Geotechnical Investigations in Kappara

Kappara contractor will be extracting earth core samples from Triq Mikiel Anton Vassalli, during the night.  Geologists will then conduct geotechnical investigations on the samples to help project engineers during the construction phase of Kappara project.  The investigations determine the earth composition beneath the surface.

The contractor will be drilling after 20:30 to cause the least traffic disruption.  Personnel will be drilling different sections in phases.  One lane will be closed tonight and each night possibly till Thursday.

Kindly follow temporary traffic signs and official’s instructions while going through the area.  Observe the speed limit and be aware of workers on site. 

Below the surface: part two

How do you know what type of rock lies beneath the surface?  How do you know if there is clay, soft stone or very hard stone?  How do you know if the rock foundations are strong enough to support the weight of your building?

Everyone knows the story of the tower of Pisa.  Beautiful architecture built on less than solid foundations.  If the tower was built somewhere else and if its angular relation to the ground remained as its builders had intended, it would surely not have been as popular, but would you want a house whose floors are all uphill?  Would you drive on a bridge built on less than solid foundations?

Enter the geologists

Geologists study the layers of rock formations on which we thread every day.  They study the type of rock, its weaknesses and strengths.  Transport Malta asked for geologists’ help to determine how strong the rock foundations of Kappara site are. The studies commissioned are called geotechnical investigations.

A drilling rig drilled holes in the ground and extracted core samples.  The operator packed the samples in heavy duty plastic containers.  The containers had rows for each sample.  The operator marked each row with a white marker.  He wrote a number showing the order in which he extracted the samples and hence the depth of each.

The geologist, architect Christian Schembri, in this case, received the whole lot of samples in his lab in Ħandaq, Qormi.  A big number of plastic containers were stashed in his lab.  Each container contained five core rock samples.  Christian visually went through all the samples, rock by rock.  He noted when rocks changed colour, when the rock type changed and the faults he could register.  He used a geological hammer to start getting a feel of how strong each rock was.  He wrote it all down.

Then Christian moved on to more precise readings.  He put a sample into a cabinet; a cylindrical rock core on a sort of steel plate of almost the same diameter. He closed the reinforced glass door and moved to the console.  He pressed a few buttons and the number displayed started to increment.  A steel plate from top pressed against the rock and the bottom plate.  It exerted a tremendous weight on the stone.  A data logger, standing a few centimetres away, plotted a graph showing the pressure as it increased by the second.  Then pah, something gave.  The sound of a projectile whizzed by. Then something else gave. The whole rock cracked.

Christian did a series of these tests and plotted a whole report. By the end of it Christian sent a report to Kappara project’s engineers.  The engineers now know the foundations quite well and can  make the right choices when constructing the foundations for Kappara Project.

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Below the surface

Kappara contractor is conducting a series of geotechnical investigations to help engineers make the right choices when laying the foundations for the Kappara Project.

The machine seems like a converted war tank.  It has tracks instead of wheels, providential given the tough terrain. The tracks and engine on top have a crane-like arm affixed to the front, a derrick.

A drilling bit protrudes from the derrick into the ground below.  The bit turns. Cooling water pours out turning the area around the drilling into a small mud pool.  The operator pulls at a series of levers pushing the drill bit deeper and then stops the drilling.  His assistant gets another section of the drilling bit, about a metre long steel cylinder.  He screws it on top of the rest of the bit.  The machine starts turning the bit again, drilling deeper. The assistant adds more sections, drilling deeper.

The operator is satisfied. He reached the desired depth.  He pulls at a few levers and the machine turns the bit the other way round.  It brings the bit back up; the assistant removes section after section and puts them on an iron frame.  The final section emerges from the ground.  The assistant grips the metal cylinder with a heavy wrench.  He puts his weight on the wrench and pulls down.  The operator gets a huge hammer and delivers a few blows to help release the section. He empties the cylinder in a heavy duty plastic case. The case takes five core samples.  Five cores of earth that have not seen daylight in years, surely tens of years, probably thousands.

The operator puts the case in the back of the truck, returns to the machine and retracts the derrick.  He changes the angle of the derrick from vertical to horizontal so that it lies completely on top of the tracks.  Pulls more levers and the machine starts to move its heavy tracks, navigating the tough terrain towards the next location.  The next digging spot.  The next sample that will be sent to the lab for analysis.