环境地质学 Environmental Geology

第三讲 环境地质学Environmental Geology 主讲人：万新南教授 Prof. Wan xinnan 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 6、Pre降水、江河与洪水7、Mass Wasting Processes表层整体再塑　　（滑坡、泥石流、溶蚀、塌陷） 8、海岸线与海岸塑造过程9、生态与植被环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 7、Mass Wasting Processes 表层整体再塑　（滑坡、泥石流、溶蚀、塌陷）环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes There is nothing inorganic.... The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries古玩家 chiefly, but living poetry like the leaves of a tree, which precedes flowers and fruit-not a fossil earth, but a living earth.... Henry David Thoreau 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes A、Flowing sand, landslides, and rock falls are examples of mass wasting, the general term for gravitationally induced downslope movement of debris. B、Mass-wasting processes operate on sloping lands; eventually the debris reaches a stream or gully where fluvial processes continue the erosional process. 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes Rockfall Rockfall occurs where a cliff of bedrock is exposed to weathering and pieces of the bedrock are pried loose and fall, bounce, or roll to rest at the base of the cliff. The resulting deposit is called talus崩塌岩堆 (Behre, 1933; Schumm and Chorley, 1966; Rapp, 1976). In an irregularly eroded cliff, talus cones may develop in the gully冲沟 head areas (Fig.6.2). In more extensive cliffs, coalescing聚集 talus cones form a more continuous blanket of debris referred to as scree 山麓碎石(Jeffreys, 1932; Adrews, 1961). 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes Rockfall Talus will not rest at an angle greater than the angle of repose. The angle of repose is measured similarly to dip of sedimentary rocks, i.e., from the horizontal, and is typically about 33-35°. Bedrock composition, as well as talus particle size, angularity, and sorting, has some effect on the angle of repose; large angular boulders may rest at up to 40°. The angle of repose of open-pit mine waste rock is approximately 38°. 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes Rockfall One of the world's most famous talus slopes is the one which formed an impedment障碍 to prospectors开拓者 during the Klondike gold rush of 1898. the snow-covered talus slope, called the Scales, was the only access to Chilkoot Pass and the Yukon River. The pass was guarded by the Canadian Northeast Police, who required every prospector to carry 1 ton of supplies up the slope and into the interior. 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes One of the world's most famous talus slopes is the one which formed an impedment障碍 to prospectors开拓者 during the Klondike gold rush of 1898. the snow-covered talus slope, called the Scales, was the only access to Chilkoot Pass and the Yukon River. The pass was guarded by the Canadian Northeast Police, who required every prospector to carry 1 ton of supplies up the slope and into the interior. 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes Creep Creep is the slow, downslope movement of soil, weathered rock, or other surficial debris. Movement is by quasiviscous flow, occurring under shear stresses sufficient to produce permanent deformation, but too small to result in a discrete failure surface such as a landslide. 环境地质学Environmental Geology

第三讲 Part three地球表层的塑造过程 Mass Wasting Processes Creep Creep may be caused by numerous phenomena. For example, in terrains subject to frost, rock or soil may get heaved up perpendicular to the slope upon freezing, and returned vertically downward during a thaw. Thus, over time, material on a slope is likely to move downhill. Micro-landslides and random movements such as overturned trees, etc., all contribute to creep. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Landslide is the process whereby a distinct mass of rock or soil moves downslope due to gravity. Landslides, unlike creep, have one or more distinct failure surfaces. Landslide velocities are typically on the order of 1 m/day to perhaps 300 km/hr as in the special case of air-entrapped landslides generated by earthquakes. Shreve (1968) believes that the prehistoric Blackhawk Landslide in California slid at immense speeds on a layer of compressed air that was trapped beneath the debris. The landslide, consisting of 320 million m3, traveled 8 km across a desert floor at an average slope of 2.5°. [Hsu (1975) challenges the airlubrication空气润滑 hypothesis假说 in favor of a debris flow mobilized by collision of particles within a dust-laden cloud.]. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Landslide activity typically increases after prolonged rains, or after the frost leaves the ground in the spring. The novelist Firtsch (1980) describes the ominous hazard of landslides which weighs heavily on the minds of people who live in the steep slopes of the Swiss Alps: 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Classification of landslides. For simplicity, landslides can be classified into two groups: 1) translational, and 2) rotational. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Translational landslides (Fig.6.8) slide along a bedding plane or other plane of weakness in the rock. The entire mass moves parallel to this plane, as illustrated in the rock slide in Fig.6.1. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Probably the largest translational landslide to occur in historic times happened in 1925 in the Gros Ventre River Valley in Wyoming (Fig.6.8A). About 40 million m3 of Pennsylvania Tensleep Sandstone slid on a bedding plane inclined about 20°. Heavy rain and stream undercutting at the base of the mountain slope contributed to the failure (Voight, 1978). A 45 km2 lake formed behind the debris; two years later the dam was overtopped by heavy spring runoff, and six people drowned淹死 in the ensuing跟着发生 flood. The 1903 landslide disaster at the mining town of Frank, Alberta, was a translational slide which developed along a prominent set of joints which dip into the valley. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Rotational landslides (“slumps” or “slips”) develop in surficial deposits or weathered rock (fig6.1). They may be natural in origin or induced by man. The failure surface is roughly arcuate弧形 in cross section (spoon-shaped in three dimensions). At some places the occurrence of a landslide at the base of a hill may leave the hillslope above unsupported, and so another landslide occurs (Crandell, 1951). The chain-reaction type of stair-stepping slope failure up a hill is called progressive failure. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides 22Mathematical analysis. Mathematical models of landslide stability are presented in Terzaghi (1950; 1962), Scheidegger (1961). Stout (1969), Jaeger (1972), Schuster and Krizek (1978), and Huang (1983). Most problems involving the stability of slopes are associated with the design and construction of unbraced无支挡 cuts for highways. A very generalized rule-of-thumb is given by Terzaghi and Peck (1948): 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides The role of rock anisotropies is very important in the design of stable slopes. Fig4.24 shows an example of a stereographic solution of a possible wedge failure due to two prominent planar anisotropies on a deep cut. The use of stereoplots in analysis of slope stability is explained in other Chapter. 环境地质学Environmental Geology

第三讲 Mass Wasting Processes Part three地球表层的塑造过程 Landslides Consider the landslide cross section shown in Fig.6.16 having a unit thickness of 1 m. Assume the debris consists of three layers of known density and shearing strength as shown. First assume a trial failure plane #1 (ABCD). The slide can be arbitrarily divided into a convenient number of slices, and the moment of each computed . Accurate drafting and measurement of moment arms is necessary. The sum of the eight driving moments is 29,507 kN-m. The resisting moment is then determined, and is equal to the shearing strength (in this case the so-called undrained shear strength Su is used) times the length of arc in each slice times the moment arm. The sum of the resisting moments is calculated to be 34,500 kN-m. The factor of safety, F.S., is equal to the ratio of resisting moment to driving moment: F.S. (2.2.9) In this case: FS=34,156/29,507=1.16 环境地质学Environmental Geology

第二部分　地球的外部过程

环境地质学 Environmental Geology