No abstract

Soil conditioning is a key factor in increasing tunnel face stability and extraction efficiency of excavated soil when excavating tunnels using an earth pressure balance (EPB) shield tunnel boring machine (TBM). Weathered granite soil, which is abundant in the Korean Peninsula (also in Japan, Hong Kong, and Singapore), has different characteristics than sand and clay; it also has particle-crushing characteristics. Conditioning agents were mixed with weathered granite soils of different individual particle-size gradations, and three characteristics (workability, permeability, and compressibility) were evaluated to find an optimal conditioning method. The lower and upper bounds of the water content that are needed for a well-functioning EPB shield TBM were also proposed. Through a trial-and-error experimental analysis, it was confirmed that soil conditioning using foam only was possible when the water content was controlled within the allowable range, that is, between the upper and lower bounds; when water content exceeded the upper bound, soil conditioning with solidification agents was needed along with foam. By taking advantage of the particle-crushing characteristics of the weathered granite soil, it was feasible to adopt the EPB shield TBM even when the soil was extremely coarse and cohesionless by conditioning with polymer slurries along with foam. Finally, the application ranges of EPB shield TBM in weathered granite soil were proposed; the newly proposed ranges are wider and expanded to coarser zones compared with those proposed so far.

Application of 3D laser scanner to civil engineering is widely studied in various fields such as tunnel, bridge, calculation of earth volume, construction measurement, observation of rock joint, etc. Some studies on utilization of the 3D laser scanner for calculating the over-break and/or under-break of tunnels have also been carried out. However, in the previous research, the scanning data were usually compared with the 2D CAD blueprint results; although the shape of tunnel structure is relatively simple, for precise calculation of the over-break and/or under-break of tunnels, three-dimensional analysis based on BIM is needed. Therefore, in this paper, a new program that calculates the over-break and/or under-break of tunnels using the 3D laser scanner and the BIM is developed; moreover the effective and rapid process of data treatment is proposed. The accuracy of the developed program was verified by applying the new system to a real tunnels construction field.

Rock mass rating (RMR) is the key factor when designing the appropriate support pattern of tunnel projects. Borehole drilling is usually performed along the tunnel route in order to determine the rock mass rating to be used for tunnel design. The rock mass rating at the non-boring region between boreholes is usually assessed through geophysical surveys such as electrical prospecting, seismic prospecting, etc. Many studies were carried out to find out the correlation between electrical resistivity and rock mass rating. However, most researches were aimed at obtaining the relationship between the two parameters utilizing experimental results obtained from laboratory tests or electrical prospectings. In this paper, efforts were made to analyze and obtain relationships between the electrical resistivity obtained from in-situ electrical resistivity logging data and the rock mass rating. Correlation studies using field data showed that the electrical resistivity is highly correlated with the rock mass rating with the determination coefficient more than 90%. The correlation analysis was also carried out between RMR classification parameters and the electrical resistivity. It was shown that the correlation between the condition of discontinuities and the electrical resistivity was very high with the determination coefficient more than 80%; that between the groundwater condition and the electrical resistivity was very low with the determination coefficient less than 57%.

Usage of underground space is increasing at metropolitan city. More than 90% of flood damages have occurred at downtown of metropolitan cities. In order to prevent and/or minimize the flood-induced damage, an underground rainwater detention cavern was proposed to be built underneath existing structures. As for underground caverns to be built for flood control, multi-caverns will be mostly adopted rather than one giant cavern because of stability problem. Because of the stress concentration occurring in the pillars between two adjacent caverns, the pillar-stability is the Achilles' heel in multi-caverns. So, a new pillar-reinforcing technology was proposed in this paper for securing the pillar-stability. In the new pillar-reinforcing technology, reinforced materials which are composed of a steel bar and PC strands are used by applying pressurized grouting, and then, by applying the pre-stress to the PC strands and anchor body. Therefore, this new technology has an advantage of utilizing most of the strength that the in-situ ground can exert, and not much relying on the pre-cast concrete structure. The main effect of the pressurized grouting is the increase of the ground strength and more importantly the decrease of stress concentration in the pillar; that of the pre-stress is the increase of the ground strength due to the increase of the internal pressure. In this paper, ground reinforcing effects were verified the stress change in pillar is obtained by numerical analysis at each construction stage. From these results, the effects of pressurized grouting and pre-stress are verified.