In initial studies, the tunnel model in the LECM was conceptualized as a longitudinal continuous Euler-Bernoulli beam, as its simple computation and flexibility in complex analysis.
And then we'll come up with general formulas for the mean and variance and standard deviation of this distribution, which is actually called the Bernoulli Distribution.
And if you do that with a Bernoulli Distribution, we learned in the video on Bernoulli Distributions, that the mean of this distribution right here is going to be equal to p.
The reason for this phenomenon is that the Euler-Bernoulli model excludes the shearing deformation of shield tunnels compared with the Timoshenko model, leading to a smaller deformation of tunnels.
It is because that the Euler-Bernoulli beam overestimates the internal forces within the tunnel, while the Timoshenko beam overestimates the bending stiffness of joints between rings.
We have a Bernoulli Distribution right over here, and we know that the mean of this distribution or the expected value of this distribution is actually going to be p.
Nevertheless, scholars noticed that the Euler-Bernoulli model failed to indicate the dislocation between rings, while it widely occurred in in-service shield tunnels.
To simplify the calculations, the Euler–Bernoulli beam model assumes that the tunnel section undergoing bending deformation is always perpendicular to the neutral axis, as shown in Figure 4.