Evaluation of the Structural Health Monitoring Results of the Applied Fiber Optics in the Pile-Raft Foundations of a High-Rise Building

Abstract

Fiber optics are increasingly being used in structural health monitoring applications. In addition to the well-known advantages, they most reliably transmit the stress–strain condition of the structure in the long term. This article presents the results of structural health monitoring on the embedding of fiber optics in the upper layer of the raft over the entire area of a high-rise building in Astana city (Kazakhstan), including the 75-storey 320 m block R. Temperature and strain data were collected constantly via a distributed fiber optic strain sensing system (DFOSS). The analysis of strains in fiber optic chainage indicated that the compression strains were observed over the entire area of the building, with values from −20 to −40 µε and with progression of the compression loaded up to −80 µε along the core wall closer to the eastern facade of the building. Tension strains were concentrated along the extreme axes of the building, with a predominance in the southern part of the R block, as well as in the immediate vicinity of the columns, in a range of −20 to −40 µε, with separate spots from −40 to −60 µε. Individual patches of tension strains near the columns have been explained by the increased deflection of the raft under the application of a concentrated load (columns). Fiber optic monitoring results at the time of testing did not exceed the permitted values for high-rise building operation; however, they characterized the general picture of the strain in the raft plane and made it possible to determine the initiation of cracks in concrete at an early stage.

Features of Testing Piles for High-Rise Buildings in Difficult Soil Conditions in Astana

“…This article discusses the experience of designing the foundations of high-rise buildings, taking into account the specified features of the types of foundations. The issues of testing heavily loaded piles and geotechnical monitoring, which are important elements in the design of high-rise buildings, are discussed in detail in previous publications [1][2][3]. Features of high-rise buildings impose increased requirements on the results of EGE (engineering and geotechnical elements) and must solve the following main tasks during their implementation: study of the geological structure of a mass of soils of large volumes (up to 60m in depth and at least 2 more widths of the foundation outside its contour); a reliable assessment of the hydrogeological and hydrochemical conditions, both in the compressible soil massif and in the pit zone and adjacent territory, with the establishment of their corrosive aggressiveness, in time; determination of deformation and strength properties of dispersed and rocky soils at large ranges of stress changes; instrumental observation and monitoring of deformations of the soil massif of the foundation base and the adjacent territory under static impacts [4][5][6].…”