Load–settlement behaviour of membrane-confined grouted pile: experimental and analytical study

In karst areas, the use of bored pile is often limited due to the loss of injected grout slurry. A novel technique is proposed to install a membrane with jet nozzle, through which jet grouting is implemented for expanding the membrane to form good interaction with the surrounding rock. Casting tests are conducted to examine how a membrane deforms subjected to a uniformly applied grout pressure. A mathematical model is derived to estimate the bulb length as a function of grout pressure and water/cement ratio. The critical bulb length is suggested to be 0.8 times the diameter of karst cave. Model-scale laboratory tests are performed on membrane-confined grouted piles under axial loading. The results show that membrane-confined grouted pile can have a much higher bearing capacity by 1.5 times and a much lower settlement by 50% compared to conventional pile. The contributions of skin friction and bulb resistance account for over 90% of the axial resistance, whereas the pile tip resistance is within 10% of the axial resistance. The pile’s bearing capacity increases with the bulb length, bulb number and bulb depth. An analytical model is further proposed to predict the load–settlement behaviour of membrane-confined grouted pile for use in practice.