A geotechnical report for selecting a trenchless technology should include sufficient information about the terrain, groundwater and construction risks of the route. At a minimum, it should provide boreholes, geological profile, water table, laboratory tests, granulometry, presence of rock or boulders, permeability, soil aggressiveness, strength parameters and geotechnical variability..
This information makes it possible to assess whether the project can be implemented through pipe ramming, horizontal directional drilling, Direct Pipe or microtunnel with open shield, EPB or hydro-shield.
Minimum recommended geotechnical information
Borings and reconnaissance of the terrain: location, depth, spacing between investigation points, cores, stratigraphic description and relation to the planned layout. They must cover the zone of advance and the areas of attack and reception wells.
Geological and hydrogeological profile: definition of strata, material changes, transition zones, fills, rock, mixed soils, fracturing, cavities, discontinuities, water table and possible water pressures.
Laboratory and in situ tests: granulometry, Atterberg limits, natural moisture, density, strength, abrasiveness, permeability, SPT/CPT tests if applicable, simple compression in rock and other parameters necessary to estimate face stability, thrust and excavability.
Presence of water and permeability: measured water table, seasonal variations, water pressure, soil permeability, risk of inflows, fines entrainment and need for pumping, treatments or pressure systems.
Problematic materials: boulders, blocks, abrasive rock, mixed soils, open gravels, saturated sands, expansive clays, anthropic fills, contaminated soils, cavities or very heterogeneous layers.
Parameters for the choice of tunnel boring machine: face stability, grain size, cohesion, friction angle, abrasiveness, rock strength, water pressure and behavior of the excavated material. These data are essential to decide between open shield, EPB tunnel boring machine o hydro-shield for water-logged terrain.
Data for wells and auxiliary civil works: depth of excavation, slope stability or support, lateral thrusts, seepage, pit bottom, need for waterproofing, soil treatments and soil conditions, etc. vertical pits for driving and microtunneling.
How the geotechnical report influences the trenchless solution
The geotechnical report conditions the choice of method, type of TBM, borehole design, expected thrust, lubrication, slurry management, expected performance, settlement risks and overall project cost.
For example, stable soils with low water presence may allow for open shield solutions. Cohesive or conditionable soils may be conducive to EPB. Saturated, permeable soils or soils with significant water pressure may require hydro-shielding. In long, complex crossings or with special layouts, it may also be necessary to compare alternatives such as HDD or Direct Pipe.
In projects under roads, railroads, waterways, urban areas or utilities in operation, the quality of the geotechnical report is critical to reduce uncertainty, define monitoring controls and anticipate risks on the infrastructure crossed. This is especially important in infrastructure crossings o actions with hydraulic and environmental conditions.
Minimum checklist of the geotechnical report: boreholes, stratigraphic profile, water table, permeability, granulometry, resistance tests, abrasiveness, presence of boulders or rock, soil variability, chemical aggressiveness, thrust parameters, geotechnical risks, well conditions and construction recommendations.
CRequest a technical geotechnical review to select appropriate trenchless technology before closing the route or putting the work out to bid.
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