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Method of self-balanced loading test differs from the traditional methods of pile test. The key equipment of the test is a
cell. The cell specially designed is used to exert load which is placed in pile body. During the test, displacement values
of the top plate and the bottom plate of the cell are recorded according to every level of load. So Q-S curves can be
obtained. In terms of test results, the bearing capacity of pile can be judged. Equipments of the test are simply and cost
of it is low. Under some special conditions, the method will take a great advantage. In Guangxi Province, tertiary
mudstone distributes widely which is typical weak rock. It is usually chosen as the bearing stratum of pile foundation. In
order to make full use of its high bearing capacity, pile is generally designed as belled pile. Foundations of two high-rise
buildings which are close to each other are made up of belled socketed piles in weak rock. To obtain the bearing
capacity of the belled socketed pile in weak rock, loading test in situ should be taken since it is not reasonable that
experimental compression strength of the mudstone is used for design. The self-balanced loading test was applied to
eight piles of two buildings. To get the best test effect, the assembly of cell should be taken different modes in terms of
the depth that pile socketed in rock and the dimension of the enlarged toe. The assembly of cells had been taken three
modes, and tests were carried on successfully. By the self-balanced loading test, the large bearing capacities of belled
socketed piles were obtained. Several key parameters required in design were achieved from the tests. For the data of
tests had been analyzed, the bearing performance of pile tip, pile side and whole pile was revealed. It is further realized
that the bearing capacity of belled socketed pile in the mudstone will decrease after the mudstone it socketed in has been
immerged. Among kinds of mineral ingredient in the mudstone, montmorillonite is much. And in the size composition,
content of cosmid is high. For specific surface area of cosmid is large and water intake capacity of it is strong, water
content has great effect on strength of the mudstone. Along with water content increasing, strength of the mudstone
declines nonlinear apparently. Since effective measures had been taken, the mudstone was prohibited from being
immerged during construction. And valuable experience has been accumulated for similar projects construction
henceforth.
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