Geotechnical Investigation in Mingachevir

Engineering geological conditions in Mingachevir

Mingachevir lies where the Kura leaves the mountains and enters the Kura depression, at the foot of the Bozdag ridge. North-west of the city are the Mingachevir Reservoir and its dam, and downstream lies the Varvara Reservoir. The terrain is stepped by the Kura terraces: from low terraces by the river it rises towards the slopes of Bozdag, which are cut by gullies and dry valleys.

The Kura terraces are built of river deposits — gravel, sands, sandy loams and loams — and their upper part is often covered by loess-like loams and sandy loams. Neogene clays, sandstones and conglomerates crop out on the Bozdag slopes, and their weathering products form the slope deposits. The cover soils, formed in a dry and hot climate, accumulate carbonates and water-soluble salts.

The city was largely built in the mid-20th century in connection with the reservoir and power station, so many plots still contain made ground from the construction period and soils moved during site grading.

Key construction risks in Mingachevir

• Collapsible soils. Loess-like loams and sandy loams of the Kura depression may be collapsible. Firm in their natural state, they settle further when wetted by pipe leaks, irrigation or rising groundwater. Collapsibility and the depth to which it extends are determined by laboratory testing.
• Influence of the reservoir and the Kura. On plots near the reservoir and the river, the water table may follow the water surface regime. Wave erosion affects the reservoir shores, while lateral erosion and bank collapse affect the riverbanks. A safe setback from the shore has to be justified separately in such places.
• Processes on the Bozdag slopes. Wetting of clay layers on the slopes leads to landslides and rockfalls, and heavy rain causes gully erosion and mudflows.
• Saline soils and aggressiveness. Sulphates and other salts accumulated in the cover soils can be aggressive to concrete, and salt leaching weakens the soil structure.
• Made ground. Fill from the construction period is unevenly distributed across a plot, and the level of natural soil beneath it can only be established by drilling.
• Seismicity. Mingachevir also lies in a seismically active part of the country. The design seismic intensity is taken from the applicable standards and codes; additional requirements apply near hydraulic facilities: AzDTN 2.3-1 “Construction in Seismic Regions” has a separate section on hydraulic structures, and within the reservoir’s water protection zone construction work may only be carried out under approved design documents (Cabinet of Ministers Decision No. 56 of 24 March 2000).

Near the reservoir, the measured groundwater level may depend on whether the reservoir is filling or drawing down. The report therefore states the date of measurement, and the possible maximum level is forecast for design. The likelihood of the loess-like stratum being wetted by groundwater depends on this forecast: if the level is expected to rise, collapse settlement is calculated for wetted soil.

Surveys typically required

In Mingachevir the programme is built around whether the plot is on a terrace, a slope or the shore. In most cases the following are carried out:

• borehole drilling and sampling, with undisturbed samples from the loess-like stratum and the depth of terrace gravels established;
• mechanical properties — oedometer tests with wetting, collapsibility assessment;
• chemical analysis of soil and water — water-soluble salt content, sulphate aggressiveness;
• along the shore, groundwater level and regime and flooding risk and drainage recommendations;
• on reservoir and river shores and the Bozdag slopes, a geohazard assessment;
• an electrical resistivity survey to map the thickness of the loess-like stratum and fill across the site;
• for buildings showing signs of distress, a foundation soil investigation for existing buildings.

How the work is organised

During the site visit we record terrace edges, gullies, water-bearing networks and signs of settlement in existing buildings. Near the protection zones of hydraulic and energy facilities, field work is coordinated with the relevant organisations, which may lengthen the preparation stage.

Undisturbed samples of loess-like soils are sealed airtight on site, since moisture loss distorts the collapsibility test result. Mingachevir is far from Baku, so equipment transport, crew accommodation and sample shipping are added to the cost; on small projects this share is relatively large. To complete all field work in one mobilisation, send the location, plot size and parameters of the planned building in advance via a quote request.