Field Study on the Side Resistance-Softening and Resistance-Reinforcing Effects of Large-Diameter Combined Grouting Drilled Shafts

The traditional design method for drilled shafts rarely considers the influence of construction effect and tip resistance on side resistance, and lacks attempts to improve the performance of drilled shafts without increasing drilled shafts sizing, economic costs and carbon emissions. In this paper, the influences of construction-effect and shaft tip resistance on the side resistance of large-diameter drilled shafts before and after combined grouting were studied by full-scale field tests. The reinforcing effect of combined grouting on bearing capacity was confirmed, and the potential of applying combined grouting to realize sustainable development, the economy, and environmental protection was introduced. The mechanisms of softening-effect and reinforcing-effect on the side resistance of large-diameter drilled shaft are discussed in depth. The field test results showed that the construction-effect and shaft tip sediments caused the side resistance to soften, and the lower the shaft tip resistance, the more serious the side resistance softening-effect. The mobilization of side resistance was affected by the soil strength underneath the shaft tip. The shaft tip bearing capacity was improved after sediment compression, which helped to reinforce the side resistance near the shaft tip. Combined grouting improved the side resistance reinforcing-effect even further and broadened the range of soil layers that can benefit from it. The fundamental reason influencing the side resistance softening-effect and reinforcing-effect of the drilled shaft was the change in soil radial effective stress. This research provided certain references for improving the performance of drilled shafts without increasing drilled shafts sizing, economic costs and carbon emissions.