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Time-domain solution for transient dynamic response of a large-diameter thin-walled pipe pile

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Earthquake Engineering and Engineering Vibration 2015年第2期14卷 239-251页

作者： Ding Xuanming Liu hanlong Chu Jian Cheng Ke Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University) Ministry of Education Department of Civil Construction & Environmental Engineering Iowa State University 328 Town Engineering Building School of Mechanical and Power Engineering Nanjing University of Technology

The propagation of stress waves in a large-diameter pipe pile for low strain dynamic testing cannot be explained properly by traditional 1D wave theories. A new computational model is established to obtain a wave equation that can describe the dynamic response of a large-diameter thin-walled pipe pile to a transient point load during a low strain integrity test. An analytical solution in the time domain is deduced using the separation of variables and variation of constant methods. The validity of this new solution is verifi ed by an existing analytical solution under free boundary conditions. The results of this time domain solution are also compared with the results of a frequency domain solution and fi eld test data. The comparisons indicate that the new solution agrees well with the results of previous solutions. Parametric studies using the new solution with reference to a case study are also carried out. The results show that the mode number affects the accuracy of the dynamic response. A mode number greater than 10 is required to enable the calculated dynamic responses to be independent of the mode number. The dynamic response is also greatly affected by soil properties. The larger the side resistance, the smaller the displacement response and the smaller the refl ected velocity wave crest. The displacement increases as the stress waves propagate along the pile when the pile shaft is free. The incident waves of displacement and velocity responses of the pile are not the same among different points in the circumferential direction on the pile top. However, the arrival time and peak value of the pile tip refl ected waves are almost the same among different points on the pile top.

关键词： pipe pile transient load analytical solution time

Recurrent neural network-based volumetric fluorescence microscopy

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Light(Science & Applications) 2021年第4期10卷 620-635页

作者： Luzhe Huang hanlong Chen Yilin Luo Yair Rivenson Aydogan Ozcan Electrical and Computer Engineering Department University of CaliforniaLos AngelesCA 90095USA Bioengineering Department University of CaliforniaLos AngelesCA 90095USA California Nano Systems Institute(CNSI) University of CaliforniaLos AngelesCA 90095USA David Geffen School of Medicine University of CaliforniaLos AngelesCA 90095USA

Volumetric imaging of samples using fluorescence microscopy plays an important role in various fields including physical,medical and life *** we report a deep learning-based volumetric image inference framework that uses 2D images that are sparsely captured by a standard wide-field fluorescence microscope at arbitrary axial positions within the sample *** a recurrent convolutional neural network,which we term as Recurrent-MZ,2D fluorescence information from a few axial planes within the sample is explicitly incorporated to digitally reconstruct the sample volume over an extended *** experiments on *** and nanobead samples,Recurrent-MZ is demonstrated to significantly increase the depth-of-field of a 63×/1.4NA objective lens,also providing a 30-fold reduction in the number of axial scans required to image the same sample *** further illustrated the generalization of this recurrent network for 3D imaging by showing its resilience to varying imaging conditions,including e.g.,different sequences of input images,covering various axial permutations and unknown axial positioning *** also demonstrated wide-field to confocal cross-modality image transformations using Recurrent-MZ framework and performed 3D image reconstruction of a sample using a few wide-field 2D fluorescence images as input,matching confocal microscopy images of the same sample ***-MZ demonstrates the first application of recurrent neural networks in microscopic image reconstruction and provides a flexible and rapid volumetric imaging framework,overcoming the limitations of current 3D scanning microscopy tools.

关键词： neural network networks

Testing and modeling of rockfill materials:A review

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Journal of Rock Mechanics and Geotechnical Engineering 2016年第3期8卷 415-422页

作者： yang Xiao Hong Liu Wengang Zhang hanlong Liu Feng Yin Youyu Wang Key Laboratory of New Technology for Construction of Cities in Mountain Area(Chongqing University) Ministry of Education School of Civil Engineering Chongqing University College of Civil and Transportation Engineering Hohai University School of Civil and Environmental Engineering Nanyang Technological University

The research development of rockfill materials （RFM） was investigated by a series of large-scale triaxial tests. It is observed that confining pressure and particle breakage play important roles in the mechanical property, dilatancy relation and constitutive model of RFM. In addition, it is observed that the conven- tional dilatancy relation and constitutive model are not suitable for RFM due to the complex mechanical behavior. Hence, it needs to propose a unified constitutive model of RFM, considering the statedependent and particle breakage behavior.

关键词： Large-scale triaxial testConfining pressureParticle breakageDilatancy relationConstitutive model

Determination of groundwater buoyancy reduction coefficient in clay:Model tests,numerical simulations and machine learning methods

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Underground Space 2023年第6期13卷 228-240页

作者： Weixin Sun hanlong liu Wengang Zhang Songlin liu Liang Han School of Civil Engineering Chongqing UniversityChongqing 400045China Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing UniversityChongqing 400045China National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas Chongqing UniversityChongqing 400045China

Groundwater plays an essential role in stabilizing underground ***,hydrostatic uplift forces from groundwater can create safety *** paper obtained the groundwater buoyancy reduction coefficients of 36 types of clays through model tests and conducted a finite element simulation to obtain the buoyancy reduction coefficients of additional clays with varying soil *** learning methods,including extreme gradient boosting(XGBoost)and random forest(RF)algorithms,were used to analyze and identify the soil parameters that have a significant impact on the reduction of groundwater *** was found that the permeability coefficient and saturation are the primary factors that influence the reduction of groundwater ***,the prediction models developed by XGBoost and RF were compared,and their accuracy was *** research findings can serve as a reference for designing underground structures that can withstand the potential risk of buoyancy in clay.

关键词： Clay Buoyancy reduction coefficient Numerical simulation Model test Machine learning

Propagation characteristics of transient waves in low-strain integrity testing on cast-in-situ concrete thin-wall pipe piles

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Frontiers of Structural and Civil Engineering 2009年第2期3卷 180-186页

作者： hanlong LIU Xuanming DING Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai UniversityNanjing 210098China Geotechnical Research InstituteHohai UniversityNanjing 210098China

The three-dimensional effects of pile head and the applicability of plane-section assumption are main problems in low-strain dynamic tests on cast-in-situ concrete thin-wall pipe *** velocity and displacement responses were calculated by a theoretical formula deduced by the *** frequency and influencing factor of high-frequency interference were analyzed.A numerical method was established to calculate the peak value and arrival time of incoming waves on top of the *** regularity along circumferential and the influence of radius or impulse width were *** applicability of plane-section assumption was investigated by comparison of velocity responses at different points in the sections at different *** waveform of velocity response at different points forked after the first peak,indicating that the propagation of stress waves did not well meet the plane-section assumption.

关键词： pipe pile low strain integrity testing dynamic response transient wave three-dimensional effect

Liquefaction evaluation of dam foundation soils considering overlying structure

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第2期7卷 226-232页

作者： Gang Wang Xing Wei hanlong Liu School of Civil Engineering Chongqing University School of Civil Engineering Southwest Jiaotong University

The liquefaction analysis procedure conducted at a dam foundation associated with a layer of liquefiablesand is presented. In this case, the effects of the overlying dam and an embedded diaphragm wall onliquefaction potential of foundation soils are considered. The analysis follows the stress-based approachwhich compares the earthquake-induced cyclic stresses with the cyclic resistance of the soil, and thecyclic resistance of the sand under complex stress condition is the key issue. Comprehensive laboratorymonotonic and cyclic triaxial tests are conducted to evaluate the static characteristics, dynamic characteristicsand the cyclic resistance against liquefaction of the foundation soils. The distribution of thefactor of safety considering liquefaction is given. It is found that the zones beneath the dam edges andnear the upstream of the diaphragm wall are more susceptible to liquefaction than in free field, whereasthe zone beneath the center of the dam is less susceptible to liquefaction than in free field. According tothe results, the strategies of ground improvement are proposed to mitigate the liquefaction hazards. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

关键词： Liquefaction Overlying structure Dam Stone columns

Prediction of lining response for twin tunnels constructed in anisotropic clay using machine learning techniques

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Underground Space 2022年第1期7卷 122-133页

作者： Wengang Zhang Yongqin Li Chongzhi Wu Hongrui Li ATC Goh hanlong Liu School of Civil Engineering Chongqing UniversityChongqing 400045China National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas Chongqing UniversityChongqing 400045China Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing UniversityChongqing 400045China School of Civil and Environmental Engineering Nanyang Technological UniversitySingapore

Excessive structural forces generated inside tunnel linings could affect the safety and serviceability of tunnels,emphasizing the need to accurately predict the forces acting on tunnel linings during the preliminary design *** this study,an anisotropic soil model devel-oped by Norwegian Geotechnical Institute(NGI)based on the Active-Direct shear-Passive concept(NGI-ADP model)was adopted to conduct finite element(FE)analyses.A total of 682 cases were modeled to analyze the effects of five key parameters on twin-tunnel struc-tural forces;these parameters included twin-tunnel arrangements and subsurface soil properties:burial depth H,tunnel center-to-center distance D,soil strength s_(u)^(A),stiffness ratio G_(u)=s_(u)^(A),and degree of anisotropy ss_(u)^(P)=s_(u)^(A).The significant factors contributing to the bending moment and thrust force of the linings were the tunnel distance and overlying soil depth,*** degree of anisotropy of the surrounding soil was found to be extremely important in simulating the twin-tunnel construction,and severe design errors could be made if the soil anisotropy is ignored.A cutting-edge application of machine learning in the construction of twin tunnels is presented;multivariate adaptive regression splines and decision tree regressor methods are developed to predict the maximum bending moment within the first tunnel’s linings based on the constructed FE *** developed prediction model can enable engineers to estimate the structural response of twin tunnels more accurately in order to meet the specific target reliability indices of projects.

关键词： Twin tunnel Bending moment Thrust force Multivariate adaptive regression splines Decision tree regressor

Numerical investigation of pile responses induced by adjacent tunnel excavation in spatially variable clays

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Underground Space 2022年第5期7卷 911-927页

作者： Xin Gu Fuyong Chen Wengang Zhang Qi Wang hanlong Liu School of Civil Engineering Chongqing UniversityChongqingChina Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing UniversityChongqingChina National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas Chongqing UniversityChongqingChina

The pile responses induced by adjacent tunnel excavation have been a hot research topic in geotechnical *** excavation may exert disturbance to the surrounding soil mass and then influence the adjacent pile *** this paper,the random finite difference analysis considering the spatial variations of soil properties is conducted to explore the effect of tunnel excavation on the adjacent pile response by varying the distance of pile away from the tunnel centerline(D),the pile length(L),the pile diameter(d_(p)),the tunnel depth(h),and the anisotropic ratio between the horizontal and the vertical scales of fluctuation(δ_(x)/δ_(y)).A set of pile response curves are developed to assess the influence of tunnel excavation on the adjacent passive pile foundations in spatially variable clays and provide guidelines for the tunnel excavation in the complex constructed environment.

关键词： Pile response Tunnel excavation Random field Spatially variable clays Random finite difference analysis

Creep behavior of EPS composite soil

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Science China(Technological Sciences) 2012年第11期55卷 3070-3080页

作者： GAO HongMei CHEN YuMin LIU hanlong LIU JinYuan CHU Jian Institute of Geotechnical Engineering Nanjing University of Technology Nanjing 210009 China Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai University Nanjing 210098 China Geotechnical Research Institute Hohai University Nanjing 210098 China Department of Civil Engineering Ryerson University 350 Victoria Street Toronto ONM5B2k3 Canada School of Civil and Environmental Engineering Nanyang Technological University Singapore 639798 Singapore

EPS composite soil is one type of premixed lightweight fills studied by numerous researchers, However, one aspect that has not been fully understood is the creep behaviors which may have significant effect on the design and application of EPS com- posite soil. In this paper, the results of a series of oedometer creep tests and triaxial undrained creep tests on EPS composite soil were presented. Four main influencing factors were identified and their effects on the creep behaviors of EPS composite soil were studied. Three well established creep models, namely, Findley model, Singh ＆ Mitchell model, and Mesri model, were used to simulate the creep behavior of EPS composite soil. This study shows that the Findley creep model fits the test re- suits the best. A semi-empirical creep model was also proposed to model the creep behavior under axisymmetric conditions. In this model, the creep strain was divided into instant and viscous elastic strain as well as instant and viscous plastic strain which were simulated by element models and empirical equations, respectively. It was shown that the proposed creep model was able to precisely predict the creep strain of EPS composite soil.

关键词： lightweight fill creep model empirical model EPS composite soil oedometer creep test triaxial undrained creep test