Construction method for improving middle partition wall CD of large-span highway tunnel

The invention provides an improved middle partition wall CD construction method for a large-span highway tunnel. The method comprises the steps of construction preparation, advanced geological forecast and measurement, pilot hole advance support construction and pilot hole excavation. Monitoring and measuring-excavating a rear pilot tunnel and erecting the primary support arch and a shotcrete-bolt support-excavating and measuring-excavating a left side wall and a right side wall in a staggered manner and erecting a steel arch and a shotcrete-bolt support-excavating and measuring-dismantling a temporary middle partition-excavating an inverted arch and erecting a steel arch to form a closed ring and shotcrete-bolt supporting, inverted arch filling, monitoring and measuring, secondary construction and next circulation. The lower step part is not provided with a temporary support, so that the working procedure operation time is shortened, large-scale mechanical equipment can be invested, the mechanical use effici