Risk is most often of a technical nature in relation to earthworks.
It often concerns the following non-exhaustive list:
Quality of geotechnical studies
Technical risk in terms of earthworks mainly stems from a lack of knowledge of the geotechnical and hydrogeological contexts.
The importance of geological and geotechnical investigation can never be overestimated. This must be adapted to the development of studies in connection with basic design, the size of the project and the geological and topographical complexity of the site (see the LCPC document Commande et contrôle des reconnaissances géotechniques de tracés (Command and control for geotechnical investigation of alignments) Ref. 59023101).
The project owner is responsible for carrying out all studies in the proper fashion (it should be borne in mind that the overall costs of studies for an operation are between 2% and 9% of the operation, in accordance with the size of the operation and the type of services provided as in-house works or subcontracts).
There should never be deadlock for reasons relating to finance or timelines.
The first error is neglecting preliminary studies (preliminary studies [EP] and overview / background summaries [APS]).
Over the last 25 years, the considerable importance given to environmental constraints, and more specifically the constraints of the natural surroundings, have meant that designers tend to attach less importance to geotechnical constraints proper, which are rarely the main factor in terms of choice of variants, and they concern themselves with these constraints only at an advanced stage of the project.
This means that technical anomalies which could serve to alert designers to carry out in-depth studies in good time on such singular matters are not identified at a sufficiently early stage.
Similarly, it is advisable to attempt to gather together investigation data for the entire project. If topography renders land inaccessible, this could in fact signal that the land is unstable.
With no exceptions, inaccessibility of land in terms of either topography or refusals by land owners cannot lead to deadlock on a certain area of the project.
Falling sections
From the technical point of view, a distinction is made between the risks of falling sections from slopes outside the land requirements and falls from slopes which form part of the project.
In rocky areas, this must be a concern from the outset of studies.
Beyond repercussions in relation to the choice of alignment, the incidence of this risk may lead to a choice of building retaining walls rather than earthworks slopes, building stone traps on the edges of the construction, and/or consideration of building protective structures on slopes.
Limited or insufficient material resources
In addition to the legal risk mentioned above, failure to appreciate earthworks balance generally leads to underestimation of this item.
There are many causes. If systematic use of programs to calculate earthworks volumes and digital models has made calculation of geometric volumes easier and reliable, it may frequently be observed that no account is taken of all items which may affect the conditions for reutilization of soils (bulking, for instance).
Areas of low bearing capacity and compressible areas
In due consideration of the fact that these areas could call the project into question or create considerable technical constraints, it is advisable for work to be carried out with a geologist to identify such areas as soon as possible visually in preliminary studies, proceeding with technical identification during the overview / background summary [APS], and subsequently during the actual project phase.
Building an embankment too rapidly on soil which is compressible and/or has a low bearing capacity can entail general instability in the bearing soil and the main body of the embankment.
Beyond the safety problems engendered by collapse of bearing soil and an embankment, stabilization work, treatment of the area and rehabilitation of structures will require substantial additional costs and prolongations of timelines.
In the specific case of embankments/fills on compressible soils, in addition to stability problems, there are two other basic problems to be addressed: the deformations caused, in particular, by settlement of the bearing soil under the embankment (settlements in the short and long term, with creep to be considered in future years, and over many years in fact), and the strains caused on surrounding structures (either already built or to be built at some future stage).
For the construction of embankments/fills on compressible soils, the consequences on the handling of the project relate to four main points, as follows:
• problems in connection with the feasibility of the structure: an embankment built on compressible soils could entail specific construction stipulations such as the use of vertical drains, construction of bench terraces, construction in stages, implementation of temporary overloads, etc.
• phasing of particular tasks, especially in terms of building structures and their foundations in particular;
• operating constraints, especially permissible settlement in the long term at platform level;
• time: whether in terms of studies, actual work or consolidation of soils and monitoring of this, time will be much more important than in the construction of a ”classic” embankment.
In cut areas, soils with a low bearing capacity must be purged or treated with hydraulic binders, and must not constitute a water trap.
Unstable slopes
It is advisable that the preliminary studies identify areas with a risk of unstable slopes (consultation of the PPR plan for prevention of foreseeable natural risks should not be neglected).
A simple analysis of geological and geomorphological charts and a compulsory visit to the site in order to examine its topography, position of trees, bushes, fence posts, etc. will reveal areas which are unstable or could become unstable.
In geotechnical studies during the phase of the overview / background summary [APS] and the actual project phase, the geologist will draw up an evaluation report of uncertainties within the study.
When stability studies specify the construction stipulations to be enacted, deadlock must never be reached in relation to such stipulations on the pretext that the slope is stable during the construction work phase.
Underground cavities
inconsistencies in connection with the various sections of a work contract are often the cause of litigation and shifts in costs.
The following are the main points to be observed:
• words in written texts which have no meaning.
For example:
- deep water
- moderate settlement
- protection against runoff water
- construction constraint as the result of … - imperfection
- the contractor will deem it necessary to …
• text that imposes unrealistic obligations on the construction manager;
• make progress subject to decisions by the construction manager (risk of site shutdown, selection of the real stoppage points);
• stipulations in the CCTP Particular Technical Specifications not included in the prices specification;
• prices including services which cannot be provided;
• inconsistencies between the provisions in the CCTP Particular Technical Specifications and the schedules of prices;
• incomplete work and / or insufficient means with respect to the technical aspects or the quality required;
• an absence of precision as to the deposit locations or transportation distances for deposits;
• unit prices whose definition is too wide or difficult to estimate;
Example of sensitive prices;
”whatever the material”
”whatever the volume concerned”
• prices including risk on levels of performance or output;
• complex prices which are charged at a flat rate or an inclusive fixed sum;
• quantities siphoned between several prices.