Evaluations of water retention characteristics of typical iron ore fines (IOF) were presented, which was part of experimental works for the estimation of liquefaction potential of IOF heaps. The water retention tests were conducted in a suction range from 0.1 to 10⁶ kPa on two IOFs and two artificial soils with various testing techniques. It is observed that water retention characteristic curves of one IOF (IOF-B) converge in terms of the relationship between suction (S) and water content (w) regardless densities of specimens when S exceeds a threshold value (S_th). Based on this finding, water retention characteristics are divided into density and materials affected zones. It is also found that IOFs generally have higher water retention ability than the two artificial soils, from which discussion is made on the effect of specific surface area and mineralogy on water retention characteristics of IOF. Finally, water retention characteristics are linked to compaction curves, from which, with the consideration that degree of saturation at peaks of compaction curves is relatively constant, a safety margin of a recently proposed regulation for maritime transportation of IOF is discussed.

A testing procedure was proposed to study water movement in compacted bentonite and the development of swelling pressure (p_s) when compacted bentonite specimens were wetted. In this procedure, a multi-ring mold was introduced for p_s measurements, after which the specimen was sliced for X-ray diffraction to find movement of water in the interlayer space of montmorillonite. Results revealed a relation between four phases of p_s development and evolution of four states of interlayer water molecule arrangement of montmorillonite (L): when p_s reached its first peak in phase I, L moved from 1 row water arrangement (1w) to at least 2w; when p_s decreased and re-increased in phases II or III, L moved from 2w to at least 3w; and when p_s reached a steady state in phase IV, L = 3w. The w distribution in the compacted bentonite was also measured as water absorption time increased. Based on those results, the global water movement was estimated in terms of diffusivity (D) following a method employing Boltzmann transform. Results of comparisons implied that D calculated using this method matched experimental data well and the method was rather easily handled.

Concerning the static liquefaction properties of an industrial cargo, i.e., iron ore fines (IOF), undrained monotonic behaviors of a type of IOF are revealed through conducting triaxial compression tests. It is found that IOF exhibit some similar behaviors as those of common sandy soils, while some very unusual behaviors are also observed. All IOF specimens with compaction degree of 84%–95% and confining pressure of 50–200 kPa exhibit dilative behavior from the beginning of axial loading until the deviator stresses reach their peaks (q_pk). Then the dilative behavior transforms to a contractive behavior, and the contractive behavior continues until reaching the residual stress without observation of phase transformation and quasi steady state. These behaviors are not usually observed for common sandy soils based on extensive previous works. More studies may be necessary as these unusual behaviors imply that flow failure, similar to the undrained monotonic behavior of very loose sand, may be triggered regardless of the density of IOF. In addition, this study also establishes the relationships of IOF between its initial conditions, peak stress conditions, and residual conditions by employing classical knowledges developed for sandy soils.

Properties of the membrane filter recently introduced as an alternative to the ceramic disk are revealed through diffusion and hydraulic conductivity tests. It is shown that diffusion of air through the membrane filter is significantly affected by suction magnitude and that hydraulic conductivity of the membrane filter can easily be affected by the quality of water used in the test. The application of the membrane filter to the soil-water characteristic curve tests (SWCC tests) shows that similar SWCCs can be obtained by employing pressure plate apparatuses with either the ceramic disks or the membrane filter installed, and that repeatability of the SWCC by using the membrane filter pressure plate apparatus is reasonably good. The application of the membrane filter to the undrained cyclic loading test of unsaturated sandy materials shows that the response (the duration to measure the equilibrated pore-water pressure of unsaturated materials) of the membrane filter pedestal in a modified triaxial system may be as short as ~2 s in certain test conditions,andfairlygoodpore-waterpressureandairpressuremeasurementscan be obtained during undrained cyclic loading with a loading frequency of 0.1 Hz.

To evaluate the liquefaction resistance of unsaturated soils by a triaxial system, it is suggested to keep a p-constant condition rather than the rh-constant condition (i.e., cell pressure constant) that is normally applied to the same test for saturated specimen. The main concern is that the pore pressure coefficient (B value) of unsaturated specimens may be far less than unity, which causes undesired effects on the behaviors of unsaturated soils. A modified triaxial system that can maintain the p-constant condition has been recently developed. By using the system, the behaviors of an unsaturated soil subjected to undrained cyclic triaxial loading are compared between the p-constant condition and the rh-constant condition, which implies that the testing conditions affect behaviors of pore pressures generation, stress strain relationship, etc. Results suggest that tests under the rh-constant condition underestimate the liquefaction resistance of soils. In addition, the modified triaxial system could effectively reduce the variation of p by more than 60 % in the full tested range, or by 75 % in a range with relatively small magnitude of the vertical loading based on test results of three sandy soils.

Over the past several years, the International Maritime Organization (IMO) has become increasingly concerned about the liquefaction of unsaturated solid bulk cargo (e.g. iron ore fines) during maritime transportation. This concern has arisen due to several accidents including the capsizing of vessels. In addition, although the resistance against liquefaction of ordinary unsaturated soils is higher than for saturated soils, possible key parameters governing the liquefaction resistance of unsaturated soils (R-L,R- unsat) have not yet been clearly identified. Therefore, in this study, undrained cyclic loading tests of saturated and unsaturated iron ore fines and two sandy soils were conducted using a triaxial apparatus to reveal the liquefaction behavior of iron ore fines and to find the key parameters governing R-L,R- unsat. Through comparisons, it was found that the liquefaction behavior of iron ore fines is similar to that of sandy soils. The degree of saturation and potential volumetric strain, which have been proposed as the governing parameters of R-L,R- unsat, were examined based on experimental data obtained in this study and by other researchers. It was shown that neither of the two parameters correlate with the liquefaction resistance ratio (LRR), a ratio of RL,,,, to the liquefaction resistance of the saturated soils (R-L,R- unsat) with a unique relationship, especially when considering soils with considerable fines content. Following the concept of potential volumetric strain, which considers the compressibility of pore air in the unsaturated soils, volumetric expansion due to the reduction in confining pressure during cyclic loading is further considered, and a new index, the volumetric strain ratio (Rv) is proposed in this study. According to the experimental data obtained in this study, Rv exhibits a much better correlation with LRR than the two former parameters. (C) 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V.

It is common to employ a traditional double cell system, of which an open-ended inner cell is installed in an ordinary triaxial apparatus, to measure the volume change of unsaturated specimens. In such a system, the total apparent volumetric strain of the specimen (epsilon(v)) is deduced from the water level change in the inner cell, monitored by a differential pressure transducer (DPT) considering, meanwhile, the top cap intrusion into the inner cell recorded by a vertical displacement transducer (VDT). Severe apparent volumetric strain, caused by the compliance of the double cell system(epsilon(v,SC)), was observed during the undrained cyclic loading tests in a previous study. Test results on a steel-spring dummy specimen revealed that epsilon(v,SC) was induced not only by such as the meniscus effect, but unexpectedly also by the asynchronous responses between the DPT and the VDT (i.e., the response of the DPT was delayed compared with that of the VDT). By doing some treatment epsilon(v,SC) could be reduced to some extent, whereas the magnitude of epsilon(v,SC) was still too high to be acceptable when the tested specimen approached the liquefied state. To radically solve these technical difficulties, a modified double cell system, named the linkage double cell system, was developed in this study. In this modified system, a linkage rod moving simultaneously with the loading shaft was introduced, through which the DPT could directly measure epsilon(v) without considering the top cap or loading shaft intrusion. Test results for the steel-spring dummy specimen as well as for saturated and unsaturated soil specimens demonstrated that the linkage double cell system has major advantages in measuring accurately the volume change of the specimen during undrained cyclic triaxial loading tests compared with the traditional double cell system.

Accidents and life loss caused serious concern on the liquefaction problem of some solid bulk cargoes such as iron ore fines during transportation at sea. To understand the liquefaction property of a type of iron ore fines, a series of tests, e.g. SEM observation, monotonic loading triaxial test, cyclic loading triaxial test etc. were conducted. Test results show that this unusual material possesses some special properties, for instance, much higher specific gravity Gs (average Gs=4.444) as compared to common materials in geotechnical engineering. SEM observation unveils that the tested iron ore fines has a multi-layer, micro-porous structure which may affect its water retention ability under unsaturated states. The result from the undrained monotonic loading test indicates an angle of internal friction of 45.6° according to the Mohr-Coulomb failure criterion. Interestingly, the peak strength and the residual strength were achieved at values of axial strain of approximately 2.5% and 13%, respectively, regardless of confining pressure among three undrained monotonic loading tests. The undrained response of tested iron ore fines to cyclic loading shows similar characteristics as those of common sands and the liquefaction resistance of this material defined based on the relationship between cyclic stress ratio (CSR) and number of cycle is not significantly affected by change of confining pressure.

A series of undrained cyclic loading tests of three types of saturated and unsaturated soils were conducted on a triaxial apparatus. To overcome the difficulties of this type of test, cell pressure control system to maintain constant p, membrane filter technique to measure pore water pressure and double cell system to measure volumetric strain (epsilon v) were introduced to the apparatus. Test results shown that the cell pressure control system reduced more than 60% variation of p which would be induced by applying vertical cyclic loading. The membrane filter technique could measure negative pore water pressure in a prompt manner and as a result suction of the unsaturated specimens was well monitored under the 0.1 Hz cyclic loading. The time delay problem of electric transducer employed in the epsilon v measurement system, which may bring significant system error, was recognized and the measurement error of epsilon(v) was discussed. Regarding the resistance against liquefaction of the unsaturated soils, the test results shown increase in resistance with reduction in degree of saturation and the p-constant condition was necessary to correctly evaluate the resistance for the unsaturated soils.

This paper presents results from measurement of SWCC (Soil Water Characteristic Curve) of two types of iron ore fines. SWCC tests in both high suction range (103 kPa-10(6) kPa) and low suction range (0.1 kPa-100 kPa) were conducted. In low suction range, pressure plate apparatuses were employed, on which either a high air entry ceramic disk or a membrane filter was installed. In high suction range, the vapor equilibrium technique and the method of electric conductivity were applied. As a reference, SWCC tests on natural material mixtures simulating gradations of iron ore fines were also carried out. Comparisons were made between SWCCs obtained by using the ceramic disc and the membrane filter as well as SWCCs of the iron ore fine and its reference sand. In addition, effects of gradation and density of tested materials on the SWCC were discussed.

Abstract

In geological disposal for high-level radioactive waste, bentonites are planned to be used as the buffer material surrounding radioactive waste in Japan. Bentonite-based buffer material requires low water permeation for delaying contact between groundwater and the waste. Because of the extremely long half-lives of radionuclides of the waste, several barriers including the buffer material are designed to maintain workability of the geological disposal facility for tens of thousands of years. However, in the disposal circumstances with high water pressure, high temperature and various groundwater chemistries, occurrence of cementation and consequently property changes of the bentonite in the buffer are concerned. Few studies are available to understand the effect of cementation on bentonite properties because of the difficulties of simulating long-term alteration process experimentally. From the viewpoint of natural analogues, cementation process of the buffer may be regarded as part of formation process of bentonite ore. Thus, in this study, permeability tests were conducted on three kinds of Na-type bentonite ores with different geological ages from respectively, Japan, USA, and China to see the influence of cementation on permeability of bentonites. For comparison, undisturbed and reconstituted specimens were prepared. The results show that difference of hydraulic conductivities of the undisturbed and reconstituted specimens for each ore is less than one order, and this difference seems not to correlate with the geological age of the ores. From these results, the influence of cementation on the hydraulic properties of bentonite buffer seems small. It may also be a counteracted result by cementation effects in terms of restriction of the swelling of montmorillonite and blockage of water flow paths.

<p>This paper describes development of a triaxial permeameter apparatus for measuring coefficient of permeability of unsaturated soils by directly measuring the head difference between two points in a specimen using local pin-type sensors. The local pin-type sensors are made of stainless steel wrapped with membrane filter to measure suction. The apparatus includes the measurement of inflow rate by Mariotte's bottle and a weighing scale, while outflow rate is measured by burettes and a differential pressure transducer (DPT). Typical results show that the steady state flow condition can be achieved by using membrane filters to allow passage of water but prevent flow of free air. At steady state flow condition and reasonably stable measured head by the local pin-type sensors, permeability values were obtained by simple average.</p>