| Author: | Lai, Hon Kit |
| Title: | Stability of segmental excavation depth for a novel excavation method by robotic system for caisson construction |
| Advisors: | Siu, M. F. Francis (BRE) Chan, P. C. Albert (BRE) |
| Degree: | M.Phil. |
| Year: | 2026 |
| Department: | Department of Building and Real Estate |
| Pages: | 1 volume (various pagings) : color illustrations |
| Language: | English |
| Abstract: | Large diameter reinforced concrete pile was a foundation system widely and popularly used at a city where numbers of high-rise buildings were built, such as Hong Kong. The construction method of this type of circular pile was somehow constructed by manual method in the past in Hong Kong. The use of this manual method was criticized as being too dangerous and harmful to the workers since numbers of accidents had been frequently recorded. Shaft collapse during the segmental excavation by hand of the whole caisson was identified as one of the common hazards or accidents recorded. Meanwhile, a lack of researches regarding assessing the stability condition of the shaft during segmental excavation were able to be located. As a matter of fact, this manual method of construction actually owns numbers of important advantages, such as low mobilization difficulty and construction cost, etc. These advantages are very beneficial and competitive according to the geographical condition in Hong Kong. The introduction of robotic system to replace the manual tasks was therefore proposed in order to re-popularize this construction method by eliminating the mentioned shortcoming. Concurrent to the prototyping of this new excavation system, a study to the subject hazards of shaft collapse during excavation phase was launched. This research was performed to realize the safety level of the segmental vertical excavation by adopting simulation method using Finite Element software followed by regression analysis to the computed results from Finite Element programming. This approach was justified to be effective since numbers of previous researches have also adopted a similar method to investigate geotechnical problems. A dataset of FOS from 400 FE models were firstly created according to the combination from ranges of various geometrical and geotechnical parameters as variables. Statistical software was then used to analyze the dataset. Certain relationships between the variables including geometric parameters of the subject caisson (such as caisson diameters, overall caisson depth from the ground, segmental excavation depth, etc.) as well as geotechnical parameters (including cohesion and friction angle of the soil) and the values of Factor of Safety (FOS) were firstly examined and then presented. After associated regression analysis to the computed outcome, empirical equations enabling for predicting or assessing the FOS of each segmental vertical circular excavation with respect to the known geometric and geotechnical parameters were eventually formulated. One of the formulated equations were examined and tested during the full-scale site trial of the prototyped excavation system. Afterwards, the regression equations were comprehensively compared to the prediction of FOS according to the method/table/chart/equations from previous researches so as to visualize the phenomena, reliability/functionality owning by the regression equations developed by the author. The contribution of this research in academic point of view is the availability of predicting FOS of a segment of a vertically excavated circular shaft. This prediction is able to ensure a minimum safety standard of a maximum excavation depth allowed without inducing potential hazard to person or surrounding. Another academic contribution from this study is the reflection to the deficiency owning the previous research outcomes since some of the important factors (such as segmental excavation interval, arching effect related to the caisson diameter, etc.) influencing the prediction of FOS of a segmental excavation interval of a vertical-circular shaft have not been fully incorporated. Another implication and benefit in a long-term basis from this research project to construction industry of foundation in Hong Kong is regarding the development of prototype excavation robot replacing the manual digging task responsible by caisson workers. This replacement of excavation tasks from manual to machine-aided provides an alternative solution for foundation works to be built in a site with limited working space or logistic assess. This alternative solution may eventually improve the competitiveness among different construction methods and achieve the purpose of cost-saving or cost-effectiveness. |
| Rights: | All rights reserved |
| Access: | open access |
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