What geotechnical hazards are most likely by soil type and how are they effectively mitigated?

Q: What geotechnical hazards are most likely by soil type and how are they effectively mitigated?

In pipe jacking, risks vary with soil type and water table. Loose sands (high NF): ground loss, siphoning; mitigation with chamber pressure control, adequate rheology and injections/lubrication. Silt and soft clays: instability and deformation; mitigation with stable advance, face pressure and back injection. Overconsolidated clays: high friction and high thrust; mitigation with greasing and thrust control. Gravels/cobbles: blockages and deflections; mitigation with reinforced head and stabilization injections. Mixed soils: abrupt pressure changes; mitigation with mixed modes (EPB/Slurry) and data-driven transition. Fractured rock/karst: water inflows and collapse; mitigation with seals, grouting and trajectory variation. Risk reduction is based on prior reconnaissance, design with adequate cover and Rmin, real-time monitoring (pressures, flows, thrusts) and alarm thresholds/stop rules.

At pipe jacking (microtunneling), the risks depend on the type of soil, the water table (NF) and the front pressure. Mitigation combines shield selection (EPB/hydro-shield/mixed), soil/sludge conditioning, lubrication and injections, y monitoring of thrusts and pressures.

Rapid risk mapping by terrain and effective response

Terrain / Condition	Probable risks	Operational (on-site) mitigation	Preliminary / design measures
Loose sands (high NF)	Loss of land, siphoning/piping, settlements	Fine control of chamber pressure, suitable rheology (EPB/hydro-shield), lubrication continues	NF pre-drainage/depression, screens/curtains, traverses with sufficient cover
Dense sands	Torque overconsumption, deviations, wear and tear	Conditioning (foam/polymers), stable feed rate, smooth corrections	Straight or Rmin wide; choice of suitable pikes and shields
Silt/soft clays	Instability of the front, deformations, ovalization	Stable pressure, constant feed rate, injected back	Local enhancement (jet/grouting) if sensitive structures are present
Overconsolidated clays	High friction, high thrusts, deviations, deviations	Lubrication (bentonite/polymers), thrust control, recalibration pauses, etc.	Conservative thrust calculation; launch liner
Gravels/boulders	Blockages, roll-downs, detours	Head with reinforced picks/cutters, high torque, injections stabilization	Input/output buffers, localized pre-treatments
Mixed/heterogeneous soils	Sudden changes in pressure, loss of terrain	Mixed-mode (EPB/Slurry), data-driven rheology transition	Previous reconnaissance (surveys, geophysics), windows inspection
Fractured rock	Water inflow, over-excavation, settlements	Front sealing, pressure control, phased advance	Pre-bolting/plastering, additional coverage
Karst/cavities	Voids, collapse, subsidence	Filling/injections, guided by radar/GPR during the work	Recognition and variant development; exclusion if the risk is critical
Anthropic landfills	Hard objects, leaks, differential seating	Low speed, reconnaissance stops, shirts temporary	Tastings/test wells, path screening
NF variable / tides	Pressure changes, water inlets	Hydroshield, bypass emergency, valve control	Programming by hydrological window, sheet piles on coastline

How to reduce probability and impact (step by step)

Do your researchThe following are some of the most important services: boreholes with recovery, piezometers, geophysics (GPR/seismic) and affected services.
Design for the worst caseminimum coverage, Rmin reasonable, calculation of thrust and choice of shield.
Prepare the ground where it touches: NF depression, injections/jet grouting, screens.
Control parameters in real timeFront pressure, flow rate/rheology, thrust and torque, injection volume; land balance.
Define alarm thresholds and stop rules: e.g., Δwarming, Δpressure, loss ratio → pause, stabilize, inject, resume.
Closes well: as-built geometric, tightness tests and QA/QC report per section.

Warning signs (act immediately)

Sudden increases in thrust o par, chamber pressure loss, imbalance between excavation and sludge return, or anomalous readings on the piezometers/aspectrometers.

Neutral technical resource: guide ITAtech - Microtunnelling Guidelines (shield selection, pressures and risk control).

If you need to contrast a layout with real geotechnical engineering, our team of Technical assistance and engineering can propose mitigations and variants; if you already have plans and soundings, request a quotation with DN, L, Rmin, NF and site restrictions.