SVIBOR - Project code: 2-11-420


Strossmayerov trg 4, HR - 10000 ZAGREB
tel.: +385 1 459 44 44, fax: +385 1 459 44 69


SVIBOR - Collecting Data on Projects in Croatia

Project code: 2-11-420


Main researcher: VRKLJAN, IVAN (93393)

Type of research: applied
Duration from: 06/30/92. to 12/31/95.

Papers on project (total): 7
Institution name: Institut građevinarstva Hrvatske, Zagreb (110)
Address: Janka Rakuše 1,p.p.283
City: 10000 - Zagreb, Croatia
Phone: 385 (0)1 6136-444
Fax: 385 (0)1 534-737

Summary: Abstract: The mechanical behavior of swelling materials may be strongly influenced by the physicochemical interaction between the pore fluid and mineral phase. The behavior of swelling clay minerals can not be discussed without the thorough understanding of physicochemical forces acting among the mineral phase particles. The action of including physicochemical effects significantly complicates attempts to define behavior of swelling materials. In case of swelling clay minerals, two basic principles of the traditional soil mechanics, i.e. the concept of effective stresses and Darcy's law, are called into question. The influence of some chemical-load variables on the swelling, compressibility and strength is analyzed through laboratory testing of the bentonite clay "Gornja Jelenska". The swelling of rocks is a serious problem during realization and subsequent use of structures built either in or on swelling-rock formations. A significant amount of stress due to rock swelling must be added to the stress notation known in traditional geotechnical practice. A survey of numerous procedures used for analyzing stress around underground structures is presented. Practical results obtained through application of some of these procedures are evaluated.

Keywords: Key words: swelling, rock, clay, bentonite, physicochemical, montmorillonite, osmosis, effective stress, hydraulic conductivity, underground structures.

Research goals: OBJECTIVES AND RESULTS The research objectives are: (a) contribute to all efforts aimed at fully defining very complex rock and soil swelling mechanisms; (b) critically analyze the existing procedures for modeling behavior of swelling rocks surrounding underground structures. The swelling is an atypical geotechnical problem requiring an interdisciplinary approach. The swelling phenomenon may be defined as a time-dependent increase in volume caused by physicochemical interaction between the solid (mineral) phase and the pore fluid. Swelling materials are usually tested in two stages: (a) swelling potential testing; (b) swelling amount testing. The swelling potential describes the relative capacity of a material to swell under particular conditions, while the swelling amount shows the level to which the swelling potential will rise. Various procedures are used in practice for defining the swelling amount and potential. All of them are burdened by several basic problems: (a) the problem of preparing undisturbed samples, due to extremely high sensitivity of these rocks to the change in humidity; (b) mechanical behavior of swelling materials does not depend only on mechanical, but also on chemical influences and temperature. In this way, the number of variables in the behavior pattern increases considerably. Taking into account the influence of physicochemical forces on the behavior of swelling clay minerals, the acceptability of two basic soil mechanics principles (the effective stress concept and Darcy's law) may be questioned; (c) the swelling process lasts a long time due to the very low permeability. The influence of various elements of external load (environmental loading) on the mechanical behavior will be analyzed through various types of laboratory testing on natural swelling clays (bentonite clays from Gornja Jelenska). In order to accomplish this task, it will be necessary to adapt the existing laboratory equipment to new requirements and to fabricate equipment presently unavailable in the laboratory. According to current plans, the following equipment will be fabricated: equipment for measuring the axial swelling stress as related to the axial swelling strain, the equipment for measuring the swelling pressure and the equipment for free-swelling testing. The following results are expected: (a) A survey of information on various swelling-rock mechanisms. A comprehensive overview of laboratory procedures most commonly used for testing swelling amount and potential of rocks and soil; (b) Recommendations for treating undisturbed bentonite-clay samples during their preparation for laboratory testing; (c) Defining mechanical behavior of treated bentonite clays. The untreated clay with original variable cations (Ca-bentonites), as well as the treated clay in which Ca-cations are replaced by Na-cations, will be tested. The process of testing these clays under various environmental loading conditions will facilitate evaluating the contribution of physicochemical forces to basic geotechnical properties (swelling, compressibility, strength); (d) Critical analysis of the existing procedures for modeling behavior of swelling rocks around underground structures.

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Last update: 11/20/95