PENENTUAN KEKUATAN JANGKA PANJANG MASSA BATUAN DENGAN METODE TIDAK LANGSUNG DARI HASIL PENGUKURAN DAN PENGUJIAN INSITU

• Main Author: DWINAGARA, BARLIAN
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/72611
• Institution: Institut Teknologi Bandung

knowledge of the long-term strength characteristic of the rock mass forming of the structure. Material which is considered as the structure forming in a tunnel is the rock mass around the wall of the tunnel. The long-term strength parameters are parameters that vary with time. The determination of rock long-term strength that is commonly conducted is that using the laboratory test results. However, this is only applicable to intact rock and the extrapolation to rock mass characteristics hasn't been accurately established. The laboratory test results from the rock specimen cannot significantly represent the characteristics of a rock mass with a larger volume. On the other hand, the in situ test for determining rock mass strength is very rarely conducted due to its impracticability and expensiveness. In addition, the obtained strength parameters are only for the ultimate strength. Back analysis of a failure may give representative values for rock mass strength in a large scale, but this can only be made if the failure happens. It can therefore be said that the determination method of rock mass long-term strength by in situ, hasn't been available yet. This research proposes an approach for the determining rock mass long-term strength using indirect method from the result of in situ test and measurement. The measurement was a creep phenomenon measurement using extensometer and convergencemeter instruments, while the Goodman's jack test was conducted to determine rock mass deformation modulus. The result of the in situ test and measurement were then combined with the mechanical and physical tests conducted in laboratory and the numerical modeling. The research station was located in X/C 6A, Block II Central of Ciurug, Pongkor Gold Mine Business Unit (UBPE-Pongkor), PT. Antam, Tbk. The rock mass was limited on tuff-breccia rock only which formed the footwall. The position of research station was influenced by the stress changes as effect of the underneath stoping. The measured deformations were then assumed to be influenced by the stress changes. A certain measurement period that represented the increasing-andthen- constant stress was taken as the representative of the creep phenomenon. From the obtained creep curve, the rheology parameter that represented rock mass behavior can be determined, whereas the magnitude of the stress changes was estimated using numerical modeling. Within the creep period, the extensometer measurements revealed that maximum displacement on the right and left walls were 1.2 mm and 1.8 mm, respectively. The deformation modulus of rock mass (Em) that was obtained from the Goodman's jack tests for the tuff-breccia rock in the right and left walls were 6.17 GPa and 6.73 GPa, respectively. Referring to the drilling core, the RQD of right and left walls were 89.8%, and 77.8% respectively. The long-term deformation modulus (ELT) of the right wall was 2.76 GPa, and that of the left wall was 1.97 GPa. This long-term deformation modulus was estimated from rheology equation developed from the creep curves of the extensometer measurements. The calculations that were based on the suggested approach showed that the minimum long-term strength (?LT) of tuff-breccia rock mass at the right wall was 9,85 MPa, and that of the left wall was 6,39 MPa. On average, the minimal long-term strength of tuff-breccia rock mass was 36,72 % of its strength. General conclusion is that rock mass strength (?cm) determined using empirical equation, rheology parameters from in situ creep phenomenon measurements, and rock mass deformation modulus (Em) from in situ test, can be use as the basic calculation for determining rock mass long-term strength (?LT). The rheological equation revealed that after a certain period of time, the modulus of deformation would be relatively constant, expressing the long-term modulus of deformation (ELT). The contributions of this research are: understanding of basic parameters for calculating the long-term strength, which is long-term modulus of deformation (ELT), development of approach for determining the rock mass long-term strength, and formula to calculate the long-term strength as given below, with the value of ? depends on rock type and rock mass characterization.