Tunnel excavation usually will causes soil redistribution and settlement. Hence, for urban areas where large building used pile for foundation, tunnelling might affect the pile integrity. Engineers pose great role in order to correctly estimating the stress changes onto pile structures. It is particularly vital to estimate the tunnelling effects when new tunnels are to be built near an existing pile. Therefore, this paper presents a physical modelling to investigate the tunnel-pile-soil interaction. Sand box test with pile and tunnel model was developed to imitate the field condition. The laboratory testing conducted with constant parameter tunnel cover to tunnel diameter ratio of 2.5 with pile to tunnel distance of 1.5 of tunnel diameter. Two rate of tunnel excavation were carried out. Laboratory tests determined the longitudinal and transverse ground surface settlement induced by tunnelling, as well as the movement and induced bending moment on a single pile foundation. For validation, initial results were compared with previous findings and shows an agreement. Further test then conducted with higher tunnelling speed. With higher speed, it was found that surface settlements, pile movements and bending moment are more affected.
This paper studies the effect of the specimen sizes and shapes on the settlement behaviour of sand soil with gypsum from Al-Najaf city in Iraq. The investigation aimed to verify the impact of the studied parameters of the prediction of the settlement using reliability-based analysis. Three sets of soil samples with different shapes and sizes, 60 mm diameter Oedometer cell, 60 x 60 mm box container and 100 x100 mm box container were remoulded with three different densities related to the maximum dry density, 100%, 95% and 92%. The results reveal that different settlement behaviours were determined at several normal stress levels during the soaking process. The samples exhibited reductions in volume due to the applied stresses, while under the same level of normal stress, the final settlement values due to soaking were higher for the samples with a lower value of initial relative compaction. Further, the test results showed that at any initial relative compaction and applied vertical stress, the higher settlement value is achieved by the larger square specimen (100x100)mm.
Tunnelling close to existing structure in urban area has become unavoidable. The progression tunneling activities induced ground movement and might affect the integrity of existing structure especially the one lies within the tunneling influence zone. It may cause catastrophic failures of structures and can cause losses of human lives. Therefore, considering its risk, this study focuses on the tunnel-soil-pile interaction by performing a physical model testing. By conducting a series of laboratory tests, the ground subsidence and pile behavior is presented herein. For a twice diameter distance of tunnel and pile, the pile axial settlement is 0.04% of the tunnel diameter respectively, while the maximum pile bending moment is 4928. 93kN.m. Maximum ground settlement is 0.56% respectively to tunnel diameter. To sum up, the axial displacement of pile decreases when the pile located further away from the tunneling zone. Similarly, the ground surface subsidence decreases when the pile location is more in distance during the tunneling advancement.
One of the common practices in the field of geotechnical engineering is the use of prefabricated vertical drains (PVDs) for ground improvement work. PVDs provides shorter drainage paths to hasten the consolidation process. The performance of the PVDs depend on the spacing, length and characteristics of the PVDs, and the condition of the surrounding subsoil. Three case studies were carried out for the validation process by comparing the actual results from PLAXIS 3D with manual spreadsheet predictions. For this research, PVDs with four 4 different spacings and lengths were constructed at the sites to obtain an optimum geometric design. Based on the analytical calculations, simulation predictions and actual results from the sites, the PVDs installed with a triangular pattern and a spacing of 1.2 m and depth of 36 m achieved the highest settlement reading and consolidation rate in 6 months, with an accuracy of 86.5% for the validation process.
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