Self-drilling Bolts Applying in Underground Car Park Foundation Projects
by Anna S. Optimization SpecialistWith the rapid development
of the global economy, there is less and less land available for development
and utilization in cities. The construction of parking lots and other
underground projects alleviated this contradiction. So in the construction of those
underground projects, foundation support engineering has been more and
more used. In some foundation support projects, the engineering site is much
complicated. For example, the miscellaneous fill dominated by construction
waste or crushed stones cannot form holes or support in the silt layer.
Traditional anchor rods and construction techniques cannot meet the
requirements. For engineering needs, self-drilling bolts are born under
such circumstances. Now let us see a real case to introduce the application of self-drilling
bolts applying in underground parking lot projects.
1. Integrate drilling, grouting
and anchoring in one operation;
2. It is most suitable for the
formation of broken and easy collapse holes, avoiding the complicated process
of casing follow-up;
3. Full and high-pressure
grouting can be achieved so that the grout fills the rock and soil cracks;
4. According to construction
needs, it can be cut into any length and any connection;
5. It can be easily connected
with various types of drilling rigs to realize comprehensive hole-making
technology.
Here combined with the concrete
case of the foundation support project of the underground parking lot of the
China Shipbuilding Industry Science and Technology Building, let us learn about
the construction and practical application effect of the self-drilling anchor.
The engineering site of
China Shipbuilding Industry Technology Building is located on the north side of
the intersection of Haier Road and Tongan Road in Qingdao. The proposed
building is 26 to 33 stories high, with two underground floors, a frame-shear
structure and a raft foundation. The pit is about 254m long and 80m wide. There
is a pond in the middle of the site with an excavation depth of 12m, which was
then backfilled.
According to the survey, the
stratum in this area mainly includes: The average layer thickness of
miscellaneous fill is 18m, mainly construction waste and gravel, with silty
soil; wet, medium-density strongly weathered granite, the mechanical properties
gradually increase from top to bottom; Because there are many underground
fissures in the Qingdao area and abundant water sources in the pit, this section is
greatly affected by underground seepage during the excavation process.
Because of this geological
condition, the design unit adopted R32 self-drilling bolts with a spray surface with a thickness of 100mm. The grouting pressure is 0.5-2MPa, the grouting water-cement ratio is 0.45-0.50, and the strength is not less than M20.
Strictly control during construction. The grouting pressure is generally
controlled at about 0.5~1.5Mpa. In the case of special formations, the grouting
pressure can be adjusted, and finally, the suitable grouting pressure is
determined according to the grouting effect. For drilling holes with
particularly serious grout leakage, a special method of filling the hole with
sand and then grouting or mixing a certain proportion of sandy components in
the grout can be used to save the amount of grout.
The foundation is set by 3
monitoring points for tracking and observation throughout the whole process.
The maximum settlement of the slope of the foundation pit is 23mm, which is
0.19% of the depth of the foundation pit, which meets the requirements of the
specification. Facts have proved that the foundation pit maintenance of this
project is generally successful, ensuring the safety of the foundation pit.
In this project,
self-drilling anchor rods can well complete the supporting tasks in the
formations that are difficult to form holes such as miscellaneous fill and
gravel soil and achieve good supporting effects. The efficient construction the technology of self-drilling bolts has also been highly recognized by the
construction party.
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Created on Aug 13th 2021 01:22. Viewed 126 times.