Investigation on Strain Characteristics and Fatigue Constitutive Model of Limestone under Osmotic Pressure and Cyclic Disturbance Coupling

Zhanping Song,Wanxue Song,Yun Cheng,Tengtian Yang,Tong Wang,Kuisheng Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4

The existing fatigue models are not sensitive to load cycles and do not consider the effect of osmotic pressure. To study the strain characteristics and fatigue constitutive model of limestone under osmotic pressure and cyclic disturbance coupling, 300 cycles of loading and unloading tests under different osmotic pressures were carried out and the evolution characteristics of irreversible accumulative deformation curve were analyzed. Then, an improved Nishihara fatigue model was established based on the theoretical results of rheological model by introducing the nonlinear function into Nishihara model. The results show that the irreversible cumulative deformation under different osmotic pressures experiences three evolutionary processes of initial deformation stage, stable deformation stage, and accelerated deformation stage with increasing cycle indexes, showing the typical fatigue deformation characteristics. The axial deformation at initial deformation stage increases significantly, the stable deformation stage shows approximately linear growth and accounts for 40% to 73% of total cycle indexes, and the accelerated deformation stage shows a sudden increase indicating the overall instability of limestone. The nonlinear function is introduced into the Nishihara fatigue model based on rheological theory, and a fatigue deformation model that can reflect the entire process of irreversible accumulative deformation curve is established. The physical meanings of model parameters are discussed, and the relationships between model parameters and cycle indexes are inverted. The model parameters have good convergence and verify the rationality and applicability of the fatigue constitutive model based on experimental data. The results have reference value for revealing the fatigue characteristics of rock under osmotic-cyclic stress coupling.

Abnormal Precursory Information Analysis of the Infrared Radiation Temperature (IRT) before Sandstone Failure

Zhanping Song,Qiang Zhang,Yuwei Zhang,Junbao Wang,Shengyuan Fan,Guannan Zhou 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.11

To study the abnormal precursory information of rock before failure, uniaxial compression tests were carried out on sandstone specimens; meanwhile, the infrared thermal camera was utilized to monitor the infrared radiation temperature (IRT) variation of the specimen surface synchronously during failure process. The test results show that with the increases of strain, the average infrared radiation temperature (AIRT) decreased gradually; when strain raises to a certain degree, the AIRT increased abruptly; thereafter, the AIRT decreased gradually with increasing strain. Therefore, the mutation point of AIRT can be regarded as the abnormal precursory information of sandstone before failure. Through analysis, the average stress at the abnormal point was 79.93% of the uniaxial compression strength of the sandstone specimens tested in this paper, and the average strain at this point was 0.9%. In addition, due to the end effect, the IRT field distribution of the sandstone specimen surface presented a decreasing tendency from top to bottom at the initial loading stage. As strain increases, the IRT field distribution tended to be high in middle and low in two ends. Closing to failure, a Y-shaped high-temperature band caused by the shear failure of the specimen appeared in the infrared thermal image. After comparison, the position of the Y-sharped high-temperature band is basically corresponding to the actually failure position of the specimen. With the increases of strain, the IRT distribution ranges decreased and the IRT frequency distribution histogram form gradually approached to the normal distribution.

A Study of the Dynamic Characteristics of Red Sandstone Residual Soils Based on SHPB Tests

Tong Wang,Zhanping Song,Jianyong Yang,Qiang Zhang,Yun Cheng 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5

To explore the response characteristics of soil under dynamic loads, cyclic impact tests with varying axial compressions and impact velocities were conducted using SHPB tests. The test results were analyzed to study the mechanical properties and energy dissipation characteristics due to impact loads. In terms of mechanical properties, for the same impact times, the peak stress of the specimen with axial compression was found to be greater than that without axial compression, but the final strain was lower than that without axial compression, indicating that axial compression affects the peak stress and final strain of the specimen. The dynamic stress strengthening of the specimen under cyclic impact loads has also been analyzed. In terms of energy dissipation, the effects of axial compression, impact velocity, and impact times on the ratios of dissipated energy, reflected energy, and transmitted energy to incident energy were compared, and it was found that the ratio of the dissipated energy did not exceed 24% under any condition. In terms of damage evolution, the damage variable gradually decreases with an increase in impact times. A critical value of the damage variable was determined, above which the transmittance continued to decrease, the reflectivity gradually increased, and the dissipation rate remained stable.

Energy Evolution Principles of Shock-Wave in Sandstone under Unloading Stress

Yun Cheng,Zhanping Song,Xiaoxu Chang,Tong Wang 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.10

Excavation process often induces the unloading rock mass to be in different damage stages, thus changing the propagation and attenuation characteristics of shock-wave energy in rock mass. This paper involved an investigation on the energy dissipation principles during unloading stress process. First, the paper presented small disturbance impact tests to acquire shock-wave data using the modified split Hopkinson pressure bar device. Then we discussed the shock-wave characteristics under different unloading stresses, attenuation characteristics of shock-wave energy at distance and its effects on unloading stress on the attenuation characteristics of shock-wave energy. Results showed that the presence or absence of unloading stress in sandstone had significant effect on shock-waveform. The shock-wave energy showed a spatial exponential attenuation characteristic, and the decay coefficient indicated that the variation degree in low unloading stress region was significantly greater than that in high unloading stress region. The unloading stress cut-off point was σ/σc = 23.88%. The shock-wave energy at different locations declined with a trend of slight decrease and rapid attenuation, illustrated that the closer the incident end of the sandstone was, the greater the attenuation degree of the shock-wave energy would be. This paper also analyzed the attenuation rate of shock-wave energy and corresponding different sensitivity to unloading stress, showed that the relationship between attenuation rate and unloading stress could be exposed by a composite linear exponential equation. Therefore, the conclusions can provide reference for the attenuation evolution analysis of shock-wave energy in the excavated rock mass.

A New Calculation Method for Tunneling-Caused Stratum Settlement

Junbao Wang,Pengyuan Zhou,Zhanping Song,Shihao Li,Qiang Zhang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.6

To improve the prediction accuracy for the stratum settlement induced by tunnels and obtain a theoretical method for determining the influence radius of settlement, a new empirical formula for the surface settlement curve is proposed in this study, and the slice method is introduced into the calculation of the influence radius of settlement. It is assumed that the disturbance boundary of the tunnel is a circular arc surface, the disturbed soil is divided into multiple slices, and the sliding force and resistance on the circular arc are obtained through a stress analysis of the slices. An arc with the same values of the sliding force and resistance can be determined as the actual disturbance boundary of the overlying strata as formed by the subsurface tunneling. On this basis, the influence radius of settlement and maximum settlement at different depths can be determined, and the settlement curve can be depicted by substituting the influence radius and maximum settlement into the expression of the settlement curve. The rationality of the proposed method is verified based on four sets of measured data. The surface settlement curves and the settlements at different depths on the center line of the tunnel obtained by the new method are generally consistent with the measured data.