Chapter 3 The formation of soil and its e ngineering properties 第 3 章 土的形成和土的工程性质

1. Chapter 3 The formation of soil and its engineering properties第3章 土的形成和土的工程性质

2. §3-1 Soil formation 1 the importance of the study of soils Soils are the results of natural geological history, at the same time soils are also the most common materials distributed on the ground surface of the earth crust. The engineering properties of soils have closely relations with the engineering activities of human being. Because of complexities of soils, many engineers have been paid much attention to the study on soils. In some sense, the complexities of soils are mainly from the complexity of formation process of soils and the complexities of soils constitution. In this chapter, We are mainly concerned with the formation, constitution of soils, the classification of soils based on the different formation, since others aspects about soils will be discussed in soils mechanics.

3. 2 the soils definition Soils are porous natural materials composed of inorganic and organic matter, soils are the end product from weathering rocks.(Also we can merely take it as a stage in the gigantic cycle of mineral recycling by the movement of tectonic plates)

4. 3 the influencing factors of soils formation parent material time climateatmospheric composition topography organisms

6. §3-2 The main types of soils based on the formation process Generally speaking, the engineering properties of soils are much influenced by the varieties of formation process. So in this aspect, it is important for a civil engineer to know the soils types based on formation process.

7. 1 Eluvial soils(残积土) The eluvial soils（residual soils）are the direct products of weathering, they are formed in the place where their mother rocks are located.

8. eluvial soils Features: ● soluble materials have been carried away ● the composition has the relation with the mother rock ● different particle size ● obvious edge and corner ● thickness change greatly lower psephicity [si’fisiti] mother rock

9. 2 Slope deposits(坡积物) Qdl The slope deposits are formed from erosion of surface flow along the mountain slope surface . after being carried to the foot of hill by surface flow(面流), where the speed of flow（流速）will slow down and the slack sediments will deposit there.

10. 冲沟形成过程图 Features: ●slack condition ● the composition has no relation with the bad rock ●fine particle size ● obvious edge and corner ● thin thickness ● lower psephicity [si’fisiti]

11. 3 Pluvial deposits (洪积物) Qpl The pluvial deposits are more commonly distributed along the connection zones between the mountainous areas and plain areas. The flood water caused by heavy rain or snow dissolved when temperature rise up is the dynamic resource.

12. A B C A the zone for groundwater level deeply buried ◆large grain size ◆ lower compressive factor ◆ Higher bearing capacity ◆lower psephicity B Zone for ground water overflowing ◆sandy soils and clay are deposited alternatively ◆ the groundwater shallowly buried C Zone for periodic dry and damp condition ◆clay ◆engineering properties depends on damp condition

13. 洪积扇地形

14. 4. Alluvial soil冲积物(Qal) （1） the definition of Alluvial soil Alluvial soils are the results of river geological Action. (including river erosion ;carrying;sedimentation)

15. （2） river geological action Side erosion and sedimentation U字型河谷 （中游） Sedimentation 成形型河谷地上河 （下游） Cut erosion V字型河谷 （上游）

16. 河流侧蚀作用 牛轭湖 的形成 The result of side erosion

17. The formation of river terrace 阶地的形成 阶座基地 （侵蚀堆积） 堆积阶地 （内迭阶地） 侵蚀 阶地

18. 河谷斜坡 一级阶地 河漫滩 河床 三级阶地 二级阶地

19. （3）Faces of River deposits ◈river bed faces（河床相）: coarse sand, gravel, boulder well psephicity ◈terrace faces（阶地相）: upper part→fine sand lower part→river bed faces ◈ oxbow lake faces（牛轭湖相）: swamp d<0.005mm ooze: high water content high porosity, lower strength, high compressive

20. 5. Lake deposits (QL)

21. 6 Sea deposits (Qm)海积物 7Wind deposits (Qeol)风积物 wind sand（风积砂） wind-loess（风积黄土） collapsible soil uniform, homogeneous porous, scattered structure 8Glacial deposits (Qgl)冰积物

22. §3-3 Mineral composition in soils 1 Primary minerals（原生矿物） 2 Secondary minerals (unsolvable with water) 次生矿物 3 Soluble salt and decomposed minerals 可溶盐类 4 Organic materials（有机物质） 河谷横断面及各部位名称

23. 阶地的类型 1 Primary minerals（原生矿物） ◈ Primary minerals are from magma rock, they are mainly quartz, feldspar, ice, amphibole ◈general feature of Primary minerals : --Stable in chemical properties --weathering resistance --Good performance of engineering Properties

24. 河谷的形态 阶地的类型 2 secondary minerals（次生矿物） ◈ Primary minerals are from the process of soils formation , they are ①clay minerals（黏土矿物） Kaolinite，montomorillonite，water mica ② SiO2, Al2O3, Fe2O3: colloidal state ③Oxidized material（） The mineral described above is very important to the engineering properties of soil. Reason are： mineral particle surface→surface power absorbing water affinity(亲和力)

25. 3 Soluble salt and decomposed minerals 可溶盐类 soluble salt: NaCl, Caso4.2H2O(石膏), CaCO3(calcium carbonate) salinized soil (盐土) Usually, soluble salt in soil don’t have much influence to soil engineering properties, because its little content (in drought area, salt can be accumulated in the upper parts of ground surface), But if soil containing much salt react with water, the connection between soil grain will disappear, so the soil’s strength and stability will be decreased.

26. 4 Organic materials（有机物质） Which usually exits in the ooze. When content of ooze is more than 5%. The influence will be obvious.

27. §3-4 The structure and tectonics of soils (土的结构与构造) 一、soils structure type(土的结构类型) Which mean the characteristics of soil grain and the relationships among grains. ◇the size of grain ◇ Shape and roughness of grain ◇ arrangement of grainand ◇ connection between different grain

28. 1.Single Particle Structure (SPS) (crushed stone, gravel, sand) --d>0.074mm --no cohesion, no capillary water --permeability is obvious --high strength and low deformatio Single Particle Structure

29. 2 honeycomb structure d<0.075mm --silt grain (粉粒d=0.075-0.005mm) --clay grain (粘粒d<0.005mm) --sand grain (砂粒d=2-0.074mm) honeycomb structure

30. 3 cotton structure which in some sense like honeycomb structure The clay usually have the honeycomb and cotton structure and have the engineering properties as below： d<0.005mm big porosity (50%-98%) easy to be deformed water content (w) >75% unstable when encounter water cotton structure

31. 二.The tectonics of soil（土的构造） soil’s tectonics mean the space shape of soil layer. ♦ In north-west area loess—vertical cracks ♦ In coast area, soft clay have usually distributed, stratified structure, isotropic soil

32. §3-5 The index of physical properties of soils (土的物理性质指标) liquid solid air soils’s three-phase composition

33. W V V：total volume of soils W: total weight(KN) Vs: solid volume Ws: solid weight Vw: water volume Ww: water weight Va: air volume Vv: pore volume V=Vs+Vw+Va=Vv+Vs W=Ws+Ww

34. unit weight of solid mineral particle unit weight of water(10KN/m3) (1)relative unit weight(G)土的相对密度

35. （2）unit weight 土的重度 （3） dry unit weight土的干重度 which indicate the density of soils grain （4）saturated unit weight饱和重度

36. （5）effectve unit weight土的有效重度 （6） water content (w)土的含水量 The water content in soils, especially in cohesive soils, has much influence on the engineering properties of soils. So the determination of water content is necessary

37. (7) saturation degree饱和度 （8）porosity(n)空隙度 (9) relative porosity(void ratio)孔隙比