The design, construction and monitoring technology of deep foundation excavation have become big difficulties gradually. The supporting and protecting wall can not only ensure normal construction and stability, but also prevent deformation, soil body moving and normal operation of surrounding buildings, roads and underground pipelines.
With the propulsion of reconstruction of old city, main high buildings are clustering in narrow and busy spaces, the construction conditions almost terrible. There are many permanent and public facilities, so it is very strict for stability and displacement control.
If deep foundation excavated in complex geological conditions, such as soft soil and high groundwater table areas, it is easy to happen slippage of soil body, instability of deep foundation, deflection of pile body, severe leakage and damage, which will cause great threat for security.
Supporting Scheme
The type of this foundation pit support is temporary. In later stage of building project, a retaining wall can be built beside slope. On the premise of safety and usability, the cost of foundation pit support engineering should be decreased as much as possible. So self drilling hollow anchor bolt is applied. At the position that under existing digging piles, ten self drilling hollow anchor bolts should be drilled. Each of the self-drilling anchor bolt should has a length of 18m, tensioning force is 165kN. Under these self drilling hollow anchor bolt, another row of them shoud be drilled, this time, each self-drilling anchor bolt should has a length of 10m with tensioning force of 60kN. The 2 rows of anchor bolts both should be downward with angle of 10.
Anchor Construction
Support construction should work in with earth excavation. When excavator excavating, it should left layer with depth of 0.2m for roof bolter. Allowable deviation of self drilling hollow anchor bolt hole distance is 100mm. Before drilling, mesopore and bit should be checked that if they are unimpeded. When bolt is drilled in the designed depth, slurry that is made of pure cement slurry with water-cement ratio of 0.4 should be grouted from mesopore. Plate and anchor head should be installed in time to fix bolt temporarily. When the strength of cement paste reaches 5.0MPa, tensioning force should be the designed value and tension the anchor head.