The Strata distributed in the hill area of Erh-Jen-Chi drainage include conglomerate shale sandstone mudstone and sandstone-shale alternation formations. Among these formations, shale mudstone and sandstone-shale alternation formations are muddy in nature. These muddy formations occupy 80% of this hill area. The structural lines in this area include Mu-Cha Fault, Chi-Shan Fault, Ku-Shan Fault, Chiao-Tzu-Tou Fault, Lung-Chuan Fault, Ku-Ting Fault, Nei-Men Syncline, Tien-Liao Syncline, Tien-Tsao-Liao Syncline, Hsiao-Kun-Shiu Anticline, Keng-Nei Structure and Lung-Chuan Structure. Most of these structural lines have passed through the muddy area or near the muddy area. These muddy formations have been more or less influenced by these structures. The data of the quantitative geomor-pological analysis of this area have been collected. The average altitude is 60-80m, average slop 6°, average Relief 40m, The density drainage is 2.31km/km2. The special land forms distributed in muddy formation area are bedlands, infependent rock bodies, mud volcanoes, meanders and ox-bow lake and hogbacks. The PH value mudstone is 7.71-9.10, but that of shale is 7.98-9.52. The salinity of mudstone is 0.06-1.5% , but that of shale is 0.06-0.6%, The clay minerals cousist of 30.32% illite, 28.34% chlorite, 27.7% fine guartz, 4.57% calcite, and 4.78% kaolinite. All of these are non-swelling clay minerals.
In southwestern Taiwan, an avea of over 1000 km2 is covered by the geological formations consisted of mainly mudstone or shale. The slopes in this region are proue to natural hazards which are related to their geological characteristics. Among these geological formations, Nanhua Mudstone is the worst one susceptible to geological hazard, especially for erosion problem.
This paper summarize the previous study about the engineering geological characteristics of the mudstones (shales) in southwestern Taiwan. Most of the geomaterial is related to Nanhua Mudstone. It also postulates the major causes of the erosion problem of Nanhua Mudstone. Finally, several hazard mitigation methods are suggestsd.
More than 1000 km2 area located in both Tainan and Kaoshiung counties in Taiwan is covered by a young and weakly cemented mudstone formation. The characteristics of the mudstone are sensitive in slaking, and weathering, with high erosion rate, and the strength decreased when the water content increased. Owing to these special characteristics, the disaster, such as erosion, plane sliding, rock falling, mud flow and subsidence, and also resulted in reducing the life of the reservoir etc. occurs frequently in the mudstone slope. The conventional slope protection methods used in mudstone area investigated. A project with full scale tests used to overcome the engineering problems of mudstone occurred in Kaoshiung county of Taiwan has been supported by the Taiwan Area National Expressway Engineering Bureau. This paper comments about mentioned methods in detail for engineering design reference for mudstone area in the southwest of Taiwan.
The first year of this study is to concentrate on developing the rootmechanical model based on the principle of equilibrium theory of mechanicsand the rule of dimension analysis. To evaluate the function of soil-rootreinforced model, in situ root tests were executed el during the period of this project.
A new apparatus with a shearing box of 20cm×20cm×l0cm has been developed forconducting the direct shear test of reinforced soil in the field. Fivedifferent varieties of biological root systems were chosen as samples examinedin mudstone areas. Also, the judgement of soil-root reinforced coefficient foreach variety of vegetation would be necessary. The limitations and suitability of this model had been studied in detail at the end of thisresearch. All the parameters are going to be figurized, tablized and computerized through the information systems developed from this project. Thetape root has been found to take over more than 85% of shear strengthincrements on the soil-root reinforced systems.
The increment of shear strength was identified to be much more significant on the soil cohesion force (C) than on the internal friction angle（Ф） in the soil-root reinforced system. It is expected that this research canoffer an index used to select right species of vegetation for side-slopeprotection based on their root bonding function in the soil-root reinforced systems located at the mudstones in southwestern Taiwan.
The purpose of this study is to find out the favorable vegetation mat which can be successfully applied on the nuded mudstone areas. Four mats were used including nonwoven fabric, straw mat, nonwoven fabric with straw mat, and nonwoven fabric with P.E net. The conclusion of this research can be made as follow : The vegetation which mat made of nonwoven fabric with P.E net is the best material for small seeds germination, vegetation growth, and hillslope stabilization on nuded mudstone areas. Next suitable material is straw with nonwoven fabric , vegetation mat made of straw only is the worst for plant growth and hillslope stabilization but beneficial for germination of larger seeds.
When cutting, embankment, and related construction in mudstone slope area, the stability problems causing by the erosion and softening behaviors of mudstone material has been bothered engineering for years. To solve these engineering problems, the flexible retaining structure, "Geotextile-reinforced earth/slope", is suggested to apply in the field. Besides reinforcing related properties, the requirements of filtration and drainage systems are also the important factors for design. This paper provide the summary of the results from series studies which where sponsored under National Science Council. The specification of the mechanical properties and the function of filtration/drainage for geotextile and material interface are properly suggested herein, for design consideration.
The compacted mudstone fragment, without adding any stabilizer is not suitable for fill material, since it is without good mechanical properties and volumetric stability. Mudstone fragment stabilized with lime has many beneficial effects: An increase in strength, an increase in bearing capacity, a reduction of swelling, a reduction of compressibility and a reduction fo the moisture-sensitivity. Adding 3%～6% lime to mudstone is the economic and reasonable one to improve engineering properties and suitable for the subgrade materials. From the point of view of soil stabilization it is not necessary to add excess pozzolanic material for mudstone fragment.
Swelling slaking phenomenon caused by surface hydration is always an inherent problem for the protection of mudtone slope. In this paper, study on swelling and slaking potentials of mudstone is the major concern. Efforts also extend to realize the mechanisms of both water absorption and clay particles' detaching of intact mudstone Laboratory experiments include swelling and slaking tests for intact mudstone merged in water and solution with different pH values. Test results include : (1) the swelling percentage of intact mudstone is about 6-10% ,(2) the swelling pressure is about 20-35t/m2 and (3) the slaking speed is about 10kg/m2/hr for the first hour immersing in water. This study concludes that drainage, sealing and water proofing are three main ways for mudstone slope protection. In practice, a covering of layers of oil and asphalt is probably an efficient solution for the surface protection of mudstone slop.