Rotary excavation construction case | Beijing-Taiwan Expressway G3 expansion of the Bengbu Tushan Huaihe Bridge

1. Project overview

1. Project name: Beijing-Taiwan Expressway G3 expansion of Bengbu Tushan Huaihe Bridge

2. Project location: south bank of Zhoujiahuai River, Qinji Town, Yuhui District, Bengbu City, Anhui Province

3. Project type: road bridge

2. Geological conditions and construction challenges

1. Geological overview:

○ Soil layer structure: upper soft soil layer, silty soil, fine sand layer round gravel soil layer, and need to be embedded in weathered gneiss

○ Special geology: Granite rock strength 800MPa

2. Main technical difficulties and challenges:

○ High rock entry depth requirements (design rock entry depth ≥ 8 meters), low drilling efficiency of hard rock layers

○ Soft soil and fine sand layer are prone to collapse and shrinkage, and the mud wall is difficult

○ Adjacent to the Huaihe River and surrounding residential areas, strict environmental protection requirements (zero mud discharge, noise control ≤ 75dB)

○ The space for cross-river construction is limited, and the flexibility of large-scale equipment entry and operation is insufficient

○ The bearing capacity of the pile foundation is high (the vertical bearing capacity of a single pile is ≥ 8000kN), and the quality control of pile formation is difficult

3. Equipment and process application

1. Pile rig equipment:3 Sany rotary drilling rigs

2. Construction process:

○ Process name: rotary drilling and boring piles + down-the-hole hammering into rock combination process, mud circulation purification treatment technology

○ Brief description of the process: First, use a rotary drilling rig to quickly penetrate the upper soft soil and sand layer, drill to the top surface of weathered gneiss, and then switch the down-the-hole hammer drilling rig for rock formation crushing and drilling; The pile position deviation (≤50mm) is controlled by the GPS positioning guidance system, and the high-quality bentonite mud wall is used to realize the recycling of mud with mud purification equipment. After the hole is formed, the hole is cleared in time (sediment thickness ≤ 50mm), the steel cage is lowered and the underwater concrete is poured to ensure the continuity of pile formation.

3. Pile foundation design parameters:

○ Pile diameter/side length: the diameter of the pile foundation of the main bridge is 1.8m, 1.5m, and the diameter of the pile foundation of the approach bridge is 1.2m

○ Pile length/depth: Main bridge pile length 65-80m (rock entry depth 8-12m), approach bridge pile length 40-55m (rock entry depth 5-8m)

4. Customer/operator feedback:

○ Evaluation of the owner's unit: The one-time pass rate of pile foundation construction quality acceptance is 100%, and the key indicators are better than the design standards, laying a solid foundation for the subsequent construction of the bridge superstructure

○ Feedback from the general contractor: the construction efficiency of the combined process far exceeds expectations, effectively shortens the construction period by 2 months, the equipment failure rate is low, and the service response is timely

○ Operator feedback: Sany SR405HK equipment is easy to operate, low failure rate, strong rock entry ability, GPS guidance system has high accuracy, reduced labor intensity, and greatly improves the working environment of mud purification equipment