Zayıf Kayalardaki Pürüzlülüğe Sahip Süreksizliklerin Makaslama Dayanımlarının Araştırılması
Özet
The purpose of this thesis is to analyze the performance of the Barton-Bandis criterion, which is frequently used in determining the shear strength of discontinuities with roughness in weak rocks. Several studies have been conducted in order to identify the input parameters used in the criterion. In the first phase of these studies, samples with standard discontinuity profiles were produced. Geomechanical parameters were determined by the experiments on the samples produced with plaster, and then shear tests were conducted. In the second phase, similar experiments performed on artificial samples were applied on ignimbrite samples.
In the studies conducted on plaster samples, the complications encountered in determining the JCS value, which is the input parameter of the criterion, with the Schmidt hammer were observed, and this observation concluded that the needle penetrometer can be used as an alternative to the Schmidt hammer in soft materials. Different methods used to determine another input parameter, the JRC, were also examined. The discontinuity surfaces were digitized using profilometry, optical scanning, and photogrammetry, and the results were compared. The digitization results of the three methods show very close values to the numerical data of the standard profiles, and it was found to be successful. Statistical parameters used in defining roughness were determined with the data obtained from the digitization methods. The JRC value was derived using these factors, and the performance of the digitization methods in determining JRC was examined. The digitization method with the profilometer was determined to be more practicable than other methods due to the processes used. The failure envelopes calculated using the Barton-Bandis criterion were compared to the results of plaster shear testing. The negativities encountered in the conditions where JCS/n>100 in the envelopes drawn with the criterion are examined. In this case, the envelopes created with the recommended threshold angle application were found to be insufficient to represent the shear test results. It has been observed that the criterion works successfully in cases where the JCS/n ratio is greater than 100 and this ratio alone is not a sufficient indicator for the application of the threshold angle. Depending on the JRC and b value, the JCS/n levels at which the criterion can operate without any problems have been determined.
Needle penetrometer has come to the fore in the determination of the JCS value in studies performed on ignimbrites. Aside from visual comparison with commonly used standard profiles, three distinct digitization methods were used to determine the JRC value, and statistical parameters were determined by these methods. The digitization with the profilometer method produced the closest results to the visual comparison. Photogrammetry was used to determine three-dimensional roughness characteristics characterizing the discontinuity surface. Shear tests on five different JRC classes in ignimbrites were undertaken, and failure envelopes created with the threshold angle were found to be insufficient to represent the test results. In the failure envelopes drawn without applying the threshold angle, the results of the experiments performed for the three JRC classes were found to be in alignment with the criterion. Against the negativities arising from the criteria, failure envelopes were drawn with alternative failure criteria using two- and three-dimensional roughness parameters. However, it has been discovered that these criteria do not accurately reflect the experimental outcomes. Despite the drawbacks of using the Barton-Bandis criterion, it has been determined that it is more effective than alternative criteria in determining shear strength. It was decided that rather than developing new alternatives to the criterion and the parameters to be utilized in the criterion, it is preferable to eliminate the detected flaws by adhering to the Barton-Bandis criterion parameters.
