Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Plans to build a vast oil production plant in Kazakhstan have called for investigation of difficult soils in a far-flung location

Kazakh customs officials had trouble believing that anything as innocuous as soil was in the canisters airlifted to the UK late last year.

When they were informed that munitions grade steel tubes filled with earth were to be exported they were, perhaps reasonably, suspicious. Spot checks were carried out to check that no illicit substances were being loaded.

The 40 tubes held samples taken from the vast, flat wilderness of north west Kazakhstan, approximately 30km from the outpost town of Aksai. A consortium of international oil firms is planning to treble the capacity of the Karachaganak oilfield with the extension of an existing production plant and construction of a new facility, says Changiz Roohnavaz, senior project manager with Mott MacDonald, which is acting as the oilfield developer's technical adviser.

"It's an extremely remote location. There is no significant infrastructure there. We knew the ground was difficult, but almost no detailed geological information existed. What's going to be built is huge – without precedent locally." A thorough site investigation was called for.
The ground consists of 30m of loess and alluvial deposits. Though it accounts for 10% of the Earth's crust, loess is a relatively little known material, Roohnavaz says.

Loess is formed from fine particles created by the scouring action of glaciers. These grains of silt and fine sand were cemented together by clay and carbonates. Depending on where they are deposited, the mineral and chemical composition differs widely. The speed of formation also had a major bearing on characteristics of the resulting loess. Loess is highly variable and has a high void to solid ratio of 0.75. While very tough when dry, it collapses when saturated. The clay bridges between particles soften and carbonate bonds dissolve away. Loess is described as a metastable material because of its liability to rapidly change state.

Roohnavaz says: "Often loess is protected from rain by a thin band of overlying clay. If you are building in loess you need to consider what will happen if your foundations create a pathway for water through that clay layer. You need to think about the consequences of a burst water main or leaky drainage. And with climate change, you need to think about the potential for wide scale flooding or a rising water table."



Loess comes in different degrees of collapsibility, he notes, but "should be treated as guilty unless it can be proved innocent. You have to assume the worst and then find out whether it's really as bad as you at first fear." Deformation resulting from collapse is commonly 10% the depth of the loess.

Investigating the engineering properties of loess requires a precise and rigorous approach, which required substantial education and training of the indigenous ground investigation and soil testing industries.

"We could have hired an international site investigation contractor," Roohnavaz says. "But there are different stages of oilfield development. It suited the project better to have local contractors, and it was important to the client that the project helped the local economy. We want to create employment opportunities and help raise local practise to international standards."

The Kazakh geotechnical industry mainly works to Russian standards. The western European geotechnical industry has advanced rapidly over the past 20 years, creating a knowledge gap. "There's nothing wrong with what they do, but the intricacies of loess are ignored," Roohnavaz says.

Borehole sampling equipment lacked the precision and power of modern rigs. And sample handling left something to be desired.

A method of anchoring down drill rig trucks had to be introduced to gain enough reaction force to reach the 30m depths required. Roohnavaz persuaded local ground investigation contractors to invest, by local standards, vast sums in new testing equipment and drill rigs.

Loess has to be handled with care. As soon as a sample is removed from the ground it relaxes and swells unless confined. Kazakh practice was to wrap soil samples for transit to the testing lab. Attempts to transfer core samples to locally available sampling tubes resulted in such severe disturbance that testing them would have been pointless. Roohnavaz, therefore, worked with contractors to develop a steel canister that could be fitted to existing drilling rigs and be used both to extract a sample and transport it. They were manufactured locally by a former munitions factory.To protect the canisters from shock during transport, each was bubble wrapped and placed within polystyrene compartments in crates. "They were treated like babies," Roohnavaz says.

Local laboratories undertook testing, working to Russian standards, that were monitored and cross-checked with UK standards. "Unsaturated soils are much trickier to deal with than soils in their saturated state," Roohnavaz says. Triaxial and double odometers tested the strength and compressibility characteristics of the loess.

To ensure the validity of local test lab results, 40 samples of the hundreds generated were flown to the UK for control and specialist testing.
Specialist testing to examine behaviour under dynamic loading included local strain testing and shear wave velocity measurement.

"It was assumed that the loess would collapse when it became wet – it can collapse under its own weight. But we found the samples actually swelled, even when some load was applied to it, and only collapsed when load reached a threshold value," Roohnavaz says. Swelling of loess was 5% to 10%.

He points out that testing is normally carried out on samples that have already been saturated, without swelling being recorded. As a result, in conventional cases, deformation measured has been large. But in reality, swelling takes place before compression and collapse. Actual settlement proved to be far lower than assumed. The implications are positive, Roohnavaz says. "It may enable the design of simpler and more economical foundations."

First phase of construction, expanding the existing oil production facility by 30%, is under way. Site investigation for the next phases, expanding the plant by a further 50%, starts this month.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.