Response Ratio Theory Research Articles

Experimental Study on the Microfabrication and Mechanical Properties of Freeze-Thaw Fractured Sandstone under Cyclic Loading and Unloading Effects.

A series of freeze-thaw cycling tests, as well as cyclic loading and unloading tests, have been conducted on nodular sandstones to investigate the effect of fatigue loading and freeze-thaw cycling on the damage evolution of fractured sandstones based on damage mechanics theory, the microstructure and sandstone pore fractal theory. The results show that the number of freeze-thaw cycles, the cyclic loading level, the pore distribution and the complex program are important factors affecting the damage evolution of rocks. As the number of freeze-thaw cycles rises, the peak strength, modulus of elasticity, modulus of deformation and damping ratio of the sandstone all declined. Additionally, the modulus of elasticity and deformation increase nonlinearly as the cyclic load level rises. With the rate of increase decreasing, while the dissipation energy due to hysteresis increases gradually and at an increasing rate, and the damping ratio as a whole shows a gradual decrease, with a tendency to increase at a later stage. The NRM (Nuclear Magnetic Resonance) demonstrated that the total porosity and micro-pores of the sandstone increased linearly with the number of freeze-thaw cycles and that the micro-porosity was more sensitive to freeze-thaw, gradually shifting towards meso-pores and macro-pores; simultaneously, the SEM (Scanning Electron Microscope) indicated that the more freeze-thaw cycles there are, the more micro-fractures and holes grow and penetrate each other and the more loose the structure is, with an overall nest-like appearance. To explore the mechanical behavior and mechanism of cracked rock in high-altitude and alpine areas, a damage model under the coupling of freeze-thaw-fatigue loading was established based on the loading and unloading response ratio theory and strain equivalence principle.

Determining tunnel stability across fault zones under seismic loading based on load/unload response ratio theory

Geological faults impair tunnel stability during earthquakes. This study establishes a tunnel dynamic stability evaluation index based on load/unload response ratio (LURR) theory. It considers a seismic wave as a load/unload parameter and tunnel structure strain response as a response parameter. The rationale behind this evaluation index and the factors affecting tunnel stability across fault zones under seismic conditions are investigated. Compared to the traditional dynamic instability criterion, the LURR accurately measures the degree of structural deviation from the steady state and better determines the potential destabilization region of the structure. As the peak value of the input seismic wave increases, the LURRs of the more unstable parts increase, while the LURRs of the stable parts remain unchanged. According to LURR theory, the size of the range affected by the fault on the tunnel during an earthquake depends mainly on inherent fault properties (i.e., the dip angle, strike, and thickness), independent of the earthquake intensity. Because the LURR can theoretically be infinite, its dynamic instability threshold cannot be determined accurately.

Experimental investigation of predicting coal failure using acoustic emission energy and load-unload response ratio theory

Coal burst is a dynamic failure phenomenon that is caused by a sudden release of strain energy during mining. It is extremely difficult to predict coal burst accurately. In this study, experimental tests were performed under uniaxial cyclic load-unload conditions using a microcomputer-controlled electrohydraulic servo stiffness compressor with acoustic emission (AE) monitoring. The experiments data, such as the AE energy, AE energy ratio and load-unload energy response ratio, were obtained. The Y value of the load-unload response ratio (LURR) was calculated based on these data. The results show that variation characteristics of the AE energy release can be related to the failure of coal specimens. The concentrated release of AE energy occurs at the beginning of the plastic deformation stage. Then, AE energy was accumulated before coal specimens' failure. The variation characteristics of the LURR (Y1) and Benioff strain (Y2) were obtained. The fluctuation of Y1 and Y2 values was exhibited to coincide with the AE energy accumulation, which allowed predicting coal failures. The predicting time point where the Y1 and Y2 values were both close to 1 could be defined as the predicting key point of coal specimens' failure. These results of experimental investigation show a meaningful attempt for predicting coal failure.

Microseismic monitoring and stability analysis of the right bank slope at Dagangshan hydropower station after the initial impoundment

The right bank slope of the Dagangshan hydropower station in China has suffered from reservoir water pressure and seepage effects since the initial impoundment process. This paper describes the microseismic monitoring system and impoundment process of the Dagangshan hydropower station. Microseismic activity was detected in the right bank slope after the initial impoundment by the microseismic monitoring system. The spatiotemporal characteristics of the microseismic events and the piezometer monitoring results are used to confirm the conductive seepage pathways, the porous rock mass and the water recharge source in the right bank slope. Based on the geological conditions of the porous rock mass identified by microseismic and piezometer monitoring, a simplified two-dimensional (2D) finite element model is developed. A 2D finite element analysis is then applied to explore the damage mechanisms of local regions of the right bank slope after the initial impoundment. In addition, the load/unload response ratio theory is used to predict the failure of the slope based on the seismic source information obtained by the microseismic monitoring system. According to the actual geological conditions of the right bank slope, a simplified 3D numerical model is developed for the stability analysis of the right bank slope after the initial impoundment. Based on the porous rock mass identified by the microseismic monitoring, the effective stress is considered in the stability analysis. The safety factor of the right bank slope including the effective stress is 1.645, which indicates that the slope was stable after the initial impoundment. The microseismic monitoring technique can record disturbances caused by seepage effects in deep rock masses after the initial impoundment process in real time.

Resilience of hydraulic structures under significant impact of typhoons

Vulnerability to natural disasters falls into three categories: exposure, resistance, and resilience, where resilience mainly refers to the capability of a pressure-bearing system to recover by returning to its initial state, that is, the ability to adapt to disaster pressure. Resilience is a major subject of research on disaster prevention and mitigation. This research mainly focuses on the ability of the hydraulic structure to recover from the significant impacts of typhoons. According to the load/unload response ratio theory, the degree of instability by which nonlinear systems can be identified according to the difference between load and unload responses was analyzed. This analysis was used as a basis to study the resilience of a hydraulic structure. Taking the Yangtze River embankments under the impact of Typhoon Matsa as an example, the ability of the typical sections of different types of embankments to adapt to the significant impact of the typhoon, i.e., the resilience of the hydraulic structure, is described with the help of the load/unload response ratio (L). The results of the calculated resilience reflect the actual conditions of the structure and can be used to determine the applicability of the embankment section. The load/unload response ratio theory is one of the effective tools for calculating the resilience of hydraulic structures under the significant impacts of typhoons.

A New Method to Calculate Damage Variable with Unload/Load Response Ratio

As an exploration and extension of load/unload response ratio theory, unload/ load response ratio theory (ULRR for short) is introduced firstly, and the relationship between ULRR (Y′) and elastic modulus (E for short) is obtained. Based on the basic theory of damage mechanics,the relationship between ULRR and damage variable (D for short) is set up and analyzed with the relationship between E and D. The unloading and loading experiments on a two-story structure carried out in the University of Naples in Italy are introduced;and calculated damage variable is compared with that calculated by Zhang Langping who put forward Weibull distribution as random distribution function. The results show that damage variable of the structure keep highly consistent with calculations of these two methods. Therefore, the relationship between Y′and D provides a new approach to a health assessment to catastrophic failure of large-scale structures and prediction of engineering.

A New Dynamic Prediction Method and its Application in Prediction of the Colluvial Landslides Induced by Rainfall

A lot of data indicates that rainfall has always played the very important role in landslide triggering. The paper discusses rainfall as a dynamic parameter in term of the load/unload response ratio theory, using the Xintan landslide as a case study. Analysis of the available data indicates that the occurrences of landslides in this region are controlled by rainfall, whose intensity and rainfall processes are the most important dynamic factors in determining the stability of slopes. Therefore, the relationship between rainfall and the movement of typical landslides has been specifically analyzed for the Xintan landslides by using the loading/unloading response ratio parameter of rainfall. The result of this study indicates that the mutation of the loading/unloading response ratio of rainfall of the Xintan landslide in the Three Gorges Reservoir regions, China occurred just before their destabilization, which shows that the loading/unloading response ratio of rainfall and its changing feature can be taken as a precursor for the landslides induced by rainfall.

Loading/Unloading response ratio theory applied in predicting deep-seated landslides triggering

Rainfall is the most relevant factor for the triggering of landslides and it is characterized by an extreme variability. Rainfall analysis is the most frequently adopted approach for predicting landslides. But predicting deep-seated landslides by means of rainfall thresholds is sometimes inadequate due to the complexity of such slopes. In this paper, further study of the loading / unloading response ratio theory applied in landslides prediction was carried out. As the aforementioned effect and character of rainfall was concerned, a prediction for the known Xintan landslide was carried out by means of the loading / unloading response ratio method, in which the action of water was regarded as loading/unloading measures. The results show that it is an effective method for landslides prediction, and it has an advantage over conventional rainfall thresholds or time sequences analysis method.

Revisiting the Tidal Activation of Seismicity with a Damage Mechanics and Friction Point of View

— The Load Unload Response Ratio theory (LURR) puts forward the idea that the ratio of seismicity during times of increased tidal loading to times of decreased tidal loading takes on anomalously large values as the preparatory region of the earthquake approaches a critical state. We repeated the calculations of LURR for several earthquakes in California, for which results had been published, using estimates of the parameters which could be determined from the published work. We were unable to confirm any LURR ratio predictive significance. We test an alternative method of evaluating the influence of tidal stresses on earthquakes based on damage mechanics. As in rock mechanics experiments, it may be that anomalous activation of seismicity prior to large earthquakes occurs only during those time intervals when the applied stress exceeds values previously attained. We applied this approach to analyze the same data set used to test the LURR hypothesis, and it also failed to reveal any significant precursory indications. It may be that time-dependent failure processes such as self-driven nucleation occur on a time scale longer than the diurnal tide, thus destroying the expected synchronization.

The load-unload response ratio theory: a new approach to earthquake prediction (in Chinese) : Yin Xiang-Chu, Chen Xue-Zhong, Song Zhi-Ping & Yin Can, Acta Geophysica Sinica, 37(6), 1994, pp 767–775

The load-unload response ratio theory: a new approach to earthquake prediction (in Chinese) : Yin Xiang-Chu, Chen Xue-Zhong, Song Zhi-Ping & Yin Can, Acta Geophysica Sinica, 37(6), 1994, pp 767–775