Mass movements are often associated with periods of heavy rainfall that penetrate the ground causing a reduction in its shear strength parameters and generating instabilities that can lead to rupture. These instabilities when in densely populated areas can cause catastrophic occurrences with loss of human life and environmental and economic damage. This article discusses the results of ground strain measurement obtained by using a special optical cable and a Distributed Temperature and Strain Sensor (DTSS) unit. The optical cable was installed on a slope in São Paulo state, Brazil. Optical fiber technology allows instantaneous and periodic monitoring of surface strain evolution that occurs over a wide area, complementing traditional geotechnical instrumentation, made up of punctual and manual measurements, which is prone to error and requires more time for verification. The optical cable used for this study acts as an intrinsic sensor, where the cable itself acts as a sensor element, thus performing the function of receiving and transmitting information, unlike other sensors, called extrinsic, which only transmit information from a point sensor. The optical fiber sensor used are lightweight, malleable and immune to electromagnetic interference, making them ideal because they are rugged and allow for practical control and reliable results. For the optical cable analyzed for this article, the maximum strain variation and maximum strain relief values were 1528.29 microstrains and -2867.69 microstrains, respectively.

The fiber optic industry had a significant development from the late 80's. Besides communication, this technology is also being used for measuring a monitoring deformation, displacement, acceleration, pressure, temperature and chemical properties among others (MORIKAWA, 2004). Among the technological advantages of the use of fiber optic sensors, the most notable are: (i) sensing the possibility of several signals over a single optical fiber (multiplexing data), (ii) ease of reading of the signals (good value signal versus noise), (iii) measurements over long distances (remote sensing), (iv) immunity to electromagnetic fields, (v) absence of spark, and (vi) low weight and low material reactivity. The use of fiber optics as a tool for different kinds of geotechnical monitoring can become a highly attractive and cost effective when compared to conventional instruments such as piezometers, inclinometers, among others. A single fiber optic cable may cover a larger monitoring area compared to conventional instrumentation, and the possibility of monitoring more than one physical quantity with the same fiber optic cable. This paper covers all steps undertaken to define the size of one type of cable Anchoring Element (AE) for monitoring soil movement in natural hillslopes. To fulfill this objective laboratory tests were carried out in LACTEC, Curitiba-PR, and results and conclusions are shown in this paper.