Research On "Embedded-in-Rock" Foundation Pits In Qingdao Area

Foundation engineering is a systematic engineering involving engineering geology, hydro-geology, engineering structure, techniques and management of construction, etc. Geological conditions are the main factors controlling selection of supporting scheme and of design computation. For the foundation pit projects of revealing the overlying sandy soil stratum and cutting a certain depth into hard bedrock in the excavation range, any mono-supporting scheme seems insufficient for the dual requirements of safety and economy. For this kind of foundation pit projects, a compound supporting system combining a variety of combination types, and hence new problems are posed in this field.In this paper one such foundation pit project in Qingdao Area, where granite is commonly seen, is taken as an engineering case. After analyses of design boundary conditions, engineering design aims, scheme selection, constitutive model, design computation, design expression, construction techniques based on information technology, etc., modeling principles of constitutive model and comprehensive determination methods of design parameters of "embedded-in-rock" foundation pits. Therefore, design and computation problems of "end-suspended pile" encountered in pile-row support scheme in "embedded-in-rock" foundation pits are thus solved.On the basis of research results, the following conclusions are reached:1. It is a fundamental principle that establishment of constitutive models of foundation pit projects should fit the actual work conditions to the utmost degree. Generally speaking, except for natural slope scheme or cantilever support scheme, phased mathematical modeling is recommended according to the actual excavation conditions, so that under all circumstances the foundation pit can meet the requirements of engineering design goals of the project.2. Owing to the imperfection of geotechnical-design theories and deficiency of practice experience, design outcomes of foundation projects can be examined and verified by construction techniques based on information technology. This is a very important verifying method, and can attain the purposes of examining, verifying and modifying design outcomes, accumulating engineering experience and promote the development of design theories. 3. "Embedded-in-rock" foundation pit projects are an engineering category of special geological conditions, and hence compound supporting system of multiple composite structures is usually adopted. A support structure combination of "pile-row + anchoring-grouting" can supply the requirements of design aims in a better way. According to actual work conditions, the design of mathematical model can be divided into three phases: pile-row model, "end-suspended pile" model and compound soil-nail wall model.Geotechnical design and computation is a complicated field beyond complete comprehension of human beings; therefore, in this paper the research results of design methods of "embedded-in-rock" foundation pits are of reference significance to peer engineers. Design process and methods comply with common principles of foundation pit design, so it can be some guidance to young geotechnical engineers.