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Application of wave equation theory to improve dynamic cone penetration test for shallow soil characterisation

Journal of Rock Mechanics and Geotechnical Engineering 2022年第1期14卷 289-302页

作者： Miguel Angel Benz Navarrete Pierre Breul Roland Gourvès Sol Solution Géotechnique Réseaux ZA des Portes de Riom Nord23 Avenue Georges GershwinRiom Cedex63204France UniversitéClermont Auvergne Institut PascalUMR CNRS 6602Clermont-Ferrand63000France Polytech Clermont-Ferrand Campus des Cézeaux 2 Avenue Blaise PascalAubière Cedex63178France

Among the geotechnical In situ tests,the dynamic penetration test(DPT)is commonly used around the world.However,DPT remains a rough technique and provides only one failure parameter:blow count or cone resistance.This paper presents an improvement of the dynamic cone penetration test(DCPT)for soil characterisation based on the wave equation theory.Implemented on an instrumented lightweight dynamic penetrometer driving with variable energy,the main process of the test involves the separation and reconstruction of the waves propagating in the rods after each blow and provides a dynamic cone load-penetration(DCLT)curve.An analytical methodology is used to analyse this curve and to estimate additional strength and deformation parameters of the soil:dynamic and pseudo-static cone resistances,deformation modulus and wave velocity.tests carried out in the laboratory on different specimens(wood,concrete,sand and clay)in an experimental sand pit and in the field demonstrated that the resulting DCLT curve is reproducible,sensitive and reliable to the test conditions(rod length,driving energy,etc.)as well as to the soil properties(nature,density,etc.).Obtained results also showed that the method based on shock polar analysis makes it possible to evaluate mechanical impedance and wave velocity of soils,as demonstrated by the comparisons with cone penetration test(CPT)and shear wave velocity measurements made in the field.This technique improves the method and interpretation of DPT and provides reliable data for shallow foundation design.

关键词： In situ test Dynamic cone penetrometer P.A.N.D.A. Wave equation Wave decoupling Dynamic cone load-penetration(DCLT)curve

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Unloading performances and stabilizing practices for columnar jointed basalt:A case study of Baihetan hydropower station

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第6期9卷 1041-1053页

作者： Qixiang Fan Xiating Feng Wenlin Weng Yilin Fan Quan Jiang China Three Gorges Corporation Beijing100038China State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

The columnar jointed rock mass(CJR), composed of polygonal cross-sectional columns cut by several groups of joints in various directions, was exposed during the excavations of the Baihetan hydropower station, China. In order to investigate the unloading performances and the stability conditions during excavation of the columns, an experimental field study was performed. Firstly, on-site investigations indicated that the geotechnical problems, including rock relaxation, cracking and collapse, were the most prominent for the CJR Class I that contains intensive joint network and the smallest column sizes.Comprehensive field tests, including deformation measurement by multi-point extensometers, ultrasonic wave testing, borehole television observation and stress monitoring of rock anchors, revealed that the time-dependent relaxation of the CJRs was marked. The practical excavation experiences for the Baihetan columnar jointed rock masses, such as blasting scheme, supporting time of shotcrete and rock bolts, were presented in the excavations of the diversion tunnels. These detailed investigations and practical construction experiences can provide helpful information for similar geotechnical works in jointed rock mass.

关键词： Columnar jointed basalt Diversion tunnels Rock unloading In situ test Hydropower station

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A miniature triaxial apparatus for investigating the micromechanics of granular soils with in situ X-ray micro-tomography scanning

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Frontiers of Structural and Civil Engineering 2020年第2期14卷 357-373页

作者： Zhuang CHENG Jianfeng WANG Matthew Richard COOP Guanlin YE Department of Architecture and Civil Engineering City University of Hong KongHong Kong 999077China Shenzhen Research Institute of City University of Hong Kong Shenzhen 518057China Department of Civil Environmental and Geomatic EngineeringUniversity College LondonLondon WC1E 6BTUK Department of Civil Engineering Shanghai Jiaotong UniversityShanghai 200240China

The development of a miniature triaxial apparatus is presented.In conjunction with an X-ray microtomography(termed as X-ray fiCT hereafter)facility and advanced image processing techniques,this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear.The apparatus allows for triaxial testing of a miniature dry sample with a size of 8 mm x 16 mm(diameter x height).In situ triaxial testing of a 0.4-0.8 mm Leighton Buzzard sand(LBS)under a constant confining pressure of 500 kPa is presented.The evolutions of local porosities(i.e.,the porosities of regions associated with individual particles),particle kinematics(i.e.,particle translation and particle rotation)of the sample during the shear are quantitatively studied using image processing and analysis techniques.Meanwhile,a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking.It is found that the sample,with nearly homogenous initial local porosities,starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress.In the post-peak shear stage,large local porosities and volumetric dilation mainly occur in a localized band.The developed triaxial apparatus,in its combined use of X-ray|iCT imaging techniques,is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.

关键词： triaxial apparatus X-ray fiCT In situ test micro-scale mechanical behavior granular soils

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On the installation of an in situ large-scale vertical SEALing (VSEAL) experiment on bentonite pellet-powder mixture

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第9期15卷 2388-2401页

作者： Nadia Mokni Justo Cabrera Frédéric Deleruyelle Institut de Radioprotection et de SûretéNucléaire(IRSN) PSE-ENV/SEDRE/LETISFontenay-aux-Roses92260France

Recently,the Institute for Radiological protection and Nuclear Safety(IRSN)has launched VSEAL(Vertical SEALing)project to investigate the impact of gas migration on the long-term performance of bentonite based vertical sealing systems(VSS).The first VSEAL In situ test was emplaced in IRSN’s Underground Research Laboratory(URL)in Tournemire(France)in 2019 and was equipped with 76 wired and wireless sensors.The test is still in progress,but the collected set of data provides already valuable information of the hydro-mechanical behavior of VSS during hydration.The swelling core consists of a mixture of highdensity pellets and powder of MX80 bentonite in a ratio of 80/20(in dry mass).An innovative method was adopted to drill a 1-m diameter and w10-m deep shaft in order to minimize the rock perturbation at the sidewalls.Because a specific protocol was adopted to install the bentonite mixture together with a careful characterization of the core during construction,VSEAL 1 constitutes the unique in situ sealing test with a well-known initial structural distribution of the pellets and the powder.Some heterogeneities occurred within the experiment during the installation process:a damaged zone developed around the shaft walls due to the interruption of the installation operations caused by COVID19 lockdown in France;a technological gap with a variable thickness between the last pellets layer and the top confining lid and a heterogeneous distribution of the bentonite powder at some layers inducing large inter pellets voids close to the bentonite-rock interface.Artificially injected water volume,relative humidity,water content and swelling pressure in both radial and axial directions were monitored.Comparison of the results showed that the presence of installation-induced heterogeneities led to the generation of preferential flow paths that influenced the swelling pressure evolution at radial and axial directions.

关键词： Bentonite pellet-powder mixture Heterogeneities Technological gap Seals In situ test

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Investigations of Processing Parameters of Thermal Poling Optical Fibers by using of In situ testing System

Investigations of Processing Parameters of Thermal Poling Op...

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Asia-pacific Optical Communications 2004

作者： Zhe Chen Peifan Jiang Institute of Optoelectronic Engineering Jinan University Guangzhou 510632 P.R.China

In order to investigate the effects of processing parameters in thermal poling, an In situ testing system used for thermal poling optical fibers was constructed with an all polarization maintaining fi

关键词： electrooptic effect poled fiber thermal poling In situ test fiber optic interferometer

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In situ tests and a stochastic structural model of rock and soil aggregate in the Three Gorges reservoir area,China

In situ tests and a stochastic structural model of rock and ...

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中国科学院地质与地球物理研究所2004学术年会

作者： X.Li~(a,*),Q.L.Liao~a,J.M.He~b a Institute of Geology and Geophysics,Chinese Academy of Sciences.Beijing 100029,China b China University of Mining and Technology,Beijing 100083,China

The loose quaternary deposit,originated from landslide deposits,weathering residues,slope wash and diluvial deposits etc, prevails in the Three Gorges reservoir area,China.This inhomogeneous geological material comprises mainly rock blocks,clay and sandy clay.To emphasize its fabric,it is termed rock and soil aggregate(RSA).The study of the mechanical behaviour of RSA is of great importance in reinforcement design for rock slopes. In situ direct shear tests on three samples of RSA in the Three Gorges reservoir area were carried out to examine its mechanical behaviour.Based on the geological investigation and statistics,a stochastic structural model of RSA was proposed.The distribution functions of the stochastic variables,including spatial location,size,shape and azimuth ofthe rock blocks inside RSA,are developed by means of the Monte-Carlo method.The mechanical response of the RSA was numerically simulated using FLAC. By comparsion,the numerical results coincided with the test results(Fig.1). It was shown from both In situ tests and numerical modelling that for the RSA with a high rock percentage,initial yielding and strain hardening appeared in its deformation behaviour.The In situ tests of RSA also indicated that the increase of Young’s modulus and ultimate shear strength was not proportional to the rock percentage.It was observed form the samples studied that the fracture patterns of RSA exhibited shear failure with fluctuating fracture planes.These characteristics are predicated by the inherent structure of RSA. The comparison of the numerical modelling with the In situ tests indicates that the numerical procedures based on the stochastic structural model can serve for studying the complex mechanical response of the RSA material,not only in simple stress states,but also under various stress conditions.Moreover,the development and propagation of the failure inside RSA can be examined by this method,which it is difficult to observe,in field tests.

关键词： Rock and soil aggregate In situ test Stochastic structural model Monte-Carlo method Numerical modelling The Three Gorges

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