Hyun-Seok Yun

Application of x-MR control chart on monitoring displacement for prediction of abnormal ground behaviour in tunnelling

The displacement data monitored during tunnel construction play a crucial role in predicting the behaviour of ground around and ahead of excavation face. However, the management criteria for monitoring data are not well established especially for the reliable analysis on varying aspect of displacement data along with chainage. In this study, we evaluated the applicability of x-MR control chart method, which is kind of applied statistical management method, for the analysis of displacement monitoring data in terms of prediction of possible collapse or induced cracks. As a result, a possible abnormal behaviour could be predicted beforehand at 5 ~ 13 m ahead or on at least one day before it occurred by using x-MR control chart method. In addition, it is noted that the moving range for the x-MR control chart should be set to 5~10 for this purpose.

Prediction of fault zone ahead of tunnel face using x-Rs control chart analysis for crown settlement

A measurement of tunnel displacement plays an important role for stability analysis and prediction of possible fault zone ahead of tunnel face. In this study, we evaluated characteristics of tunnel behaviour due to the existence and orientation of fault zone based on 3-dimensional finite element numerical analysis. The crown settlement representing tunnel behaviour is acquired at 5 m away from tunnel face in combination with x-Rs control chart analysis based on statistics for trend line and L/C (longitudinal/crown displacement) ratio in order to propose risk management method for fault zone. As a result, x-Rs control chart analysis can enable to predict fault zone in terms of existence and orientation in tunnelling.

Setting of the range for shear strength of fault cores in Gyeongju and Ulsan using regression analysis

A fault is one of the critical factors that may lead to a possible ground collapse occurring in construction site. A fault core, however, possibly acting as a failure plane in whole fault zone, is composed of fractured rock and gouge nonuniformly distributed and thus can be characterized by its wide range of shear strength which is generally acquired by experimental method for stability analysis. In this study, we performed direct shear test and grain size distribution analysis for 62 fault core samples cropped from 12 different spots located in the vicinity of Kyongju and Ulsan, Korea. As a result, the range of shear strength representing the characteristics of fault cores in the study regions is determined with regard to vertical stress using a regression analysis for experiment data. The weight ratio of gravels in the samples is proportional to the shear strength and that of silt and clay is in inverse proportion to the shear strength. For most samples, the coefficient of determination is over 0.7 despite of inhomogeneity of them and consequently we determined the lower limit and upper limit of the shear strength with regard to the weight ratio by setting the confidence interval of 95%.

Determination of representative elementary volume of fault core materials by particle distribution analysis

Fault core materials (fault breccia and fault gouge) exhibit heterogeneous particle size distributions due to many factors, including the type of cataclasis, the degree of weathering, and the scale and mechanism of the fault system. When studying particle size distributions in fault core materials, there is no clear standard of the sample size that should typically be used for testing and analysis. In this study, we present a method to establish the ideal sample size by statistically assessing a suite of laboratory tests on 451 fault-core samples from 21 locations in South Korea. These samples were divided into five different classes according to grain size. Weight ratios of gravel, sand, and silt/clay were calculated from laboratory tests on each sample, and the means and standard deviations were subsequently assessed via analysis of variance and multiple comparison analysis. The results of the analysis of variance suggested that classes 1–5 are different from each other in at least one factor. Tukey’s HSD tests and Duncan’s LSR tests were also applied to identify groups within the classes that might be statistically similar to each other. In this manner, it was found that classes 1 and 2 could be grouped together (group A), as could classes 3, 4, and 5 (group B). Standard deviation means and distribution ranges within groups were used to deduce that group B, rather than group A, contained the sample sizes that best represented the site. Furthermore, class 3 (which had the smallest weight among the different classes in group B) was determined as being the representative elementary volume (REV). This deduction is consistent with the recommendation for reference sample size used in soil particle size analysis (as defined by the American Society for Testing and Materials).

Classification of geological and engineering properties in weak rock: a case study of a tunnel in a fault zone in southeastern Korea

Given that the rock mass classifications of weak rocks observed in tunnels are evaluated only as ‘poor rock mass’ or grades IV–V using existing rock mass classification methods, a new scheme is needed that would better distinguish the various geological properties of weak rocks. In this study, geological and engineering properties of weak rocks were classified based on the analysis results of a total of 55 faces in a tunnel that passes through a fault zone in southeastern South Korea. Geological observations, point load tests, and Schmidt hammer tests were conducted to analyze the properties of the weak rocks. Through this analysis, the weak rocks were classified into two weathering types: ‘disintegrated rocks’ and ‘decomposed rocks’. This division is based on the tectonic mechanisms and parameters necessary to determine the engineering geological properties of individual rock-weathering types according to their geological properties. The ‘disintegrated rocks’ have been physically weathered by brittle deformation and are classified into three subtypes using the rock quality designation (RQD) and joint set number (Jn), which can characterize the discontinuity properties of the rocks. Point load tests were conducted on these individual subtypes to calculate the point load index (Is(50)). The resultant values are clearly related to the assigned three subtypes. The ‘decomposed rocks’ have been chemically weathered by ductile deformation and are classified into five subtypes based on the results of Schmidt hammer tests conducted on faces and Is(50) values calculated using the average of the Schmidt hammer values. The geological properties of the individual subtypes of the ‘disintegrated rocks’ and ‘decomposed rocks’ are clearly related to their engineering properties. Based on these results, rock mass classification diagrams are proposed that can be simply and easily applied to weak rocks.

Database Construction for Tunnel Management in Korea

In the present study, we introduce the database constructed for tunnel maintenance. The item of database is standardized by selecting elements necessary for maintenance of approximately 400 tunnels on general national roads in South Korea. The forms and items for database standardization were derived by analyzing various data of tunnel such as design documents, specifications, maintenance data, calculation reports, drawings, and panoramic photographs. We analyzed statistically geological and geotechnical factors of 202 tunnel cases based on support patterns. The database system can be used for optimum performance, accident prevention, quick selection of deformation repair and reinforcement methods and efficient management of deteriorated facilities during tunnel operation.