By determining the earth moisture content of artificial forestland between 0 and 6 m deep in the Loess Plateau of Shaanxi province, the vertical change of moisture content, distribution and formation causes of a dried earth layer are researched. The results show that the average moisture content is 9.3%-9.5% between 2 and 4 m under artificial forest of over 10 year's growth in Guanzhong Plain, and chronic weak dried earth layers are developed which show that the dried earth layers are distributed extensively on the Loess Plateau. The southern boundary of the dried earth layer has reached the northern foot of the Qinling Mountains. When precipitation reaches 600 mm, there are weak dried earth layers between 2 and 4 m under artificial forest of more than 10 years old. When the precipitation is between 400 and 500 mm, there are moderate dried earth layers. When precipitation is above 800 mm, there are no dried earth layers. There are no dried earth layers under meadow land, corn land and less than 5 years old of artificial forestland in central and southern parts of the Loess Plateau. The development of dried earth layers under cypress forest is weaker than broad-leaved forest. Under the same climatic conditions, the development of dried earth layers under the loess tableland is nearly at the same level as the 2nd and 3rd river terrace. Dried earth layers developed in membrane water zone, and the buried depth is small and motion velocity is slow in the Loess Plateau, which is the direct water factor of the formation of the dried earth layer, while differences of tree age and tree species are the plant factors that consumed much moisture. From the depth of the gravity water and the membrane water in Guanzhong Plain, it is clear that the formation cause of dried earth layers is mainly due to natural factors. The dried layers generally develop in middle-aged artificial forestland that consumed too much moisture, which is the general character of earth moisture in subhumid and semiarid zones. The appearance of dried layers doesn't show that the forest doesn't develop in this area; this is depended on their development intensity. Artificial forest of Chinese poplar, locust tree and Chinese scholartree consuming less water can be planted in the areas where dried earth layer developed weakly, but can not be planted in the areas where dried earth layer developed intensely.
Based on weathering characteristics of the fifth palaeosol layer (S 5 ) of four sections in GuanzhongPlain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordinary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argillans, the weathered and leached loess layer, Fe 2 O 3 , CaCO 3 and Sr content under the S 5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual precipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S 5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S 5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.Guanzhong Plain, the fifth palaeosol, weathering characteristics, paleo-gravity water, paleo-moisture content, soil evaporation Loess and environment changes in China have been extensively studied. It is now widely recognized that loess in China maintains a relatively complete record of terrestrial biotic evolution, climatic change, environment change and so on [1 6] over about 2.5 Ma. Loess can be used as important criteria for contrasts between global terrestrial environmental changes [7 10] . Former studies also recognized that the loess was the indicator of cold and dry climate strengthened by winter monsoon whereas the red paleosol the indicator of relatively warm and wet climate strengthened by summer monsoon [11 13] , and that the climatic change recorded by loess-soil stratigraphy has an obvious cycle [9,10,14] . Former researches on loess at Luochuan showed that the fifth paleosol (S 5 ) was weak brown forest soil [15] . The researches for nearly 10 a have revealed that eolian deposit in the northwest of China began from the Tertiary and the climate had become dry at that time [16 19] . However, these studies did not involve the condition of the soil moisture such as the depth of gravity water distribution, the existence of dried earth layers and the change of precipitation against the soil evaporation, and researches on the depth of chemical composition migration of paleosol were insufficient. These new issues not o...
Vertical cycle karst zone has been studied for more than 100 years, however karst subzones in the zone have never been divided and affected depth of CO 2 from rainwater in the zone has never been studied. On the basis of field observation, survey and chemical analysis, the difference of karst processes indicated by CaCO 3 and pH values in fine and loose sedimentary strata as well as limestone strata, and the vertical cycle zone ascertained by predecessors can be divided into three subzones, that is, the upper first subzone, characterized by unsaturated water solution and strong dissolution processes, the middle second subzone, characterized by supersaturated water solution and precipitation, and the lower third subzone, characterized by unstable water solution and weak dissolution or weak precipitation. The three subzones can indicate the vertical CO 2 cycle. In fine and loose sediment strata, the bottom of the first subzone is the lower boundary strongly influenced by CO 2 from rainwater, soil and air; all CO 2 from rainwater, soil and air is almost exhausted in the second subzone. In the early developmental period of karst process in limestone strata, karst funnels and vertical caves do not form, vertical seeping of rainwater and soil water is very slow, and CO 2 from soil, rainwater and air almost can reach the third subzone, but in the middle and late developmental periods, karst funnels and vertical caves occur, CO 2 from soil, rainwater and air can reach deep seasonal change zone and horizontal cycle zone and quicken development of karst morphology. Deep karst morphology near groundwater level under vertical cycle zone develops better in the middle and late periods of karst process.
Combustible ice is a kind of efficient and clean energy that has the potential to be exploited in the future, exploiting combustible ice needs to understand its mechanical properties. Combustible ice is another important feature of soil which is different from soil, in order to correctly understand the distinction, this paper using soil mechanics triaxial test method, to study the mechanical properties of combustible ice. Different from previous study, this article put forward the concept of simulated combustible ice, namely through baking powder, sodium chloride, and Marine sedimentary soil to simulate flammable ice, explore a new method for sample preparation to study the mechanical property of combustible ice.
This paper adopts large diameter drill hole cast-in-place Pile of one Highway Bridge as the study case, using the pile calculatingly program, GPILE, that is a part of the common program software system of finite element method, SAP84, to analysis the pile group effect of large diameter drill hole cast-in-place Pile with different coefficients of pile group effect. This paper suggests using the ratio of the volume of pile and soil in the ambient range of pile group to express the new reduced coefficient and introducing the p-y curves of pile group after reduced as horizontal interaction model. Under these conditions, pile group nonlinearly effect of large diameter drill hole cast-in-place Pile is analyzed. At the same time, some different coefficients of pile group effects were calculated using this method. Compared these results, the feasibility and conciseness of reduced coefficient are testified.
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