Groundwater Dynamic And Its Effect For Disasters In Heifangtai Platform

Heifangtai platform is a typical platform in the loess plateau region, because of its special strata structure, since the 1960s irrigation, the springs flow at the edge of platform dramatically increased. At the same time, a large number of landslides were induced around of the platform edge. The groundwater’s activity is a main cause of the landslides, spring as natural outcrop of groundwater, and the space-time distribution of water quality and flow closely related to landslides types. In this paper, the basis of field investigation of the spring water flow, through systematic sampling of the typical spring points at platform edge and the back scarp of loess landslides, using the method of weight and the equipment of ion chromatograph, making a detailed analysis in the spatial distribution of the spring flow characteristics and landslides types, the relationship between spring water flow time distribution and landslides time distribution, the characteristic of typical spring sampling point and the spatial distribution of landslide. The main conclusions are listed as follows:(1) The spring dew point of the loess-bedrock landslide are mostly located in the bedrock layer and the loess landslide located in the loess layer. Groundwater of Heitai and Fangtai platform are primarily discharging from the eastern edge, north of the Heitai platform, the southeast edge and northeast edge of the Fangtai platform. The spring salinity of discharging section is generally low. Influenced by groundwater flow direction, the spring salinity of the northern edge of Heitai platform and southern edge of Fangtai platform increase follw the directions that from west to east and from south to north. A large number of loess landslides, accounting for 62.5%, developed in the primary discharge section of groundwater of Heitai platform, and spring flow accounting for 65% of the sum of all the spring, the two proportions are very close.(2) The amount of irrigation has an influence on the spring flow, and there is a delay in supply time. The different month’s spring flow of Heitai platform has a certain degree of change, but the change is unconspicuous. The spring flow of different sections changes and have their own disciplinarian. After frequently Loess-bedrock landslides and loess landslides, frequency of landslides occurrence are suddenly drops, indicating the brief stability. Widespread irrigation and melting of the freeze perched water in slope foot are the main reason of loess landslide development in March for the high frequency in the month. The existence of advantage channel influence the development of landslide by discharge irrigation water in form of spring.(3) The spring of Heitai platform is salt water or brine, showing slightly alkaline, and hydrochemical type is the Na-Cl type. Percent of different kinds of cationic accounted for total cations are basically stable, Cl- and SO42- accounted for the total number of anion has some change, different cations accounted for total cations rate are basically stable, and Cl- and SO42- accounted for the total anion number has certain change. The main cations and anion are Na+、Cl- and SO42- in spring. Ca2+、Mg+, Na+, K+, Cl- and NO3- of spring have the same source, the above ions are derived from the dissolution of soluble salt in loess. The value of c(SO42-)/c(Ca2++Mg2+) in spring near the 3,6 and 9 respectively, salinity of spring samples of value close is larger than 60g/L, from 35g/L to 55g/L value near 6, smaller than 30g/L value near 9, This reveals three water system have a influence of the concentration of SO42-. the most of spring quality are not influenced by cation exchange. Evaporation plays a vital role for the groundwater chemical composition Heitai platform. groundwater evolution stages of Heitai platform is at the stage of dissolving soluble salt, and speculates that the late mineralization will gradually drop, giving priority to the dissolution of minerals. Loss of soluble salts in the soil may be main reason of collapse of large area in Heitai platform.(4) Discharge salt of spring is closely related to the type of landslide. The discharge salt relatively large section generally develop in the loess landslides, on the contrary, the discharge salt relatively large section general develop in the loess-bedrock landslides. The anions concentration of spring are Cl" larger than SO42-for the development of loess landslides, and the anion concentration are SO42- larger than Cl" for the development of loess-bedrock landslide. The main reason may be the spring of discharge from the bedrock for the development of loess-bedrock landslide, whereas section spring flow from the bedrock of the development of landslide and SO42- accounted for soluble salt in bedrock is higher. The chemical types of springs for the development of loess-bedrock landslide are closed to the type of sulphate, the type of springs for the development of loess landslide are the type of chlorine salt.