The AE Test Study Of Calcareous Sand

Calcareous sand, generated in marine environment and widely distributed in South China Sea, is a special geotechnical medium which has the different mechanical properties, compared with the land originated sand, due to its fabric. And the calcareous sand generally consists of marine organisms, which tends to crush relatively easily, then the energy resulted by particle breakage will be released in the form of sound wave. It is know that Acoustic Emission(AE) is one of the passive nondestructive tests, which is widely used to evaluate the sock's mechanical properties indirectly and have the merits such as equipment and test's convenience, nondestruction, no pollution. Hence there is a new method to help us to understand the mechanical properties of calcareous sand, that is to combine the calcareous sand's research with AE test . The conventional triaxial apparatus and the AE apparatus are used to research the AE test of calcareous sands. The main research findings as follows:1. The AE signal can be detected under the condition of conventional triaxial test in calcareous sands, whose strength is related to the condition of test. The particle breakage and the slide between particles contribute to the main AE source in the calcareous sands, one of which plays different role in different level. In the AE test of calcareous sands, there is more low frequency than high frequency2. During the stage from the strain softening to the strain hardening in calcareous sands, because the AE count's peak is happened nearby the strength peak in the stress-time curve, it's seemed that the AE count-time curve is similar to the stress-time curve of calcareous sands, hence the AE count-time curve of calcareous sands can be used to describe the mechanical properties of it.3. Calcareous sands, at, or near the its stress peak is the most emittive, in which the AE counts rate is the highest. Then passing through the stress peak, it is still emittive until the end of tests. 4. In the consolidated drained(CD) test, the AE hits'number increases when the confining pressure is from 100kPa to 200kPa, and then decreases when the confining pressure is from 200kPa to 800kPa. In the consolidated undrained(CU) test, the AE hits'number increases when the confining pressure is from 100kPa to 400kPa, and then decreases when the confining pressure is from 400kPa to 800kPa. In the unconsolidated drained(UU) test, the AE hits'number increases when the confining pressure is from 100kPa to 800kPa except that the confining pressure of 400kPa.5. Acoustic emission activity in calcareous sands under the CD condition increases then decreases as strain rate increases meanwhile the principal strength peak decreases. Acoustic emission activity in calcareous sands under the CU condition increases as strain rate increases meanwhile deviator stress increases then decreases. Acoustic emission activity in calcareous sands under the UU condition increases as strain rate decreases then increases meanwhile total stress have the reverse tendency.6. During both CD and CU tests , there is the critical void ratio for AE in calcareous sands, in which acoustic emission activity of samples is the lowest. The acoustic emission activity increases according to change of void ratio except the critical void ratio. Meanwhile, the principle stress peak decreases as void ratio increases in CD tests. The deviator stress is higher than any others in CU tests at the point of critical void ratio, in which it's seemed that there is no influence for pore stress peak of calcareous sands when void ratio changes.7. Acoustic emission activity in calcareous sands under both the CD and CU condition is affected by gradation, particularly in the late part of tests. The better the gradation, the lower the acoustic emission activity of calcareous sands. In CD tests, the better the gradation, the higher the principle stress peak, but both the deviator stress peak and the pore stress peak are no affected by the gradation in CU tests.8. Compared with the AE hits'number of rock, that of calcareous sands is less, occupied only 0.12% of total number of the former, but the amplitude of calcareous sands(45-55kHz) is higher than that of oriented sands(4-8kHz).