Greater Hyderabad Municipal Corporation proposed to build Extra dozed bridge across Dhurgam Cheruvu Lake at Madhapur, Hyderabad. The main pylon foundation is at merge point of the downhill and lake. Temporary shore protection bund of 4m height proposed to retain the lake water for constructing the open foundation. HDPE sheet and sand bags were provided on bund to control the seepage. Submersible pumps used to dewater the excavated area. Base of foundation rests on hard rock which is 7m below existing ground level and 11m from top of temporary bund. Deep excavation designed by PLAXIS software with safe slope of 1H: 1V for top 6m soil along with bund and 1H: 3V for weathered rock of 5m depth till excavation level. But during excavation weathered rock encountered at greater depth, because of which slope angle of excavation increased and fouling with foundation. Bund was re-aligned during the process of excavation with many challenges. Steeper slope angles adopted with toe protection. Continuous seepage found along the slope during bund rectification. Paper highlights the difficulties faced during excavation due to change in soil strata and describes the challenges faced in slope protection using conventional methods for safe construction of foundation. Approximately 1070 cum of concrete had been laid successfully for foundation construction by overcoming many challenges.
Subjects: Deep excavation, Dewatering, Foundation construction, PLAXIS, Seepage control, Slope protection.
Author: Raja Rajan K., Asst. Engg. Manager, Nagarajan D., Sr. Engineer and Vijayakumar T., Head of Division
Publisher: DFI