Brittle-ductile transition stress of different rock types and its relationship with uniaxial compressive strength and Hoek-Brown material constant (mi).

Rocks deformed at low confining pressure are brittle, which means that after peak stress, the strength declines to a residual value established by sliding friction. The stress drop is the variation between peak and residual values. But no tension reduction takes place at high confining pressure. A proposed definition of the brittle-ductile transition is the transition pressure at which no loss in strength takes place. However, studies that consider information about the brittle-ductile transition, the criterion's range of applicability, how to determine mi, and how confining pressures affect mi's values are scarce. This paper aims to investigate the link between brittle-ductile transition stress, uniaxial compressive strength and Hoek-Brown material constant (mi) for different kinds of rock. It is essential to accurately determine the brittle-ductile transition stress to derive reliable values for mi. To achieve this purpose, a large amount of data from the literature was chosen, regression analysis was carried out, and brittle-ductile transition stress (σTR) was determined based on the combination of Hoek-Brown failure criteria and the recently used brittle-ductile transition stress limit of Mogi. Moreover, new nonlinear correlations were established between uniaxial compressive strength and Hoek-Brown material constant (mi) for different igneous, sedimentary and metamorphic rock types. Regression analyses show that the determination coefficient between σTR and UCS for gneiss is 0.9, sandstone is 0.8, and shale is 0.74. Similarly, the determination coefficient between σTR and mi for gneiss is 0.88. The correlation between Hoek-Brown material constant (mi) and σTR was not notable for sedimentary and metamorphic rocks, probably due to sedimentary rocks' stratification and metamorphic ones' foliation.

Comparative study of topical 80% trichloroacetic acid with 35% trichloroacetic acid in the treatment of the common wart.

BACKGROUND: Common warts caused by the human papillomavirus (HPV) are considered to be the most common infectious skin disease. No individual treatment for common warts is effective as monotherapy in eradicating the lesions. The aim of this study is to evaluate the clinical efficacy of a 35% and an 80% trichloroacetic acid (TCA) solution in the treatment of the common wart. METHODS: In this single-blinded clinical trial, 62 eligible patients with common warts referred to the dermatology clinic of Ghaem Hospital in Mashhad, Iran. Patients were randomly divided into two groups, each treated with a TCA solution (group A, TCA 80%; group B, TCA 35%) once per week until complete clearance of the lesions or for a maximum duration of six weeks. Seven patients were excluded from the final analysis (one patient in group A and six patients in group B) for various reasons, including irregular follow-up, using physical tools such as razor blades to remove the lesion, and failure to complete treatment; and 55 patients were included in the final analysis. RESULTS: Improvement to treatment responses was classified as: no change (no changes in the number of warts), mild (clearing of less than 25% of warts), moderate (clearing of 25% to 75% of warts), and good (clearing of more than 75% of warts). At the end of follow-up, the clinical improvement of group A (n=30) was: 10 patients (33.3%) with a mild response, 6 patients (20%) with a moderate response, and 14 patients (46.7%) with a good response. In group B (n=25), 16 patients (64%) showed a mild response, 6 patients (24%) a moderate response, and 3 patients (12%) a good response. There was a statistically significant difference in improvement between the two treatment groups (P=.017). Improvement was greater with a higher concentration of TCA solution. CONCLUSION: This study showed that a different concentration of TCA solution was an effective form of treatment for common warts. Trichloroacetic acid 80% is more effective, but this solution must be used only with careful consideration by a physician.