Study on Unloading Relaxation Characteristics of Columnar Jointed Rock Masses Based on Displacement Back Analysis

We aim to understand the relaxation of columnar joint rock masses during the excavation process of the diversion tunnel of the Baihetan hydropower station. This paper inverts the deformation parameters of the relaxed columnar joint rock based on the displacement monitoring data, and introduces a relaxation factor to describe the deterioration degree of anisotropic parameters of the relaxed columnar jointed rock. The equivalent strain is proposed as the criterion of unloading relaxation and the threshold is also given. Based on the software Flac3d, a program for calculating anisotropic elastoplastic model is developed. The distribution of the relaxation zone of the diversion tunnel after excavation is simulated, and compared with the results of the acoustic detection to verify the correctness and rationality of the program, which can provide a necessary reference for the design and construction of hydropower projects.

A Study on Evaluation of Slope Stability and Range of Rockfall Hazard of Daljeon-ri Columnar Joint in Pohang, Korea

In this study, we evaluated the slope stability of the Pohang Daljeon-ri columnar joint (Natural Monuments # 415) and calculated the maximum energy, jumping height and moving distance of rockfalls using a simulation. Based on the results, we established the range of rockfall risk. The slopes of the Pohang Daljeon-ri columnar joint have dip directions of 93.79°, 131.99°, 165.54° and 259.84° from left (SW) to right (NE). Furthermore, they have a fan-like shape. The Pohang Daljeon-ri columnar joints are divided into four sections depending on the dip direction. The measurement results of the discontinuous face show that zone 1 is 125, zone 2 is 261, zone 3 is 262, zone 4 is 43. The results of slope stability analyses for each section using a stereographic projection method correspond to the range of planar and toppling failure. Although it is difficult to diagnose the type of failure, risk evaluation of currently falling rocks requires further focus. The maximum movement distance of a rockfall in the simulation was approximately 66 m and the rockfall risk range was the entire area under slope. In addition, it is difficult to forecast where a rock will fall as it rolls in various directions due to topographic factors. Thus, the installation of measures to prevent falling is suggested to secure the stability based on the results of the rockfall simulations and its probabilistic analysis.

ANALISIS DATA RESISTIVITAS DAN POLARISASI TERIMBAS GUNA MENDETEKSI KEBERADAAN MINERALISASI DAERAH KARANGSAMBUNG

Karangsambung merupakan salah satu tempat tersingkapnya batuan campuran yaitu komplek melange lok ulo yang berumur kapur akhir hingga paleosen. Aktivitas vulkanik dan tektonik pada daerah Karangsambung mengakibatkan tersingkapnya intrusi batuan beku diabas dengan struktur columnar joint. Penelitian ini bertujuan untuk mengindikasi keterdapatan mineralisasi yang disebabkan fluida hidrotermal sebagai produk sisa dari sebuah proses magmatisme. Fluida hidrotermal akan menerobos batuan samping, kemudian melewati celah-celah batuan yang telah ada akibat berkembangnya struktur geologi. Penelitian ini memanfaatkan dua metode geofisika berupa metode resistivitas dan polarisasi terimbas dengan konfigurasi dipole-dipole. Metode resistivitas digunakan untuk mendeteksi persebaran litologi batuan, sedangkan metode polarisasi terimbas digunakan untuk mendeteksi adanya mineral ubahan penciri alterasi bertipe sulfida seperti pirit, serisit dan sebagainya. Pengukuran dilakukan sebanyak 5 lintasan dengan panjang setiap lintasan 200 meter. Pengolahan data menggunakan Microsoft Excel, RES2DINV, Mapinfo Discover 3D, dan Rockworks15. Analisis penampang resistivitas dan polarisasi terimbas terindikasi adanya mineralisasi ditunjukan dengan nilai resistivitas yang tinggi yaitu 700 Ωm dan nilai chargeabilitas yang tinggi pula yaitu 300 ms. Area tersebut diduga kuat sebagai pengaruh dari proses silisifikasi atau pengkayaan silika, serta terdapat beberapa indikasi yang menunjukan pengaruh dari propilitik. Analisis dari korelasi semua penampang polarisasi terimbas pemodelan 3D diidentifikasi bahwa mineralisasi berorientasi dari arah utara-selatan serta volume zona mineralisasi diperkirakan sebesar 70.500 m3.