This two-part set of papers reports some recent experiences in the design of jet-grouted piles (under predominantly lateral load) when their intended use is primarily structural, as is certainly the case when reinforcing steel is present. Although unusual, a number of such design solutions have been documented – several of them recent and applied to major structures. In the absence of specialist rules for the design of jet-grouted piles with steel reinforcement, codes of practice for reinforced concrete (RC) are usually adopted and applied as discussed in this paper. However, certain important differences between concrete and jet-grouted soil (fully discussed in the companion paper) must be clearly understood and allowed for by designers with the result that analysis and design from first principles should be undertaken instead of relying automatically on RC codes of practice. This use of first principles must be combined with a refined construction method to improve the accuracy of construction if the designer is to utilise the potential benefits of the system.
In this paper, selective laser melting fabricated specimens in non-heat-treated and heat-treated conditions were subjected to Vickers microhardness testing, by using a full range of loadings: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Microhardness of longitudinal sections and cross-sections were correlated and the obtained values were plotted against loadings and indentation size effect was studied, in order to find the optimal loading range, that gives the material true microhardness, or load-independent hardness. The load dependence of the measured Vickers hardness values was described quantitatively through the application of the Meyer’s law, proportional specimen resistance, and the modified proportional specimen resistance model. It was found that the microhardness rises as the loading is higher, causing a reversed indentation size effect, clearly indicating the range of true hardnesses of the tested material. Also, proportional specimen resistance and modified proportional specimen resistance models were found to have the highest correlation factors indicating their higher adequacy compared to Meyer’s prediction model.
Part 1 of this two-part set of papers was intended to raise awareness of the specific problems encountered with the design of jet-grouted piles, the latter being usually based on reinforced concrete codes, as there is a lack of specialist documents on the subject. Among the problems identified in Part 1, those associated with the variability and uncertainty of both the material characteristics and the construction tolerances are prominent. The present article discusses the implications of the latter problems for the design of reinforced-concrete grouting structures and proposes guidelines that aim to minimise the risk of inappropriate design solutions, which are usually among the main causes of structural failures.
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