What can you learn from pore pressure data?

pore pressure data (Bozzomitrs) is used to draw ground water curve which is very important for design the dewatering system  or before starting excavation 

In addition to correcting against the effects of in-situ moisture and overburden stress, pore pressure data helps to ensure consistent measurements and soil classifications among different types and sizes of CPT cones.

Pore  pressure data is used to determine the compressibility and permeability of the soil, as well as indicating groundwater conditions. It is used to correct or “normalize” the sleeve friction and tip resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than100 feet.

pore water pressure  or neural  stress are  hydraulic properties of soil  if the pores of a soil mass are filled with water  and if a pressure is induced  the pore water tries to  separate  the grains , then this pressure is termed as porewater pressure . when in a soil mass ,  if the effective pressure reduce to to zero due to increase in the porewater pressure the soil will be in a state of quicksand condition. this phenomenon is also known as boiling. 

To better understand and analyze the underground soil, water, oil and more before and during work.

First thing get in my mind when I hear about the pore pressure is (Retaining Wall)

We treat soil sort of like a fluid, like water,the pressure it exerts increases linearly with depth in the downward direction, but unlike water in that it exerts less pressure horizontally than vertically.

You've got a density. Convert that to a unit weight - density is mass/volume, multiply by gravity to get weight/volume.

 Now draw a diagram of your wall. The pressure at the top of the soil is zero. As you go down, it increases linearly 

pressure = unit weight * depth 

You'll notice that this multiplication gives us

(weight/volume)*length = weight/area,

which is a pressure. So do the pressure at the top (zero), and the pressure at the bottom, and draw a line connecting the two. This is the distribution of vertical pressure on the wall. To determine horizontal pressure, we multiply by a coefficient which is determined by soil parameters. 

Pore pressure is simply a measure of the in-situ groundwater pressure, i.e. the water pressure in the “pores” between soil grains. This data is used to determine the compressibility and permeability of the soil, as well as indicating groundwater conditions. It is used to correct or “normalize” the sleeve friction and tip resistance readings in the presence of in-situ moisture and overburden stress. This is especially important in soft, fine-grained soils where in-situ moisture takes longest to dissipate, and in tests at depths greater than100 feet.

A CPT cone that is equipped with one or more pore pressure sensors is called apiezocone, and a CPT test using a piezocone is often indicated with the abbreviation CPTu. Piezocones may have between one and three pore pressure sensors, located on the cone (denoted u1), directly behind the cone (u2), or at the top of the friction sleeve (u3). Most piezocones for everyday applications use one sensor located at u2 (see image below). 

The pore pressure sensor consists of a porous filter (usually made of plastic resin), a small cavity of incompressible, low-viscosity fluid, and a pressure transducer.The filter and tubing between the filter and transducer must be fully saturated with fluid, usually glycerin or silicon oil, to ensure fast and accurate readings. The filter must be replaced frequently so that it does not become clogged with soil.

The procedure for the CPTu test is slightly different than the basic CPT test, where tip resistance and sleeve friction data are taken continuously as the cone is pushed into the ground at a constant rate. To collect pore pressure data, the pushing of the cone must be paused long enough to take an initial reading, then allow pore pressure around the cone to dissipate as subsequent readings are taken. 

When the cone is pushed into the ground, pore pressure builds up around it until the in-situ moisture dissipates into the surrounding soil. The rate of dissipation depends upon the soil’s coefficient of consolidation, which indicates the compressibility and permeability of the soil. 

A fixed period of dissipation may be used, or in other cases dissipation is allowed to continue until reaching a specific value ofU (usually50%), calculated by the following ratio:

U = (ut – uo)/(ui – uo) x100%ui = pore pressure measured at start of dissipation testuo = equilibrium in-situ pore pressure (the pressure at which no further dissipation is observed)ut = pore pressure measured at time t

In addition to correcting against the effects of in-situ moisture and overburden stress, pore pressure data helps to ensure consistent measurements and soil classifications among different types and sizes of CPT cones.

 This is what I found on this subject  ... a method is used to obtain pore pressure in shaly sand- stones based upon an ... Knowledge of pore pressure using seismic data helps in planning the drilling