Advances in the use of biological stabilisers and hyper-compaction for sustainable earthen construction materials.

In the majority of cases, earthen construction materials for real buildings require amendment to deliver suitable material properties, which could be some additional strength or resilience to erosion. In modern earthen construction, in India, Australia and other parts of the world, cement and lime have been successfully used as stabilisers, providing both strength and durability benefits. However, the use of cement is detrimental to the green credentials of earthen construction materials, due to the large carbon footprint of that material’s manufacture and, for some time, researchers have been motivated to find more appropriate stabilisers and manufacturing methods. In this paper, we present recent findings from two projects that are linked by this motivation, and involve the study of bio-based stabilisers and alternative manufacturing methods for insitu and unit-based materials. Results are presented from laboratory testing of strength and durability of a range of materials, bio-stabilisers and manufacturing processes, indicating that there could be viable alternatives to cement and lime, certainly for many current uses of earthen construction materials

The effect of the remoulded void ratio on unit shaft friction in small-displacement piles in chalk

Small-displacement pile driving in chalk produces an annulus of crushed and remoulded putty-like material through which shaft friction is believed to be mobilised. Ultimate shaft friction is assumed to be a function of the effective angle of friction of the putty chalk interface and the radial effective stress acting on the pile shaft. The mechanisms that affect the magnitude of the latter are not well understood. It is hypothesised that the stress levels attained during shaft friction mobilisation are related to the change in void ratio that takes place as structured chalk becomes crushed during pile installation. Therefore, a general notion exists that piles installed in dense chalks will mobilise larger shaft capacities than piles driven in more porous materials, and that this is related to the void ratio of the remoulded annulus. In this context, this paper presents the results of a series of monotonic constant volume simple shear tests conducted to assess the role of the void ratio in the mobilisation of shaft friction. Results suggest that void ratio is a controlling factor and that a state-based approach for the characterisation of void ratio-shaft friction relationships may be possible