Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Baked in Place Natural Casings

Prinicipal Investigators:

Jean-Louis Briaud

Sponsor:

National Science Foundation

Completion Date:

November, 1992

Final Report ID#

A36(Click to view final report abstract)

When a hole is drilled in a soil, there is always a possibility that this hole will collapse, and creating some defect in the construction of a bored pile for example.  This is especially true in the case of drilled and grouted piles.  For the oil industry, holes that plug during the drilling of a well because of collapsed soil are also a major source of problems.

The goal of this research is to develop a new drilling technique to prevent holes from collapsing.  The idea is to create “baked in place natural casings”.  When clay is heated, it gains strength and is transformed into ceramic.  Once this state is reached, it cannot come back to its original soft consistency.

In this new technique the wall of a borehole is subjected to very high temperatures to strengthen the soil at the time of drilling.  These baked in place casings will prevent borehole collapse and may even lead to natural pile foundations.

An experimental probe was developed and studied.  It was heated at temperatures up to 1000 C and the heat transfer in the soil was analyzed both theoretically and experimentally.  A finite element model was designed to simulate the heat transfer on Abaqus.

Heating the soil to strengthen it has been used for a long time in brick masonry and in pottery science.  Ceramic engineers know a lot about transformation of clay into ceramic, but little work has been done to study the heating of clay for borehole stabilization.  Past studies developed by Sheriff and Burrous  (1969),  have shown that there is a linear relationship between the logarithm of shear strength and the moisture content of the soil.

The treatment has been used in the USSR by Litvinov (1959) to stabilize loess on a large area.  Litvinov showed that a  clay can become 6 times stronger by thermal stabilization.  Maurer (1980) has used heat for innovative drilling techniques.  Maurer pushed a hot probe in the soil, which became softer and the drilling process became easier and faster.  This apparent paradox is explained.  The use of heat to transform clay into ceramic in order to create a natural casing has not been extensively studied yet.

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