The "guiding wall + large pipe shed" is
basically the only method for tunnel entry at present. When the surrounding
rock condition is good, it is a waste to use guiding wall and large pipe shed,
whereas when the surrounding rock condition is bad, it is insufficient in
specificity and safety. Therefore, the Coulomb soil pressure theory is used to
calculate and analyze the soil pressure on the front slope of the tunnel
entrance during the construction process, obtaining the conclusions that the
end wall of the entrance is an important measure to stabilize the front slope
of the entrance and controlling the primary support settlement is the key to
the construction of the portal section. Then, the Rankine earth pressure
principle is used to calculate the "shallow buried equal pressure"
burial depth of surrounding rocks at all levels of the tunnel. The tunnel
support structure is in a favorable stress state without bending moment under
shallow buried equal pressure, and that is in the most unfavorable stress state
under only lateral load. The maximum internal force of the support structure is
calculated, and the reasonable thickness of the structure is obtained. This
serves as a reference value for increasing the stiffness of the
"exposed" and near exposed shallow buried eccentric pressure tunnel
support structure by increasing the thickness of the structural section. The
essence of the bias state is the vertical deflection of the direction of the
main stress action under the positive pressure state, which simplifies the
calculation and analysis of the primary support under bias pressure to the
deflection of the main stress direction under the positive pressure. Finally,
an engineering example is used to illustrate the advantages and disadvantages
of the "guide wall + large pipe shed" method and the "shed
hole" method for tunnel entry, proving that the current tunnel entry plan
still needs to be optimized. As weill, an engineering example with fully-and
stronglyweathered granite geology with significant shallow buried bias with
support structure "exposed" is used to verify the advantages of the
above technology. It is concluded that using retaining walls to stabilize the
front slope of the tunnel entrance is a key measure for tunnel entry; the
construction of the portal section should focus on controlling support
settlement, the method of increasing the stiffness of the support structure in
the exposed part of the shallow buried bias tunnel with exposed support
structure should be adopted.