Abstract: Based on 19 field pile load tests in 6 sites of Zhengzhou third ring rapid road engineering, pile bearing and deformation characteristics, load transfer laws, pile tip bearing capacities and pile friction behaviors of the pile tip grouted large-diameter bored pile are studied by comparing the field test results of the post grouted pile and pile without grouting. The results show that the bearing capacity of large-diameter bored pile is significantly improved under the condition of pile tip grouting. The influence of the capacity increasing amplitude is significantly influence by the grouting age. In alluvial deposits with soils mainly of medium dense to dense silt, fine sand and plastic to hard plastic silty clay in the middle and lower reaches of the Yellow River, the large-diameter bored pile with a length of about 40 m shows characteristics of friction pile. However, the loads that are transferred to the lower part of the pile shaft and pile bottom of the pile tip grouted pile are smaller. Hard cement sediment concretion body be form under the pile tip by the pile tip post grouting, which is effectively deal with the problem of the sediment under the pile tip. Moreover, cement bond body with mesh distribution be also form in the soil with a depth of nearly 1 m under the pile tip through the fracturing and penetration effect of the post grouting. Coupled with the compaction effect of pile tip soil by the high pressure grouting, the bearing performances of the pile tip and the bearing stiffness are significantly improved; pile side friction ultimate resistances of the large-diameter bored pile is significantly improved by the pile tip post grouting. However, the pile-soil relative displacements which are correspond to the pile ultimate side friction resistances are reduced by the grouting. These are why the post grouted large-diameter bored pile shows higher bearing capacity in the small settlement.

Key words: large-diameter bored pile, pile tip post grouting, field test, bearing characteristic, pile-soil shear displacement