Experimental Investigation On The Motion And Dynamic Response Of Tunnel Element In The Process Of Immersing

The paper is carried out in the background of Hong Kong-Zhu Hai-Macao Bridge Project’s immersed tunnel, based on a series of physical model experiments, to study the motion and dynamic response of tunnel elements in the immersion under the ocean environment conditions (the irregular waves and currents).First, the current and wave fields are tested in the immersed tunnel trench. Second, the influences of the significant wave height Hs, the peak frequency period Tp, the velocity of current v, the overweight of tunnel element η and the immersing depth d are considered, the motion responses of the tunnel element and suspension lines force are measured emphatically in the model experiments. Based on this, the law of motion and dynamic responses of the tunnel element under the action of current and wave are analyzed.Conclusions are as follows:(1) In the range of the experiments, the immersed tunnel trench has a a significant effect on the current. The vertical distribution of current velocity in front of the trench has a good consistency with the theoretical vertical distribution.The ratio of reduction of current surface velocity in the center line of the immersed tunnel trench is up to50-70%. The vertical distribution of current velocity in the trench is linear along the water depth. The influence of the trench is little to the waves.(2) Under irregular wave action, the conditions of significant wave height is no more than1.2m, when the negative buoyancy is greater than1.3%(the more strict standard is greater than1.6%), the maximum value of six components of motion of the immersed tunnel element is more stable, which can be called stable region of the motion of immersed tunnel. The conditions of significant wave height is1.8m, even negative buoyancy is greater than2.0%, the maximum value of six components of motion of the immersed tunnel element remains instability; Therefore, the conditions in the stage of immersing are suggested significant wave height is no more than1.2m and the negative buoyancy is not less than1.3%.(3) In the range of the experiments, compared with the simple wave action, when the current velocity in front of the trench is not greater than1.0m/s, the changes of laws of motion of immersed tunnel occurred mainly in the condition of negative buoyancy η=0under the action of wave and current. This change mainly reflected in:the random extreme surge of immersed tunnel is significantly increased under the action of wave and current; Current, in a certain extent, played a carm effect in pitch and heave motion of immersed tunnel; The presence of current increases the yaw motion of immersed tunnel.(4) In the range of the experiments, with the increases of the significant wave height, mooring lines tension increases. The tension of mooring lines in the side facing the waves is a little greater than the back side. The maximum force of mooring lines in the immersed tunnel has little difference with the maximum force of mooring lines in the immersed barges. The maximum mooring lines force in the immersed tunnel and barges changes basically in the range of50-280KN. The maximum suspension lines force changes basically in the range of1000-5500KN. The difference between suspension line force and mooring lines force is up to one order of magnitude or more.(5) With the increases of the negative buoyancy, the maximum suspension lines force increases;In the range of the experiment (6-14s), the maximum suspension lines force occurs in the peak frequency period Tp=8s. In order to ensure the stabilization of immersed tunnel in the process of immersing、suspension lines tension is evenly distributed and do not back to0, the negative buoyancy shoud not be less than12%.(6) When the condition of negative buoyancy is1.32%, the immersing operation window determined by the motion response is Tp=6s, Hs=0.6m. The freeboard elimination stage is the most unstable phase in the process of immersing.(7) With the maximum suspension lines force500t as standard which is allowed, the immersing operation window determined by the dynamic response is Tp=6s, Hs=1.5m.