求翻译：Installation of Steel Frame in the Tunnel Initially，a 13s movie and two 10s darkness between each movie will be installed.Assume the average train speed right after leaving the station is 50km/hr,then the total length will be about 520m.The first box will be installed at a distance 30m-50m from the station.Steel frame will be installed on one side of the tunnel wall as shown in Figure 1 and Figure2.是什么意思？

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