Sustainable Tunneling and Underground Use

Drilled shafts are widely used in Dubai as the main foundation option for high towers and bridges. Hundreds of meters of drilled shafts are installed in Dubai every day. Piling industry has grown widely in Dubai over the past 2 decades. Piles of large diameters as 2.5 m and lengths up to 100 m are common. It is evident that the current practice of geotechnical axial load capacity estimates in general is conservative, and actual pile axial load capacities as demonstrated by static and dynamic loading tests is much higher than the theoretical design capacities in almost the majority of cases.

The main purposes of this study is to review the shortcomings of the commonly used theoretical axial load estimate procedures, and examine the factors and parameters controlling the estimated axial capacity (input parameters). Optimization of the conservative design procedure is suggested by careful selection of main input parameters, and calibration to static loading tests.

This paper presents the effect of Soil Parameter on the long drive micro-tunneling process. Terzaghi’s Silo Theory and Elastic Stress Relief Formulas are used for calculating the normal stress against the pipes. A detailed study tabulated for Al Jadaf Area across Oud Metha Road in Dubai, United Arab Emirates to check the effect of soil parameter, such as depth of excavation or invert level of micro-tunnelling, depth of ground water table, SPT Value and other soil properties. The study demonstrates that long term surface settlements confirm to the design theory limit. The high ground water table, fractures within the rock and close proximity to existing creek makes it very difficult to reduce the water table level in launching/receiving Pit and have difficulties in breaking the hard ground within the Pit. Determination of the surface settlement spot level difference is done physically at site by using latest surveying instrument, as described in the field exploration programme. By determining the difference between the two spot levels on a same coordinate, the amount of settlement and its effects on surface area can be established, which can be used as a guide line for future project and authentication of the theory.

With the growing economic appreciation of urban areas in large cities, building techniques that are technically and economically feasible have been widely employed to maximize utilization of spaces. Such techniques resort to large excavations to expand the land occupation rate. In this context, this paper analyzes a 24-m deep excavation located in São Bernardo do Campo, a city in the metropolitan region of São Paulo Metropolitan Region, Brazil. The local subsoil is composed by residual gneiss soil, and the retainment was executed in soil nailing. The length of the nails is variable in depth; the longer nails are introduced in the first 8 m of the excavation, and then reduced in greater depths. During the development of the retainment design, numerical analyses via limit equilibrium using deterministic and probabilistic methods considering the variations in properties of materials, demonstrated that the nails close to the end of the excavation are weakly influenced by the changes in nail lengths and diameters. In this sense, new analyses were performed to simulate the replacement of 1/3 of the nail rows for one or two rows of tiebacks at the end of the excavation to maintain stability of the retainment and reduce costs. The results for safety factor were obtained in deterministic and statistic (mean) terms. In the latter case, the reliability index and the probability of failure of the analyses performed are also presented. The results demonstrate the importance of conducting investigative analyses to determine the critical rupture surface by means of statistical analyses. In the case shown, this type of analysis proved to be more critical than the deterministic method of analysis of stability of retainment.

The excavation of shallow tunnels in urban areas requires a previous evaluation of their effects on the existing constructions. In the case of shield tunneling, the different achieved operations is a highly three-dimensional soil/structure interaction. It is very complex to represent in a complete numerical simulation and therefore, the assessment of the tunneling-induced soil movements is difficult. In this paper, three dimensional simulation procedure, taking into account in an explicit and complete manner the main sources of movements in the soil mass, is proposed. It is illustrated in the case of Lyon’s subway for which experimental data are available. The comparison of the numerical simulation results with the in situ measurements shows that the 3D procedure of simulation proposed is pertinent.

The assumptions of the application of the characteristic lines method, a homogeneous ground in particular, with an isotropic state of stress, made it a powerful and fast tool of pre-dimensioning the deep tunnels. For which the at-rest earth pressure coefficient is approaching 1 and subsequently the state of stress could be likened to an isotropic state. This method consists of taking into account the interaction between the soil and the structure, and thus supposes that the soil, in the hypotheses mentioned above, following a digging, discharges and converges towards the center of the excavation accompanied by an increase in the load applied on the support supposed perfectly circular and homogeneous until equilibrium.

Except these assumptions, among others when the tunnel is shallow, which is the case for almost all urban tunnels, the application of this method is no longer relevant, despite its practice! The generalization of the characteristic lines method that is proposed here consists in modeling the tunnel by a shell-type structure to which the initial ground stresses have been applied, the soil-structure interaction is considered as springs whose rigidity depends on the mechanical characteristics of the surrounding ground. The particularity of the springs is that they work as well in compression as in traction, indeed, the compression models the resistance of the ground to the thrust of the supports, as for the traction, it models a possible reduction of the stress applied by the ground on the support after its convergence.

This paper deals the analysis of the behavior of an underground saline cavity under the cyclic load due to traffic landing gear from the Boeing 747-400 airplane using the pseudo static approach. This cavity was located at a depth of 2.5 m from the free surface of the second runway at Es-Senia airport in Oran (Algeria). Where, this airstrip is built in very complex geotechnical conditions, which several cavities are formed by dissolution of gypsum, have been observed during the geological investigations. In-situ geotechnical studies and experimental tests carried out in the laboratory have permitted to identify the hydromechanical behavior parameters of the great Sebkha soil of Oran city. The Oran airport base is composed of a mixture of clay and silty gypsum sand with an overconsolidated behavior.

This article focuses on numerical modeling of the second airstrip of Oran airport. This modeling was performed using the finite difference software Flac^3D (v.3.1), while assuming that a spherical subterranean cavity is located 2.5 m deep. The obtained results have allowed representing the real behavior of the underground cavity and that of the runway under the action rear main landing gear of the Boeing 747-400 considering only the poromechanical behavior in this part of study.

Rigid pipes installed under high embankments are often installed using the induced trench technique by introducing a compressible zone above the pipe. A new application of tire-derived aggregate (TDA) for induced trench rigid pipes is evaluated in this study. An experimental investigation that has been conducted to measure the earth pressure distribution on a rigid pipe buried in granular material and backfilled with TDA is presented in this study. A setup has been designed and built to allow for the installation of an instrumented pipe in granular material and measuring the contact pressure acting on the pipe wall. Results show that the use of TDA as a compressible material can provide similar beneficial effects to rigid pipes compared to expanded polystyrene (EPS) geofoam and other commonly used soft inclusions. The earth pressure is found to decrease significantly all around the pipe compared to the conventional installation with aggregate backfill. The average measured earth pressure above the crown of the pipe was found to be as low as 30% of the overburden pressure for installations with granular backfill material. The pressure at the invert also decreased by about 75% with the introduction of the soft TDA zone above the pipe.

A new concept for the selection of rational construction and engineering parameters for the building of large deep-set edifices is set out for an environment where the requirements on preservation of historical sites and rational usage of land in big cities are growing more taxing. Based on the proposed geotechnical model, and the assessment of the results of numerical modeling, research and experiments, a number of techniques have been developed intended to optimize the technological modes of construction under adverse urban conditions involving hard-to-handle soils and congested urban development.

The Rohtang tunnel is about 8.8 km long and is one of the important road tunnels in the Himalayas which facilitates all round connectivity between Manali (in the south) and Keylong (in the north), with its Lahul & Spiti district headquarter. This tunnel lies in complex geology with many folds and faults intersecting it at various locations. Three major rock types include uniformly dipping sequences of phyllites, schists and gneissose rocks with a minimum overburden of about 600 m and a maximum of 1900 m. The geological complexity of area further increases due to anatexis and migmatization of rocks. In order to assess the tunnel stresses and displacement, a closed-form solution is used. The obtained results are validated using finite element analysis. The role of complex geology and high & varying overburden is considered for suitable designing of tunnel support system.

The main objectives of the experimental and numerical geo-environmental and geotechnical simulations and analyses carried out in the present study are to investigate the static stability, safety margins and engineering failure of the tomb of Sons of Ramsses II (KV5), under their present conditions, against unfavorable environmental circumstances (i.e. extensive weathering due to water and flash floods impact in the past and present), utter lack of preservation, geostatic overloading of structural rock support pillars, geotechnical and extreme seismic conditions. Also to design an appropriate geotechnical support system, according to the engineering rock mass classification, in particularly the rock mass rating RMR and quality rock tunneling index Q-system. Based on the underground engineering stable equilibrium theory and rock mass classification, three support structure techniques are provided and detailed illustrated with the case of KV5 in this study.

The water distribution network of a city is one of the most critical infrastructures. The damage it sustains during earthquakes and the ease of the restoration process define the resiliency of the system and impacts other critical lifelines. This paper presents a summary of the damage in two cities of Japan after the 2011 Tohoku Earthquake and the 2016 Kumamoto Earthquake. It focuses on the recovery process, exhibits logistical inter-dependence with other lifelines and provides information on the post-disaster data collection. An example of the actions required for recovery is given. Conclusions provide advice on the most important factors to consider for reducing damage in future events, and on the appropriate way to collect post-disaster information that can be used for decision support systems.

Tunnel beds are typically formed by massive concrete bodies. In the paper, a mechanically stabilized granular layer with a triaxial geogrid is considered as an alternative solution for tunnel beds. Experimental research was executed on a full scale model of the bed construction in the laboratory. Total settlements, resulting horizontal pressures on the walls and lateral deformations of the base of layers during static and dynamic loading with up to 2 million loading cycles were monitored and evaluated. The tests and results will be described and discussed in the paper. The construction of a mechanically stabilized granular bed derived on this basis can be presented as an innovative and effective solution for infrastructure tunnel projects.

An anchor body is formed by two parts as root zone (bonded length) and the free zone (unbonded length). The main resisting part against the pull out force is the root zone. The similar phenomena is valid for pile or pier foundations, which work according to the side friction arising from external pulling elements. Serious problems can be occur in case the loss of adhesion or frictional resistance between injected grouting material and soil interaction surface. Twelve boreholes were drilled with 22.0 cm in diameter and 2.0 m in length within the aim of assessing this problem. Four different concrete mixtures consist of standard injection mix, gravelly, fine sandy and clayey soils were poured into the holes over 1.0 m from the bottom level. Tremie pipe was also used to elimination of segregation. An anchor cable was placed in the center of each hole with 3.5 m length before the pouring process of mixtures. At the end of 28 days, after completion the setting time of concrete, tendons were subjected to the pull out tests in vertical direction. Pulling force, side friction and displacement values were compared. Thereby, the influence of impurities such as gravel, sand and clay on the adhesion strength were compared that change the mix properties during concrete pouring or injection into the anchor hole.

Due to the rapid growth of urban development, on many occasions, it may be essential to have construction activities nearby or directly above existing tunnels. In this case, the amount of additional stresses reaching the tunnel becomes a point of concern. The arching action plays the main role in the stress redistributions occurring around the tunnel, and thus the amount of increase in the lining straining actions. Therefore, the goal of this paper is to study how different soil models capture the arching effect on the stress distributions around tunnels. The predicted stresses in any geomechanical problem can be highly dependent on the yield criterion of the material model used in the analysis. The paper compares between the predictions of arching using elastoplastic and poroplastic material models. The Mohr-Coulomb model is used to represent elastoplastic models. Whereas, the Modified Cam-Clay model is used as a poroplastic model. Two-dimensional plane strain models are conducted using the finite element software PLAXIS in which the Mohr-Coulomb and the Modified Cam-Clay are integrated. Although all the used models in this study are calibrated to the behavior of the same soil, different stress redistribution behavior and values are predicted for different constitutive models.

There has been an increasing demand for new tunnels in respond to rapid growth in cities. Earth pressure balanced or slurry shield tunneling method is commonly used to construct tunnels in soft ground to improve stability and safety. The use of this kind of reinforcement in tunnel segments allows several advantages mainly related to durability aspects or when provisional lining is forecast. This paper is going to consider the mechanism of failure for tunneling in clay and to find the solution by one of the most respectable kind of reinforcement. The use of GFRP rebars as structural reinforcement in precast tunnel segments, allows several advantages in terms of structural durability or in cases of temporary lining that will have to be demolished later. The application of glass fiber reinforced polymer (GFRP) reinforcement in concrete structures has encountering an increasing interest worldwide, for several applications in civil engineering.