A reasonable strength criterion should reflect the hydrostatic pressure effect, minimum principal stress effect,and intermediate principal stress effect. The former two effects can be described by the meridian curves,...A reasonable strength criterion should reflect the hydrostatic pressure effect, minimum principal stress effect,and intermediate principal stress effect. The former two effects can be described by the meridian curves, and the last one mainly depends on the Lode angle dependence function. Among three conventional strength criteria, i.e.Mohr–Coulomb(MC), Hoek–Brown(HB), and Exponent(EP) criteria, the difference between generalized compression and extension strength of EP criterion experience a firstly increase then decrease process, and tends to be zero when hydrostatic pressure is big enough. This is in accordance with intrinsic rock strength characterization. Moreover, the critical hydrostatic pressure Icorresponding to the maximum difference of between generalized compression and extension strength can be easily adjusted by minimum principal stress influence parameter K. So, the exponent function is a more reasonable meridian curves, which well reflects the hydrostatic pressure effect and is employed to describe the generalized compression and extension strength.Meanwhile, three Lode angle dependence functions of L,L, and L, which unconditionally satisfy the convexity and differential requirements, are employed to represent the intermediate principal stress effect. Realizing the actual strength surface should be located between the generalized compression and extension surface, new true-triaxial criteria are proposed by combining the two states of EP criterion by Lode angle dependence function with a same lode angle. The proposed new true-triaxial criteria have the same strength parameters as EP criterion. Finally, 14 groups of triaxial test data are employed to validate the proposed criteria. The results show that the three new true-triaxial exponent criteria,especially the Exponent Willam-Warnke criterion(EPWW)criterion, give much lower misfits, which illustrates that the EP criterion and Lhave more reasonable meridian and deviatoric function form, respectively. The proposed new true-triaxial strength crit展开更多
The acoustic bottom backscattering strength was measured at the frequency range of 6–24 kHz on a typical sandy bottom in the South Yellow Sea by using omnidirectional sources and omnidirectional receiving hydrophones...The acoustic bottom backscattering strength was measured at the frequency range of 6–24 kHz on a typical sandy bottom in the South Yellow Sea by using omnidirectional sources and omnidirectional receiving hydrophones. In the experiment, by avoiding disturbances due to scattering off the sea surface and satisfying the far-field condition, we obtained values of acoustic bottom backscattering strength ranging from –41.1 to –24.4 dB within a grazing angle range of 18°–80°. In the effective range of grazing angles, the acoustic scattering strength generally increases with an increase in the grazing angles, but trends of the variation were distinct in different ranges of frequency, which reflect different scattering mechanisms. The frequency dependence of bottom backscattering strength is generally characterized by a positive correlation in the entire frequency range of 6–24 kHz at the grazing angles of 20°, 40° and 60° with the linear regression slopes of 0.222 9 dB/kHz, 0.513 0 dB/kHz and 0.174 6 dB/kHz, respectively. At the largest grazing angle of 80°, the acoustic backscattering strength exhibits no evident frequency dependence.展开更多
基金supported by the National Natural Science Foundation of China (Grants 51204168, 51579239)the China Postdoctoral Science Foundation funded project (Grants 2013M531424, 2015M580493)+1 种基金the National Basic Research 973 Program of China (Grants 2013CB036003, 2014CB046306)the Fundamental Research Funds for the Central Universities (Grant 2012QNB23)
文摘A reasonable strength criterion should reflect the hydrostatic pressure effect, minimum principal stress effect,and intermediate principal stress effect. The former two effects can be described by the meridian curves, and the last one mainly depends on the Lode angle dependence function. Among three conventional strength criteria, i.e.Mohr–Coulomb(MC), Hoek–Brown(HB), and Exponent(EP) criteria, the difference between generalized compression and extension strength of EP criterion experience a firstly increase then decrease process, and tends to be zero when hydrostatic pressure is big enough. This is in accordance with intrinsic rock strength characterization. Moreover, the critical hydrostatic pressure Icorresponding to the maximum difference of between generalized compression and extension strength can be easily adjusted by minimum principal stress influence parameter K. So, the exponent function is a more reasonable meridian curves, which well reflects the hydrostatic pressure effect and is employed to describe the generalized compression and extension strength.Meanwhile, three Lode angle dependence functions of L,L, and L, which unconditionally satisfy the convexity and differential requirements, are employed to represent the intermediate principal stress effect. Realizing the actual strength surface should be located between the generalized compression and extension surface, new true-triaxial criteria are proposed by combining the two states of EP criterion by Lode angle dependence function with a same lode angle. The proposed new true-triaxial criteria have the same strength parameters as EP criterion. Finally, 14 groups of triaxial test data are employed to validate the proposed criteria. The results show that the three new true-triaxial exponent criteria,especially the Exponent Willam-Warnke criterion(EPWW)criterion, give much lower misfits, which illustrates that the EP criterion and Lhave more reasonable meridian and deviatoric function form, respectively. The proposed new true-triaxial strength crit
基金The Opening Fund of Pilot National Laboratory for Marine Science and Technology(Qingdao)under contract No.QNLM2016ORP0209the National Natural Science Foundation of China under contract Nos 41330965,41676055 and 41527809the Taishan Scholar Project Funding under contract No.tspd20161007
文摘The acoustic bottom backscattering strength was measured at the frequency range of 6–24 kHz on a typical sandy bottom in the South Yellow Sea by using omnidirectional sources and omnidirectional receiving hydrophones. In the experiment, by avoiding disturbances due to scattering off the sea surface and satisfying the far-field condition, we obtained values of acoustic bottom backscattering strength ranging from –41.1 to –24.4 dB within a grazing angle range of 18°–80°. In the effective range of grazing angles, the acoustic scattering strength generally increases with an increase in the grazing angles, but trends of the variation were distinct in different ranges of frequency, which reflect different scattering mechanisms. The frequency dependence of bottom backscattering strength is generally characterized by a positive correlation in the entire frequency range of 6–24 kHz at the grazing angles of 20°, 40° and 60° with the linear regression slopes of 0.222 9 dB/kHz, 0.513 0 dB/kHz and 0.174 6 dB/kHz, respectively. At the largest grazing angle of 80°, the acoustic backscattering strength exhibits no evident frequency dependence.
