Acceptance of concealed works before backfilling a foundation
A contractor is ready to backfill the foundation of a warehouse after installing the waterproofing, the drainage, and the foundation reinforcement. The technical supervision engineer is on leave and the contractor wants to proceed to keep the schedule. The site engineer has photographs of the reinforcement and the waterproofing, and the as-built drawings are signed by the contractor's own quality service. The client's representative says the photographs are enough and asks the site engineer to sign the concealed works certificate. The foundation is designed for a design load of 250 kPa on soil with a calculated resistance of 220 kPa, and the designer's note says the difference is covered by a 0.3 m replacement layer that was not installed.
1. Should the site engineer sign the concealed works certificate? What are the conditions for lawful acceptance?
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No. Concealed works must be accepted before they are covered, by the persons empowered to do so, with a certificate drawn up in the established form and with the participation of the technical supervision engineer and, where the project requires, the designer. Photographs and the contractor's own quality-service signature do not replace that procedure. Signing a certificate for works that have not been inspected by the authorized persons, and for a foundation where a required element is missing, would be a false attestation.
The lawful conditions are: the works must correspond to the approved design; the technical supervision engineer must inspect and confirm them; the certificate must be signed by the authorized parties; and any deviation must be documented and approved before covering. If supervision is absent, the contractor must wait or obtain a replacement supervisor; schedule pressure is not a legal ground.
2. The replacement layer is missing and the load exceeds the soil resistance. What is the engineering consequence and the correct sequence of actions?
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The design load of 250 kPa exceeds the calculated soil resistance of 220 kPa. The designer's note relies on a 0.3 m replacement layer to raise the bearing capacity. Without that layer, the foundation is being loaded beyond the calculated resistance, which risks excessive settlement and shear failure.
Sequence of actions: stop backfilling; record the deviation in the site log; notify the client, the technical supervision engineer, and the designer in writing; have the designer confirm whether the foundation as built is acceptable or require the replacement layer to be installed; if the layer is required, install and compact it to the specified density, verify by testing, and only then obtain acceptance of the concealed works. The site engineer should not sign the certificate until the deviation is resolved and the works are inspected in the proper procedure.