Strength estimation of evaporitic rocks using different testing methods

Rock strength is defined as the limit of the ability of a rock to resist stress or deformation without breaking. Testing methods recommended by ISRM (International Society of Rock Mechanics) and ASTM (American Standards Testing Material) include unconfined compressive strength (UCS), point load index (PLI), indirect tensile strength (ITS), Schmidt hammer rebound (SHR), sonic velocity (Vp and Vs), and slake durability index 2nd cycle (Id2). This contribution compares the results of these methods and explores the influence of rock composition and texture on Lower Miocene evaporites from Al Ain city, United Arab Emirates (UAE). These sedimentary rocks are common in the Arabian Peninsula as exposures or in the subsurface where they may constitute the foundations of buildings. A large number of UCS, PLI, ITS, SHR, SV, and Id2 tests were carried out on both core samples and rock blocks according to ASTM Standards. Examination of compositional and textural characteristics of representative rock samples was performed using XRD, XRF, polarized-light microscopy, and SEM. The results reveal variable correlations between the rock strength parameters with specific significant values between 0.53 and 0.72. The effect of composition and texture of the evaporitic rocks on their strength behavior is related to impurities such as clay minerals and celestite and grain interlocking textures. Despite the limited compositional variability of the evaporitic rocks (5–10%), the textural variability may present a challenging feature in rock strength testing and should be taken as a primary factor for consideration during applications

Solar activity of the past 100 years inferred from 10Be in ice cores – implications for long-term solar activity reconstructions

Differences between 10Be records from Greenland and Antarctica over the last 100 years have led to different conclusions about past changes in solar activity. The reasons for this disagreement remain unresolved. We analyze a seasonally resolved 10Be record from a firn core (NEEM ice core project) in Northwestern Greenland for 1887-2002. By comparing the NEEM data to 10Be data from the NGRIP and Dye3 ice cores, we find that the Dye3 data after 1958 are significantly lower. These low values lead to a normalization problem in solar reconstructions when connecting 10Be variations to modern observations. Excluding these data strongly reduces the differences between solar reconstructions over the last 2000 years based on Greenland and Antarctic 10Be data. Furthermore, 10Be records from polar regions and group sunspot numbers do not support a substantial increase in solar activity for the 1937-1950 period as proposed by previous extensions of the neutron monitor data.This article is protected by copyright. All rights reserved