M J Lipinski

Saturation criteria for heavy overconsolidated cohesive soils

Saturation criteria for heavy overconsolidated cohesive soils The paper concerns significance of properly carried out saturation procedure and its role in evaluation of undrained response of heavy preconsolidated cohesive soils. In particular the saturation criteria are addressed which should be fulfilled during saturation of preconsolidated clay specimens of various plasticity. Influence of incomplete saturation on shear strength parameters is briefly characterized. On the basis of experimental data the back pressure method is shown to be the most efficient method in obtaining full saturation in overconsolidated clay of various plasticity. Analysis of the test results made possible to propose full saturation criteria for low, medium and high plasticity clays which are based on reduced value of Skemptons B parameter. Kryteria pełnego nasycenia dla gruntów spoistych silnie prekonsolidowanych Jednym z najczęściej popełnianych błędów w laboratoryjnych badaniach właściwości mechanicznych gruntu jest niekontrolowany stan nasączenia gruntów. Artykuł dotyczy kryteriów, jakie powinny być spełnione podczas nasączania próbek różnych gruntów w badaniach trójosiowych. W pracy scharakteryzowano wpływ niepełnego wypełnienia porów gruntu wodą na błędy uzyskiwane w wynikach badań. Przedstawiono metodę ciśnienia wyrównawczego jako najbardziej skuteczny sposób doprowadzenia do pełnego nasycenia gruntu. Zaprezentowano wyniki badań dla prekonsolidowanych gruntów spoistych o różnej spoistości, tj. glin piaszczystych, glin i iłów. Analiza tych wyników pozwoliła na określenie minimalnych wartości parametru Skemptona B dla tych gruntów jakie powinny być spełnione dla otrzymania prawidłowej (niezafałszowanej) reakcji gruntu podczas ścinania w warunkach bez odpływu.

Laboratory assessment of permeability of a groundwater protective barrier

Laboratory assessment of permeability of a groundwater protective barrier The paper presents results of laboratory assessment of permeability of cement-bentonite self hardening mixtures which have recently been the most often used for construction of cut-off walls mitigating hazard of sanitary landfills. Laboratory tests were carried out on reconstituted and natural (undisturbed) material of the barrier. Due to the fact that actual permeability characteristics of reconstituted material are time and density dependent, changes of permeability are described against those variables. Comparison of these data with test results obtained for undisturbed material help to understand the process of changing properties of the barrier in the environment. Ocena przepuszczalności przesłon przeciwfiltracyjnych w świetle badań laboratoryjnych W artykule przedstawiono wyniki badań laboratoryjnych, na podstawie których dokonano analizy i oceny przepuszczalności samotwardniejącej mieszaniny cementowo-bentonitowej. W ostatnim czasie, tego rodzaju materiał jest często wykorzystywany m.in. do konstrukcji przesłon przeciwfiltracyjnych zmniejszających zagrożenie pochodzące ze składowisk odpadów. Badania przeprowadzono na próbkach rekonstruowanych bezpośrednio w aparacie trójosiowym, a także na materiale o nienaruszonej strukturze pobranym z przesłony wykonanej w terenie. Przepuszczalność materiału rekonstruowanego określono w relacji do gęstości materiału i czasu jego tężenia od chwili przygotowania. Porównanie tych rezultatów z wynikami badań uzyskanymi na próbkach o nienaruszonej strukturze jest podstawą zrozumienia procesów zmiany właściwości filtracyjnych bariery przeciwfiltracyjnej w trakcie jej eksploatacji.

Capability and limitations in laboratory determination of stiffness parameters of soils

Abstract The paper concerns laboratory methods for determination of soil stiffness. Major criterion for selection of analysed equipment is range of strain in which stiffness can be reliably determined. Substantially, various configurations of triaxial apparatus are referred to i.e. with standard cell and with the modified one. Additional system for internal measurement of strain is described and rational (based on test results) for use of it is presented. As to shear wave velocity measurement as a mean to obtain initial stiffness, requirements for proper measurement and interpretation was given. Finally, an approach to determine Poisson’s ratio on the basis of combined results of cyclic triaxial and resonant column tests was presented.

A strain dependent stiffness of stiff cohesionless and cohesive soils

Abstract In the last three decades an interest has grown in prediction of soil stiffness. In case of dense cohesionless soils or natural overconsolidated cohesive soils the working strain to which soil stiffness is referred to covers the range 0.01-1.0%. On the basis of results of comprehensive experimental worked based on advanced triaxial tests results two formulae for Young’s modulus distribution accounting for strain range were derived for fine dense sand and heavy overconsolidated sandy clay. The formula for sand accounts also for stress level. In case of overconsolidated sandy clay, stress history, in the form of yield stress, is also accounted for.

Influence of Fines Content on Consolidation and Compressibility Characteristics of Granular Materials

Various behaviour of soil under loading results to large extent from kind of soil considered. There is a lot of literature concerning pure sand or plastic clays, while little is known about materials, which are from classification point of view, between those soils. These materials can be considered as cohesionless soils with various fines content. The paper present results of tests carried out in large consolidometer on three kinds of soil, containing 10, 36 and 97% of fines content. Consolidation, permeability and compressibility characteristics were determined. Analysis of the test results allowed to formulate conclusion concerning change in soil behaviour resulting from fines content.

Shear Wave Velocity for Evaluation of State of Cohesionless Soils with Fines

The paper concerns evaluation of cohesionless soils containing fines. In clean sands, state of soil is usually quantified by relative density DR with use of field techniques like static or dynamic probes. However, in cohesionless soils containing considerable amount of fines, relative density alone, which is based solely on void ratio values, is not representative. This results from the fact that in case of cohesionless soil there is no unique intrinsic compressibility line, like it is in case of cohesive soils. Thus state of soil depends not only on void ratio but also state of stress. For this reason it is necessary to look for an alternative means to quantify state of soils with fines. The paper concerns possibility of evaluation of state of soil containing various amount of fines on the basis of shear wave velocity measurement. The idea rests on the fact that void ratio and state of stress are the major factors which contribute to a state of soil and shear wave velocity as well. When measured shear wave velocities are normalised with respect to stresses the resulting values might be strictly correlated to void ratio. To validate this approach, an experimental test programme (based on series of sophisticated triaxial tests) was carried out on four kinds of sandy material containing various amount of fines up to 60%. The experimental data made possible to establish basic correlation between soil states and shear wave velocity for each kind of soil. Normalized shear wave velocity was compared with void ratio and state parameter as well. The obtained results revealed that determination of void ratio on the basis of shear wave velocity in a certain range of fines can be much more adequate than for clean sands. However, if the fines content exceeds certain value, the obtained correlation is no longer as good.