The Engineering Characteristics and Classifications of Rock Masses along Road Section from Prambanan to Patuk, Yogyakarta, Indonesia

Several attraction places and agriculture area that essentials for tourism and villager to do their activities are located approximately 6 km along the road of Candi Ijo to Ngoro-Oro in between Prambanan and Patuk sub-districts, Yogyakarta, Indonesia. Many jointed rock masses along the road have the potential to fail. This paper describes the rock mass characteristic and quality determined using the Geological Strength Index (GSI) and Rock Mass Rating (RMR) classifications. The rock mass characteristic and quality were essentially the preliminary results of a study to evaluate stability of the rock slopes along the road of Candi Ijo to Ngoro-Oro. Field observation and laboratory tests were carried out to determine parameters of the GSI and RMR. The results show that the slopes in the study area consisted of tuffaceous sandstone, vitric tuff, lithic tuff, cemented tuffaceous sandstone, lapilli tuff, subarkose, laminated mudrock, and laminated tuffaceous sandstone. The intact rocks were classified as weak to very strong. The research area consisted of three rock mass qualities, namely fair rock mass quality having GSI between 30 and 45 and RMR between 41 and 60, good rock mass quality having GSI between 46 to 65 and RMR between 61 and 80, and very good rock mass quality having GSI > 65 and RMR between 81-100. The relationship between GSI and RMR obtained in this study was in good agreement with that proposed by Hoek et al. (1995).

Application of electrical resistivity tomography (ERT) for rock mass quality evaluation

Rock mass quality evaluation is a challenging task in geotechnical investigations given the natural heterogeneity and the limited data. These investigations mainly depend on the traditional drilling tests. However, such tests are expensive and time consuming, provide point measurements, and cannot be conducted in steep topographic areas, and thus cause uncertainties in the geological model. Conversely, geophysical methods such as electrical resistivity tomography (ERT) are non-invasive, user-friendly, and fast. In this work, we establish empirical correlation between ERT and limited drilling data to obtain rock mass integrity coefficient (Kv). The estimated Kv provides 2D/3D imaging of the rock mass quality evaluation via weathered/unweathered rock and faults detection in order to cover the entire area even where no drilling test exists. Compared with the past geotechnical investigations, our work reduce the ambiguities caused by the inadequate well tests and provide more accurate geological model for infrastructures design. Our work proposes that, in case of sparse borehole data, the established empirical equations can be used to determine Kv along different geophysical profiles via 2D/3D insight of the subsurface. Our approach is applicable in any hard rock setting, and the established correlations can be used in areas even where no well test exists.

A Study of the Effects of Geological Conditions on Korean Tunnel Construction Time Using the Updated NTNU Drill and Blast Prediction Model

This paper analyses the construction time and advance rate of a 3 km long drill and blast tunnel under various geological conditions using an upgraded NTNU drill and blast prediction model. The analysis was carried out for the five types of Korean tunnel supports according to the rock mass quality (from Type 1, meaning a very good rock mass quality; to Type 5, meaning a very poor rock mass quality). Four kinds of rock properties, as well as the rock mass quality, for each tunnel support type were applied to simulate different geological conditions based on previous studies and the NTNU model. The construction time was classified into five categories: basic, standard, gross, tunnel and total, according to the operation characteristics to more effectively analyse the time. In addition, to consider the actual geological conditions in tunnelling, the construction times for the three mixed geological cases were analysed. It was found that total construction time of a tunnel covering all the operations and site preparations with a very poor rock mass quality was more than twice that of a tunnel with a very good rock mass quality for the same tunnel length. It is thought that this study can be a useful approach to estimating the construction time and advance rate in the planning or design stage of a drill and blast tunnel.

Application Research Of 3D Digital Evaluation And Analysis Method In Geological Engineering

In order to adapt to the construction and development of informatization and digitization of engineering survey industry, a method of rock mass quality classification based on 3D geological modeling analysis is proposed. Based on a hydropower station as an example, this paper build a refinement 3D geological visualization model, simulate and analysis engineering geology of the hydropower station from the perspective of the three-dimensional digital. According to features of rock mass damage and elastic-plastic mechanics of dissipation energy principle, which gives the optimize evaluation index and method of rock mass quality classification in water resources and hydropower engineering, endowed with classification attribute values of each level and restructured model shows the spatial distribution characteristics of rock mass quality. In conclusion, this method improves the efficiency and intuitiveness of the engineering geology analysis and engineering rock mass quality classification. Furthermore, the 3D digital evaluation method was verified more rationality and intuitiveness in geological engineering comparing with traditional 2D geological analysis method.

Reliability Analysis of Rock Supports in Underground Mine Drifts: A Case Study

Support failures in mine drifts represent potential hazards threatening underground mine safety and productivity. The aim of this study is to determine the reliability index associated with the rock supporting elements used in Ridder-Sokolny mine, an underground mine located in East Kazakhstan. Numerical simulations of the drift support and the first order reliability method (FORM) were employed to carry out the analysis. Several support cases were considered including; shotcrete, bolting, concrete, and combined bolting and concrete as well as unsupported drift case. For each support case, the factors of safety (FS), the reliability index (β) and the probability of failure (PF) were determined in accordance with the corresponding rock mass quality and excavation geometry. The results indicated the average FSs varied little for the different support cases (except for shotcrete); while β and PF vary more significantly between 0.62–3.25 and 0.05–27 (×103 %) factor depending on the rock conditions and support installed. The probability of failure of the rock support increases with a decrease in the rock mass quality. Similar trends were observed with an increase of the width/height ratio of the excavations for the same rock domain. These results illustrated that a single FS value obtained from a deterministic method may not always provide a sufficient indication of safety. This is in agreement with the field observations (many of the supports failed). Hence, on the basis of the reliability index of the supports, the requirement in terms of coefficient of variability of the rock mass quality to meet the target performance level was proposed. It is concluded that the results of this study could help improving the drift support design in Ridder-Sokolny mine.

Research on Rapid Evaluation of Rock Mass Quality Based on Ultrasonic Borehole Imaging Technology and Fractal Method

The distribution of discontinuities in the deep stratigraphic rock mass is random and irregular, and the spatial distribution has statistical self-similarity, which can be analyzed by fractal theory. The borehole wall image obtained based on the ultrasonic borehole imaging technology can clearly reflect the rich structural surface information such as the inclination, density, and crack width of the structural surface in the rock mass. Due to its inherent fractal characteristics, the fractal box dimension of the hole wall image can be used to describe the complexity of the structural surface. In the study, the fractal box dimension of the hole wall image and the RQD value of the rock mass are compared, and it is found that there is a linear correlation between the two. Therefore, the rock quality can be evaluated according to the fractal box dimension value of the hole wall image. Finally, a rapid quantitative evaluation method for rock mass quality classification is established based on ultrasonic borehole imaging technology and fractal method.

Effects Of Different Empirical Design Approaches For Size Galleries On The Behaviour Of Rock Masses During The Excavation Operation: Excavation Case At BAE Well

The characterization of rock massifs is a delicate job; indeed, it is possible to understand the behaviour of intact rocks individually by laboratory tests but it is difficult to characterize them on the whole rock mass, which has undergone a complex geological history. Empirical approaches play an important role in the excavation of galleries and the design of support systems. These approaches are considered very effective in optimizing the tunnel excavation process. Several reliable empirical approaches have been developed, but the selection or use of an appropriate empirical method to design the tunnel excavation remains a difficult task. Therefore, in this work, the analysis of four approaches, the most used, of different empirical design was carried out to determine the behaviour of the rock mass during its excavation in a state of high in situ stress. This study was carried out on the scale of the ST2 rock mass of the worksite (BAE well 3) at the Bouazzer mine. These approaches include the AFTES classification, rock mass index (RMR), rock mass quality (Q) and geological resistance index (GSI). Based on the simulated statistical results obtained from said empirical approaches, through the finite element calculation, it was found that the application of the rock mass quality approach is very efficient in the excavation of the rock mass. gallery of size because it makes it possible to take into account the equivalent dimensions of the gallery, the stress condition in situ due to the excavation and the heights of overburden which are considered as major elements of the stability of the gallery. The method provides an optimized reinforcement and support design. In addition, this study will serve as a valuable basic document for the geotechnical engineer to design and plan support systems in the excavation of galleries under high in-situ stress.