Abstract
A series of dynamic triaxial tests were performed to investigate the dynamic deformation properties of the muck soil, in the Pearl River Delta region of Shenzhen, China, under different consolidation ratios, loading frequencies and cyclic stress with SPAX-2000 triaxial testing system. The results showed that the initial stress-strain hysteresis curve of the muck soil under the low-frequency cyclic loading developed rapidly and the curve shape changes from sparse to tight and to slightly sparse. The cumulative plastic strain of muck soil increased nonlinearly with the dynamic stress amplitude, and there was a critical dynamic stress. As the dynamic stress amplitude reached its critical value, the strain increased sharply and the soil microstructure was destroyed. There was a frequency threshold between 0.25 Hz and 0.5 Hz, and the cumulative plastic strain development mode was from stable model to over-destructive model. The stiffness of the muck decreased gradually, and the plastic deformation increased as the number of cycles increased. Therefore, the lower the loading frequency developed, the greater the plastic deformation would be. The dynamic elastic modulus decreased as the plastic deformation increased, while the dynamic elastic modulus increased as the consolidation stress increased. Moreover, the empirical formulas of dynamic elastic modulus and plastic strain index were established with the consolidation stress ratio as the parameter, and the validity was verified by experimental data.
Highlights
Muck is widely distributed in coastal areas and inland lakes [1, 2]
Low-permeability; (2) The loading frequency was mostly greater than 1 Hz, while low-frequency traffic load research had rarely been reported in previous references; (3) Most of the analysis models of deformation, such as cumulative plastic strain model and softening model did not consider the influence of consolidation stress; (4) Soft soils have different composition, structural structure and physical properties due to their different formation environments which produces great variation on the properties of dynamic deformation [24, 25]
Dynamic triaxial tests under different consolidation ratios, loading frequencies, and cyclic stress amplitudes were performed for 30 specimens of muck soil, and the dynamic deformation characteristics of muck soil under low frequency loading were as follows: 1) The energy of the loss increased as the stress amplitude, the area of the hysteresis loop and the length of the open section increase with the stress amplitude under the same cycle frequency and number of times
Summary
Muck is widely distributed in coastal areas and inland lakes [1, 2]. With the large-scale construction of houses, roads, railways and urban traffic engineering in soft soil areas, and the rapid development of offshore platforms, many new geotechnical problems arise. The dynamic characteristics of soft soil and its composite foundation under cyclic loading (seismic loading, traffic loading, wave loading) have attracted wide attention [3,4,5]. Boulanger [11] conducted a staged loading triaxial test with Sherman soft soil in California, and analyzed the effects of loading frequency, stress history, cycle number, and soil structure on dynamic parameters. The relationship between normalized shear modulus, damping ratio and shear strain, consolidation stress and loading frequency of soft soil was built [12]. References [13, 14] presented a relationship between the dynamic stress and dynamic strain of soft clay under traffic loading, there existed a critical dynamic stress ratio and vibration frequency threshold value at the dynamic stress-dynamic strain curve
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