Tiago Gerheim Souza Dias

Data Analysis of Pile Tunnel Interaction

AbstractTunnel construction in interaction with deep foundations is often a matter of concern in urban areas. However, a great deal of uncertainty is still evident in the differences between regulations for minimum tunnel clearance and in the design of preventive measures for the pile–tunnel interaction effects. To address this problem, this paper presents, analyzes, and compares over 50 reports of case studies, physical models, and full-scale and centrifuge tests on a wide range of layouts and soils. The effects of new tunnels on existing piles are described in terms of mechanisms, induced settlements, and structural forces. The data analysis reveals patterns that could not be found within the limited number of tests of each separate study. Quantitative measurements of pile settlements and axial stresses have been related to the pile position, working load, and tunnel volume loss. The results indicate that most piles do not reach failure and that for piles at a lateral distance of more than two times the...

TBM pressure models: observations, theory and practice

Mechanized tunnelling in soft ground has evolved significantly over the last 20 years. However, the interaction between the tunnel boring machine (TBM) and the ground is often understood through idealized concepts, focused mostly on the machine actions in detriment of the reactions from the ground. These concepts cannot be used to explain several mechanisms that have been observed during the construction of mechanized tunnels. Therefore, this paper presents the path from field observations to the theoretical developments to model the TBM-ground interaction more realistically. Some ideas on how these developments can be applied into practice are presented. Finally, a discussion is proposed about how an effective collaboration between academia and industry can alleviate the current concentration of knowledge in the state of practice.

TBM pressure models: calculation tools

Mechanized tunnel construction in soft ground has evolved significantly over the last 20 years, especially on the matter of settlement control. This was achieved by guiding the TBM operation to control the main factors that induce soil displacements, namely the face pressure and the closure of the soil-lining void. Nowadays, TBMs can be operated within strict serviceability requirements. However, several mechanisms of the excavation cycle are still not taken into account when estimating the induced soil deformations. Therefore, it is important to properly model the processes around a TBM, but in order for such models to be assimilated in the state of practice, they should be combined in a design framework where the operational characteristics can be assessed together with the induced soil displacements and lining forces for different project conditions. This paper presents the first step of this general project by focusing on the tail void grouting pressures. A model for the grout flow is associated with a finite element model to calculate the induced soil displacements in a dynamic equilibrium between the boundary pressures and the soil-lining gap. These two elements are combined in a calculation tool with a user friendly input-output layout.

A different view on TBM face equilibrium in permeable ground

The construction of mechanized tunnels in soft ground has evolved significantly over the last 20 years, especially in the control of the face pressure and the closure of the soil-lining void to reduce the induced settlements. On the other hand, several mechanisms of the TBM excavation cycle are still not taken into account for routine design calculations, such as the increment of water pressures in front of the tunnel face, the flow of excavation fluids around the shield, the dynamic equilibrium between the grout pressures and the excavation convergence, among others. This paper discusses specifically the issue of face pressures and how several mechanisms, which are routinely not considered, can be easily verified and incorporated into the state-of-practice of design.

A new teaching concept for axially loaded piles

It is a common feature of teaching methodologies to divide the content into modules for lectures or book sections. However, these divisions are often not intrinsic to the real problems. Students, and consequently future professionals, may fail to bridge these artificial gaps, bringing into practice a mind-set organized by educational divisions instead of the functional demands of each problem. An example of this is the division between capacity and deformability of axially loaded piles, which follows the approach of regulatory manuals dividing stability and serviceability calculations. The real underlying mechanism is that pile resistance, both on the toe and along the shaft, is only mobilized through a certain amount of displacements. This is widely recognized and often mentioned in basic literature and general educational sources. However, it still features as a side note and is not directly incorporated in the calculation methodologies. This paper evaluates an instruction methodology to tackle this issue. Pile behavior is presented within a flexible framework that directly incorporates the concept of displacement dependent mobilized capacity. Through a straightforward formulation, based on the load-transfer method, general features, such as pile compressibility, residual loads and negative friction can be explicitly dealt with. Therefore, even though these different aspects may be presented individually, they can all be pulled together for an assessment of their interdependent effects on the pile response to axial loads.