Understand Static Cone Penetration Test Through History
01. Mechanical Static Cone Penetration Test Probe
CPT origined from Holand, initially named Dutch Cone. Static CPT can be traced back to 1932. A Dutch engineer named Pieter Barentsen discovered that when inserting a cone into the soil, it is easier to penetrate when the soil is soft and much harder when the soil is dry and tough.
Pic 1. Pieter Barentsens' Discovery
According to his discovery, invented a simple static CPT system (pic.2). A 15mm Pile inserted into a 35mm casing, allowing the pile to move up and down freely; The cone shape head with a 10cm2, pin point of 60 degrees. With the load pressure, it drives the cone into the ground. The cone can penetrate of 10 – 12m deep depending on the force give onto the cone.
Pic.2 Barentsens' Static CPT system and early mechanical CPT heading
Pieter Barentsen entrusted GMF Gouda to help produce the first Global Mechanical Static CPT Equipment (pic.3). The equipment was tested by Gouda and determined that the equipment proposes a highly efficient working theory and effectiveness, and therefore globally promoted (pic.4).
pic.3 First Globally Manufactured Mechanical Static CPT Equipment (left), pic.4 Static CPT application in Africa (right)
1934, Barentsen and GMF Gouda company has registered patent over the CPT system. Hence, Holand GMF Gouda became the worlds first CPT equipment supplier. 1996, GMF Gouda Geotechnical division and Holand Conewel company merged together and became the now known Geomil Equipment B.V. Company. The two CPT equipment leaders creating the worlds most history known static CPT equipment supply company.
1935, Holan delft laboratory designed and created the first 100kN thrust capacity system (pic.5)
pic.5 1935 Dutch Cone Penetration System
1948, Vermeiden and Plantema has modified the penetration system and added a cone shaped protection system (pic.6). The purpose is to prevent soil entering between the casing and the cone.
pic.6 The cone shaped protection of the dutch cone.
1953, Begemann added a friction cone into the system (pic.7). This allows the CPT cone to also read tip and side frictions. The test reading is recorded and analyzed every 20cm. (pic.8).
pic.7 Begemann CPT Cone with friction cone.
pic.8 reading system graph of cone resistance vs skin friction
02. Electrical Measurement Type Static CPT Cone
The Electrical Static CPT Cone is far easier and cheaper to operate. Its disadvantage is that the friction of the sleeve and the cone, soil entering between the layers can result in lower precision testing. Since 20th Century, people have continued to invent electrical CPT cone, till 1965, Holand Fugro and TNO invented a Electrical Measurement CPT cone (pic.9). This cone shape and size is the modern static CPT initial model, and later on has been awarded with international physicals and ISSMFE standards.
pic.9 Fugro Electrical Static CPT cone design
This Electrical Static CPT cone design aims to enhance certain improvements:
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Eliminate the precision problem caused by the friction sleeve and the cone itself.
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Create a stable cone penetration testing with continuous penetration
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Improving the signal delivered to provide more simple and reliable results
03. Pore pressure CPTU cone
1974, there has invented a pore pressure of static CPTU cone. The early CPTU cones have different shapes, installment processes are also different, main criterias are u1, u2 and u3 of the picture. The 3 different positions detect different pore pressures, but in the application process, the main detection point is u2 (pic. 10). Through measuring pore pressure, we can adjust the conical point pressure, allowing easier access into soft soils.
pic.10 CPTU pore pressure cone conical point heads and measurement spots.
Pore pressure CPTU system has a higher advantage through:
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Using the pore pressure measurement systems sensitivity to precisely separate layers of soil.
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Determination of the strength of the soil layer
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Through pore pressure dissipation test to determine the permeability coefficient and hardness coefficient of the soil layer.
04. Digital Static CPT
1985, the invention of digital static CPT, with company Vertek being the symbol (pic.11). Digital Static CPT has its advantages through analog switched is done under the pore, allowing a prevention of signal weakening problems due to cable too long etc. Moreover, all digital static CPT signals can be sent through the same cable, drastically reducing the problem of over-cable wiring. Allowing more measurement spaces, not affected by the distribution or wires.
pic.11 USA Vertek Digital Static CPT and Measurement System
05. Integrated Static CPT System
With a constant change in demand for testing, static CPT equipments have slowly moved towards the development of integrated static CPT systems, with Geomil being the leading manufacturer. (pic.12 onshore CPT systems, pic.13 Offshore CPT systems). Integrated static CPT systems are able to sustain in harsh environments and still demonstrate its function under different conditions.
pic.12 Panther 200
pic. 13 Seabed Static CPT System Manta 200
