Complete load transfer behavior of base-grouted bored piles

A field study on the behavior of three destructive piles in soft soils subjected to axial load was presented.All the three piles with different diameters were base-grouted and installed with strain gauges along the piles.The complete load transfer behavior of the base-grouted pile was analyzed using measured results.Moreover,the thresholds of the relative pile-soil displacement for fully mobilizing skin frictions in different soils were investigated,and pile tip displacements needed to fully mobilize tip resistances were analyzed.The results of the full-scale loading tests show that the skin frictions are close to the ultimate values when the pile-soil relative displacements are 1%-3% of pile diameter,and the pile tip displacements needed to fully mobilize the tip resistances are about 1.3%-2.0% of pile diameter.The load transmission curve of the soils around the pile tip corresponds to a softening model when the pile is loaded to failure.

On Physical and Mechanical Behavior of Natural Marine Intermediate Deposits

Coastal structures may be built on natural sedimentary intermediate grounds, which mainly consist of silty soils and fine sandy soils. In this study, extensive field and laboratory tests were performed on the natural marine intermediate deposits to demonstrate the difference in behavior between natural marine clayey soils and natural marine intermediate deposits. The natural intermediate deposits have almost the same ratios of natural water content to liquid limit as those of the soft natural marine clays, but the former have much higher in-situ strength and sensitivity than the latter. The research results indicate that grain size distributions of soils affect significantly tip resistance obtained in field cone penetration tests. The mechanical parameters of natural marine intermediate deposits are also significantly affected by sample disturbance due to their high sensitivity and relatively large permeability. Unconfined compression shear tests largely underestimate the strength of natural marine intermediate soils. The triaxial consolidated compression shear tests with simulated in-situ confined pressure give results much better than those of uncomfined compression shear tests.

Estimation of Axial Pile Bearing Capacity According to Shear Strength Parameters of Soil

At pesent, it is very popular to estimate pile bearing capacity by use of empirical formula and physical indexes of soil provided in the design codes for civil construction in China. This paper attempts to apply mechanical indexes of soil and semi-empirical formulas, which are based on soil mechanical theories and were summarized and presented by Meyerhof in 1976, to calculate the axial pile bearing capacity. Loading test results of 24 single piles in Tianjin area have been collected and compared with the proposed calulation approach.

Numerical modeling of an advancing hydraulically-driven pile in sand

The penetration of a model pile through sand was investigated via a numerical analysis. Data from nine triaxial compression tests on dense specimens at different stress levels was generalized and used to create an empirical non-linear plastic hardening stress-strain relation for use in the analysis. As the computer program used is capable of large displacement analyses in radial symmetry, we expected that the analysis would easily reproduce the tip resistance penetration profile of the model pile in sand of known density and stress. However, initial attempts led to over-prediction. Successful analyses required both successive reformations of the mesh and the complete elimination of the dilatant peak in soil strength, which is naturally eliminated under large confining stress directly beneath the advancing tip, and that soil in the far-field had strained insufficiently to reach peak strength. Thus, the soil around the shaft must have been sheared to a critical state as it flowed past the tip. The hypothesis that the resistance to displacement piles in sand is mainly a function of the deformability of the sand was again proven, and the use of peak strength in the traditional bearing capacity formulae was found to be inappropriate. Independent investigation in this direction is needed to quantify the hypothesis.