soil liquefiable soil will always have a low tensile strength the hydraulic fracturing is accomplished in this example by applying air pressure water pressure or air pressure over water in fact the drain pipe 10 may be filled with water or other liquid via the fracture fluid pipe 16 and then the fracturing pressure may be applied by air release from an air pressure tank typical fracture pressures will be maintained for a period of 5 to 20 seconds after fracturing has occurred the water may be pumped from the drain to further develop the preferential flow pass created by the fractures as is taught in u s pat no 6 312 190 the structure illustrated in fig3 illustrates a variation of the structure shown in fig2 wherein instead of applying fracturing pressure to the entire drain depth simultaneously as disclosed in fig2 in fig3 hydraulic fracturing pressure is applied only to selected depths or segments in this arrangement two sets of spaced internal packers 17 and 17 u2032 are employed and the bottom end of fracture fluid tube 16 is closed off and is provided with an exit 21 intermediate upper and lower internal packer units 17 and 17 u2032 this confines the hydraulic fracturing to a preselected segment of drain pipe 10 in yet another embodiment of the present invention it is desirable to supply a propping agent to the surrounding soil after fracturing for propping fractures in the soil in order to maintain the.