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The absolute prevention of damage occurrence is not possible, thus reducing the probability of failure in a system and its impact is very important regarding the operation of a whole system. A failure in a system or in its subsystems makes negative results such as the stop in the production process, rising labor costs, and increasing the cost of maintenance. Reliability, in recent years, is mentioned as one of the most significant aspects of the quality of goods and services. In the past, reliability concerned sensitive and complex industries such as military, nuclear, and aerospace where the lack of their reliability could cause irreparable damage to the entire system. However, today it has become a universal concern. Tunneling equipment has grown in size and complexity and therefore, lack of reliability may cause massive costs to this equipment. Therefore, reliability determination in order to identify the components and subsystems with low reliability is essential. The aim of this study is to review the methods of tunneling equipment reliability analysis including statistical analysis, failure mode and effects analysis, Markov and fault tree methods. In addition, previous available research on the reliability analysis of tunneling equipment is presented.

In-situ stress is one of the most important input data to study stability analysis of underground and surface geomechanical projects. The measured vertical stress has a linear relation with depth. The average value of unit weight (g) was obtained 0.026 MN/m3 (2.56 ton/m3) using 1041 test results of different rocks with 0.001 difference with 0.027 MN/m3 which is a reliable coefficient for estimating vertical stress. The ratio of horizontal (sh) to vertical (sv) stress (K =sh/sv) is estimated by theoretical and empirical methods. The results showed that the estimating ratio of horizontal to vertical stress (K) by a theoretical method such as Terzaghi and Richard is much smaller than 1, and the estimation of the K value utilizing empirical methods such as Hoek and Brady is much greater than 1, with its value even approaching 4 in the near ground surface. To overcome the lack of an applicable comprehensive relation for the estimation of the K ratio and improve the shortcomings of previous methods, a new empirical relation was developed to estimate the K ratio utilizing a significant number of in-situ test results. Stability analysis of Masjed Soleyman powerhouse caverns was carried out by numerical modelling for five values of the K ratio obtained by previous stress estimation methods and this study. The in-situ stress estimation method (K ratio changes) showed a significant effect on stresses, displacements, strains, depth of the plastic zone and significantly affect the stability analysis and support system design of the powerhouse and transformer caverns.

For problematic soils, conventional (cement and lime) additives can provide the necessary improvements in geomechanical properties for various infrastructure constructions. However, these additives have a high environmental impact and they are not always cost-effective, such that potential alternative additives (e.g. obtained as industrial by-products) require investigation. This paper examines cement kiln dust (CKD), obtained as a by-product of cement clinker manufacturing, for improving the geomechanical properties of an Iranian loess soil (sandy silt). Compaction, unconfined compressive strength (UCS), direct shear (DS) strength and soaking durability tests were performed on the loess soil and its mixtures with 5-20% CKD, investigating the effect of curing period (of up to 28 days) on the mobilised strength. Observations from mineralogical and microstructural examinations are also presented in this paper. Compared to the unamended loess, the strength and elastic modulus substantially increased for increasing CKD content and curing period. Improved strength and durability (under soaking) of the soil-CKD mixtures is explained by particle aggregation (of the loess soil), inclusion of the fine CKD material and the action of calcium-derived gel (linking) products. Hence, as well as reducing the disposal problem (of the CKD by product) in the cement industry, the use of this material, as additive for soil stabilisation applications, would provide an effective and sustainable option for improving the geomechanical properties, as demonstrated for the investigated loess soil.