Proceeding of the 2018 DFI-EFFC International Conference on Deep Foundations and Ground Improvement, Rome, Italy, (DFI, EFFC)
Innovative Design and Quality Control of Single Stage High Pressure Injection Micropiles, Waal-Compact-Piles
Floris Schokking Director and Jan van der Wiel
The study of a series of load tests on single stage high pressure (80-100 bar) injection micropiles has led to an innovative design method for these piles with diameters up to 350 mm. An important issue in the new design approach is the development of a grout bulb in the soil under the high pressures, which could be observed after retrieval of the piles. During installation the formation of this bulb acts as a forced deformation on the surrounding soil and resulting from this are an increase in horizontal stress, strength and elasticity parameters. The bearing capacity of the piles in compression appears as a result in majority delivered by the developed skin friction and vertical displacements are observed to be low. Comparison of the static pile load test data with the results of finite element modelling (FEM) of the tests, incorporating the above described installation features, supported the load-deformation behaviour observed in the tests. The outcome of the modelling suggests that FEM could be used in future design for this type of micropiles, provided that a consistent dimension of the grout bulb in the soil can be secured. To be able to guarantee the forming of an adequate grout bulb a quality control programme has been developed based on a set of parameters related to grout composition, grout velocity, grout pressures and the total volume of grout injected vs. the expected volume of the bulb. A first attempt is made to define guiding confidence boundaries for these parameters based on gained experience in recent installation projects.
|article #3012; publication #1040 (ROME-2018)|