Xiao Ying He

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.

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.

Model and Application on Displacement Calculation of Abutment by Considering Earthquake Effects

The response characteristics to the seismic action of displacement for abutment are the important part of security evaluation, earthquake resistance and disaster mitigation in the seismic region. This paper decomposes the displacement of abutment into the slip displacement and rotation displacement two parts, respectively proposes the translational and rotational displacement model of abutment and establishes the corresponding calculation formulas. The case analysis indicates that the response characteristics of abutment displacement to the seismic action are comparatively sensitive, in which the translational displacement appears positive response relationship with the acceleration of seismic, while the rotational displacement appears negative response relationship. However, it holds significant mutation from 0.5g to 0.6g for both of the translational displacement and rotational displacement. In other words, the seismic acceleration from 0.5g to 0.6g should be paid highly attention in doing seismic resistance design in the seismic region.

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.

Study on Numerical Simulation for Failure Process of Girder Bridge under Seismic Influence

Based on the finite element analysis software Midas, it takes response spectrum analysis, and posts the failure mechanism and characteristics of Girder Bridge under intense earthquake. Through the seismic response spectrum displacement maps of Girder Bridge, it finds out that the abutment and foundation deformation is in evidence, especially the top of abutment foundation. Through the study of seismic internal force variation on girder and pier, it indicates that the longitudinal earthquake controls axial force, vertical shearing force and in-plane bending moment, transversal earthquake dominates transversal shearing force and out-planes bending moment. And it shows that the pier and mid-span section are seismic response sensitivity parts. The three parts, axial force, longitudinal shearing force and in-plane bending moment, becomes the controlling index of pier intensity. According to the seismic response spectrum displacement for pier and abutment, the transversal anti-seismic stiffness of pier is smaller than longitudinal one, longitudinal seismic force shows no effect on transversal displacement, and the transversal seismic force can augments longitudinal displacement. At the same condition, longitudinal seismic force changes the longitudinal distributing form of abutment and concaves it deeply, and the transversal seismic force can not change its shape, but augment its value.

Numerical Analysis of Concrete Arch Bridge on the Situation of Seismic Damage

Based on the example, red-Flag Bridge in Chongzhou City, using the finite element to analyze the response spectrum of seismic performance for the concrete arch bridge under two conditions. Through the numerical analysis of vibrational damage on the whole bridge, reveals the nether structure and elements of bridge is affected by the seismic waves under the seismic effect and the great stiffness in upper structure, and posts that the anti-inertia in longitudinal direction is more powerful than the transverse and vertical ones. The deformation of arch ring is mostly affected by the displacement on transverse line, DY direction, and less in the longitudinal, vertical and rotational direction. According to the analysis of spectrum value displacement on abutment, finds out that the transverse direction of abutment is mostly affected by the displacement on DZ direction, for the abutment displacement, less in the middle, big in both sides. And for the vertical one, it is mostly affected by DY displacement, in the DY displacement of abutment, big in top, less in base.

Study on Damage Mechanism for Foundation Pile of Girder Bridge under Seismic Influence

Based on the analysis for seismic load and failure modes of pile foundation, this article adopts dynamic Winkler foundation beam model, and employs continuous distributional and independent spring and damper, instead of the dynamic resistance of the soil around the pile, and to explore interaction between pile and soil dynamic at horizontal load. In consideration of six kinds of boundary conditions combination, this paper proposes the solution method for displacement and internal force on pile. From analysis of cases, it finds that the effect of pile’s length on dynamic response can be negligible when pile slenderness ratio l/d>20, and the pile can be simplified into infinite long pile. Dynamic response of pile increases with the increase of stiffness ratio. When establish the control equations, influence of axial force can not be ignore. Otherwise, results will be small than the actual value.

Study on Duration for Perilous Rock to Form

As one geological disaster in the area of the Three Gorges Reservoir of China, perilous rocks dominate stability of slopes in the area. Most cliffs or steep slopes are alternately composed of inflexible rock such as sandstone and soft rock such as mudstone in the area, and due to different weathering velocities rock cells in soft rock below inflexible rock are usually developed. Any perilous rock belongs to a part of inflexible rock. To appraise the safety of perilous rock, it is essential to approach duration for perilous to form is of interest. In the present paper, authors analyze weathering velocity of rock cell and establish method to calculate length of critical rock cell. Duration for perilous rock to form can be divided into three parts, (1) duration to form critical rock cell, (2) damage duration of control fissure, and (3) fracture duration of control fissure. Further, methods to calculate these durations are established in details based on damage mechanics and fracture mechanics.

Wavelet Method to Extract Shock Signal of Debris Flow

The shock signal’s fluctuation characteristics of debris flow stem from two aspects, one is the composition of debris flow with the solid and the liquid, another is the surging property of debris flow in motion. Based on the initial shock signals collected in model experiment in laboratory, 9 shock spectrum levels are decomposed by the db8 wavelet method, i.e., 0~0.195Hz, 0.195~ 0.391Hz, 0.391~0.781Hz, 0.781~1.5625Hz, 1.563~3.125Hz, 3.125~ 6.25Hz, 6.25~12.5 Hz, 12.5~25Hz, and 25~50Hz. Taking the peak each shock spectrum as the standard, the energy distribution curves of 9 shock spectrum levels are obtained. These curves display that the shock energy of debris flow focus on the low frequency smaller than 1.0Hz, and the percentage below 6.25Hz is about 95%. The results provide a reference to select wallop peak as the design load of structures against debris flow disaster.