Application of Distributed Optical Fibre Sensor for Strain and Temperature Monitoring within Continuous Flight Auger Columns

A Review of Recent Distributed Optical Fiber Sensors Applications for Civil Engineering Structural Health Monitoring

“…Figure 53a displays the continuous axial strain profile at several loading stages of the working load (WL). The authors reported witnessing a consistent DOFS strain increment as the load increased along with unexpected spikes (between 16 m to 43 m depth) on all four independent fibers likely due to the pile's stiffness variation (similarly to [123]). Despite acknowledging the strong possibility of the bored pile's shape non-uniformity and concrete stiffness inconsistency, due to the inaccessibility of the stiffness data, the authors assumed it constant for the calculation of its axial forces (Figure 53b).…”

“…Instead, as foreshadowed in Section 2 , OFS are characterized by corrosion immunity, high durability, resistance to electromagnetic interference, small size, lightweight and, most crucially, they easily surpass the punctual measurement limitation. In more detail, as clearly illustrated in Sienko et al [ 123 ] for the example of pile monitoring, traditional monitoring tools can carry out measurements only on a punctual scale (as visible in Figure 49 a). Whilst the situation can be improved by installing several sensors along the monitored axis (quasi-distributed sensing illustrated in Figure 49 b), the resulting profile still lacks sufficient accuracy to properly represent the actual pile strain profile.…”

“…Yet, as stated by Seo [ 7 ], the use of the CFA is not entirely failure-proof. Indeed, the force distribution along a column and its base’s load-bearing capacity might be affected by issues such as cross-sections reductions or bulge formations (soft soils), soil mining problems (loose gravel and sand can be mixed with concrete materials at the bottom of the pile), hole stability and auger rates control problems (ground with voids or water pockets) [ 123 ]. The assessment of the column force distribution and base load-bearing capacity is, therefore, a key aspect of SHM and was, therefore, the topic of numerous experimental campaigns.…”

“…Sienko et al [ 123 ] also performed a 12 m long strain and temperature OFDR DOFS monitoring on a CFA pile. The article reported the pile strains sampled during a multi-load steps compression test in addition to its accumulated shortening.…”

“…Measurement schemes for concrete piles: (a) spot, (b) quasi-continuous, (c) distributed[123].The two kinds of pile whose testing methodologies have received a significant performance boost from the integration of DOFS are the Continuous Flight Auger (CFA) or Auger Cast Piling and the Rotary Bored Piling. Research articles on their testing procedures are herein reported.…”