Experiment Study On The Interface Coupling Characteristics Between Distributed Sensing Optic Fiber And Soil Mass Considering Multiple Factors

The destruction of natural geological environment has become more and more serious and geological disasters happen increasingly frequent.A large number of projects related to the national economy and people's livelihood will intensify and trigger geological disasters in the process of construction and operation.In order to grasp the formation mechanism of geological disasters and guarantee the safety of construction,it is extremely important to monitor the displacement,stress and strain for the rock/soil mass and its supporting structure in geological disaster prone areas.The monitoring projects in the field of geological engineering are characterized by large quantity,long distance and highly real-time demand,so the traditional monitoring method cannot fully meet the needs of demand.In recent years,distributed fiber optical sensing technology(DFOS)has been widely used in the monitoring of geological hazards,such as landslide and ground subsidence.However,the previous research is lack of investigation on the reliability of the soil deformation data monitored by the embedded optic fiber sensor,especially lack of the study of decoupling mechanism and the factors that influence the interface coupling characteristics between distributed sensing optic fiber and soil mass.In engineering practice,engineers are adding anchorage point on the sensing optical fiber to increase the interface coupling performance between distributed sensing optic fiber and soil mass.However,the mechanism that the anchor follows is unclear.This article has conducted a series of laboratory experiments on the above issues and has obtained the following results:(1)Designed a new type of sensing optical fiber(SOF)-soil interface coupling test device.This device can be used to obtain the sensing optical fiber's force-displacement curve under different confining pressure in the process of decoupling.(2)Through conducting the SOF-soil interface coupling test considering the effect of embedded length of the SOF,it shows that the effective pullout displacement and the maximum pullout force increases with the increase of embedded length of the SOF linearly.However,the interfacial shear strength decreases with the increase of embedded length of the SOF.It showed that the failure of the SOF-soil interface is of highly progressive.That is to say,the longer the embedded length of the SOF is,the more obvious the progressive failure appears,the smaller the apparent interfacial shear strength shows.(3)Through conducting a series of SOF-soil interface coupling test considering the effect of anchorage,this article studied the SOF-soil deformation compatibility influenced by anchorage point,the diameter of the anchorage point and the interval of the anchorage point.The results showed that adding anchorage point on the SOF,decreasing anchorage point interval and enlarging the diameter of anchorage point could enhance their deformation compatibility.Therefore,it should be reasonable to set anchorage points on SOF to enhance the accuracy of DFOS monitoring data when conducting model testing and engineering practice.(4)Through conducting a series of SOF-soil interface coupling test considering the effect of confining pressure,this article studied the SOF-soil deformation compatibility influenced by confining pressure.The results showed that the effective pullout displacement and the maximum pullout force increase with the increase of confining pressure linearly.The effective monitoring range and SOF-soil interface shear strength increase with the increase of confining pressure.It is suggested that the confining pressure should be appropriately increased when embedding the SOF in engineering practice for improving the monitoring effectiveness.(5)Through carrying out SOF-soil interface coupling test based on high spatial resolution strain measurements.Namely,the Brillouin optical fiber time domain analysis(BOTDA)technology was used to measure the strain distribution along the sensing optic fiber during its gradual decoupling process from the soil mass.The shear stress distribution of fiber-soil interface was also calculated and the progressive failure was integrally revealed.At the same time,the strain distribution along the anchored sensing optic fiber during its gradual decoupling process from the soil mass was measured which verified the positive effect of anchorage point from a micro perspective.