滑坡型泥石流转化机理研究—以四川省达县青宁乡滑坡为例

Slide-debris flow is debris flow which is transformed from landslide consecutively in a short time, it comprises of two phases: First, Landslide starts to slide; Second, landslide changes to debris flow. Slide-debris flow which brings great property and life loss happens frequently at home and abroad. In order to forecast the happening possibility and scope of slide-debris flow, transfromation mechanism of Slide-debris flow must be studied. Research on transformation mechanism of slide-debris flow is intersectant science of landslide kinetics and debris flow starting theory, It is a fringe problem as well as front problem of geological hazard. This paper takes Qingning slide-debris flow in Da County, Sichuan Province for example and has studied the mechanism of its instability and transfromation into debris flow through indoor test (including usual soil test and ring shear test) and digital modeling method.The research gets the following conclusions. Qingning Landslide took place mainly because of confined water head arising from rainfall infiltration. Before Landslide occurring, it rained continuously for 22 days, accumulated precipitation arrived at 521.6mm.Investigation shows that strata of Qingning Landslide contains quaternary loose accumulation, slip soil and highly weathered bedrock, which is a good condition for formation of confined water in the slope. Further more, groundwater seepage in the slope body and corresponding slope safety factor before landslide occurring have been computed through finite element method. The result shows that because of infiltration of rainfall, confined water head in the slope arose sharply, accordingly, the safety factor of the slope declined quickly. The result also shows that force put on the slide body by the rock mass detached from Dazhaiyan mountain was the direct factor for landslide occurring. Qingning slide-debris transformation mode has been summarized, the process the landslide changed into debris flow is divided into three phases in the prospective of macroscopic geological condition: landslide occurring, transformation and debris flow. Landslide occurring phase is from slope’ local creeping slide to Landslide occurring; transformation phase contains slide body sliding on the slide bed after slide occurring and sliding on the slope after shearing opening; debris flow phase is that slide body breaks up completely and flows downward into the ditches. The transformation mechanism of Qingning slide-debris flow has been studied through indoor ring shear test of slip soil. The result shows that transformation mechanism contains two points: first, during slide body sliding on the slide bed and slope after shearing opening, shearing shrinkage, grain crushing and grain layering brought about declining of its volume and produced excess pore water pressure, and because producing velocity of excess pore water pressure is much greater than its dissipating velocity, shear strength of slide body decreased sharply because of accumulated pore water pressure. Second, grains crushing and grains layering during slide body sliding brought about thick liquefied layer at the bottom of the slidebody, liquefied layer contained high water content and its shear strength was very low, its thickness increased as the sliding displacement increasing. Liquefied layer makes slide body sliding fast and easily break down to debris flow. Excess pore water pressure and liquefied layer made shear strength of slidebody became very low, furthermore, water in the pit of slope joining in the slidebody was also a facter that made slidebody accelerate the transformation. Influence of slide body thickness and fine grains content to transformation of slide-debris flow has been studied through ring shear test. The result reaches two conclusions. First, thickness of slide body affects transformation of slide-debris flow by two ways, porewater pressure and effect of “soft base” increases as thickness of slide body increasing.so the thicker slide body is ,the easier transformation is. Second, actual dissipating velocity of porewater pressure should be considered when studying the influence of fine grains content to tranformation of slide-debris flow. There should be a critical content of fine grains which makes the difference of producing and dissipating velocity of water pore pressre greatest, this value is the best for slide-debris transformation. The whole process of slide-debris flow transformation is reproduced through discrete element method. Transformation mechanism of slide-debris flow is studied through monitoring various parameters including pore water pressure, grain crushing and grain layering in the slide body during the transformation. The result confirms and supplements the transformation mechanism of slide-debris flow got from ring shear test well.

南沙群岛工程地质环境分区与珊瑚礁工程地质特性研究

Nansha Islands as sacred territory of China, containing abundant natural resources is the important area of sustaining development of Chinese people. Safeguarding and developing Nansha Islands has become one important part to develop ocean resource of China in 21 century. Engineering geological problems will be faced inevitably in the processes of engineering construction. Coral reef is a new kind of soil and rock and has special engineering characteristics. This doctoral dissertation researches deeply and systematically the regional engineering geology environmental properties and quality, engineering geological characteristics of coral reefs sand on the basis of synthetic analysis of hydrology, climate, geology, geomorphology and engineering field exploration information and combining the experimental data. 1. Put forward the division program of engineering geological environment of Nansha Islands according to the data of hydrology, geology and sediments, and also deeply study the properties of each division. Evaluate the quality of engineering geological environment by fuzzy mathematics and draw the evaluation map of quality of engineering geological environment. The research work provides background support of engineering geological environment to program of resource development in Nansha Islands. 2. Structures of coral reefs have been analyzed. The model of engineering geological zone has been proposed on the basis of geomorphologic zone and combining the strata and ocean dynamic environment. The engineering construction appropriation of each zone is praised. 3. The physical and mechanical properties of coral sands are researched. The results show that coral sands have high void ratio, non-regular shape, easy grain crushing and large compressibility. Shear-expansion takes place only at very low confining pressure and shear-contraction of volumetric strain occurs at higher confining pressure. Internal friction angle decreases with the increasing of confining pressure. The grain crushing property is the main factor influencing the mechanical characteristics. 4. A revised E-ν constitutive model is proposed which considers the change of internal friction angle with confining pressure, and parameter values are also determined. 5. The stability of Yongshu Reef by is analysed for the purpose of serving engineering struction. The process and mechanism of deformation and failure of foundation and slope is analyzed by finite-element method.

HG 186.15-186.25-3

Major grain crushing towards the centre of the section. A few lineations and grain stacks also present.

HG 186.15-186.25 Thin Section

Coarse grained sample with multiple fine grained domains. Clasts range from small to medium and sub-angular to sub-rounded. Mainly contains grain crushing (with grains crushed into one another) and short distance lineations. A few rotation structures are seen and fine grained sand domains can also be seen.

HG 186.9-187.0 D.E.

Coarse grained sediment with a few fine grained matrices. Brown sediment with small to medium sized clasts. Clasts range from sub-angular to sub-rounded. Organic material present. It contains rotation structures throughout as well as edge-to-edge grain crushing. Fine grained clay domains are present and lineations can also be seen. Minor amounts of grain stacking can also be seen.

HG 188.60-188.70 Thin Section

Dark brown sediment with mainly small grains. Clasts are sub-angular. Abundant in lineations, grain stacking, and minor grain crushing. Lineations are oriented in multiple directions.

HG 196.20-196.30 Thin Section

Brown, coarse grained sediment , with clay material. Clasts range from small to large, and sub-angular to sub-rounded. Organic material can be seen. Lineations are abundant. Grain stacking edge-to-edge grain crushing can also be seen. Organic material can be seen. Edge-to-edge grain crushing is seen throughout the image. Contains the inclusion of a finer domain.

HG 198.20-198.35 Thin Section

Coarse grained brown sediment with angular-sub-angular grains. Contains mainly medium sized clasts with a few smaller aggregates. A dark organic rich domain can be seen within this sample. Grain crushing (edge-to-edge and into one another) can be seen alongside with grain stacks, and silt caps.

HG 206.85-206.95 Thin Section

Coarse grained sample with sub-angular to sub-rounded clasts. Clasts range from small to medium sized. Major grain crushing seen throughout the sample. Grain stacking and lineations are also present. A dark organic rich domain can be seen within the sample.

HG 215.65-215.75 Thin Section

Brown to dark brown sediment with small to medium sized clasts ranging from sub-angular to sub-rounded. This sample contains a coarse grained domain and a fine grained domain. Clear boundaries can be seen. Grain stacking can be seen in the coarse domain, while lineations are the dominant microstructure in the fine grained domain. Minor grain crushing can also be seen. Some of the coarser domain is rich in clay and organics.

HG 216.35-216.45

Brown, coarse grained sample. Clasts range from small to medium in size and sub-angular to angular. Patched of clay rich domains can be seen throughout the sample. Rotation with and without a central grain can be seen throughout the sample. Edge-to-edge grain crushing and grain stacking can be seen throughout the sample.

HG 225.15-225.25 Thin Section

Dark brown sediment with sub-angular to sub-rounded grains, that range from small to medium in size. Lineations with fractured grains are abundant, and grain crushing can also be seen. Minor rotation can also be seen.

HG 230.75-230.85 Thin Section

Coarse grained sediment with fine grained domains, clay material, rotation structures and lineations. Clasts range from sub-angular to sub-rounded. Mainly brown sediment with darker patches of brown throughout. Major amounts of grain crushing can be seen in the coarse grained material.

HG 244.40-244.55-B Thin Section

Coarse grained sample with sub-angular to sub-rounded clasts ranging from small-large in size. Rotation structures, grain crushing and lineations were seen throughout the sample.