The Analysis Of The Engineering Geological Effects Of Overburden Detecting For Engineering Geophysical Methods

As one of a essential method in hydrogeological exploration, engineering geological and environmental geological exploration, engineering geophysical methods play an increasingly important role in construction. In recent years, because of the wide range of exploration and low-cost, engineering geophysical exploration methods as a kind of indirect detection method, have been widely used in engineering construction.In many large geotechnical engineering projects,we need to detect buried bedrock, therefore the parameter of overburden such as depth is essential to engineering construction.The complexity of the underground media makes the diversity of the exploration methods. Because each geophysical methods based on different principles, its detection methods will be different. As we all know, gravity, magnetic, electrical and seismic are the main methods of the Geophysical exploration,each of them detect the underground medium by gravity anomaly, the difference of dielectric constants, the apparent resistivity difference and wave impedance difference.Each of the method detect by single Physical Parameter, because of the indeterminacy of the detection,the interpretation of the data may be different with the real Geological conditions.Overburden is made of Quaternary stratigraphy, most of the Quaternary stratigraphy is in the majority of the soil.Each of the soil has its own mechanical property, general soil because of good mechanical properties, it is smaller influence on engineering construction; Some of the special nature of the soil, such as in collapsible soil, red clay, soft soil and so on, because its poor mechanical properties, take the overburden not into consideration, the project will be uneven settlement,or poor stability and other effects. Because of the high expensive of the detection, which can explore the detailed geological information, but not all the information can acquire from this way, it is the Geophysical exploration that help us detect the geological information underground, combine with the drilling information,we can detect the overburden absolutely. However, there are many different kinds of engineering geophysical prospecting method, the detection of the overburden should be combined with physical conditions, comprehensive factors such as geological conditions and terrain characteristics. Select one or more reasonable geophysical methods to achieve the best engineering geological effects,not only can improve the work efficiency but also cost savings.This paper is based on a program with overburden detection, by performing reconnaissance study of the site geology and geophysical conditions,combine with the principles, applicability and effectiveness of the Geophysical exploration, in the analysis of the related on the basis of the advantages and disadvantages of geophysical prospecting methods and complementary, apply high density resistivity method, shallow seismic reflection method and ground penetrating radar to detect overburden, compared with the drill data,we can find that in the same conditions, Shallow seismic reflection method in overburden thickness with minimum deviation drilling data;Because of the high density resistivity method detection, as well as rock and soil water content on the impact of different coating materials based on electrical differences, the result will be high-density electrical method of detecting a large change;Geological radar need to choose the appropriate frequency, when choosing antenna to adapt to the field of geological and geophysical conditions, to achieve the depth of exploration;Shallow seismic is the use of seismic wave impedance difference to detect,general speaking, each rock has its own wave impedance, therefore the result is similar to the reality.Because of this background, when detecting the overburden, we can learn from this result,reduce the workload as well as improve efficiency. Of course,due to the uncertainty of geophysical data, in the case of local conditions do not allow drilling can also be combined with other geophysical conditions, improve the detection accuracy.