Predrag Miščević

Testing shear strength of soft rock at different stages of laboratory simulated weathering

U radu je opisano određivanje promjene cvrstoce temeljeno na simuliranju procesa rastrosbe u laboratorijskim uvjetima, koristeci uzorke lapora iz flisne formacije s podrucja Dalmacije. Na temelju provedenih ispitivanja zakljuceno je da je predloženi postupak simuliranja rastrosbe u laboratoriju provediv unutar prihvatljivih vremenskih okvira. Zbog uocene promjene parametara posmicne cvrstoce na vrijednosti koje odgovaraju cvrstoci materijala koji se opisuje kao tlo, ponekad je potrebno, zbog raspona velicine opterecenja koje se nanosi u pojedinom tipu uređaja, koristiti i uređaje za tlo.U radu je opisano određivanje promjene čvrstoće temeljeno na simuliranju procesa rastrošbe u laboratorijskim uvjetima, koristeći uzorke lapora iz flišne formacije s područja Dalmacije. Na temelju provedenih ispitivanja zaključeno je da je predloženi postupak simuliranja rastrošbe u laboratoriju provediv unutar prihvatljivih vremenskih okvira. Zbog uočene promjene parametara posmične čvrstoće na vrijednosti koje odgovaraju čvrstoći materijala koji se opisuje kao tlo, ponekad je potrebno, zbog raspona veličine opterećenja koje se nanosi u pojedinom tipu uređaja, koristiti i uređaje za tlo.

Estimation of embankment settlement caused by deterioration of soft rock grains

Embankments made from crushed soft rock grains can be susceptible to additional settlement caused by a deterioration of the grains inside the embankment. This additional settlement is not caused by the change of the stress state inside the embankment and cannot be predicted by standard calculating methods using the embankment modulus of deformability measured after compaction of the embankment. The deterioration of the grains is mainly caused by the weathering process, which, in soft rocks such as marl, is mainly induced by the wetting and drying processes. If marl grains in an embankment are subjected to the wetting and drying process, the result is breakage of the grains, as well as decomposition into soil material. Disintegrated material then fills the macro-pores of the embankment grain structure and gradually causes additional settlement. This process in soft rock material lasts from a few months to a few years. We propose a calculation procedure to estimate the possible value of the additional settlement, based on measured settlements gained from examples of laboratory-weathered samples. The samples were made of crushed marl in laboratory conditions. A test was conducted with a modified oedometer apparatus. In the proposed model, the deformation is calculated based on possible volume changes due to the deterioration of the grains and transport of the detached material into the macro-pores; this is done with the intention of estimating the settlement without measuring the deformation modulus change caused by the weathering.

DISCRETE LATTICE ELEMENT APPROACH FOR ROCK FAILURE MODELING

This paper presents the ‘discrete lattice model’, or, simply, the ‘lattice model’, developed for rock failure modeling. The main difficulties in numerical modeling, namely, those related to complex crack initiations and multiple crack propagations, their coalescence under the influence of natural disorder, and heterogeneities, are overcome using the approach presented in this paper. The lattice model is constructed as an assembly of Timoshenko beams, representing the cohesive links between the grains of the material, which are described by Voronoi polygons. The kinematics of the Timoshenko beams are enhanced by the embedded strong discontinuities in their axial and transversal directions so as to provide failure modes I, II, and III. The model presented is suitable for meso-scale rock simulations. The representative numerical simulations, in both 2D and 3D settings, are provided in order to illustrate the model’s capabilities.

Mjerenje posmične čvrstoće meke stijene u uvjetima laboratorijski simulirane rastrošbe

U radu je opisano određivanje promjene cvrstoce temeljeno na simuliranju procesa rastrosbe u laboratorijskim uvjetima, koristeci uzorke lapora iz flisne formacije s podrucja Dalmacije. Na temelju provedenih ispitivanja zakljuceno je da je predloženi postupak simuliranja rastrosbe u laboratoriju provediv unutar prihvatljivih vremenskih okvira. Zbog uocene promjene parametara posmicne cvrstoce na vrijednosti koje odgovaraju cvrstoci materijala koji se opisuje kao tlo, ponekad je potrebno, zbog raspona velicine opterecenja koje se nanosi u pojedinom tipu uređaja, koristiti i uređaje za tlo.U radu je opisano određivanje promjene čvrstoće temeljeno na simuliranju procesa rastrošbe u laboratorijskim uvjetima, koristeći uzorke lapora iz flišne formacije s područja Dalmacije. Na temelju provedenih ispitivanja zaključeno je da je predloženi postupak simuliranja rastrošbe u laboratoriju provediv unutar prihvatljivih vremenskih okvira. Zbog uočene promjene parametara posmične čvrstoće na vrijednosti koje odgovaraju čvrstoći materijala koji se opisuje kao tlo, ponekad je potrebno, zbog raspona veličine opterećenja koje se nanosi u pojedinom tipu uređaja, koristiti i uređaje za tlo.

Direct method for determination of shallow foundation settlements

Prikazan je direktan postupak za određivanje slijeganja plitkih temelja, koji kombinira modificiranu hiperbolnu funkciju za nelinearan odnos naprezanja i deformacija te korelacije iz rezultata penetracijskih pokusa. U korelacijama se koristi opterećenje za 10%, odnosno 1% omjera slijeganja i ekvivalentnog promjera temelja. Za ovaj novi postupak nisu potrebni laboratorijski pokusi, što je velika prednost za krupnozrna tla. Pokazuje se za ovako izračunane krivulje slijeganja u ovisnosti o opterećenju da je vrlo dobro poklapanje, s izmjerenim slijeganjima tijekom probnih opterećenja pet kvadratnih temelja različitih dimenzija na pijesku.A direct procedure for determining settlement of shallow foundations, combining the modified hyperbolic function for nonlinear stress and strain ratio with correlations from penetration test results, is presented in the paper. The 10% load, i.e. 1% of settlement to equivalent foundations diameter ratio, is used in correlations. Laboratory tests are not needed in this novel procedure, which is a considerable advantage for coarse-grained soils. A very good correspondence was established between the load-based settlement curve calculated in this way, and the settlements measured in sand during load testing of five square foundations of variable size.

Direktan postupak za određivanje slijeganja plitkih temelja

Prikazan je direktan postupak za određivanje slijeganja plitkih temelja, koji kombinira modificiranu hiperbolnu funkciju za nelinearan odnos naprezanja i deformacija te korelacije iz rezultata penetracijskih pokusa. U korelacijama se koristi opterećenje za 10%, odnosno 1% omjera slijeganja i ekvivalentnog promjera temelja. Za ovaj novi postupak nisu potrebni laboratorijski pokusi, što je velika prednost za krupnozrna tla. Pokazuje se za ovako izračunane krivulje slijeganja u ovisnosti o opterećenju da je vrlo dobro poklapanje, s izmjerenim slijeganjima tijekom probnih opterećenja pet kvadratnih temelja različitih dimenzija na pijesku.A direct procedure for determining settlement of shallow foundations, combining the modified hyperbolic function for nonlinear stress and strain ratio with correlations from penetration test results, is presented in the paper. The 10% load, i.e. 1% of settlement to equivalent foundations diameter ratio, is used in correlations. Laboratory tests are not needed in this novel procedure, which is a considerable advantage for coarse-grained soils. A very good correspondence was established between the load-based settlement curve calculated in this way, and the settlements measured in sand during load testing of five square foundations of variable size.

Modelling of Internal Fluid Flow in Cracks with Embedded Strong Discontinuities

This chapter presents a discrete approach for modelling failure of heterogeneous rock material with discrete crack propagation and internal fluid flow through the saturated porous medium, where the coupling conditions between the solid and fluid phase obey the Biot’s porous media theory. Discrete cracks and localized failure mechanisms are provided through the concept of embedded discontinuity FEM. Furthermore, the basis for presented discrete 2D plane strain model representation of heterogeneous material consisting of material grains, is an assembly of Voronoi cells that are kept together by cohesive links in terms of Timoshenko beams. Embedded discontinuities are built in cohesive links thus providing the discontinuity propagation between the rock grains in mode I and mode II. The model can also take into account the fracture process zone with pre-existing microcracks coalescence prior to the localized failure. Several numerical simulations are given to illustrate presented discrete approach.