Research Of Engineering Geology Zoning In Yao River And Fenghua River Basin

In order to guarantee Yao River and Fenghua River basin whose acreage is about 600 square kilometers suatainable development, research of engineering geology is quested and effective method is to find out engineering geologic condition in Yao River and Fenghua River basin. Then based on the engineering geologic condition, Yao River and Fenghua River basin is divided into engineering geology zoning so that scientific data are provided for project’s planning, surveying, design and construction.Based on the existing data about the study area and analysis results from four drills in the study area, quaternary geological structure, engineering geologic condition, engineering geologic zoning about the study area have been researched by use of surface survey, drilling, geophysical exploration, geochemical exploration, in-situ tests and soil test. The achieved results are as follows:1、Quaternary stratigraphic units from the new to the old in the study area are Zhenhai Formation of Holocene(Qhzh), Ningpo Formation of upper Pleistocene(Qpn), Dongpu Formation of upper Pleistocene(Qpn) and Qianjiang Formation of mid Pleistocene(Qpq). Zhenhai Formation and Ningbo Formation are deposited in Yao River valley. Zhenhai Formation, Ningpo Formation, Dongpu Formation and Qianjiang Formation are deposited in Ningfeng plain.2、Since the late Pleistocene, there have breen three transgression periods and two transgressive intervals in the study area. From top to bottom, they are corresponding with MIS1、 MIS2、MIS3、MIS、MIS5 resulted from marine oxygen isotope in the eastern coastal plain of China. Transgression of Holocene is corresponding with MIS1 transgression period. Transgression of mid-late Epipleistocene is corresponding with MIS3 transgression period. Transgression of early Epipleistocene is corresponding with MIS5 transgression period.3、Zhenhai Formation is composed of sediment during MIS1 transgression period of Holocene. Ningpo Formation is composed of sediment during MIS2 transgressive interval of late Epipleistocene and MIS3 transgression period of mid-late Epipleistocene. Dongpu Formation is composed of sediment during MIS4 transgressive interval of mid Epipleistocene and MIS5 transgression period of early Epipleistocene.4、From top to bottom, there are four hard pans in the study area. They are the first hard pan of late Epipleistocene, the second hard pan of mid Epipleistocene, the third hard pan of early Epipleistocene, and the fourth hard pan of late mid-Pleistocene. The distribution ranges of the first, the second hard pan are larger. The third, fourth hard pans are sporadic distribution in the study area.5、There are ten engineering geological layers(from ① to ⑩) of Quaternary, thirty-nine engineering geological subhorizons of Quaternary and one engineering geological layer of underlying bedrock. Within sixty meters from the surface in the study area, the bearing strata of foundation or pile foundation are engineering geological layers of ④,⑤,⑥ and engineering geological layer of underlying bedrock. In detail, they are engineering geologic subhorizons of ④1, ④3-2, ④3-3,⑤1, ⑤3-1, ⑤3-2, ⑥1, ⑥3-1, ⑥3-2, ⑥4 and engineering geological layer of underlying bedrock. Their physical and mechanical indexes and parameters of engineering design have been suggested.6、According to features of depth, combination and distribution between every bearing stratum, The study area can be divided into six engineering geologic zonings. Then, bearing strata and foundation type of every engineering geologic zoning have been suggested.7、Regional stability of the study area is better. Geologic disaster doesn’t often happen in the study area too. But, we should pay attention to ground setting resulted from projects of city construction, excavation, rail transportation, highway and so on. Moreover, the lithology about engineering geological subhorizons of ②Ib,②2,③1-1,③1-2 in the study area is silt or silty clay, so they will have a soft soil subsidence during the earthquake.