandy gravel, as well as clay and sand. Dry specimens with different maximum grain size () ranging from 10 to 60 mm, and thus with different particle size distribution, are prepared by scalping technique, replacement technique and parallel gradation technique to reduce the particle size of in-situ soil. The soil for test is a sandy gravel, and the specimens are at the same relative density of zero. It is found that, for the same specimen, decreases with increasing effective vertical stress . A description of the considering effective vertical stress of the sandy gravel is established and verified. For the specimens prepared by the same preparation technique, decreases with increasing . An approach to estimate the of in-situ sandy gravel under different is developed. According to the results of unloading test, dramatically increases with the increasing value of overconsolidation ratio (OCR). An empirical equation, which can well describe the relationship between OCR and , is obtained.