Abstract:

 In response to the difficulties in driving piles into mudstone foundation, insufficient bearing capacity, and the difficulty in preparing a model foundation due to the disturbance of soft rock, a simulation pile driving and static load test device based on undisturbed soft rock was preliminarily developed. The device mainly includes undisturbed soft rock constraint model box unit, hammer-driven unit, guide rail support unit and static load unit. Calibration tests and application tests were carried out to verify the feasibility and stability of the device. The penetration and bearing characteristics of driven pile were analyzed, the mechanical characteristics of mudstone around pile caused by pile driving damage were defined, and further research prospect and engineering application suggestions were put forward. The study shows that: 1) The results of tests are consistent with that of field test, and the penetration characteristics and bearing characteristics are both the same as those of field test, which verifies the feasibility of the test device. 2) The stability of the load transfer factor α further proves that the load transfer of the test device is stable and reliable. 3) As mudstone has intensive soft and hard interbedding, as a result, there is a significant difference in penetration resistance represented by the number of blows per 10 mm of penetration, and the static load failure of low strength soft interlayers presents a precipitously increasing settlement. 4) The mudstone within 2d (d is the pile diameter) around the pile is damaged by pile driving; for every 0.5d interval, the strength loss is 66.0%, 40.5%, 17.0%, 7.0% and the elastic modulus loss is 80.5%, 54.5%, 26.5%, 11.0%, respectively.  5) The reduced values of the undisturbed mechanical parameters should be selected according to the damage characteristics induced by pile driving in the design and bearing capacity evaluation of mudstone. The test device has the advantages of stability, reliability and controllability, which can provide support for related research on pile driving in mudstone.

Key words: undisturbed soft rock, test device, pile driving, static load test, mudstone strength around pile, model test