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The PPT Profile Procedure
Side Sensing PPT Cone
The side-sensing PPT cone is pushed into a landfill by hydraulic rams mounted on a 20-ton cone truck. As
the PPT is advanced into the landfill the data is displayed in real time and is recorded on a computer. The tip
resistance or end bearing indicates the density of the Municipal Solid Waste (MSW). The sleeve resistance
or side friction can indicate an increase of moisture in the MSW as the friction values decrease. Typically, as
a PPT sounding in MSW progresses, the side-sensing transducer has been indicating a slight vacuum due
to dynamic pull as the cone passes the MSW. The dryer the MSW the greater the dynamic vacuum. When the
sounding is stopped to add another push rod (standard length 1 meter) the vacuum reading typically returns
to zero. It is during this pause that a vacuum zone will be registered as the vacuum influence from a nearby
extraction well. The PPT can map the zone of influence of an existing collector. It is quite common to
measure vacuums and gas pressures in the same sounding . Vacuums moves out from a collector like
fingers, it is not like a balloon.
Figure 1
Figure 2 below is a colorized overlay of two PPT logs. The soundings were performed 1 week apart and
only five feet apart. The logs show the repeatability of the instrument. The gas pressure in the first sounding
measured over 200 psi, the log scale is in tons per square foot not psi. The green color represents gassy
liquid. This occurs when water is introduced to old refuse from over irrigation of the landscape and
increases the gas generation within the liquid. This is very dangerous when this condition is near a slope.
A seismic event can release the bound up gas like shaking a soda and blow out the side of the landfill. To
relieve this pressure the site engineer wanted a push-in well installed at this location a week later. Please
go to Push-in Collector to learn more about this process.
Note: the release of the gas pressure in the second sounding in the same trend as the first sounding
indicates the rate of the gas release before the PPT hole for the first sounding was sealed up.
Figure 2
Side Sensing PPT Cone
The side-sensing PPT cone is pushed into a landfill by hydraulic rams mounted on a 20-ton cone truck. As
the PPT is advanced into the landfill the data is displayed in real time and is recorded on a computer. The tip
resistance or end bearing indicates the density of the Municipal Solid Waste (MSW). The sleeve resistance
or side friction can indicate an increase of moisture in the MSW as the friction values decrease. Typically, as
a PPT sounding in MSW progresses, the side-sensing transducer has been indicating a slight vacuum due
to dynamic pull as the cone passes the MSW. The dryer the MSW the greater the dynamic vacuum. When the
sounding is stopped to add another push rod (standard length 1 meter) the vacuum reading typically returns
to zero. It is during this pause that a vacuum zone will be registered as the vacuum influence from a nearby
extraction well. The PPT can map the zone of influence of an existing collector. It is quite common to
measure vacuums and gas pressures in the same sounding . Vacuums moves out from a collector like
fingers, it is not like a balloon.
Figure 1
Figure 2 below is a colorized overlay of two PPT logs. The soundings were performed 1 week apart and
only five feet apart. The logs show the repeatability of the instrument. The gas pressure in the first sounding
measured over 200 psi, the log scale is in tons per square foot not psi. The green color represents gassy
liquid. This occurs when water is introduced to old refuse from over irrigation of the landscape and
increases the gas generation within the liquid. This is very dangerous when this condition is near a slope.
A seismic event can release the bound up gas like shaking a soda and blow out the side of the landfill. To
relieve this pressure the site engineer wanted a push-in well installed at this location a week later. Please
go to Push-in Collector to learn more about this process.
Note: the release of the gas pressure in the second sounding in the same trend as the first sounding
indicates the rate of the gas release before the PPT hole for the first sounding was sealed up.
Figure 2
Figure 3
The pore-pressure column in Figure 3 illustrates clearly the difference between the presence of liquid by the
hydrostatic slope and the straight line of the LFG pressure in the lower part of the log.
Figure 4
One of the most important factors in using the profiling technique is to prevent installing a collector through a
perched liquid zone and providing a conduit for the liquid to migrate to the bottom of the landfill and leak to the
groundwater or flood the collector. Please push the button labeled Push-in Collectors for more information
on a better, faster, cheaper method for LFG extraction. The push-in well screen is placed only where the gas
plume is known to be, which is usually deeper than 20 feet and not in liquid containing zones.
The PPT can be used to map the vacuum influence of existing collectors. This information can be used to
increase the production of the collector or to determine why a collector is not producing as it once did. If the
PPT indicates no vacuum and no gas pressure then the organic component of the refuse is either too dry or
the gas potential of the organic material is used up.
Approximately 500 to 800 feet of PPT sounding can be performed in a 10 hour day.
During the field operations if it is decided that Push-in collectors should be installed immediately following
the soundings, the PPT logs, which are plotted in the field, are used to determine where to install the screen
sections of the collectors.
If a PPT 3-D Profile is to be created following the field operations, the PPT soundings must be surveyed with
elevations and coordinates, The PPT data is color coded as in Figure 4 and is inputted into Auto CAD and
Micro Station. The survey coordinates and precise depths are also inputted into the computer. To create a
3-D profile the PPT soundings performed in the field must be in a box formation to provide depth to the
image. Plan views and cross sectional plots can also be created.
| Copyright © 2010 STI Engineering/ Regis Renaud ALL RIGHTS RESERVED |
The brown color identifies the dense/daily
cover layers that have an influence on the
pore-pressure readings.
The yellow color identifies the gas pressures
encountered, which are usually found trapped
under the dense layers.
The blue color represents liquid layers, which
are usually found on top of dense layers.
cover layers that have an influence on the
pore-pressure readings.
The yellow color identifies the gas pressures
encountered, which are usually found trapped
under the dense layers.
The blue color represents liquid layers, which
are usually found on top of dense layers.
