Trial pits

The traditional geotechnical survey is characterized by discrete information. It means that old survey methods cannot provide comprehensive data on the geological structure, substance composition and properties of the whole pipeline route. This principle is not observed in all the three main gas pipeline cases. The technical documentation of the Baku-Tbilisi-Ceyhan pipeline, the South-Caucasus Pipeline system, and particularly of the North-South Caucasus Gas Pipeline does not include longitudinal geotechnical profiles of the route and the pipeline corridor in the geotechnical maps. Trial pits and boreholes that are arranged approximately 1,5-... 

As usual, the pre-construction survey stage coincides with the construction period. In order to check the issued geotechnical decisions and the recommendations the following should be envisaged for control purposes authors supervision. geotechnical documentation of trenches, construction trenches and other boreholes and trial pits as well as the regime and survey works in order to accurately identify the engendering construction activities. 

Trial pits up to 5 m depths are dug manually or using an excavator. Retrieval of soil samples and in situ tests can be carried out at particular depths as pit is excavated. The exposed side slopes lend themselves to be mapped for geological structures. 

Natural variability between boreholes or trial pits, even with the best methods of interpretation (e.g. interpolation using seismic traces) will still leave uncertainty here. Indeed, the action of the sea between the design survey and construction can actually affect shallow underlying material. For example, the motion of the beach material under wave action can abrade clay or soft chalk platforms underlying the beach surface. 

UV radiation the time period that plastic garbage can survive in the environment can be very long. Trial pits in landfill bodies have shown that plastic packaging, plastic foils and especially polyethylene bags remain unchanged to a large extent for decades even in this very rich microbiological environment. 

Fig. 9.6. Trial pitting of a composite liner after drainage layer installation showing that the geomembrane has been placed and ballasted without ensuring flatness. The waves have not been smoothed out by the load. Courtesy Schicketanz Consulting Engineers, Aachen...

The manufacturer of the monitoring system must also take out a suitable liability insurance policy (operational liability 2.5m Euro cover, product liability a minimum of 2.5m Euro cover). This should explicitly include liability for follow-up costs that emerge from false leak alarms in intact liners during acceptance measurement or the period of guarantee. The basic rule is that a leak alarm requires compulsory trial pitting, inspection and repair. 

Exploration procedure Trial pits and surface samples... 

Taking samples from a trial pit is usually a form of surface testing, because it is not possible economically to dig shafts of any great depth into limestone rock. 

The chemical analyses of the drilled cores can be stored section by section, with associated data relating to the co-ordinates of the borehole, the depth and the thickness of the deposit. By making use of appropriate programs it is moreover possible to store the results obtained from inclined boreholes and from trial pits and, with due regard to the dip of the strata, to obtain a strata-related representation of the geochemical conditions. 

Site specific geotechnical characterisation Borehole logs Trial pit logs Lab test results... 

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