Influence of test quantity on loose sand shearing strength parameters

Investigation of the shear strength properties of Klaipėda sand by simple shear test is presented. The characteristic values of the angle of internal friction φk and the cohesion ck are obtained via the least squares method and various factors of influence are elucidated. The investigation reveals the test quantity to have a significant influence on the characteristic shear strength parameters for loose sand. The processed characteristic magnitude of the angle of internal friction varies within 16.140 (3 tests) and 27.020 (36 tests) bounds, that of the characteristic cohesion varies within -74.18 kPa (3 tests) and 1.12 kPa (36 tests) bounds. The above mentioned shear strength properties confirm the linear Mohr-Coulomb strength criterion obtained via processing the test data. The same scatter of characteristic shear strength parameters variation is obtained when the peak shear stress are recorded for horizontal displacement magnitude of 5 mm. In this case the obtained characteristic angle of the internal friction varies within the bounds of 17.380 (3 tests) and 26.79 0 (36 tests), and that of characteristic cohesion within various within -68.82 kPa (3 tests) and 1.18 kPa (36 tests) bounds. The authors recommend performing at least 18 experimental tests in order to avoid high influence on statistical coefficient of confidence level tα and on the number of degrees of freedom k

Experimental study on bearing resistance of short displacement pile groups in dense sands

The prediction of the behavior of structures interacting with soil is one of the main challenges in structural design. Accurate evaluation of soil–structure interaction ensures a rational design solution for the superstructure and foundation of a building. In structural analysis, one of the key problems is the identification of relevant movements of the foundation considering the interaction between the superstructure, foundation and ground (the soil mass around the foundation). The correct assessment of soil–structure interaction contributes to the rational constructional design of the superstructure and foundation and allows avoiding violations of requirements for ultimate and serviceability limit states possible due to unpredicted additional stress on the structural system. Resistance predictions for pile group foundations is a complex problem, which may be the reason for scattered and insufficient information available despite numerous experimental and numerical studies, predominated by the focus on partial empirical relationships. This experimental study analyzed the prototype of a short displacement pile group with a flexible pile cap in terms of the bearing capacity and deformation behavior while subjected to static axial vertical load. In particular, attention was given to the resistance–stiffness evolution of single piles acting in a pile group with different spacing. Test results of short displacement pile groups were used to verify known models for the bearing resistance prediction of the pile group

Global sensitivity analysis for transformation of Hoek-Brown failure criterion for rock mass

A variety of engineering activities require reliable evaluation of rock strength. For instance, the stability of rock slopes depends on structural geology of rock massif in which the slope is excavated. Hoek-Brown (HB) failure criterion applied in rock design practice introduces factors based on the properties of jointed rock. The non-linear finite element safety calculation is conveniently used for calculation safety the factor of slope stability. The Mohr-Coulomb (MC) failure (strength) criterion for soil is widely applied in geotechnical design. Therefore, the appropriate transformation from HB to the equivalent MC, employing angle of shearing resistance φ and cohesion c, is necessary. This article studies the effect of jointed rock massif properties on the transformed MC parameters by using Sobol’s global sensitivity analysis (SSA) and HB transformation equations. Statistical parameters needed for the evaluation of sensitivity analysis are processed using classical statistical methods upon the emulation of Latin Hypercube Sampling simulation methods. Developed and adapted by authors techniques are illustrated by processing real rock investigation data from survey of the trachyte massif located in the Czech Republic. The first and higher order effects of random inputs are identified using SSA. It is illustrated that the effects of inputs on the MC parameters varies significantly depending on the discontinuity distribution and height of the slope

Determining characteristic sand shear parameters of strength via a direct shear test

The article considers the peculiarities of determining quartz sand shear strength according to the Mohr-Coulomb strength criterion, via a direct shear test and that of factors influencing the characteristic angle of internal friction and cohesion values of the obtained strength parameters. The air-dry sand of the Baltic Sea region from Lithuanian coastal area near Klaipėda city has been analyzed. The solid density of the investigated sand grains was ρs = 2.65 g/cm3. The initial density of the tested samples made ~1.48–1.50 g/cm3. Processing data on the shear test yielded that the quantity of 18 tests was sufficient for the relevant accuracy of determining characteristic sand shear parameters of strength. This quantity of tests allow avoiding the influence of statistical coefficient tα that depends on a degree of freedom (K = n – 2). The paper presents additionally analyzed three different approaches to determining the characteristic shear parameters of strength and that of a comparative analysis of the applied approaches

Comparison study of spherical and multi-spherical particles under cyclic uniaxial compression

Numerical simulation of cyclic compression of granular material by performing oedometric test has been performed. Discrete Element Method (DEM) has been employed for simulation. A comparison study has aimed to examine the differences in macroscopic behaviour of material discretized by spherical (S) and non-spherical shape models of a particle. During the study, microscopic data of sand from Klaipėda were used for modelling the shape of particles. The nonspherical particles were described by multi-spherical (MS) models retaining distributions for size and aspect ratios. Two DE models of tested specimens were developed and the deformation behaviour under cyclic uniaxial compression was simulated numerically by applying the commercial EDEM code. The variation of the oedometric elasticity modulus was investigated and influence of particle shape on void ratio changes was demonstrated. It was clearly shown that application of S particles is much more sensitive to rearrangement of particles during densification DEM. Simulations illustrated that the elasticity modulus of material corresponding to MS particles is approximately 1.9 times larger comparing with material corresponding to S particles. Therefore, one must improve the magnitude of elasticity modulus by introducing a respective correction factor

Experimental and numerical investigation of sand compression peculiarities

Investigation of the compression properties of Klaipėda sand by oedometric testing and numerical modeling is presented. Klaipėda sand is characteristic of the Baltic seashore region sand. Experimental investigation was performed with fraction corresponding to diameter variation bounds of 0.6 and 0.425 mm. Compression test was realized with initial maximal void ratio (e 0 = 0.800) of sand. Employed vertical stress ramp value is 800.0 kPa/min, maximum loading σmax = 400.0 kPa. Applying loading within the range of 50.0 to 120.0, two vertical stress jumps have been identified. A rubber sample compression test has been performed aiming to deny an assumption, that vertical stress jumps are influenced by device construction. Experiment viewed that not any vertical stress jumps have been recognized. Numerical simulation yielded exactly the same two vertical stress jumps found by compression with oedometer. It proves that the nature of rearrangement of sand grains has been properly reflected by modeling compaction process by DEM. Sand compaction velocity is higher versus applied vertical stress ramp. This is the reason for appearing of the vertical stress jumps. Numerical simulation viewed that location of the largest compression in oedometer is at the top of the sample

Study of bearing capacity of vibratory pile applying acceleration record

The article focuses on the method for evaluation of ultimate bearing capacity for a vibratory pile having acceleration data recorded during the tests. The simulation vibratory pile installation test was performed in the testing stand. Accelerations were recorded on the top of the simulation vibratory pile during the test. The static test was performed for the installed pile. After the review of rheological models of the base, the Smith rheological model was chosen for determination of bearing capacity of the vibratory pile as this model, the rigidity of the final element of the spring is modelled as the finite rigidity of the base. Between the base of the modelled pile and the soil, a finite interface element is used. The interface element transfers only compression but it does not transfer tension to the base rheological model. The general stiffness of spring's finite element in the chosen rheological model is determined from experimental data of the static pile test. During the modelling, the damping coefficients and the ultimate displacements (responses) of the pile's shaft and base, to which the friction element became active, were determined so that the modelled pile accelerations and displacement (response) would coincide as much as possible with measured accelerations and their calculated response. The modelled and measured accelerations and responses showed high similarity

On reliability-based optimization in rigid-plastic frame design/Apie tikimybinę optimizaciją standžiųjų-plastinių rėmų skaičiavime

Straipsnyje nagrinėjamas duoto patikimumo diskretinės rėminės konstrukcijos projektavimo uždavinys. Konstrukcijos geometriniai parametrai, apkrovų pridėjimo, pavojingų pjūvių vietos yra apibrėžiamos fiksuotai (determinuotai). Išorinės apkrovos ir konstrukcijos medžiaga—stochastinės. Nagrinėjamas vienintelis galimas konstrukcijos suirimo tipas—plastinio suirimo mechanizmo susidarymas. Išorinės apkrovos apibūdinamos kaip kvazistatinės, nesukeliančios dinaminių efektų. Konstrukcijos įtempimų būvis charakterizuojamas lenkimo momentų vektoriumi M, i.e. neįvertinant šlyties ir sukimo efektų. Taigi konstrukcijos laikomoji galia apibūdinama ribinių lenkimo momentų vektoriumi M o , kurio komponentai priklauso nuo skerspjūvio charakteristikų ir medžiagos takumo ribos. Konstrukcijos plastinio suirimo mechanizmas apibūdinamas deformacijų (deviacijų) Θ ir poslinkių [udot] greičių vektoriais. Optimizacijos uždavinys (1)-(2) gali būti formuluojamas naudojantis kinematiniu ir statiniu principais. Naudojant kinematinį principą ribinį būvį aprašančios lygtys (4) išreiškiamos per deformacijų ir greičių vektorius. Atskirų plastinių suirimo mechanizmų tikimybės (5) yra nustatomos naudojant patikimumo indeksus β i . Šių mechanizmų identifikavimui sprendžiamas uždavinys (6)-(8). Šį uždavinj galima spręsti formuluojant jį kaip neiškiliojo matematinio programavimo uždavinį (9)-(10)—(7)-(8). Sprendinio lokalinius minimumus atitinka galimi suirimo mechanizmai, atitinkantys patikimumo indeksus β i . Nustaičus visus suirimo mechanizmus, atitinkančius reikiamą patikimumo lygį (3), sprendžiamas optimizacijos uždavinys (11)-(14). Sprendimo eiga: fiksuojant vektorių [Mbar] o sprendžiamas uždavinys (9)-(10)—(7)-(8), randami pagrindiniai plastiniai suirimo mechanizmai; po to sprendžiamas uždavinys (12)-(14). Šis iteracinis procesas kartojamas tol, kol pasiekiamas reikiamas konvergavimo tikslumas. Naudojant statinį principą, ribinį būvį apibūdina statinio leistinumo sąlygos. Pagal A.Čyro pasiūlytą sprendimo būdą optimizacijos uždavinys formuluojamas kaip matematinio programavimo uždavinys (16)-(21). Taip formuluojant uždavinį galima įvertinti ir kintamo plastiškumo sąlygotus suirimo būdus. Sprendžiant šį stochastinį uždavinį jis pakeičiamas determinuotu matematinio programavimo uždaviniu. Toks sprendimo būdas yra labiau taikytinas praktiniams projektavimo uždaviniams spręsti. First Published Online: 26 Jul 201

Determination of Rational Parameters for the Advanced Structure of a Pedestrian Suspension Steel Bridge

. High strength cables and steel plates or prestressed rc members (also named as stress-ribbons) usually serve the main load carrying elements of up-to-date pedestrian bridge structures. An application of these elements is prescribed actually by large magnitude of permanent load. However, a realisation of such structures requires many material resources. This investigation presents an advanced structure type for pedestrian suspension bridge created from hot-rolled cable or welded members of finite flexural stiffness. Development of displacements in such structure subjected by symmetric and asymmetric loadings is analysed. A method of stabilising displacements via flexural stiffness variation and its efficiency is considered. Displacement variation and strength of advanced load carrying structure of structure are investigated, the developed analytical expressions for determining inner forces and displacements are presented. An analysis of rational parameters for advanced structure of pedestrian suspension bridge yields expressions for determining the necessary flexural stiff- ness, cross-sectional height and area of load carrying structural elements. A rational primary shape of structure versus ratio of permanent and variable loadings is analysed. A technical-economic efficiency is illustrated via numerical simulation of rational parameters for advanced structure of pedestrian bridge