Installing a tank in presence of an aquifer means, first and foremost, properly managing the water table level and hydrostatic pressure.
Table of Contents
Preliminary Assessments of the Water Table Level
Before designing the excavation, the first step is to determine the maximum water table level that can be reached at different times of the year. This step is necessary to identify the maximum hydrostatic pressure that may act on the tank and the foundation/anchoring structures.
In practice, the goal is to have a clear understanding of the most challenging scenario, so that subsequent decisions (drainage, excavation, foundation slab, tie rods) can be made correctly.
Drainage Before Excavation: Why It’s Necessary
Before proceeding with the excavation, it is necessary to install adequate drainage systems to lower the water table. This makes the excavation possible and creates the conditions for working in a more controlled manner.
This phase is closely linked to the initial assessment: the more critical the aquifer is (in terms of water level and seasonal variability), the more crucial it becomes to plan for adequate drainage before beginning excavation.
Excavation and Stability: Methods and Slopes
When the water table is present, simply “digging” is not enough: the excavation method and the slope angle must be evaluated to prevent landslides. The choice depends on the type of soil and the water table level.
The key point here is stability: decisions regarding the excavation geometry and slopes must be consistent with the actual conditions encountered (soil and water), because they directly affect the safety and quality of the subsequent backfilling.
Phase 1: Foundation slab and tank anchoring (hydrostatic thrust)
Phase 1 includes:
- Carrying Out Excavation with a Specified Cross-Section
- Construction of the concrete foundation slab
- Securing the tank to the foundation using cables or tie rods
A key point: the dimensions of the foundation and tie rods must be calculated based on hydrostatic pressure. In other words, verifying the maximum groundwater level (first section) translates here into the proper sizing of the structural elements that ensure the safety of the reservoir.
Phases 2–3: Installation, Backfilling, and Controlled Filling
After Phase 1, proceed with the installation and backfilling operations “as described in the previous backfilling procedures (in the absence of an aquifer),” dividing them into Phases 2–3.
Step 2: Filling and Tank Filling
Planned activities:
- Subsequent backfilling with fine sand or silt
- Next, fill the tank
The sequence of operations is part of the system’s control logic: while backfilling is underway, the tank is also being filled as planned.
Step 3: Finishing Touches, Extensions, and Sealing
Planned activities:
- Further backfilling with fine sand or silt
- Installation of metal extensions, if any
- Properly sealed extensions
At this stage, in addition to continuing the filling process, the required accessory components (such as extensions) are installed, with particular attention paid to sealing.
Step 4: Backfilling and Assessment of Surface Loads
Phase 4 involvescompleting the backfilling. At the same time, if the surface is accessible to heavy vehicles, you should consult a professional to determine whether a slab capable of distributing the loads is needed before installing the final pavement.
Important note: The heat-dissipating slab must have a larger plan area than that of the tank in order to effectively dissipate the loads.
Hydraulic Connections: Pipes and Flexible Fittings to Reduce Risk
In presence of aquifers, it is recommended to consider installing the following on water supply connections:
- appropriate piping
- flexible joints
The goal is to minimize the risk of potential failures as much as possible. This measure is directly related to the “dynamic” conditions typical of environments with groundwater, where it is useful to incorporate elements that help manage stresses and movements.
Conclusion
Burying a tank in presence of an aquifer requires a systematic approach: verify the maximum groundwater level, install drainage systems, plan the excavation and slopes to prevent landslides, construct the foundation slab and anchors to withstand hydrostatic pressure, and then complete the installation and backfilling in the four planned phases.
