The control of composition, texture and weathering on the physical and strength properties of selected intrusive igneous rocks from North Pakistan

This work characterizes intrusive igneous rocks from north Pakistan in terms of their mineralogy, texture and weathering grades and their effect on the physical and strength properties. The mafic and intermediate rocks showed a low cumulative percentage of quartz, feldspar and plagioclase with high specific gravity, strength (i.e. UCS and R-value) and UPV values compared to the felsic rocks. Likewise, samples with anhedral grain shape, irregular boundaries, fine to medium grain size (UD, ANS, CGN) showed higher strength values, that is, 121, 118 and 91 MPa compressive strength and 11, 9, and 12 MPa tensile strengths, respectively. The weathering grades assigned to the investigated samples, such as fresh (WG-I), slightly weathered (WG-II) and highly weathered (WG-III) corresponded well with the physical and strength properties, that is, as the grade increased from WG-I to WG-III, the porosity and water absorption increased (0.28% and 0.72% respectively), whereas the specific gravity, compressive strength and tensile strength decreased (2.04, 20 MPa and 2.5 MPa, respectively, for CGA). The presence of quartz affects rock strength; however, no significant correlation was observed for strength and maximum and mean grain sizes of different minerals.

Experimental Investigation into the Influences of Weathering on the Mechanical Properties of Sedimentary Rocks

The time-dependent behaviors of the sedimentary rocks which refer to the altering of the mechanical and deformable properties of rock elements in the long-term period are of increasing importance in the investigation of the failure mechanism of the rock strata in underground coal mines. In order to obtain the accurate and reliable mechanical parameters of the sedimentary rocks at different weathering grades, the extensive experimental programs including the Brazilian splitting test, uniaxial compression tests, and direct shear tests have been carried out on the specimens that exposed to the nature environments at different durations. The correlation between the weathering grades and mechanical parameters including uniaxial tensile strength, uniaxial compression strength, elastic modulus, Poisson’s ratio, cohesion, and friction coefficient was proposed. The obtained results suggested that uniaxial tensile strength, uniaxial compressive strength, elastic modulus, and cohesion dramatically decreased with increasing weathering time, characterized as the negative exponential relationship in general. The influences of various weathering grades on fracture behavior of the rock specimens were discussed. The cumulative damage of the rock by the weathering time decreased the friction coefficient of the specimens which led to the initiation and propagation of microcrack within the rock at lower stress conditions. The obtained results improved the understanding of the roles of weathering on the mechanical properties of sedimentary rocks, which is helpful in the design of the underground geotechnical structures.

Analysis of the Possible Reactivation of the Krbavčići Landslide in Northern Istria, Croatia

The Krbavčići landslide occurred in January 1979 near the town of Buzet, Croatia, after a long period of heavy rainfall. It is located in Northern Istria in the area built of flysch rock mass where numerous mass movements in the past and recent history have been recorded. A flysch rock mass is highly susceptible to weathering, which leads to material disintegration, changes in geotechnical properties, and shear strength decrease, finally resulting in instability processes in flysch slopes. This paper describes existing information about the Krbavčići landslide occurrence, laboratory testing of siltstone samples from a flysch rock mass, and numerical slope stability analyses of a possible landslide reactivation caused by possible long rainy periods and further weathering of the flysch rock mass. Slope stability analysis using the Rocscience, Slide software, as well as landslide numerical simulations using the LS-Rapid simulation software were performed on the basis of the digital elevation model (DEM) and laboratory test results of siltstones with different weathering grades. A DEM of the Krbavčići landslide was obtained on the basis of the unmanned aerial vehicle (UAV) survey conducted in March 2016. The residual shear strength of siltstones to predict a reactivation of landslides is of highest importance and was determined by ring shear and direct shear tests on siltstone samples with different weathering grades. The results of the numerical simulations show that an increase of the groundwater level in the landslide body in combination with the further weathering of the flysch rock material at the sliding surface would have the main influence on a possible landslide reactivation and the further development of the landslide displacement.

The Impact of Mechanical Weathering on the Durability Strength Index of Ayer Hitam Shale Under Various Weathering Grades and Conditions

Shale is significantly weaker and less durable than other types of rock and is easy to break when it is exposed to continuous wetting and drying activities. As a construction material, the durability strength index of weathered shale in Ayer Hitam, Johor, Malaysia is poorly investigated and not well understood. The purpose of this study is to investigate the effect of mechanical weathering on the durability strength index of Ayer Hitam weathered shale under several different conditions. Three hundred sixty samples of weathered shale which are classified as weathering grade II to IV were tested within the fifth cycles of the slake durability test under three different conditions namely: Natural weathering, dry, and saturated sample. The results showed that the weathered shale with the highest moisture content of 27.78% and the lowest strength index with 1% after the fifth cycle at week 8 was the weathering grade IV under saturated condition. It was also found that the reduction in the durability strength index was more than 90% with increased moisture content and weathering grades. In conclusion, the durability strength index of shale depends upon the number of cycles or weathering grade, duration of water immersion as well as moisture content.

Weathering Influence on Properties of Siltstones from Istria, Croatia

Slaking and weathering of weak rocks result in slope instability. Siltstones from flysch rock masses are highly susceptible to weathering, which causes rapid changes in the geotechnical properties and durability. This study investigated siltstone samples of different weathering grades from flysch rock masses from the Istria Peninsula, Croatia, and determined the effects of weathering on their engineering properties. Laboratory testing of siltstone samples of different weathering grades was conducted to determine the specific gravity, grain size distribution, Atterberg limits, and uniaxial compressive strength. The standardized slake durability index is not sufficient to classify the durability of weak rock masses such as siltstones. Therefore, the durability of siltstone samples of different weathering grades was quantified from the fragment size distribution after each of five slaking cycles. The tested samples were classified based on the disintegration ratio, and the modified disintegration ratio was used to determine potential long-term degradation of the tested samples. The results indicated that weathering has a significant influence on the plasticity, uniaxial compressive strength, and durability characteristics and thus affects the landslides and erosion processes in siltstones in the flysch zone of the Istria Peninsula.

EFFECT OF WET TROPICAL WEATHERING ON THE STRENGTH OF SANDSTONE

The influence of moisture content to the strength of wet tropically weathered sandstone of Jurong Formation found in Nusajaya, Johor was studied. The rock materials have been affected by weathering action; hence the alteration of its engineering properties is incontestable due to these effects. A total of 36 samples representing various weathering grades were collected from the field and tested at various moisture content by immersing them in water at different duration of time, ranging from 15, 30 and 60 minutes. Point load tests for the determination of the strength index Is(50) of the rock were then carried out. For weathered sandstone (Grade II to IV), the mean initial moisture content ranges from 0.15% to 11.00% respectively, while the initial mean strength index has maximum and minimum values of 7.76 MPa and 0.38 MPa. The results reveal that there is a significant relationship between the weathering grades, moisture absorption and strength. The moisture absorption is dependent on the amount of clay minerals present in the rock material, which indirectly affects the strength, as observed with the increment of weathering state. In conclusion, this study indicates that sandstone with higher moisture content and increase in weathering grade exhibits lower strength values.