Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
SlideShare a Scribd company logo

Techniques for measuring insitu stresses

•Download as PPTX, PDF•
•
Z
Zeeshan Afzal

There are some methods that tells about insitu stresses and these are very important methods in Geology as well as well coring and also digging of well as well as in mining these methods are very helpful. So, main idea about is to information about these methods.

1 of 11
Topic :Techniques for measurement of in situ stresses.
TECHNIQUES FOR MEASUREMENT OF INSITU STRESSES  Stresses can be measured in borehole, on an outcrop and in the walls of underground galleries.  Three of the best known and most used techniques are:  HYDRAULIC FRACTIURING  FLAT JACK METHOD  OVER CORING
 Each of these techniques have their advantages and disadvantages.  These techniques exert pressure and disturb the rocks to create a response that can be measured and analyzed.  They are explain in the next slides one by one.
HYDRAULIC FRACTURING  This technique is performed on Dams, Onshore buildings etc.  It is designed for cable tool drilling.  In hydro fracturing decision is taken from shut in pressure. and shut in pressure is defined as:  “The pressure which is exerted by water in bore hole when becomes equal to resistive forces is called shut in pressure”.
MECHANISM  The rock is cracked by pumping water into a bore hole.  The known tensile strength of the rock is inferred and concentration of stress at the well bore are processed to yield the initial stresses in the plane perpendicular to bore hole.  Increase in pressure burst the walls and Final pressure Ps gives safe passage to cracks for the pressure release and it become zero.
 After all processes factors of safety are applied by the formula:  n/3+sq.ft
FLAT JACK METHOD This technique is applied on the rock face of sub surface rocks.  Rock faces are found in tunnels, mining or in excavations.  In this method points are marked on equal distances depending upon tens meter.  When marking is completed then bolting is applied.  Plates of gauges are attached after bolting with the help of hammering.  The micro fractures that are developed by hammering are given by the attached gauges.
MECHANISM  The rock is partially unloaded by cutting a slot and then reloaded;  The insitu stress normal to the slot is related to pressure required to null the displacement that occurs as result of slot cutting.
Over coring This technique is used to identify tensile stress.  It is also applied on rock face.  Bore hole is made on rock face.  The gauges are installed in the hole.  These gauges gives us the results that how much is the hole changing its diameter or shrinkage of diameter.  Diameter is increased via trimming.
 Trimming is done on one side of the hole to increase the diameter.  Then change in stresses is checked.  Resulting in low pressure due to increase in volume.
Thank you

More Related Content

Techniques for measuring insitu stresses

  • 1. Topic :Techniques for measurement of in situ stresses.
  • 2. TECHNIQUES FOR MEASUREMENT OF INSITU STRESSES  Stresses can be measured in borehole, on an outcrop and in the walls of underground galleries.  Three of the best known and most used techniques are:  HYDRAULIC FRACTIURING  FLAT JACK METHOD  OVER CORING
  • 3.  Each of these techniques have their advantages and disadvantages.  These techniques exert pressure and disturb the rocks to create a response that can be measured and analyzed.  They are explain in the next slides one by one.
  • 4. HYDRAULIC FRACTURING  This technique is performed on Dams, Onshore buildings etc.  It is designed for cable tool drilling.  In hydro fracturing decision is taken from shut in pressure. and shut in pressure is defined as:  “The pressure which is exerted by water in bore hole when becomes equal to resistive forces is called shut in pressure”.
  • 5. MECHANISM  The rock is cracked by pumping water into a bore hole.  The known tensile strength of the rock is inferred and concentration of stress at the well bore are processed to yield the initial stresses in the plane perpendicular to bore hole.  Increase in pressure burst the walls and Final pressure Ps gives safe passage to cracks for the pressure release and it become zero.
  • 6.  After all processes factors of safety are applied by the formula:  n/3+sq.ft
  • 7. FLAT JACK METHOD This technique is applied on the rock face of sub surface rocks.  Rock faces are found in tunnels, mining or in excavations.  In this method points are marked on equal distances depending upon tens meter.  When marking is completed then bolting is applied.  Plates of gauges are attached after bolting with the help of hammering.  The micro fractures that are developed by hammering are given by the attached gauges.
  • 8. MECHANISM  The rock is partially unloaded by cutting a slot and then reloaded;  The insitu stress normal to the slot is related to pressure required to null the displacement that occurs as result of slot cutting.
  • 9. Over coring This technique is used to identify tensile stress.  It is also applied on rock face.  Bore hole is made on rock face.  The gauges are installed in the hole.  These gauges gives us the results that how much is the hole changing its diameter or shrinkage of diameter.  Diameter is increased via trimming.
  • 10.  Trimming is done on one side of the hole to increase the diameter.  Then change in stresses is checked.  Resulting in low pressure due to increase in volume.