Experimental Validation of Deflections of Temporary Excavation Support Plates with the Use of 3D Modelling

Abstract

Almost every project is accompanied by earthworks, very often involving various types of excavation, and the work of people in the excavations. One of the most important tasks in earthworks is to ensure that the walls of the excavation are protected against sliding and that people working in and around the excavation are safe. Very often, in addition to criteria relating to safety and stability of the excavation, economic considerations are also an important criterion. This issue arises as early as the design stage and is related to the choice of construction and materials of which the shoring is to be made in such a way as to be able to withstand the pressure of the soil, ground loads resulting from stored excavated material and the operation of working machinery. Ongoing monitoring of the excavations and their reinforcement is also very important. The paper describes the unique results of experimental field tests, the purpose of which was to analyse the values of deflections of steel support plates of temporary excavation carried out on the object in 1:1 scale. The course of the experiment is presented for excavation support plates with a total depth of 6 m. Direct tests of the deflection arrow were carried out using two techniques, traditionally with a patch, and with laser scanning. Field tests were carried out for the designed situation without backfill load as well as for backfill load of 3.84, 15.36, 26.88 and 38.4 kN·m−2, respectively, for two measurement stages. Stage-I of the study consisted in collecting the results for soil in intact condition, whereas Stage-II collected results for loosened soil. The research experiment was supported by numerical calculations performed using the finite difference method in variational approach. The measured maximum deflections ranged from 14.40 to 16 mm, and the calculated values were 14.95 and 14.99 mm. The comparison of calculation results and tests proved to be very consistent. The analysis of the values of deflections showed that backfill load does not have a significant effect on the deflection of the lower plate, but it does affect the deflection of the first plate up to a depth of 1.2 m. Based on the obtained results, it is recommended to assume the limit (maximum) deflection arrow for support plates of temporary excavations at least as wgr= L/130, where L is the span of the plate. The calculation of deflection values was based on deflection values obtained experimentally and numerically for two steel variants: S235JR and S355JR. The wgr indicator of the maximum deflection arrow proposed by the authors is not stipulated by the industry standards, but it can be very helpful for the designing of excavation reinforcement.

Review of Sensor-Based Subgrade Distress Identifications

“…Poor design and construction quality of subgrade slope, improper control of parameters such as verticality, levelness, slope and standard thickness, large earthwork excavation, and poor supporting measures, or natural disasters such as rainfall, flood, landslide, and earthquake will also have an important impact on subgrade slope, which will lead to the problem of subgrade slope collapse. Buried sensors [80,81] Terrestrial Laser Scanning (TLS) [82][83][84][85] Slope crack Buried sensors [86][87][88][89][90] Subgrade slope crack refers to the crack phenomenon that appears on the road or railway subgrade slope. These cracks are usually caused by geological conditions, natural environments, or human activities.…”

“…Abdelhalim et al [87] pointed out that the method of evaluating the strength of a weak slope by using a ground laser scanner makes the evaluation faster, safer, and more systematic. Kopras Marek et al [88] used a laser scanner to obtain the complete data of subgrade slope geometry and analyzed the slope stability according to the data. Zheng Xiangtian et al [89] used a ground laser scanner to output the landslide as point cloud data, built a three-dimensional model of the main hidden arc of secondary sliding on site, and provided data for the residual dangerous rock mass according to the surface deformation monitoring, which provided support and a decision-making basis for the slope instability research.…”