|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
ABSTRACT Sedimentary phase in Nanning, Guangxi, P.R. China were formed in paleoclimatic sequence of arid, semiarid, humid, semi-humid, semiarid, and semi-humid, etc.As a result of ancient atmosphere circumstance evolution, weak consolidation becomes an important property of the gray lagoon deposited mudstone layers in the Nanning Basin. On the other hand, it is difficult to divide the categories for a weathered soft rock, which may be affected by the sedimentary formation of soft and hard interbed alternately. Categorizing weathered soft rock largely depends on the experiences of engineers. There is a significant lack of knowledge in categorizing soft rock during site investigation because soft rock cannot be kept intact during drilling borehole. Mudstone is considered as a typical soft rockwhich is in an intergradation between rock and soil. It is very important to find a simple, convenient and feasible method to judge the borderline of distinguishing between ‘rock’ and ‘soil’ for mudstone. In this study, mudstone stability subject to water will be taken as the standard evaluation method of the borderline between rock and soil, the experimental results show that the method is applicable in practical engineering. 1 INTRODUCTION 1.1 History of depositional evolution Area of the Nanning basin is approximately 948 square kilometers. It is the system of Gary's fold in the southeast of China located on the compound upheaval belt, namely, a raising belt of the earth's crust, of the early Paleozoic era and the late Paleozoic era in the DaMing mountain-Kunlun Mountains. It has an asymmetrical wedge-shape. The Nanning basin is separated as NW-SE NaLong hollow and NE-EW BeiHu hollow by Yangmei basin protuberance in the middle of basin. BeiHu hollow is an irregular diamond shaped fault basin, which is steeply inclined along the north plane of the fault and is sloped gently along the south plane. The basin subsidence had controlled by the fault in the northern margins of the basin, the southern plane of the fault is a flat belt of a slope. The majority of materials of the Cainozoic era sedimentary origin in the Nanning basin comes from the northern and western direction of the basin, while the secondary sedimentary origin were provided by the northern and southern direction in the basin. The two directions to the north and west are the far sedimentary origin rivers delta sedimentary phase, the down-throw side of the fault in the northern margin of the basin is a fan-shaped delta sedimentary phase and that in the southern margin of basin is nearly a sedimentary origin river delta sedimentary phase. The BeiHu hollow is divided into six large sedimentary phases, i.e.,Dry alluvial fan-shaped sedimentary phase, Wet alluvial fan-shaped sedimentary phase, Fan-shaped delta sedimentary phase, Delta sedimentary phase, Normal lacustrine sedimentary phase. Salty lacustrine sedimentary phase. The depositional phases were influenced by the palaeo-structure topography, palaeoclimatology, sedimentary origin and palaeo-hydrology, etc., which indicates obviously regional, inheritable and gradual characteristics.
ABSTRACT: Based on centrifugal model tests on expansive soil railway embankments in Nanning-Kunming railway in south China•this paper studied varied stress and formation states of the embankment under different physical conditions, the centrifugal tests show that it is most important to control the compactness of embankment; considering the maximum settlement of the embankments cannot exceed 30 centermeter, limit height of embankment made of expansive soil is 15 meter. In road embankment design, 34°can be the slope angle. Compactness should be controlled at 90%. Safety measure must be taken to protect the slope from rain. INTRODUCTION In civil engineering, stress caused by soil gravity is the most important, mechanical characteristic varies with stress condition. Normal small-scale model cannot represent specialty of prototype due to small deadweight; to settle the problem, enhance the deadweight is the only approach. Laboratory test could describe the complexity of soil, if combined with field observation, centrifugal test can be a useful tool in civil engineering. Since 1980's, much effort has been put in this field in China. More attention is attracted in Geotechnical centrifugal model testing, its research results promote basic theories of soil mechanics, and are used in dock engineering, nuclear power station, high dam construction, high road embankment and high retaining wall. EXPANSIVE SOIL IN NANNING-KUNMING RAILWAY IN SOUTH CHINA There are almost 100 km2 expansive rock areas in Nanning-Kunming railway. It is forced to use this material to fill embankments. But the strength of the expansive rock is low, the average cohesion of triaxial shear test is 32.3 kpa, and inner friction angle is 8.1°with high swelling potential, the expansive rocks have a free expansion ratio of 75%—93%, expansion force is 367.5 kpa. Centrifuge model tests are carried on three different stress-strain conditions.