Durability Characterization of Marls from the Region of Dalmatia, Croatia

Abstract

Durability is one of the most important engineering properties of weak and clay-bearing rocks. Weathering can induce a rapid change in rock material from initial properties to soil-like properties. The sensitivity of a rock type against weatherability is usually described by a durability parameter, such as the slake durability index. However, marl resistance is not detected satisfactorily by the durability indices by using slake durability test as suggested by ISRM for two wetting-drying cycles. The results of this study are obtained from samples of compact or laminated eocene marls from region of Dalmatia, Croatia. The samples were subjected to 4 cycles of slake durability, point load tests, determination of dry density, determination of carbonate content and absorption of water. The scatter of data suggests that strength probably has no influence on the durability of marls. On the other hand a separate group of marl samples have a second-cycle slake durability index higher than approximately 85%, and the durability of these samples is classified as ''medium-high'' to ''high'', although the visual inspection of samples after testing, suggests that they should have ''medium'' to ''low'' durability classification. According to obtained results these samples of marl fulfil the criterions for the durability classification: a carbonate content lower than approximately 65%, a dry density lower than 2.4 Mg/m 3 , and values of water absorption higher than 5%.

Application of geological strength index for characterization of weathering-induced failures

“…Several authors [33][34][35][36][37][38] suggest that more than two standardized wetting and drying cycles, usually between three and five cycles, can be performed for rocks of higher durability. Bryson et al [39] introduced LSI (Loss Slake Index) to account for the influence of different duration of weathering cycles on the durability of shales after only one wetting and drying cycle.…”

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

“…Marl, which in addition to clay and calcite contains 10-30 % of silt detritus is called silty marl and if it also contains fine sand it is called sandy-silty marl [26]. Marl used in this study has been sampled from the same locations as in previous studies [28]. An average mineral content of the analysed marl samples is: calcite 40-77 %, dolomite 0-7 %, quartz 3-11 %, plagioclase 1-9 %, chlorite 0-9 %, smectite 6-20 %, vermiculite 0-6 % and micaceous minerals 3-12 %.…”

“…It can be observed that smaller index values generally indicate softerless durable rock, while higher index values indicate hardermore durable rock. However, current research questions whether this proposed classification is suitable for all types of soft rocks, and whether there is a need for changes or additional criteria [28,29]. One way to deal with this problem is to increase the number of cycles to four or more, taking one or more values of durability index as relevant.…”

“…First set was tested in laboratory conditions with moisture preserved and without simulated weathering, whereas the number of wetting and drying cycles was increased for each subsequent series. Two, four, eight, or more cycles were used for samples that can be classified as Type I [28]. One, two and three cycles have proven to be sufficient for Type II.…”

Weathering Influence on Properties of Siltstones from Istria, Croatia

“…This test is recommended by both the International Society for Rock Mechanics [15] and the American Society for Testing and Materials [16]. However, the use of the denominated slake durability index in the second cycle (I d2 ) to quantify a rock's susceptibility to slaking is not satisfactory for characterizing weak rocks [8,11,12,17]. Because the observed weathering of rocks during testing is much greater than what is predicted by the slake durability test, new classifications of weak rocks have been proposed by several authors.…”