A
bstract
A method to search for particles of unknown masses in final states with two invisible particles is presented. Searching for final states with missing energy is a challenging task usually ...performed in the tail of a missing energy related distribution. The search method proposed is based on a 2-Dimensional mass reconstruction of the final state with two invisible particles. Thus, a bump hunting is possible, allowing a stronger signal versus background discrimination. Parameters of the new theory can be extracted from the mass distributions, a valuable step towards understanding its true nature. The proof of principle is based on the existing SM top pairs in their dilepton final state. The method is applicable in many interesting searches at the LHC, including dark matter candidates or heavy top partners.
The present paper investigates the problem of the stability of the tunnel face under seepage flow conditions based upon the so-called “method of slices”. This computational model improves the limit ...equilibrium method of Anagnostou and Kovári (1996) by treating the equilibrium in the wedge consistently with the overlying prism, i.e. without an a priori assumption concerning the distribution of the vertical stresses. Furthermore, it shows that tensile failure of the wedge may be more critical than shear failure, if the gradient of the hydraulic head in the ground ahead of the face is high. For an approximate distribution of the hydraulic head in the ground around the tunnel face, we derive a closed-form solution for the necessary face support pressure. In addition, we provide normalized diagrams, which allow for a quick assessment of the stability of the tunnel face.
•We analyze the stability of a tunnel face reinforced by bolts.•We propose a computational method based upon the so-called “method of slices”.•The method can consider heterogeneous layered ground and ...different bolt layouts.•We show the effects of length, distribution and installation sequence of the bolts.•We report design diagrams for homogeneous grounds with uniformly distributed bolts.
We propose a computational method for assessing bolt reinforcement of the tunnel face in cohesive-frictional soils. The method is based on limit equilibrium considerations and can be applied to heterogeneous, layered ground as well as to reinforcement layouts that are arbitrary in terms of the spacing, length, longitudinal overlapping and installation sequence of the bolts. A closed-form solution is presented for the special case of a homogeneous ground with uniform face reinforcement. An investigation is made into the influence of the unsupported span and the reinforcement scheme on face stability. The case of a stress-dependent bond strength is analysed and the results are compared with results of numerical analyses. Design nomograms are presented for the assessment of tunnel face stability in a homogeneous ground with uniformly distributed bolts, constant or variable bond strength and various installation sequences.
When planning a TBM drive in squeezing ground, the tunnelling engineer faces a complex problem involving a number of conflicting factors. In this respect, numerical analyses represent a helpful ...decision aid as they provide a quantitative assessment of the effects of key parameters. The present paper investigates the interaction between the shield, ground and tunnel support by means of computational analysis. Emphasis is placed on the boundary condition, which is applied to model the interface between the ground and the shield or tunnel support. The paper also discusses two cases, which illustrate different methodical approaches applied to the assessment of a TBM drive in squeezing ground. The first case history—the Uluabat Tunnel (Turkey)—mainly involves the investigation of TBM design measures aimed at reducing the risk of shield jamming. The second case history—the Faido Section of the Gotthard Base Tunnel (Switzerland)—deals with different types of tunnel support installed behind a gripper TBM.
Anhydritic claystones consist of a clay matrix with finely distributed anhydrite. Their swelling has led to severe damage and high repair costs in several tunnels. Gypsum growth combined with water ...uptake by the clay minerals is the main cause of the swelling process. Identifying the conditions under which gypsum rather than anhydrite represents the stable phase is crucial for understanding rock swelling. As existing studies on the anhydrite–gypsum–water equilibrium appear to be contradictory and do not provide all of the information required, we revisit this classic problem here by formulating and studying a thermodynamic model. In contrast to earlier research, our model is not limited to the anhydrite–gypsum equilibrium, but allows for the determination of the equilibrium concentrations of the individual anhydrite dissolution and gypsum precipitation reactions that underlie the sulphate transformation. The results of the paper are, therefore, also valuable for the formulation of comprehensive sulphate–water interaction models that consider diffusive and advective ion transport simultaneously with the chemical dissolution and precipitation reactions. Furthermore, in addition to the influencing factors that have been considered by previous studies (i.e., fluid and solid pressures, concentration of foreign ions, temperature), we consistently incorporate the effect of the surface energy of the sulphate crystals into the thermodynamic equations and discuss the effect of the clay minerals on the equilibrium conditions. The surface energy effects, which are important particularly in the case of claystones with extremely small pores, increase the solubility of gypsum, thus shifting the thermodynamic equilibrium in favour of anhydrite. Clay minerals also favour anhydrite because they lower the activity of the water. The predictions from the model are compared with experimental results and with predictions from other models in the literature. Finally, a comprehensive equilibrium diagram is presented in terms of pore water pressure, solid pressure, temperature, water activity and pore size.
•Technical and economical evaluation of deformable segmental linings.•Discussion about radially and tangentially deformable linings.•Development of design aids for practical application.•Structural ...and cost comparison: resistance vs. yielding principle.
The rock pressure developing when shield tunnelling through squeezing rock may damage the segmental lining. This paper analyses the extent to which the application range of shielded TBMs in squeezing rocks might be widened by using deformable lining systems, while considering the aspects of structural safety, construction management, TBM technologies and construction costs. Deformable lining systems exploit a basic feature of squeezing ground: the rock pressure decreases when deformations are allowed to occur. Two basic options are available: radially deformable linings, where rock deformations occur outside the lining extrados; and tangentially deformable linings which can accommodate a reduction in their circumference. Comparative analyses of radially or tangentially deformable linings and conventional, practically rigid segmental linings show that deformable lining systems offer advantages only for deep tunnels crossing rocks of relatively fair quality. In such cases, rock pressure can be decreased significantly by allowing deformations to occur, so that a deformable lining (particularly, a tangentially deformable one) offers a more effective use of the available bored profile than a thicker stiff lining of the same concrete quality.
► We simulate the complete artificial ground freezing process in 3 underground projects. ► We succeeded to obtain class A predictions which agree well with the monitoring data. ► We determine the ...thermal parameters of uncommon materials via back analysis. ► We analyze a problematic case and show a potential reason for the not-closure of the frozen body.
The artificial ground freezing method is often used for ground improvement in urban tunnelling through water bearing soft ground. The paper presents and quantitatively analyses results from the monitoring of three challenging applications of artificial ground freezing in urban underground construction projects. The interpretation of the field measurements is based upon coupled thermo-hydraulic numerical simulations using the finite element code FREEZE. The first case study concerns the construction of a twin tunnel for the Fürth subway in Germany in soft ground with significant seepage flow. The emphasis of this study was on a realistic simulation of the overall project situation during the growth stage of the frozen body. The second case study relates to a platform tunnel in a station of the Naples metro and aims to determine the relevant thermal parameters via back analysis and to make comparisons between model predictions and field measurements. In the third case, that of a tunnel beneath the Limmat river in Zurich, the numerical simulations were used to identify potential problems in the application of artificial ground freezing caused by geometrical irregularities in the actual borehole-layout, in combination with seepage flow.
Compressed air energy storage （CAES） systems represent a new technology for storing very large amount of energy. A peculiarity of the systems is that gas must be stored under a high pressure （p - ...10-30 MPa）. A lined rock cavern （LRC） in the form of a tunnel or shaft can be used within this pressure range. The rock mass surrounding the opening resists the internal pressure and the lining ensures gas tightness. The present paper investigates the key aspects of technical feasibility of shallow LRC tunnels or shafts under a wide range of geotechnical conditions. Results show that the safety with respect to uplift failure of the rock mass is a necessary but not a sufficient condition for assessing feasibility. The deformation of the rock mass should also be kept sufficiently small to preserve the integrity of the lining and, especially, its tightness. If the rock is not sufficiently stiff, buckling or fatigue failure of the steel lining becomes more decisive when evaluating the feasible operating air pressure. The design of the concrete plug that seals the compressed air stored in the container is another demanding task. Numerical analyses indicate that in most cases, the stability of the rock mass under the plug loading is not a decisive factor for plug design.
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