Geotechnical Engineering Online Library

Static loading tests, O-cell tests, were performed on two long, strain-gage instrumented, bored piles in HoChiMinh City, Vietnam, where a series of twelve apartment towers were to be constructed. The test piles were constructed to 76 and 91 m depth and tested to maximum O-cell loads of 10 and 18 MN, respectively. For both piles, the O-cell level was placed at a depth of about 20 % of the pile length above the pile toe. The soil profile consisted of very soft organic clay to about 10 to 15 m depth underlain by firm to stiff clayey soil to about 25 to 45 m depth. Hereunder, the soil consisted of a compact to dense sandy silt. Neither of the tests was able to fully engage the shaft resistance of the piles above the O-cell level, but did so below the O-cell level. Back-calculation of the load distributions determined from the strain-gage measurements showed the shaft resistance, even where fully mobilized, to be very small: the beta-coefficient applied in an effective stress analysis was only about 0.13 to 0.14. The evaluations of shaft resistance development showed a maximum shear resistance to occur after a movement of only 3 to 4 mm, after which the response became plastic and strain-softening. The toe resistance was very low because the construction had left soil debris at the bottom of the drilled hole. Ongoing regional settlement leads to concerns about the possibility for the production piles to have a similarly low toe resistance. This would locate the neutral plane of the shorter piles in settling soil and create a downdrag situation for the piled foundation.

Dynamic response characteristics of reinforced concrete group piles with embedded pile-cap condition are investigated in the field under varying levels of coupled harmonic excitations. The piles are constructed by bored cast-in-situ method. The site is located at Indian Institute of Technology Kharagpur, West Bengal, India. The soil properties are determined by laboratory tests on both disturbed and undisturbed soil samples collected from various boreholes at the site. Two in-situ tests, namely, standard penetration tests to determine N-value and cross hole seismic tests for determining the shear-wave velocity of soil are conducted at various depths of soil layer. Forced coupled vibration tests are conducted on pile groups using Lazan type mechanical oscillator with four different eccentric moments. Both the horizontal and rocking motions of pile groups are measured simultaneously for different operating frequencies of oscillator. Two resonant peaks are observed at two different frequencies. It is also observed that as the eccentric moment increases, the resonant amplitude increases, but the natural frequency decreases for both horizontal and rocking responses. The test results on piles are then compared with the numerical approach with two different soil-pile models – (i) A linear visco-elastic medium composed of outer infinite region and an inner weaker layer with reduced shear modulus, and (ii) a boundary zone with parabolic variation of shear modulus and with a non-reflective interface. From the comparison between the test results and numerical results using the first model it is found that the prediction of nonlinear response of the pile foundation is in good agreement with the test results. For the second model, the numerical results are not found satisfactory when compared to the test results. The nonlinear parameters like separation length, shear modulus ratio, weak zone damping factor and thickness ratio are also predicted for the group piles under coupled vibration.

A berth structure, 600 m long and 60 m wide, for handing of loaded containers was completed in early 2013 as one of the facilities of Thi Vai International Port located on the bank of the Cai Mep river in Viet Nam. The berth is a quay structure supported by 885 driven spun concrete piles and 156 driven steel pipe piles. Four test piles, named TSC1, TSC2, TSP1 and TSP2, with different pile lengths and diameters were driven at the project site in 2011 prior to construction of working piles. Static load tests (SLTs) were conducted for the test piles to determine the design pile capacity. Dynamic load tests (DLTs) were also carried out for the TSC1 and TSP1 in order to obtain information for selecting the pile driving system used for the working piles and to examine the applicability of wave matching analysis (WMA) to derive the static load-displacement curves. A wave matching analysis program developed by the authors was employed in the WMAs. Good agreement between the derived and measured static responses was obtained for the TSC1 and TSP1. The identified soil parameters obtained from the final WMA of the TSC1 and TSP1 were used to predict the static responses of the TSC2 and TSP2. The predicted load-displacement curves were reasonable matches to the measured ones, indicating that the identified soil parameters of the test piles could be used for prediction of the static responses of other constructed piles. Moreover, pile driving termination criterion in this site was examined through the test piling.