Discussion on Test Methods of Engineering Property for Friable Geomaterials

Conventional test method does not consider the distortion of the test result caused by the particles breakage of brittle geomaterials. In order to explore the test method of the engineering properties of brittle geomaterials, the gradation test, specific gravity test and relative density test of coral sands were carried out in view of the special properties of coral sands with internal pores and fragile, which may be caused by the internal pores and particle breakage. The results showed that the internal porosity and fragile nature of coral sands affected the reliability of the test results of engineering properties. The characteristic particle diameter of coral sands changes greatly due to particle fragmentation, which cause the changes of the permeability characteristics, compression characteristics, mechanical properties and other aspects of geomaterial characteristics of coral sands. Non-contact test methods such as digital image processing can effectively avoid particle breakage and can truly reflect the particle size of brittle materials. It is difficult for the liquid to penetrate into the inner pores of the particles only by submerging, and pure water as the test liquid will dissolve the salts on the surface of the particles, all of which will affect the accuracy of the test results. Kerosene as the test liquid can prevent the salt on the surface of the particles from dissolving; and the measured value is more consistent with the calculated value. There was little difference in the minimum dry density obtained by funnel method and the volumetric cylinder method. The minimum dry density measured by the volumetric cylinder method is slightly lower. So it is recommended to use the measuring cylinder method to test the minimum dry density of coral sands. The hammering will inevitably break up the coral sands particles, which will cause the results of the maximum dry density test to be severely distorted. The test results of pressurized vibration method are more reliable. It is recommended to use saturated coral sands and pressurized vibration method or surface vibration method to test the maximum dry density, which can effectively avoid the distortion of the results caused by particle breaking.