Effects of different processes of tunneling on displacements soil using 3D Finite Element Method

The excavation process of tunnels induces stresses and deformation in the surrounding soil. The method of excavation is one of the major problems related to the safety of the operators and the ground stability during the construction of underground works. So, it is necessary to choose an ideal method to minimize the displacements and stresses induced by tunneling. The main aim of this study is to simulate numerically the effect of different processes of tunneling on ground displacements, the settlements at surface soil and the internal efforts induced in the lining tunnel; in order to select the best process of excavation, which gives us a less effects on displacements generated by tunneling, thus, ensuring the stability and the solidity of the underground constructions. In addition, this study allows us to control and to predict the diverse movements generated by tunneling (displacements, settlements, efforts internes) exclusively for the shallow tunnel nearby to the underground constructions in the urban site. This modeling will be done by employing five different processes for tunnel excavation using the NATM (New Austrian Tunneling Method) method. The first process, the modeling of the excavation tunnel, is done almost in the same way as in reality; the partial face excavation, with seven slices, made by the excavation. The second process, by partial face excavation, is divided into eleven slices, next, we used the partial face excavation by nine slices, and then in thirteen slices. Finally, the dig is made by full-face excavation. The paper contributes to the prediction of the response of the soil environment to tunnel excavation using the NATM method and to minimize the diverse movements generated by tunneling. The appropriately chosen methodology confirms that displacements and subsidence are strongly influenced by the tunneling method. The three-dimensional Finite Elements Method using Plaxis3D program has been applied in the numerical simulation. The study resulted in the recommendation of a process that minimizes the effect of excavation on subsidence and ground displacement for a particular Setiha tunnel.

Use of Underground Constructions Enhanced with Evaporative Cooling to Improve Indoor Built Environment in Hot Climate

Underground constructions (UGCs) have been used globally to accommodate a wide range of building usage, such as offices and shopping malls. Most of these constructions suffer from a lack of natural ventilation as well as daylight, as they are completely built under the surface of the earth. This has caused many issues related to discomfort, impacting the activity and the productivity of users. This study aimed to analyse the effect of the use of UGCs in hot regions, enhanced by partly elevated external walls which reach aboveground to ensure natural ventilation and daylight, with relatively small amounts of glazing to minimise the influence of solar heat gain. The study used a real built underground room with field measurements for indoor temperature and relative humidity. Moreover, the study used the computer tool EDSL TAS to simulate the performance of the model throughout the year after a field validation. It was concluded that the use of UGCs in hot climates should be encouraged as natural ventilation and daylight can decrease temperatures by 3 °C in summer, and the utilisation of evaporative cooling can cool the indoor environment by nearly 12 °C. Furthermore, heat transfer was highly affected by the external environment. It was found that the amount of heat transfer doubled in comparison between under and aboveground constructions. The use of small windows for ventilation caused high humidity, even in hot regions, during summer.

Can Underground Buildings Be Beneficial in Hot Regions? An Investigation of Field Measurements in On-Site Built Underground Construction

Globally, there has been a remarkable growth in the number of underground constructions (UGC) such as railways, offices, hospitals and shopping malls. This expansion is a result of urban area extensions that are limited by the availability of buildable land. Underground construction can also be used to protect people from the harshness of the outdoor conditions. The aim of this research is to investigate the impact of underground construction in hot regions. The major issue with most of the current UGC is the lack of natural ventilation and daylight. This has a clear negative impact on the user’s perception and comfort. The new design elevates the external walls to place some of the windows above ground for the purpose of natural ventilation and providing a view. The study conducted an experiment using an underground room enhanced with field measurements to ascertain the indoor temperature as well as relative humidity. In addition, the study used an energy simulation to calculate building heat transfer and solar heat gain. It was revealed that the use of UGC in hot regions promoted with the addition of natural ventilation can lower the indoor temperature by 3 °C in summer.

Bulking instability analysis of the horizontally stratified rock reinforced with bolts based on cusp catastrophe model

The sedimentary rock masses are commonly seen in underground engineering, and it is a threat to the safety of underground constructions greatly. Bolt supporting reinforcement works effectively in enhancing the rock in underground engineering. In this study, the roofs made of the horizontally layered rock were simplified to the rock plate structure with two different constrains, and a cusp catastrophe model was established based on the structural mechanics. With the application of the developed cusp catastrophe model, the influences of ratio of span to thickness, the amounts, and the preload of the bolts on the stability of the stratified rock were studied. Findings show that the installation of bolts can increase the anti-bulking capacity of the layered rock. The bolts can change the failure of the layered rock from bulking failure to shear failure. Improving the integrity of the layered rock is also helpful for enhancing the resistance to the bulking instability.

Assessing the impact of the development of an urban district on shallow groundwater using the integrated urban hydrological model URBS

<p>The urbanisation leads to modifications in the water budget, not only at the surface but in groundwater as well. Few urban modelling studies deal with this topic, due to the lack of appropriate models. The URBS (Urban Runoff Branching Structure) model has been developed since several decades to simulate water transfers at the scale of an urban district. An integrated modelling approach is deliberately adopted to account for the numerous elements that influence urban hydrology: the spatial distribution of the sealed surfaces, interactions between the urban soil and water networks or underground, sustainable drainage systems…. In URBS, the spatial discretization of a catchment is based on Urban Hydrologic Elements (UHE) constituted by cadastral parcels and the adjacent streets, connected to the drainage network. URBS is able to perform continuous and long-period simulations (typically several years) of water fluxes in urban districts for small time-steps (typically few-minutes), with rainfall and potential evapotranspiration as input data.</p><p>The URBS model is adopted to study the hydrological impact of the Moulon district layout, a 200 ha development operation of the Paris-Saclay Cluster (currently underway). The project should result in an increase of sealed surfaces from 14% to 35% and a densification of underground constructions such as networks and basements. A shallow unconfined aquifer extends on the whole area. The fluctuations of ground-water levels have been monitored at an hourly time-step with 8 piezometers since 2012. Water-table levels exhibit significant variations, with near-saturation levels during winter and several meters depths during summer, although the piezometers do not all exhibit the same dynamics.</p><p>A calibration of the URBS model is first conducted for a 2-year period using only piezometric data and no flowrate data. The calibration is solely performed for the parameters influencing the soil compartment: soil permeability and parameters of the sewer infiltration process. Model performances are rather satisfactory with good representation of the observed levels for several piezometers, despite some difficulties for two piezometers exhibiting atypical variations. Once the URBS model is calibrated for the initial situation, simulations are conducted for the project layout (accounting for land-use modification and underground constructions) so as to evaluate the hydrological impacts of the development. Simulation results suggest that an increase of water table levels might be expected after the development of the district (this somehow surprising result may partly originate from the decrease of evapotranspiration fluxes associated with the increased of sealed surfaces).</p><p>The analysis of these first simulations also suggests that large uncertainties might be expected regarding the water levels computed by URBS. A simplified uncertainty analysis (based on Monte-Carlo simulations) is thus conducted to evaluate and distinguish uncertainties associated with model parameters and the total uncertainties in model outputs. While the results clearly evidence the importance of total uncertainties (although the uncertainties due to the model parameters remain low), they also confirm that groundwater depths could be reduced by the construction of the Moulon district.</p>

On the design of the dewatering system of a large excavation in Barcelona (Spain) used for the construction of the high speed train tunnel

<p>Underground constructions in urban environments are more and more frequent, and usually, they are undertaken below the water table. The interaction between groundwater and underground constructions is a relevant topic that has to be carefully considered because unforeseen incidents may appear during these constructions. This paper shows the methodology used to design the dewatering system of a large excavation below the water table in a high populated urban area. The excavation was required for the construction of the assembly shaft of the tunnel boring machine that was used to excavate the high speed train tunnel below Barcelona (Spain). This methodology was useful to design an efficient dewatering systems that allowed constructing the assembly shaft in safe conditions and without producing appreciable impacts around the construction site. The most important step of the proposed method was the hydrogeological characterization of the soil because this allowed building a realistic and representative numerical model. This work shows the importance of interdisciplinary approach because the dewatering system was designed combining field work, classical analytical solutions and numerical methods.</p>

SPECIFICS OF FORMING OF STRESS BEHAVIOR OF CONTAINING BLOCK OF UNDERGROUND CONSTRUCTIONS OF HYDROTECHNICAL COMPLEX IN PROCESS OF ITS ERACTION

On the results of numerical simulation of stress-strain behavior of containing block near machinery hall and transformer room of Rogunskaya Hydro Power Plant carried out using method of finite integral equations for model of linear deformable quasi-isotropic surrounding of laminated rock solid the character, regularities and specifics of stress behavior distribution of containing block are established. The estimation of impact of gradual revelation of full cross section of machinery hall on changing of elastic convergence “machinery hall bottom – cope” and forming of nonelastic deformation zones near its contour is given.