| Seepage in rock and soil is the main factor that induces all kinds of geological disasters.How to grasp the distribution and migration principles of seepage field in the rock and soil is an important subject of the research of geotechnical engineering and engineering geology.Due to the limitation of monitoring principle,method and material,the traditional seepage monitoring technology can not meet the needs of monitoring,analysis,evaluation and early warning of rock and soil mass.Distributed optical fiber sensing technology(referred as DFOS),has broken through the limitations of the traditional monitoring technology,and realize continuous,long distance and distributed measurement,which is an important development direction of engineering technology and monitoring technology in twenty-first Century..In this paper,the distributed optical fiber monitoring technology was studied,which is based on three different kinds of rocks and soils,the seepage of rock mass,sandy soil and cohesive soil,respectively.Based on distributed temperature sensing(DTS),an internal heating type of carbon fiber sensing cable was designed and developed and the concept of characteristic temperature value of the temperature was proposed,the characteristic temperature value between the flow rate and the rock and soil was established,the monitoring system for the rock and soil seepage field was designed based on DTS as well.The feasibility and reliability of the system were verified by laboratory model tests and field monitoring.The work carried out in this paper and the results achieved are as follows:(1)The monitoring technology of the seepage field of rock and soil was summarized,and the advantages of distributed optical fiber monitoring technology and its applicability in the monitoring of seepage field of rock and soil were introduced detailedly in this paper.(2)The rock and soil were divided into fractured rock mass,sand soil and cohesive soil based on the characteristics and the law of flow movement in every seepage fields,respectively.The seepage field models were analyzed,as well as the corresponding issues in monitoring technology was reviewed in this paper.(3)The heating principle of temperature measurement technology of optical fiber was presents,at the same time.An internal heating type of carbon optic fiber was designed.The temperature difference between the rock mass and flow can be increased actively.The sensitivity for seepage field monitoring was enhanced greatly,as well as the monitoring range and accuracy has been greatly improved.(4)By using DTS system,the seepage characteristics of three kinds of field,fractured rock,sand soil and cohesive soil were clearly achieved.The characteristic temperature was confirmed based on the laboratory tests.The linear function relation between seepage rate and temperature was calculated.It is proved that the monitoring system can be effective and can achieve quantitative monitoring of rock and soil seepage field,which provided a new means for the study of seepage field in rock and soil.(5)A DTS monitoring system for seepage field of rock and soil mass was established.The design principle of the system was proposed based on the characteristics of seepage of rock and soil,the basic principle of seepage field monitoring and the design of event monitoring,global monitoring and quantitative monitoring were introduced,as well as a set of complete seepage field monitoring program,the characterization of flow data and processing method were also introduced.(6)Combined with a pit of groundwater extraction process in Changzhou,China,the distributed temperature sensing cable was used and the effectiveness of DTS system in seepage monitoring was verified.The steps details of the field test were explained,also,the burying and monitoring method for optical fiber temperature measurement was designed.During the 9 days' monitoring process of the pumping test,the temperature date of sensing fiber near the location of the pumping process was monitored and the temperature anomalies were found,which indicated the location of seepage event.The sand soil produced a steady seepage in the events of pumping process by analyzing the temperature data. |
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