The construction of new airports often present interesting geotechnical engineering opportunities in the form of large scale ground improvement solutions for runway and taxiways as well as major foundation schemes for large terminal buildings. The scale of these projects frequently lends itself to pre-construction trials and testing in order to get best value from the design. Safety considerations become even more important when working airside on construction at existing airports with constraints for example on piling rig headroom being a significant factor.
The design of high rise buildings frequently leads to highly concentrated column loads which may necessitate deep foundations in the form of bored piles or barrettes. The load capacity of deep foundations can be enhanced by a variety of techniques depending on ground conditions. These methods include shaft and base grouting, threading and ribbing the shaft as well as underreaming the base. Basement construction particularly in the commercial building sector may require deep embedded retaining walls constructed by secant pile or diaphragm walling techniques. A number of factors including depth and ground conditions will influence which method (continuous flight auger, cased flight auger, fully cased secant pile or diaphragm wall) will achieve the required performance.
The location of many onshore power generating plants, whether fossil fuel, energy from waste or nuclear, in areas where ground conditions are often unfavourable, provides opportunities to innovate in foundation and sub structure design. For example, the use of cellular diaphragm walls can be used in very soft ground to create deep underground spaces for end usage as pumping stations, intake structures and refuse bunkers.
Highway construction presents many interesting challenges for the geotechnical engineer. Whether it is the design of piled foundations for major bridge crossings, the engineering of high embankments on soft ground using ground improvement techniques or the strengthening of deep cuttings associated with widening schemes using soil nailing, ground engineering can play a key role in a successful outcome.
The increasing size of container vessels has driven the construction of new container ports with ever deeper berthing facilities. The associated quay wall structures are subject to a complex combination of load cases arising from gantry cranes, vessel berthing and mooring, tidal conditions and earth pressure. Forms of construction include steel combi walls, caissons, deck on piles and diaphragm walls. All must be designed and constructed to take into account the potentially aggressive corrosion environment with associated challenges to durability. In such cases, good concrete mix design and production is particularly important. The provision of cathodic protection can extend design life.
Very deep excavations often several hundred metres in depth are required to reach valuable earth's natural resources such as precious stones and uranium ore and the application of ground engineering techniques such as dewatering and cut-off walls can be used to optimise the design and mitigate the short and long term impact of such excavations.
The challenges to be faced during the upgrading of existing railway facilities include possession working during narrow non-operational windows and working within limited space and headroom. Often innovative methods of mini piling provide the only practical foundation solution. In the case of new build, rail alignment is heavily influenced by environmental impact and earthworks considerations including balancing cut and fill materials. A staged approach to ground investigation is essential as the alignment becomes more clearly defined and land becomes available for access. Underground railway construction within an urban environment presents many ground engineering challenges including the construction of deep underground station boxes with minimum adverse effects to adjacent buildings. Top down construction, groundwater re-charge and compensation grouting are all techniques which are used to mitigate such effects, deployed in tandem with an effective geotechnical monitoring scheme.
Water seepage losses beneath existing dams can be greatly reduced by cut offs constructed by grouting or plastic concrete cut off walls using clamshell grab or hydromill techniques. Deep sewage storage may require tunnels and diaphragm wall shafts which can be realised to depths up to 100 metres. However, tunnel break in and break out zones may need special consideration both in terms of structural design and groundwater control. Whilst the former may be dealt with by detailing soft eyes in the diaphragm walls, the latter may require additional measures such as grouting or freezing at the junction between tunnel and shaft.