Published at : 19 Jul 2021
Volume : IJtech
Vol 12, No 3 (2021)
DOI : https://doi.org/10.14716/ijtech.v12i3.4158
Fahmi Aldiamar | Institute of Road Engineering, Ministry of Public Works, Jl A H Nasution No 264, Bandung 40294, Indonesia |
Masyhur Irsyam | Bandung Institute of Technology, Jl Ganesa No 10, Bandung 40132, Indonesia |
Bigman Hutapea | Bandung Institute of Technology, Jl Ganesa No 10, Bandung 40132, Indonesia |
Endra Susila | Bandung Institute of Technology, Jl Ganesa No 10, Bandung 40132, Indonesia |
Desyanti | Institute of Road Engineering, Ministry of Public Works, Jl A H Nasution No 264, Bandung 40294, Indonesia |
A shield
tunnelling technique is usually selected using earth pressure balance or slurry
methods for tunnel construction in urban areas with soft and saturated ground. Although
shield tunnelling has many advantages, incorrect determination of face pressure
could cause ground surface settlement or lifting during tunnel construction.
Numerous approaches for determining face support pressure have been published
internationally, but a suitability evaluation based on local ground conditions
in Indonesia has not been conducted yet. The completion of Mass Rapid Transit Jakarta
(MRTJ) tunnel construction project using the earth pressure balance method,
along with its adequate data, has become a sample case of the effectiveness of
each method to determine face support pressure. The study discussed in this
paper aimed to determine the linear relationship between the calculated value
and the actual measurement of face support pressure and to identify which
method most closely represents the actual condition according to the MRTJ case
study. An analytical approach using the limit equilibrium method and the numerical
approach using Plaxis 3D were conducted, followed by statistical evaluation in
the terms of coefficient of variation. The result shows that the limit
equilibrium method is effective in predicting the mean value face support pressure
and the upper and lower perimeters for tunnel construction, while the overall
face support pressure result using the shell model of the finite element method
are lower than the actual measured values. The result probably indicates the
balance state condition at the tunnel face, and the additional 80 kPa after the
second phase of excavation could indicate the need for greater pressure for tunnel
boring machine movement.
Face support pressure; Finite element method; Mass rapid transit; Tunnels
In
urban areas, tunnel construction through soft and saturated ground requires special
caution because unsuitable construction methods can disturb the surrounding
infrastructures causing them to collapse. Under such conditions, shield
tunnelling is usually selected using the earth pressure balance (EPB) method or
slurry method. Both methods reduce the disturbance at the tunnel face and
around the excavation area using a tunnel boring machine (TBM). Although shield
tunnelling has many advantages, incorrect determination
of face pressure could cause ground surface settlement or lifting during tunnel
construction. Numerous analytical, empirical, and numerical approaches for determining
face pressure have been published in international journals or in technical
guidelines, but a suitability evaluation according to local ground conditions
in Indonesia has not yet been conducted. The Mass Rapid Transit Jakarta (MRTJ)
tunnel construction project was recently completed using the EPB method, and
face pressure data according to earth pressure gauges, along with soil profile
and the results from in situ and laboratory testing, are available as a sample case demonstrating the effectiveness of the
limit equilibrium method and the 3-dimensional (3D) finite element method to
determine the face support pressure. The study discussed in this paper aimed to
determine the linear relationship between the calculated value and the actual
measurement of face support pressure and to identify which method most closely
represents the actual condition according to the MRTJ case study.
The EPB method is based on equilibrium between soil pressure and water pressure with jacking force applied on the cutterhead. A screw conveyor has the ability to adjust or control the face pressure during an excavation. For a tunnel constructed below the ground water level, the length of the screw conveyor must be designed to withstand hydrostatic pressure and transform water pressure into atmospheric pressure. An illustration of the EPB machine used in the MRTJ project is shown in Figure 1a, and the position of the pressure gauge instrumentation is shown in Figure 1b. pressure gauges were installed to measure the soil pressure exerted on the cutterhead and to inform the machine operator as to whether the estimated pressures were still safe.