The aim of the paper was to document the use of 3D subsurface geological-geotechnical modelling to optimise the planning and development of subsurface structures in city areas. The proposed procedure was applied to the analysis of the subsoil of the City of Turin (Northern Italy). The results of more than 300 boreholes were analysed to develop a model of the geological setting up to a depth of 60 m from the surface. The cementation variability of the alluvial sediments was also spatially described and the influence of this aspect on the soil excavation resistance was highlighted. In order to face the need of archiving, correlating and analysing a large amount of data, a 3D GIS (Geographical Information System) was used to better manage the model and to achieve a useful methodological reference that would be available for the planning and construction of future underground works.
A portion of the geological model, related to the centre of the city of Turin (Italy), was chosen to set up a more detailed geotechnical model, based on laboratory tests and back-analysis procedures, as data input for some engineering applications.
Two case studies were performed concerning:
– analyses used to forecast the subsidence induced on the ground surface by the excavation of the metro line;
– the influence of the works of the metro line on the new Underground Railway Link (interference between two important underground works).
A comparison between the forecasts of the degree of cementation, supplied by the 3D model along a metro tunnel tract, and the excavation specific energy effectively absorbed by the head of the boring machine is reported to testify the reliability of the model of the subsoil of Turin centre. This comparison shows the good reliability of the model and its potential to choose of the optimal boring machines for the future development of the Underground Metro System in Turin. 相似文献
When a cut slope in a saturated clay is undertaken, a transient water flow occurs and stress transferences from the water
to the soil skeleton take place in time (consolidation). Mainly in strongly overconsolidated clays, these stress transferences
may determine swelling of soil and therefore reduction of its shear strength in time. However, the lowering of the water level
associated to the cut increases effective mean stress, which may therefore counterbalance the above-mentioned effect. In the
paper, the behaviour of a cut slope in an overconsolidated clay is analysed by a finite element program that incorporates
the Biot consolidation theory (coupled analysis), with constitutive relations simulated by the p–q–θ critical state model. In addition, the variation in time of the overall stability is assessed with a computer program that
uses the finite element results and formulations of the critical state soil mechanics. In order to achieve a more complex
geotechnical interpretation of the problem, the analysis in time of the excess pore pressures, effective stresses, displacements
and stress levels is also presented. Finally, comparisons of stability results are analysed by changing some parameters, namely
the problem geometry (weight of excavated soil) and the over-consolidation ratio of the clay. 相似文献
The overturning failure of a 13 storey residential building in Shanghai, China, has been investigated by plane strain finite element analysis (FEA). The results of the FEA indicate that ultimate failure of the building was probably initiated by the formation of tensile cracking in the reinforced concrete piles located under the side of the building adjacent to an excavation. This eventually led to complete structural failure of the piles located along the excavation side, which probably caused further settlement of the building, leading eventually to a toppling failure resulting in overturning of the entire building. Excessive tensile stress in the piles was probably caused by the combination of excavation of soil at one side of the building and the temporary dumping of the excavated soil on the opposite side of the building. It is likely that the effect of temporary dumping of the excavated soil adjacent to the building was either not considered or not properly taken into account in the foundation design nor the construction operations. A simple but important lesson to be draw from this failure is the need for engineers who design foundations in soft soil regions to consider not only the final loading conditions, but also any temporary and transient loading conditions during the construction process. 相似文献
This paper focuses on the derivation of an approximate analytical solution to predict ground surface settlements along the centre-line perpendicular to a slurry-supported diaphragm wall panel. An analytical model of trench excavation is constructed by applying linearly-distributed total earth pressure changes on the sidewalls and the base of the trench in a homogeneous, isotropic, elastic half-space. By applying the principle of superposition appropriately, an explicit solution to calculate ground surface settlements is derived by integrating Mindlin’s displacement formulae. The validity of the solution is verified by three-dimensional finite-element analyses and case studies. Based on the results obtained from a parametric study using the newly derived solution, an algebraic formula is obtained as a first approximation for calculating ground surface settlements. 相似文献
A series of parametric studies was performed to examine the influence factors affecting the settlement influence zone induced by excavation in soft clay. It was found that the excavation depth, width, the soft clay bottom depth and the rock-like soil depth are all related to the settlement influence zone. The potential failure surface, as deduced from the failure mechanism, covering the above-mentioned parameters, is consistent with the settlement influence zone. Thus, a simple method based on the analysis results is proposed to predict the settlement influence zone. Ten case histories and statistical data for the settlements in the Shanghai area were used to verify the proposed method. 相似文献
A simplified framework is proposed for evaluating the probability of “serviceability failure” in a braced excavation in a spatially random field. Here, the “serviceability failure” is said to occur when the excavation-induced wall or ground movement exceeds specified limiting values. Knowledge of this probability can aid in engineering decision-making to prevent damage to adjacent infrastructures. The proposed framework consists of five elements: (1) finite element method (FEM) for analyzing wall and ground responses in a braced excavation, (2) fuzzy set modeling of parameter uncertainty, (3) spatial averaging technique for handling spatial variability, (4) vertex method for processing fuzzy input through FEM model, and (5) interpretation of fuzzy output. The proposed framework is demonstrated through a well-documented case history. The results show the proposed framework is simple and effective for assessing the probability of serviceability failure in a braced excavation in a spatially random field. To focus on the proposed fuzzy FEM approach, the scope of this paper is limited to one-dimensional modeling of spatial variability with an assumed exponential autocorrelation function. 相似文献
This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan.Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone(EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks.The EDZ fractures terminate against pre-existing shear fractures.Therefore,even for excavations in soft sedimentary rocks,formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes. 相似文献