# Natural Creation of Large Rock Cavern: Can We Construct Them? Jenolan Caves as a Case Study
## 5 Question About Creation of Large Man-Made Rock Cavern  
With reference to Rock Engineering Systems [20], parameters such as rock mass quality, that are related to rock structure and joints spacing or density; rock strength; rock joint shear strength; in situ stress field; and the shape of the opening, interact with and influence one another. Although we have a basic understanding of the engineering responses among these parameters that interact with each other, the two sections on the investigation exercise results and discussion of the results provide a clear explanation to describe the relationship and interaction among those parameters in regard to rock openings. However, there are no appropriate solutions or charts to conclude their relationship. Some questions and unclear phenomena are raised in relation to these parameters for creating a maximum size of stable rock opening using the rock-reinforcement technique. These questions are as follows:  
1. Basic structural fixed-arch/beam models are acknowledged; however, how does the in situ stress field influence the reinforced rock arch that is adopting the rock-reinforcement technique with different geometries for the arch roof design for the rock opening created in a range of rock mass conditions?2. With the numerical analysis results of Models MM-1 and MM-2, which are unsupported man-made openings of the same size and with the same ground conditions, the detected vertical stress that could be considered a rock load acting on the crown of the opening in the low-rise arched-roof opening of Model MM-1 is higher than that of the high-rise arched-roof opening of Model MM-2. Is it adequate/appropriate to estimate the rock support load based on the Q-system [47], for example, with respect to the different geometries of the arch roof design created in a range of rock mass conditions of a rock opening? 3. Rock mass quality and rock joint density have a direct relationship with the rock mass deformation modulus [42; 45; 46]. Structural beam models show that beam stiffness is a function of the beam material's deformation modulus, the beam size, and the supporting span. Thus, how wide can a rock cavern be open in a range of rock mass conditions with different arch shapes when using rock reinforcement as a stabilization measure? 4. Given the results of Models M1, M3, and M5, when conducting a numerical model analysis for jointed rock mass openings, what is the best practice of interpreting rock joint settings, such as joint spacing, joint persistent, length of joints, etc., for a range of rock mass qualities to include in a numerical model for engineering design in order to obtain reliable agreement results that are close to the as-constructed engineering response, e.g., opening periphery deformation? 5. According to the discussion on the finding of rock reinforcement as a stabilization measure above, how much rock mass strength can be improved within the bolted zone when it is adopting rock-reinforcement technique via pattern rockbolting for a range of rock mass conditions? To clarify the above questions, further studies, such as desktop investigations using 2D/3D numerical modeling, may be required to examine relationships among rock mass parameters. These parameters, including rock structure, rock mass quality, joints density, rock strength, in situ stress field, and the shape of the opening, will be used to investigate if a possible maximum span of rock opening can be created in a range of rock conditions using the rock-reinforcement technique. Suppose that the future investigations might solve Questions 2 and 3 eventually. The results could be used to pre-identify the maximum cavern size at the specific location based on the available site-specific background data for underground space-development planning at an early stage.