Search

Classical bearing capacity theory was developed mainly based on spatially uniform soil properties, which cannot account for the influence of inherent soil variability. If the soil strength is heterogeneous, then using the average strength may overestimate the bearing capacity of foundations, because the failure mechanism may preferentially mobilise the weaker soils. In this study the aim is to establish a theoretical model using upper-bound solutions applied to the bearing capacity analysis of shallow foundations on undrained clay considering spatial variability. The model is derived on the principle of least energy dissipation using a four-parameter variation on Prandtl's mechanism. The theoretical model developed is verified by the random finite-element (FE) method in spatially varying soil conditions. The results show that the model can accurately capture the effect of spatially varying strength on the shallow foundation failure mechanism. The difference of bearing capacity factor between the proposed model and the FE model is within 5%, which demonstrates that the four-parameter model has an accuracy that is comparable to FE analysis with many hundreds of degrees of freedom. Another advantage of the theoretical model is that the possible non-convergence in FE analysis can be avoided, and hence, the calculation efficiency is significantly enhanced. The model is therefore suitable for rapid quantification of bearing capacity in spatially varying soils.

Fused deposition modelling (FDM) has been widely used in the field of sensor production, however, sensor fabricated adopting FDM in monitoring water pressure is seldomly discussed. In this study, one Fiber Bragg Grating (FBG) water content sensor has been designed and fabricated in order to monitor the variation of water pressure at the field. It’s worth noting that the advanced material, Polylactic Acid (PLA), has been used in fabricating sensor with favorable stability. After the fabrication of FBG sensor, calibration test was conducted by controlling and measuring water content of soil sample in a sealed chamber through manipulating pressure volume controller. It has been validated that this pressure sensor adopting FDM fabrication process has quick response and high sensitivity. Afterwards, field application of this type of sensors have been used in measuring the variation of soil water content continuously, while reading from different depth of this sensor can be compared and analyzed to summarize the influence of nature rainfall condition about the ground. To validate and verify the reliability and authenticity of developed FBG sensors, the conventional sensors have been implanted at the same depth of FBG sensors and comparison have been conducted in the entire monitoring period. It has been verified that FBG sensors have good performance when embedded into the melted PLA material, while its application in measuring soil water pressure is more sensitive and accurate.