Hong Mei Tang

Study on Failure Mechanism of Gongjiafang Bank Slope in Wu Gorge of the Three Gorges, the Yangtze River, China

During running period of the Three Gorges reservoir ,failure mechanism of bank slope is one of the important scientific problems of geological disaster mitigation for reservoir bank. GongJiafang bank slope is located in left of Wu Gorge in Three Gorges of the Yangtze River, where damage events appeared in 175 m experimental water storage in 2008 and 175 m normal water storage in 2011.Study shows that, GongJiafang bank slope located in the core of the Heng Shi stream anticline developes two group of tectonic fractures .The first one is unloading fracture of bank slope, whose upper part is in transfixion or intermittent transfixion status,and the second one belongs to shear shear fracture. Bank slope presents cataclastic rock mass structure ,whose water physical properties are poor. The shear strength parameters of bank slope soil reduce after being immersed, a decreas of about 52 % on cohesion, and 30 % on friction. Regional new tectonic stress field control the macroscopic law for failure of GongJiafang bank slope .Especially max2 shear zone in new tectonic stress field is consistent with the first group fracture, which strengthen progress of the unloading fracture developement .Bank slope basically appear unstable failure along with the first group fracture. About 50% unbroken lower part of unloading fracture in GongJiafang bank slope locate in reservoir water level change belt between 145m and 175m.During the reservoir water level rising, stability coefficient of bank slope decreases from 1.31 to 0.88 after being immersed, and it is inevitable for bank slope to fail suddenly. Research results for further exploration on the formation mechanism of bank landslide in the Three Gorges reservoir and its mitigation has positive significance.

Stability Analysis of Perilous Rock in Views of Damage and Fracture Mechanics

Perilous rock rupture is dominated by damage and fracture of the dominant fissure. Define factor of safety of perilous rock as the ratio of the damage fracture tenacity at the end area of the dominant fissure to the union fracture strength factor; Transfer loads acting on perilous rock to the dominant fissure, and divide them into four components, i.e., water pressure in fissure, average shear stress, moment around the end of the dominant fissure, and average tension stress, further, contribute methods to calculate fracture strength factor every components in view of fracture mechanics; Based on these individual fracture strength factors, establish the method to calculate the union fracture strength factor along fracture orientation near the end area of the dominant fissure. Further, on the basis of damage duration of the dominant fissure, provide the formula to solve the fracture tenacity of rock in damage area near the end of the dominant fissure in detal. Case analyses identify that it is reasonable to consider orientation earthquake force in stability analysis of perilous rock, which promulgates the stability status of perilous rock more effective than that by the limit equilibrium principle.

Excitation Action Triggered by Perilous Rock Avalanche to the Stability of Perilous Rock

The mechanism failure of massive perilous rock should consider the interaction among perilous rock masses. Study on the stability of adjacent perilous rock from the excitation wave, which is produced by the perilous rock mass at the collapse instantaneousness, has important significance. Focusing on the falling-type perilous rock, physical model of perilous rock with excitation wave is considered and the stress characteristics for the excitation wave of perilous rock avalanche on dominant fissure with normal incidence is analyzed. Based on the fracture mechanics, a method to calculate the combined stress intensity factors of dominant fissure under falling excitation action of perilous rock is established. As the instance results showed, two cites of nature and rainfall, the stability coefficient are both reduce, specially in the horizontal, stability coefficient reduced by about 10% respectively, while in vertical about 2%. The results provided some scientific progresses disasters prevention and mitigation of perilous rock.

Experimental Study on Gravel Soils of Matrix Suction

Soil-water characteristic curve（SWCC）is closely relevant to two main factors which are structure and moisture content. According to the two factors the values of matrix suction of 45 groups experimental specimens within different moisture content and soil -stone ratio of unsaturated soil are get through filter paper method. Date analysis shows that relation between matrix suction and soil-stone ratio at different moisture states is of different characteristics. Relation between matrix suction and water content is notably nonlinear. Distribution of matrix suction is curved surface in the moisture and soil-stone ration state space which is the function of water content and soil-stone ratio, in which the axial plan is parallel to the axis of soil-stone ratio.At low water content,the matrix suction on the moisture content change is very sensitive, at high moisture content and closed to saturation stage matrix suction hardly changes along with water content and soil-stone ratio change. The curved surface which Located in the middle section ,the matrix suction on the change of water content are more sensitive, reduced with water content increasing; and in this phase the matrix suction is insensitive to the variation of soil-stone ratio. Finally, it is concluded that the saturation to describe the soil water characteristic curve is a bad choice, with moisture to depict the so. In contrast, directly using the water content to describe the soil water characteristic curve is better.

Experimental Study on the Process of Geomorphic Evolution of Debris Flow on Slope

To reveal the process of geomorphic evolution of debris flow on slope, the qualitative-semi-quantitative model experiment was built from experimental model, characteristics of soil and rainfall scheme. The results indicate that the essence of geomorphic evolution of debris flow on slope is the interaction of soil and water. And the change of geomorphology is reflected by the elevation of topsoil. In antecedent rainfall, the elevation of topsoil is in increasing trend generally except some parts. During short heavy rainfall, the soil creeps intensively, mixes with water and becomes fluidization gradually. The elevation of topsoil on the top is decreasing generally, while on the button, the elevation is increasing. Moreover, because water infiltrates into slope and interacts with soil needing a period of time, the change of geomorphology falls behind the rainfall process.

A New Method to Estimate Routine Based on the Motion Modes of Rockfall

This article divides the motion route into four phases: free fall, initial collision, in-flight and subsequent collision. There could be bounce, slippage or rolling movement in the phases of initial collision and subsequent impact. Based on the theory of movement mechanics, the certain methods on the motion direction, velocity and distance of each movement mode is established and the effected discrimination standard to distinguish the motion phases and modes is put forward.

Study on Wavelet Denoising of Pulse Impact Force of Non-Viscosity Debris Flow

Noise filtering of impact load spectrum is the key to ensure the impact load of debris flow during the control engineering design of debris flow. As the laboratory impacting test indicates, noise effect in pulse impact force spectrum can be denoised using Daubechie(dbN)and Symlet(symN)wavelet methods, both of which contain hard threshold method and soft threshold method. Analyzed the pulse impact force of non-viscosity debris flow testing results by wavelet denoising method, the testing conditions are A-3(whose grain size is range from 0.3cm to 0.8cm), B-3(whose grain size is range from 0.8cm to 1.5cm) and C-3(whose grain size is range from 1.5cm to 3.0cm),all of whose solid phase ratio are 0.16.The analyzing results show that the denosing effect adopting Db5 wavelet function is superior to ones adopting Sym2 wavelet function, meanwhile, the denosing effect adopting hard threshold method is superior to ones adopting soft threshold method. The results also indicate that the bigger the solid phase ratio is, the bigger the Signal Noise Ratio is, the better the wavelet denosing effect is. These results could provide scientific basis for further accurate experimental study to ensure impact load of non-viscosity debris flow.

Mutation Instability Model of Perilous Rock and Calculation Methods for Corresponding Dynamic Parameters

Failure mechanism of perilous rock and its corresponding dynamic parameters is one of the basic theoretical questions for the security alert implement about collapse disaster. Focusing on the dominant fissure of perilous rock, it is divided into linking patch and locked patch, and the constitutive model of dominant fissure is proposed. Based on the energy principle, it proposes the deformation energy formula of perilous rock with dominant fissure’s creeping displacement. On the mutation theory, it establishes the failure cusp mutation model of perilous rock, and the calculating formulas of creeping displacement on failure starting point and end point and the controlling factors of dynamic instability are gained. With scientific theory, elastic energy releases and transforms to the elastic and impulsive kinetic energy at the moment of dynamic instability, and a method to calculate the violent-slide velocity and acceleration on collapse mass at that moment is proposed. Practical examples indicate that this method is useful in engineering practice.

Study on Consolidation Mechanism of Debris Flow Deposit

The damage of debris flow effected on highway subgrade, pavement, protective structure, bridge and culvert laid on debris flow impact fracture and buried damage. Thus far, research on debris flow burying mechanism is still fuzzy. According to the two-phase flow theory of debris flow deposit, analyzed the consolidation mechanical mechanism of highway debris flow deposit. On the basis of Terzaghi one-dimensional consolidation theory, established the consolidation formula, which described the change process of excess pore water pressure, consolidation degree, settlement and compression with the consolidation time and deposit size, and then verified the correctness and feasibility of the formula by the indoor consolidation test. It adopted these results and combined it with the field survey data, it could develop a proper program for emergency mitigation of highway debris flow buried disaster more quickly and accurately.

Experiment of the Rockfall Impact Characteristic onto Gravel Cushion

Rockfall is one of common geological disasters in the mountainous area. The experiment gained the impact waves for cushion soil mass contained 12density, 4 soil-rock ratio, 4 cushion obliquity, 3 moisture content, 3 rockfall quality, 5 height of rock fall. Used the wavelet theory to deal with the experiment waves, analyzed the experiment results: with rock’s mass, the height and density increased, the impact force is increasing, or the impact force is decreasing with the moisture content and cushion inclination increasing. The impact force spreads from the point of rockfall to all directions. The impact force data of the experiment is a little large than others, so this method provides a gist for choosing the prevention and cure measure for rockfall.