Face Pressure Calculator
This computer software is produced for calculation of face support pressure for tunnels being excavated by Earth Pressure Balanced Shields (EPBS) which is usually utilized for tunnel construction in urban areas. Deterministic and probabilistic approaches have been used for face pressure assessment.
The software aims to reduce the effects of human error and diminish result’s uncertainty. Tunnel face support pressure against collapse is calculated from the proposed methods of Jancsecz and Steiner, COB and a method base on the German standard, DIN 4085. A limit method is also applied for blow-out.
In the deterministic approach, a single value is the output of every method while in the probabilistic approach, required soil parameters such as cohesion, friction angle, natural and saturated unit weight are each simulated 10000 times. The proposed values of face support pressure by user are used to compute factors of safety which are compared to the predetermined factors of safety to calculate the probability of failure.
General features
The type and number of required parameters depends on the selected calculation approach. In the first step of data acquisition, general features and the calculation approach are chosen.
General features of the under-study profile
Determination of calculation approach
Name and type of soil layers form surface to tunnel invert
Deterministic approach
The required soil parameters of every layer are the main inputs in this approach. The final output is displayed in a new window after the definition of other variables such as partial factors of safety.
General information about the profile, soil layers’ properties and calculation results are illustrated in the output window.
Probabilistic approach
The required soil properties are simulated according to real data. The simulation process is conducted by means of the Monte Carlo technique and Box-Muller estimation method. 10000 values are generated for each soil property through the simulation process. There are 5 built-in distribution functions (Burr, Gumble Min, Generalized extreme value, Wakeby and normal). If the best fitted distribution function to the real data is one of the aforementioned functions, Its parameters can be used to generate simulated data. On the other hand, the simulation process can be conducted elsewhere and the results can be loaded from a .txt file. It is also possible to consider a single value for a property in case simulation is impossible.
The simulated data can be stored on hard drive in a .txt file. The data is saved as four 100×100 line matrices in a column and can be read from the file for for other profiles. As a result, the simulation process can be done only once for a whole project.
Selection of density function for simulation of layers’ properties
Save and load of layers’ properties
A single value instead of simulation
Definition of distribution function parameters
Predetermined factors of safety
10000 values of face support pressure are calculated through the simulation process. Factors of safety against collapse and blow-out are set by user as indices. The user also defines a number of proposed face pressure values in order to calculate 10000 values of factor of safety. Relative density of generated face pressure values are represented to help user to define the face pressure values.
A comparison of results indicates the probability of factor of safety being less than the index (predetermined) values which can be considered as probability of failure.
Final output
A curve representing the probability of failure alongside the profile’s general features are illustrated in the output window. The user is able to define which method results to be shown in the output.
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