Cone Penetration Testing

Methods

Cone Penetration Testing

Methods

Holland is the most Western part of The Netherlands. It is majorly built up by soft top soils, a mix of organic peats and soft clays. Building anything on such soils has always been a challenge. In the 1920’s and 1930’s the Dutch Staatsspoorwegen (train authorities) and Rijkswaterstaat (PWD) struggled with failures of railway embankments on the soft organic peat soils in parts of Holland. This resulted in various accidents with casualties. In order to prevent this from happening again, the Dutch knew they needed to find different ways to build the railways and that more information on the bearing capacity of the soil was required. In softer soil it should be easier to penetrate an object than in hard soil. Mr Barentsen translated this principle into a testing method and the Cone Penetration Test (CPT) was born. The new technology was used to determine the best possible routing for the new proposed railway line from Gouda to Alphen (the line is still operational to date). Mr Barentsen was acquainted with the owner of the Goudsche Machinefabriek (literally the Gouda Machine Factory and the official predecessor of Geomil), and asked for his help to further develop his idea. In 1934 they together filed for a patent which was finally awarded in 1938. The pictures below show the so-called Barentsen-device as well as the original Dutch patent (courtesy of Geomil Equipment B.V.).

Following this, CPT technology evolved quickly:

1932: The Barensten-device consisted of a pushing device with a hydraulic piston and pressure gauge, a 35mm diameter gas pipe outer tube and 15mm diameter push rod with a 60° conical tip

1935: The Delft Soil Mechanics Laboratory was undertaking 10 tonne tests with the method being used in Holland and Belgium for evaluating pile bearing capacity.

1948: Advent of the ‘Dutch cone’ or ‘jacket cone’

1953: The ‘Begemann cone’, named for the Dutch engineer was introduced which had all of the components of modern cones including friction sleeve in addition to measurement of cone resistance. The cone is still fundamentally a mechanical / analogue apparatus by this point.

1965: Fugro introduce the first commercially developed electrical cone with the particular advantages of simpler and more reliable measurement allowing for continuous reading of measurements of cone tip resistance and sleeve friction.

1980: Through the 1970s various probes were introduced which attempted to measure porewater pressure during penetration. By 1980, the piezocone was in routine use which allowed for simultaneous measurement of cone tip resistance, sleeve friction and porewater pressure via a porewater pressure transducer. The piezocone remains the industry standard to this day.

Recent developments: In recent decades, development of CPT practice has centred around advances in data collection, storage and processing. In addition, the CPT apparatus has been purposeful in environmental and magnetometer-based investigations (i.e., UXO surveys). More recently, cones can be fitted with geophone modules to allow seismic refraction surveys which are purposeful in refining the soil parameter estimates and soil type estimates. Videocones have found some niche viability also.

In summary, the Cone Penetration Test is a Ground Investigation method for soils, whereby a conically shaped tip is advanced into the ground, and whilst doing so measurements are being taken. The CPT data provides insight about strength and behaviour characteristics of the soil. The penetration speed is standardized at 20 (+/-5) mm/s, typically using hydraulic rams. The conically shaped tip is known as a cone and can be mechanical or electrical of nature. In case of an electrical CPT the cone is instrumented and measures in-situ/downhole while providing data to the operator in real-time. A typical electrical cone will provide (at least) the 3 basic parameters:

· Cone resistance (qc)       · Sleeve friction (fs)       · Pore pressure (typically u2)

           · Cone resistance (qc)

           · Sleeve friction (fs)

           · Pore pressure (typically u2)

Cone Penetration Testing

Methods

Holland is the most Western part of The Netherlands. It is majorly built up by soft top soils, a mix of organic peats and soft clays. Building anything on such soils has always been a challenge. In the 1920’s and 1930’s the Dutch Staatsspoorwegen (train authorities) and Rijkswaterstaat (PWD) struggled with failures of railway embankments on the soft organic peat soils in parts of Holland. This resulted in various accidents with casualties. In order to prevent this from happening again, the Dutch knew they needed to find different ways to build the railways and that more information on the bearing capacity of the soil was required. In softer soil it should be easier to penetrate an object than in hard soil.

Penetration Test (CPT) was born. The new technology was used to determine the best possible routing for the new proposed railway line from Gouda to Alphen (the line is still operational to date). Mr Barentsen was acquainted with the owner of the Goudsche Machinefabriek (literally the Gouda Machine Factory and the official predecessor of Geomil), and asked for his help to further develop his idea. In 1934 they together filed for a patent which was finally awarded in 1938. The pictures below show the so-called Barentsen-device as well as the original Dutch patent (courtesy of Geomil Equipment B.V.).

Following this, CPT technology evolved quickly:

1932: The Barensten-device consisted of a pushing device with a hydraulic piston and pressure gauge, a 35mm diameter gas pipe outer tube and 15mm diameter push rod with a 60° conical tip

1935: The Delft Soil Mechanics Laboratory was undertaking 10 tonne tests with the method being used in Holland and Belgium for evaluating pile bearing capacity.

1948: Advent of the ‘Dutch cone’ or ‘jacket cone’

1953: The ‘Begemann cone’, named for the Dutch engineer was introduced which had all of the components of modern cones including friction sleeve in addition to measurement of cone resistance. The cone is still fundamentally a mechanical / analogue apparatus by this point.

1965: Fugro introduce the first commercially developed electrical cone with the particular advantages of simpler and more reliable measurement allowing for continuous reading of measurements of cone tip resistance and sleeve friction.

1980: Through the 1970s various probes were introduced which attempted to measure porewater pressure during penetration. By 1980, the piezocone was in routine use which allowed for simultaneous measurement of cone tip resistance, sleeve friction and porewater pressure via a porewater pressure transducer. The piezocone remains the industry standard to this day.

Recent developments: In recent decades, development of CPT practice has centred around advances in data collection, storage and processing. In addition, the CPT apparatus has been purposeful in environmental and magnetometer-based investigations (i.e., UXO surveys). More recently, cones can be fitted with geophone modules to allow seismic refraction surveys which are purposeful in refining the soil parameter estimates and soil type estimates. Videocones have found some niche viability also.
In summary, the Cone Penetration Test is a Ground Investigation method for soils, whereby a conically shaped tip is advanced into the ground, and whilst doing so measurements are being taken. The CPT data provides insight about strength and behaviour characteristics of the soil. The penetration speed is standardized at 20 (+/-5) mm/s, typically using hydraulic rams. The conically shaped tip is known as a cone and can be mechanical or electrical of nature. In case of an electrical CPT the cone is instrumented and measures in-situ/downhole while providing data to the operator in real-time. A typical electrical cone will provide (at least) the 3 basic parameters:

  • Cone resistance (qc)
  • Sleeve friction (fs)
  • Pore pressure (typically u2)