Numerical Simulation on Energy Concentration and Release Process of Strain Rockburst

Ang Lu,Peng Yan,Wenbo Lu,Ming Chen,Gaohui Wang,Sheng Luo,Xiao Liu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.10

Rockburst mechanism has been a hot topic in the stability analysis of underground carven excavation, and the accurate description of energy evolution process is very critical to rockburst prediction. To study the evolution process of rockburst, such as V-shaped rockburst pit, theoretical formula derivation and numerical simulation are adopted to research the dynamic response characteristics during the formation process of rockburst pits quantitatively. The results show that rockburst intensity distribution varies with failure depth. It can be divided into three zone: slow-increase, rapid-increase and slow-decrease. For a circular tunnel with radius R, the strain energy release rate and vibration response of surrounding rock increases gradually within (0 − 0.06) R; reaches the peak value around (0.06 − 0.1) R and drops to a balance beyond 0.1R. Due to the same law of them, the rockburst risk can be conveniently predicted by monitoring vibration of surrounding rock with a certain depth. This work is beneficial to provide a good reference for rockburst prediction.

High Shock-Resistant Design of Piezoresistive High-g Accelerometer

Yongle Lu,Zhen Qu,Jie Yang,Wenxin Wang,Wenbo Wang,Yu Liu 한국정보처리학회 2023 Journal of information processing systems Vol.19 No.2

To improve the shock-resistance of piezoresistive high-g accelerometer, we propose a design of piezoresistivehigh-g accelerometer. The accelerometer employs special-shaped proof masses system with a cross gap. Fourtiny sensing beams are bonded above the cross gap. The expression of the deformation, natural frequency anddamping is deduced, and the structural parameters are optimized. The accelerometer structure is simulated andverified by finite element method (FEM) simulation. The results show that the range of the accelerometer canreach 200,000 g, the natural frequency is 453.6 kHz, and the cross-axis sensitivity of X-axis and Y-axis is0.25% and 0.11%, respectively, which can apply to the measurement of high shock. Contrastively, the crossaxissensitivity of X-axis and Y-axis is respectively, reduced by 93.2% and 96.9%. The sensitivity of ouraccelerometer is 0.88 μV/g. It is of great value for the application of piezoresistive high-g accelerometer withhigh shock-resistance.

Evaluation of Rock Vibration Generated in Blasting Excavation of Deep-buried Tunnels

Jianhua Yang,Wenbo Lu,Peng Yan 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.7

The experimental tunnels of the China Jinping Underground Laboratory are constructed in a maximum overburden depth of 2375 mand subjected to extremely high in situ stress more than 50 MPa. When these deep-buried tunnels are excavated with the method ofdrill and blast, the surfaces created by blasting are generated almost instantaneously, and thus the initial stress on these surfaces is alsosuddenly released. This transient release of in situ stress causes elastic waves to propagate in rock masses and may have an importanteffect on the subsequent rock vibration. In this study, a three-dimensional FEM modeling in combination with site investigation isconducted to research the Peak Particle Velocity (PPV) attenuation and frequency characteristics for the rock vibration induced bytransient stress release and its combined actions with blast loading. The results indicate that the transient release of the high stressgenerates considerable vibration velocity that is comparable to that of blast loading. It is not a negligible excitation for the rockvibration generated in blasting excavation of deep-buried tunnels. Furthermore, the vibration induced by transient stress release hasmuch lower frequency than that caused by blast loading. This causes the unloading vibration to decay more slowly and become themajor vibration component at far distances. Also, the effect of transient stress release is found to enhance intensity of the totalvibration and furthermore cause an increase in its low-frequency content. On the basis of this, the allowable charge amount per delayand the minimum safety distance are finally discussed with a special emphasis on the contributions of the transient stress release tothe total vibration.

Sonochemical synthesis of flower-like ZnO assembled by hollow cones toward water vapor permeability and water resistance enhancement of waterborne film

Yan Bao,Lu Gao,Caiping Feng,Jianzhong Ma,Wenbo Zhang,Chao Liu,Demetra Simion 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.82 No.-

In this study,flower-like ZnO assembled by hollow cones (F-ZnO-HCs) were synthesized viasonochemical route and the related morphology and structure of product were characterized. Then,F-ZnO-HCs nanostructures were employed to polyacrylate and the effect of F-ZnO-HCs on the propertiesof waterbornefilms was investigated. Meanwhile, the morphological evolution of F-ZnO-HCs wasproposed and the superiority of F-ZnO-HCs on synchronously improving the water resistance and watervapor permeability of polyacrylatefilm was discussed. The results showed that F-ZnO-HCs possessed anaverage diameter of800 nm and a large specific surface area of 16.01 m2 g 1. Adjusting the watercontent and citric acid dosage, the morphology of ZnO transformed from F-ZnO-HCs to ZnOnanoparticles, F-ZnO-NSs, F-ZnO-SCs and F-ZnO-NRs. F-ZnO-HCs nanostructures asfillers not onlysignificantly enhance the stability of polyacrylate latex but also simultaneously improve the water vaporpermeability and water resistance of polyacrylatefilm. Moreover, compared with other morphologicalZnO, F-ZnO-HCs was the best for simultaneously improving the water resistance and water vaporpermeability of polyacrylatefilm. F-ZnO-HCs is an ideal candidate for resolving the contradiction of thewater resistance and water vapor permeability of waterbornefilms.

Two Types of Immunoassay Based on Nile Blue Labeling Polydopamine Nanospheres

Lili Liu,Wenbo Lu,Chang Liu,Ying Wang,Jian Dong,Weiping Qian 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.8

The sandwich-type immunoassays have been developed by using electrochemical and surface-enhanced Raman scattering (SERS) techniques for the detection of carcinoembryonic antigen (CEA). Nile blue as a kind of Raman dye has been decorated on nanospheres with polydopamine resin (PDR) via π-stacking interaction. The Nile blue displays the strong SERS signals as well as a characteristic electrochemical reduction peak at -0.33V (versus Ag/AgCl). The implementation of the PDR nanospheres mixing with Au nanoparticles (AuNPs/PDR) exhibits a better electrical conductivity and large SERS enhancement. The immunoassays based on Nile blue-labeled AuNPs/PDR nanospheres have been fabricated by using electrochemical and SERS techniques for the detection of CEA. The proposed immunoassay shows higher sensitivity, high selectivity, lower detection limit and long-term stability. The performances of the electrochemical immunoassay are better than that of SERS immunoassay. For the electrochemical immunoassay, the linear range occurs from 1 pg/mL to 100 ng/mL (R = 0.995) with a detection limit of 0.68 pg/mL and signal-to-noise ratio of 3 in the detection of CEA. The data for the analysis of human serum samples by using the electrochemical method are acceptably consistent with those obtained from the enzyme-linked immunosorbent assay (ELISA). The proposed immunoassay exhibits a promising potential for application in clinical diagnosis.

A SPH-Lagrangian-Eulerian Approach for the Simulation of Concrete Gravity Dams under Combined Effects of Penetration and Explosion

Guangdong Yang,Gaohui Wang,Wenbo Lu,Peng Yan,Ming Chen,Xinxia Wu 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.8

The damage prediction of high dams under the attacks of earth-penetrating weapons has gained significant importance in recentyears. For this purpose, a SPH-Lagrangian-Eulerian coupled approach is proposed to describe the damage processes of concretegravity dams subjected to the combined action of the penetration and explosion. The SPH method is used to model the concretematerial with the large deformation near the penetration and explosion regions. The Lagrangian algorithm is adopted to simulate thehigh-velocity projectile and dam body with the small distortion. And the Eulerian algorithm is employed to describe the dynamicbehavior of the water and air media. The validity of the penetration model is calibrated against a previous penetration test. Meanwhile, the SPH-Lagrangian-Eulerian coupled method is verified by implementing an underwater explosion test in a concretecube. The computed distribution of cracking damage is consistent with the result of the experimental test, which validates the validityof the proposed SPH-Lagrangian-Eulerian coupling method. Subsequently, the penetration processes of a concrete gravity dam underthe high-velocity projectile are presented. After the rapid penetration, the explosives are detonated in the dam with the initialpenetration damage. The shock wave propagation characteristics in the dam and reservoir water are discussed. The failure processesand dynamic responses of the dam subjected to the combined action of the penetration and explosion are investigated. The influenceof the initial penetration damage and the reservoir water on the failure processes of the dam subjected to the internal blast loading is alsodiscussed. The results show that the penetration of the high-velocity projectile only causes a local damage to the concrete gravity dam. However, the combined effects of the penetration and explosion cause significantly more damage to the upper region of the dam.

Coring Damage Extent of Rock Cores Retrieved from High In-situ Stress Condition: A Case Study

Peng Yan,Qi He,Wenbo Lu,Yanli He,Wei Zhou,Ming Chen 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.7

The distribution of damage in deep rock cores is critical for assessing its influence on rock mechanical characteristics. This paper presents a case study on estimating the coring damage extent induced by the stress redistribution through a combined method of numerical simulation and X-ray Computed Tomography (CT) scanning. Rock cores are taken at 1900 m depth from the test tunnel at Jin-ping Second Stage Hydropower Station (JPII) in China. Firstly, the stress path experienced by the rock core during coring has been examined by the numerical simulation, and the distribution of tensile zone in the cross-section of rock core is also discussed. Then two kinds of samples, collected from the same position under different stress levels, are scanned to obtain CT images, and a special CT value analysis strategy was adopted to evaluate coring damage intensities of these samples. The result indicates that the stress state can be regarded as the principal factor for the distribution of coring damage. During coring in the Test Tunnel of JPII under the quasi-hydrostatic stress condition, high tensile stresses (over 5 MPa) are observed at the exterior edge of rock cores, which may lead to the nucleation of microcracks around the core boundary, and the coring damage then propagates to the core centre. The CT scanning also illustrates that the coring damage zone may cover approximately 70~80% of the entire cross-section from the outside inside (stress level of 50 MPa), and that the central part of the core is less damaged or eventually undisturbed. Thus, intact rock samples can be expected to be obtained by overcoring the original rock cores. However, the applicability of the overcoring method seems to be largely dependent on the state of in-situ stress at the coring site. The whole core may be damaged if the lateral stress coefficient reaches a critical value (e.g. greater than 3.0), in which case a special coring equipment should be adopted to improve the stress state during coring.

Analytical moment expression for linear element in diagonal form fast multipole boundary element method

Haijun Wu,Weikang Jiang,Wenbo Lu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.7

The moment of diagonal form fast multipole boundary element for the Helmholtz equation in essence is the surface integration of exponential function on an element. In this paper, the moment for a linear triangular element can be integrated analytically by transforming the coordinates from global Cartesian coordinates to local area coordinates. The derived analytical moment evaluation is compared with the classical numerical calculation, and results show that analytical method makes the moment calculation efficient, stable, and accurate.

Effects of Strain Energy Adjustment: A Case Study of Rock Failure Modes during Deep Tunnel Excavation with Different Methods

Liang-Tao Xie,Peng Yan,Wenbo Lu,Ming Chen,Gaohui Wang 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.10

The strain energy adjustment processes and rock failure modes corresponding to different excavation methods, such as Tunnel Boring Machine (TBM) or blasting, are quite different during construction of deep tunnel. Based on the diversion tunnel excavation of Jin-Ping II hydropower station (JPII) in southwestern China, the distribution characteristics of damage zones and adjustment process of rock strain energy under different excavation methods are analyzed and discussed, and the occurrences of rock bursts in the diversion tunnels are also monitored and analyzed. Research reveals that, the adjustment process of rock strain energy and the distribution of damage zones are obviously different under different excavation methods, and the depth and distribution of damage zone are positively correlated with the accumulation depth of rock strain energy. For blasting excavation, due to the combined effects of blast loading and in situ stress transient unloading, the surrounding rock is damaged seriously. The accumulation depth of rock strain energy is significantly larger than that by TBM excavation, while the accumulation peak of rock strain energy is smaller. For TBM excavation, the strain energy releases smoothly and slowly, and much more strain energy is accumulated in the vicinity of excavation face. Under similar geological conditions in the JPII, the rock bursts of intensive and mediate grades can be more frequently observed after blasting for the impact of severe excavation disturbance, and the strain energy transient adjustment may be the main disturbance contributor. While during TBM excavation, due to the smooth adjustment process of rock strain energy, the disturbance to surrounding rock is limited, and the accumulation peak of rock strain energy is higher and closer to the excavation face, which may result in more spalling events or minor rock bursts.

Discussion on Failure Mechanism and Strength Criterion of Sandstone Based on Particle Discrete Element Method

Shuguang Zhang,Lei Chen,Pingping Lu,Wenbo Liu 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.6

In order to study the mechanism of loading failure process of deep rock mass, particle flow numerical simulation (PFC2D) was used to carry out rock mechanical unit tests under different loading strain rates for sandstone in Haitangshan Tunnel, Fuxin. The applicability of several classical strength criteria was compared according to the test. The results show that, except Poisson's ratio, the other mechanical parameters are positively correlated with the loading strain rate, including peak strength, elastic modulus, cohesion, internal friction angle and tensile strength. And the Poisson's ratio is negatively correlated with the loading strain rate. And the crack initiation stress σci and dilatation stress σcd increased gradually, but the effects on σci/σpk, σcd/σpk and σci/σcd were not obvious; and at the same volume strain, the corresponding axial strain decreased gradually. The anisotropy of normal and tangential contact forces between particles increases with the increase of loading strain rate. The normal contact force was approximately symmetrical distributed up and down, while the tangential contact force was approximately symmetrical distributed in the center. The cumulative number of cracks and the number of cracks every 10 steps gradually increased with the loading strain rate, and the crack development and failure degree gradually increased, and the crack hot spot map at the shear fracture zone gradually tended to be irregular. By comparing different strength criteria, it was found that the error of ROCKER strength criterion was relatively small, and the calculation was simple. It was considered that ROCKER strength criterion was more suitable for sandstone strength prediction under different loading strain rates.