hi to everyone, i'm facing some probelms during process of concreating a cast-insitu bored pile. my method for this bored pile is reverse circulation method.the bored hole (60 metres in deep) keep collapse (because there are some soft layer which contain silty and clayey sand) despite i'm using bentonite and soil(red colour) to protect that particular boring wall. so, my questions are:- a)what is the best way to prevent bored hole from erosion/collapse if there were sandy condition? b)what is the solution if tremmie pipe cannot be installed exceed the water level of ready mixed during concreating process? c)is there any calculation of 'how many kilogrames of bentonite have to use for 1 meter of boring hole'? d)where can i buy a cheaper and better quality of bentonite? thanks and i would highly appreciate to anyone who willing to answer my questions.my e-mail add is email@example.com.
Dear Ming, If there are some soft layer which contain silty and clayey sand) you have to use bentonite mixture with water.The bentonite have to mix with water seperate in a tank and storage for 24 hours bevor use.(the mixture is 50-60 kg of bentonit powder for 1000 liter water.After the 24 hours quelltime you have to airflushing the bentonite to liquid form to use for the stabilisation of the borehole.Keep the bentonite level in the borehole permanent 1m below ground level and you have never any collaps in the hole. After cleaning the base in the borehole with a cleaning bucket install the reinforcement and after the tremie pipe 30 cm above the base.When you concreting you have to cut the tremie every 2-3 truck of concrete after meassuring the concrete level in the borehole but keep sure 3-4m tremie permanent in the concrete.
With my over 35 years experiance in piling and foundation i am sure you have no any problems when you follow the right method to do piling.