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ABSTRACT The caves and cantilever-like cliffs, which are called natural rock structures in this article, are caused by the dissolution and/or erosion of rock masses by sea waves, winds, river flow or percolating rainwater. They may present some engineering problems especially in urbanized areas along shorelines and riversides. The stability problems may arise in the form of huge sinkholes and cliff failures. The authors have been recently involved with the stability assessment of natural rock engineering structures in Ryukyu limestone formation as well as the intact and in-situ properties of Ryukyu limestone. The present article presents some procedures for the assessment of stability of the natural rock structures in Ryukyu limestone formation. The stability estimations from various methods are described and compared with each other and their implications in geo-engineering field are discussed in this article.. 1. Introduction The caves and cantilever-like cliffs, which are called as natural rock structures, are caused by the dissolution and/or erosion of limestone by sea waves, winds, river flow or percolating rain water and they may present some engineering problems especially in urbanized areas along shorelines and riversides. The stability problems may arise in the form of bending failure, shearing failure and toppling failure depending upon the natural discontinuities of rock mass as well as the geometry of natural rock structures. However, there are very few studies for evaluating the stability of rock cliffs and natural rock caves. Ryukyu limestone is widely distributed all over Ryukyu Islands and they form very steep cliffs along the shorelines of Ryukyu Islands. The toe of these cliffs is often eroded by sea waves and they result in overhanging rock cliffs. When the erosion depth reaches to a given depth, they topple as seen in Figure 1. One can see such examples along the shorelines of Ryukyu Islands. Similarly, the percolating ground water along faults and rock fractures can create natural caves of various scales. There are many spectacular examples in the Islands of Ryukyu. Some of the carstic caves are Gyokusendo, Ishigaki, Nakabari and Kin. Figure 1 shows an example of toppled and overhanging cliffs together with two caves at the site of Gushikawajo remains in Itoman city of Okinawa island. 2. Properties of Ryukyu Limestone The Ryukyu limestone is porous and its porosity varies between 4% to 30%. It is generally classified as sandy limestone and coral limestone and their physical and mechanical properties are 1516 given in Tables 1 and 2 [1,2,3]. Although coral Ryukyu limestone is quite porous it may be classified as medium strength rock and it is less prone to water content variations. 3. Rock Mass Characterization The authors carried out visual observations and explorations on Ryukyu limestone cliffs. The cliffs and caves at Gushikawajo site are constitued by coral limestone and bedding thickness is generally greater than 1โ2m. There are widely spaced subvertical joints in Ryukyu limestone layers.
ABSTRACT Simple index tests such as penetration tests are available in literature to infer properties of rocks and they are widely used. Particularly the needle penetration test technique is widely used in tunnels excavated in soft rocks. The authors developed a penetration test device which can be also used for medium and high strength rocks. The experimental results indicated that if the nominal strain is defined in terms of penetration displacement divided by rod diameter, the measured responses are independent of rod diameter. This testing technique is applied to various rocks and also to investigate the effect of saturation degree on the properties of soft rocks. In addition to experimental studies, some theoretical and numerical methods are used for how to infer the properties of rocks from the responses measured by this special experimental technique. The developed testing device and experimental results are presented together with those of theoretical and numerical methods. The applicability of the technique in rock engineering is briefly. 1. Introduction The estimations of mechanical properties of intact rocks are generally desired for the assesment of stability of rock structures. They are also important elements of the rock classifications used in empirical assessments of rock masses. Laboratory tests are generally used for this purpose. Nevertheless, they are time consuming due to the sample preparation as well as experimental procedures. Furthermore, they require high capacity loading devices especially for hard rocks. Some penetration tests are available in literature and they are widely used. Among them, the needle penetration test technique is widely used in tunnels excavated in soft rocks. However, there are almost no penetration test technique for medium or high strength rocks. The authors developed a penetration test device utilizing a low capacity loading device and a special rod-like loading platen with a flat-end. This testing technique is applied to various rocks ranging from soft rocks to hard rocks. A theoretical method for interpreting the experimental responses together with the use of numerical methods. This article describes the characteristics of the developed testing device and experimental results together with those of theoretical and numerical methods. It also discusses the applicability of the technique in rock engineering and the potential for further advancement of the method. 2. Penetration Test Device The penetration test device utilize a low capacity loading device and a special rod-like loading platen with a flat-end as shown in Figure 1. The device is presently used under laboratory conditions. However it can be easily taken to construction site. The diameter of rod-like platen ranges between 1 to 3 mm. However, experimental results indicates that there are some undesired stress concentrations when the diameter is less than 1mm and the rod-like platen may buckle when For the interpretation of the experimental results, the nominal strain is defined in terms of penetration displacement divided by rod 21 4 diameter. Furthermore, the applied stress is defined by dividing the applied load by the area of the flat-end.
- Asia > Middle East (0.47)
- Asia > Japan (0.29)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT The dynamic responses such as acceleration, velocity and displacement of geo-materials during fracturing have not received any attention in the fields of geo-engineering and geo-science. The recent advances in measurement, monitoring and logging technologies enable us to measure and monitor the dynamic responses of geo-materials during fracturing. The authors have been carrying such experiments on geo-materials ranging from very soft materials such as clay to hard rocks such as siliceous sandstone by using different loading schemes and loading frames. This article describes some of these experiments and experimental results concerned with the acceleration, velocity and displacement responses of geo-materials during fracturing under laboratory conditions. The velocity and displacement responses are obtained through the EPS integration technique proposed by the authors. We further discuss their implications in geo-engineering and earthquake engineering in relation to permanent surface deformations. 1. Introduction The dynamic responses of geo-materials during fracturing have not received any attention in the fields of geo-engineering and geo-science. However, these responses may be very important in the failure phenomenon of geo-engineering structures (i.e. rockburst, squeezing, sliding) and the ground motions induced by earthquakes. For example, the estimation of the travel distance and path of rock fragments during rockbursts in underground excavations is very important for assessing the safety of workmen and equipments. It is also known that the ground motions induced by earthquakes could be higher in the hangingwall block or mobile side of the causative fault as observed in the 1999 Kocaeli earthquake [1] and the 1999 Chi-chi earthquake[2]. The recent advances in measurement, monitoring and logging technologies enable us to measure and to monitor the dynamic responses of geo-materials during fracturing. Therefore, the studies concerning the dynamic responses of geomaterials during fracturing can now be easily undertaken as compared with that in the past. The authors have been carrying out such a study in recent years. The experiments have been performed on geo-materials ranging from very soft materials such as clay to hard rocks such as siliceous sandstone by using different loading schemes and loading frames [3,4]. This article describes some of these experiments and experimental results concerned with the acceleration responses of geo-materials during fracturing and discuss their implications in geoengineering and earth science. 2. Experimental Set-ups and Rocks The experiments have been carried out at the rock mechanics laboratories of three institutes, namely, Tokai University (TU) and Ryukyu University (RU) in Japan and Middle East Technical University (METU) in Turkey [3]. The loading machines of the TU and the RU are low-stiffness machines with a loading capacity of 2000 kN while the loading machine of the METU is a servo-control high stiffness machine with 2000 kN capacity. Figure 1 shows the experimental set-up at two institutes.
- Asia > Japan (0.70)
- Asia > Middle East > Turkey (0.35)