The Island of Taiwan is divided into 7 geological provinces, based on plate tectonic characteristics, lithological formations and structural configurations. These differences are manifested upon differences in large-scale engineering properties.
Neotectonics of Taiwan is mainly controlled by the oblique convergence between the Eurasian plate and the Philippine Sea plate. In addition to this oblique convergence mechanism, the shape of the backstop and structural highs significantly influences most of the foreland structures. Sandbox experiments have been conducted to simulate the neotectonics of western Taiwan. The kinematics of deformation comprises a combination of compression, rotation and extension, which results in a local partitioning between thrusting and strike-slip movements. Most of the deformation in association with the 921 Taiwan earthquakes appears to be indicated by such a deformation mechanism.
Taiwan is located in the Circum-Pacific Belt and suffered many hazardous earthquakes in the historical time. However, systematic study on active faults has not been made intensively. The data on the slip rates and recurrences of the active faults in Taiwan are still not fully available. Several projects have been already launched by now and after the 1999 Chi-chi earthquake more resources could be allocated to the earthquake-related research. We hope these projects will result in reducing earthquake risk in the near future.
Not very long after the launch of Landsat-1 in 1972, Taiwan established a task force to promote the research and development of remote sensing technology in 1976. Eight years later, a satellite imagery receiving station was set up in the National Central University. Then in 1999, Taiwan launched the ROC-1 satellite. Therefore, the procurement of satellite imagery in Taiwan is very convenient.
Remote sensing techniques have provide an invaluable source data for the reconnaissance and feasibility stages of engineering geology projects. Remote sensing imagery (including satellite images and aerial photographs) has been successfully applied in the mapping of geologic hazards, study of active faults, monitoring of shoreline change and assessment of soil erosion in Taiwan.
Taiwan is approximately 75% mountainous. The number of landslides has been rising in recent years due to the development and new construction in the mountainous areas. The major factors causing landslides are the geological environmental reasons as they relate to the development efforts in the mountainous area. This paper chose several landslide cases for discussion. The purpose of this topic is to increase dialogue and understanding about landslide mechanisms with respect to various geomorphologic feature, geomaterial composition, structural geology, hydrogeologic conditions and geologic processes.
Taiwan is located at an active neoteconics area , associated with young-aged strata and a large amount of annual rainfall to establish an unique geologic environment . This paper introduces the engineering geologic characteristics and failure modes of tunnelling in Taiwan , and some suggestions of future research and investigation for geologic difficulties of tunnelling are also mentioned.
In Taiwan, squeezing condition is encountered from time to time, especially while tunneling through weak rocks or faulted zone. This problem lasts over three decades, Based on experience of four squeezing tunnels in Taiwan, this paper investigates the phenomena and mechanism associated with tunnel squeezing with emphasis on the mechanical properties of rocks.Based on Jeng (1998), rocks with the following characteristics are most vulnerable to squeezing condition: wetting deterioration, shear dilation and creep of rock as well. These three mechanical characteristics of weak rock are presented in this paper. According to the experimental results, obvious strength reduction and excess deformation are observed. When these behaviors of rocks are incorporated into the analysis of tunneling, much more deformation is obtained, compared to the conventional elastic or elasto-plastic models.
Highly fractured rock blocks and fault gouge are the common materials found within a fault zone. Fault gouge is a fine soil with silt and clay particles, which is the product yielded by the physical and the chemical actions during the shearing process of the fault. As fault gouge has been severely sheared, it possesses poor permeability, over-consolidated behavior and has a high potential to dilate, when confining pressure is relieved, as well.The mechanical properties of the fault gouge sampled in Taiwan are analyzed and compared. It is found that fault gouge in Taiwan contains very little swelling clay minerals, e.g. montmorillonite. Therefore, the squeezing condition encountered in tunneling practice in Taiwan cannot be the consequence of chemical swelling but the mechanical swelling of the gouge instead. It is also observed that: the greater the OCR, the less the swelling index and the greater the secondary swelling index. Gouge sampled deep in tunneling sites has much greater tendency to dilate than those sampled near ground surface. Finally yet importantly, the shearing rate dominates the frictional stability of gouge, whether stable slide or instable stick-slip displacement would occur. In turn, this factor may serve as the under-lain mechanism whether an active fault will creep stably or will induce earthquake during the shearing movement.