In Cyprus, two neighbouring plots can sit on noticeably different ground. Marl or soft limestone that looks as hard as rock in the dry season can soften when it gets wet, and some clays swell in winter and shrink in summer, moving light buildings and floor slabs with them. This guide explains why these materials cause problems, what a site investigation in Cyprus involves, which laboratory tests reveal the risk and how the design engineer uses the results.

Ground changes over short distances

Sedimentary deposits such as marl, chalky and soft limestones, calcarenite and clay are widespread across much of the island. They are layered, and individual layers thin out, thicken or give way to a different material within short distances. The degree of weathering also varies with depth and from place to place: a weathered, clayey zone near the surface may pass into firmer material a few metres down. Old fill and past excavations add to the picture.

That is why conclusions drawn from the plot next door, a nearby road cutting or a single excavation can be misleading. A site investigation is there to establish the conditions where the structure will actually stand.

Marl and soft limestone: hard when dry, weaker when wet

Marl is a sedimentary material made up of clay and calcium carbonate. When dry it can resist a pick and look like rock, but depending on its clay content it may soften, break down and lose a large part of its strength once it is wetted. Repeated wetting and drying speeds up this deterioration. Weakly cemented soft limestones and calcarenites can likewise contain hard and loose bands within the same layer.

A mistake we often see is judging the ground by how hard it feels in a foundation excavation dug in summer. If the formation is left open to rain or seepage, it can soften before the concrete is poured. Testing, not appearance, shows how the material behaves with water.

Expansive clays that swell and shrink

Some clays, particularly those containing smectite-group minerals such as montmorillonite, swell when they take up water and shrink when they dry out. A wet winter followed by a long, dry summer changes the water content of the ground from season to season and repeats this volume change every year. Deep cracks opening in clay ground in summer are one visible sign of it.

The structures most affected are those that put little load on the ground: one- and two-storey houses, ground-bearing floor slabs, garden and retaining walls, footpaths, external slabs and buried pipes. Where one part of the ground gets wetter or drier than another (a leaking pipe, rainwater collecting against the building, garden watering or the roots of large trees), the movement is uneven. That can lead to cracked walls, sticking doors and windows, and heaved floors.

What a site investigation includes

The scope depends on the structure and the site. An investigation usually involves:

Planning and site reconnaissance: the number, position and depth of test points are set for the project, and ground and geological conditions are assessed on site.
Test pits: dug with an excavator so that the layers can be seen, described, photographed and sampled directly. For light structures on shallow foundations they are among the most informative methods.
Geotechnical drilling and logging: where information with depth is needed, boreholes are drilled, with SPT carried out as required; cores are boxed and photographed, TCR, SCR and RQD are recorded for rock cores, and groundwater is observed. Soil and rock descriptions are presented on borehole logs.
DCP testing: the dynamic cone penetrometer is used in accordance with ASTM D6951/D6951M-18(2023) to find shallow layer thicknesses and an estimated CBR. It gives a quick profile of road subgrade and pavement layers; because the CBR is estimated from a correlation, it does not replace a laboratory CBR test.
Sampling: samples are taken from each layer, with depths recorded, for laboratory testing.

Details of our fieldwork are on the site investigation and DCP testing and geotechnical drilling pages.

Laboratory tests that identify the risk

Samples from site are tested in our laboratory as shown below. Our technical lead’s doctoral research was on the statistical modelling of the plasticity of Cypriot clayey soils.

Test	Standard	What it shows
Water content	TS EN ISO 17892-1:2014+A1:2022	Water content of the sample as taken; basic data for interpreting the other results
Particle size distribution	TS EN ISO 17892-4:2016	Proportions of gravel, sand and fines
Atterberg limits	TS EN ISO 17892-12:2018+A2:2022	Liquid limit, plastic limit and plasticity index; an indicator of sensitivity to water and swell potential
Linear shrinkage	BS 1377-2:2022	Reduction in length on drying; tendency to change volume
Soil classification	TS EN ISO 14688-2:2018	Soil class

The results are read together. A high plasticity index and high linear shrinkage point to a soil prone to volume change. These are index tests, however: they do not measure the amount of swell or the swelling pressure directly. Whether further testing is needed is for the project engineer to decide. For roads and fills, Proctor (TS EN 13286-2:2013) and CBR (TS EN 13286-47:2021) tests are often added. The full list is on our soil laboratory testing page.

What the results are used for, and who decides

We carry out the tests and report the results in line with the relevant standards. Our site investigation report sets out the ground conditions, layer thicknesses, test results and our assessment of the ground. The design engineer uses this information to choose the foundation type and depth, and to decide whether a clayey or weak layer should be removed, whether the floor slab can bear on the ground, what drainage and moisture control are needed and, for roads, which design CBR to adopt. These design decisions belong to the project engineer; our report informs them and does not replace them.

Timing depends on the number of test points and samples. Tests such as water content and linear shrinkage need oven drying, so laboratory results are not available on the day of the fieldwork; we confirm the delivery date with the programme. Commissioning the investigation before the design is drawn up, and ideally before the land is bought, means the results can actually shape the design.

Frequently asked questions

Does a single-storey house need a site investigation?

Light structures are the ones most affected by expansive clays, so knowing the ground matters for a small building too. The scope can be scaled to the size of the structure; a few test pits with index tests are often a sensible start. We agree the scope with the building’s design engineer.

The ground looks dry and hard. Is testing still needed?

Yes. Marl and clayey ground look hard in the dry season. That hardness says nothing about how the ground will behave when wet; water content, plasticity and shrinkage tests show that.

Can a DCP test replace drilling?

No. A DCP test gives shallow layer thicknesses and an estimated CBR quickly and is useful for road subgrade and pavement layers. To see deeper layers, rock quality and groundwater, drilling is needed. Which method suits depends on the structure and the site.

If you are planning a site investigation for a plot, a building or a road, we can agree the scope with you. Our site investigation and DCP service page has the details, and you can send us your project information through our contact page.