Dar Magazine I9 Page 34

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On solid ground

On Solid Ground

Improving the Dammam

Correctional Facility's Soil

by Mohammad Mardini, Dar Al-Handasah

Dammam Correctional Facility

The Dammam Correctional Facility is one of four
planned facilities commissioned by the Saudi Arabian
Ministry of Interior, along with Riyadh, Jeddah and Taif.
The planned facility is around 35 km from Dammam
and will eventually accommodate 7,300 prisoners.

Dammam's subsurface conditions

With a sprawling area of 1,545,000 m

and no less than

190,000 m

in builtup area at stake, the project's soil

conditions had to be stable and were therefore a vital
primary consideration.

Dar AlHandasah's team began by performing
standard penetration tests on drilled boreholes in
the ground to evaluate the relative density of the
foundation soil. Initial tests revealed that the site was
underlain by very loose, loose to medium dense, and
dense poorly graded sand with silt. The soil's relative
density increased with depth.

Next, a hydeogeological study was performed. It found
that the site was bisected by a major wadi. Moreover,
the site was lower than the surrounding area, with
external roads raised and acting as a dyke around the
site. Groundwater was found at 0.5 m to 1.50 m below
ground level.

Finally, chemical analyses of the soil were carried out, and
they revealed a calcium carbonate content of about 34% .

The team concluded that Dammam's soil suffered
from several problems that needed their attention:
· Loose sand layers of an average depth of 4 m
· Irregularly distributed soil relative density
· High groundwater levels
· Liquefaction hazards.

Soil improvement: a necessity

How important is soil improvement to building? Very, it turns out.
Soil improvement can increase bearing capacity and stability,
reduce postconstruction settlements and mitigate the risk
of liquefaction. Furthermore, soil improvement has inherent
advantages. It eliminates the need for deep foundations and
satisfies safe and stable subsurface conditions for buildings at a
relatively reasonable cost.

Crushed stone technique

The first process the contractor experimented with was the
crushed stones technique. It involves spreading crushed stones
on areas with loose granular soil and then compacting these
stones with a heavy roller.

Testing the technique

A trial area was setup onsite to study the efficiency of this
approach. Layers of crushed stones between 25 mm and 125 mm
in size were spread no thicker than 250 mm. The layers were then
heavily compacted with vibratory 25ton rollers until no further
settlement was possible. This process is shown in Figure 1 .

Figure 1

Crushed stone technique