Abstract:The landside section of Xiamen Xiang¢an subsea tunnel was under unfavorable ground condition with small buried depth and 3-lane large-section,which mainly is constructed by center cross diagram(CRD) method. Measured displacements and construction method of CRD were also analyzed. Results indicated that the estimation of measured displacement of CRD method should be dependent primarily on arch-crown subsidence and secondly on horizontal covergence. The curve of measured arch-crown subsidence of CRD method vs. time normally was in a shape of uplifted zigzag with a final stable value,and the subsidence is caused by each heading constituted of a certain proportion of final subsidence,which could be used as an index to forecast and control the final subsidence. The primary lining of CRD1 should be closed as soon as possible for reducing the final subsidence since half of which was caused during excavation of CRD1;experiences in this case show that the total arch-crown subsidence of CRD1 should be controlled within 200 mm for the safe operation. Combining measured displacements with field construction experiences,it shows that the guarantee of structure safety in Xiang¢an subsea tunnel is 10–15 m for space between border upon headings,1.0–1.5 m for each round of excavation(only 0.5 m for extreme poor ground condition),6 m for maximal of step length in heading,and the invert arch should be closed as soon as possible. The suggestion is verified in construction of Xiamen Xiang¢an subsea tunnel.