Site investigation boreholes Site investigation boreholes - PowerPoint PPT Presentation

Site investigation boreholes Site investigation boreholes • Percussion drilling – soils/soft clay rocks – core recovery • Rotary coring R t i – soil or rock >100m deep – core recovery • Rock probing – rotary percussion rig – soil or rock soil or rock – no core recovery

Rotary rig Rotary rig

Core bit Core bit

Core drilling Core drilling

Rock core Rock core

Total Core Recovery (R) Total Core Recovery (R) Summed length of core recovered R = Length Length drilled drilled Depends upon: Depends upon: • quality of the rock mass? • stability of/lack of vibration in, the drill rig t bilit f/l k f ib ti i th d ill i • choice of core barrel/skill of the operator

Rock Quality Designation (RQD) or Modified Core Recovery M difi d C R Σ x = L i RQD Q x i = lengths of individual pieces of core ≥ 10 cm g p i L is the total length of the drill run

Indirect Methods of determination of RQF f RQF Seismic Method - Seismic Method RQD= (V f / V l ) 2 * 100 Ratio of velocity in the field to that in the lab R ti f l it i th fi ld t th t i th l b Volumetric Count - RQD = 115- 3.3* J v where J is a measure of number of joints where J v is a measure of number of joints within a unit volume of rock mass