spillway of a flood detention reservoir in alpignano

SPILLWAY FOUNDATIONGiven that the subsoil consists of morainicmaterial (Fig. 3), an overlapped bored pile wallas foundation proves to be a suitable solution. Itenables the construction in the dense,overconsolidated subsoil and achieves thedesired impermeability of the verticalfoundation.

Results• For the foundation depth and position, theseepage analysis showed to be particularlydecisive

• A combination of transverse and longitudinalbored pile walls reaching a depth of 20 m and10 m respectively with a diameter of 0.9 m issuggested (Fig. 4)

• The reinforcement in the upper part of thelongitudinal bored pile wall shall guarantee theshear force and moment absorption

• A multi-layer design is proposed for the boredpile wall in the transition area from plate to pilefoundation

• With the proposed solution, the conductedgeotechnical verifications are satisfied

SLOPE STABILISATIONAIPo provides for a combination of two cantileverretaining walls with a micropile wall next to theplanned street in the middle for the decisive cross-section of the downstream slope.

Results• The analytical verifications confirm the stability ofthe upper cantilever retaining wall in the final state

• The planned steel micropile wall is designed tobe triple tied back for stability during constructionby AIPo

• The dimensioning of the temporary prestressedstrand anchors results in an inclination to thehorizontal of 20°, 7 m free anchor length and 7 mgrouted length (Fig. 5)

• The embedment depth of the micropile wall of atotal length of 20 m proves to be sufficient

• The analysis of the steel micropile wall shows highsafeties during the construction and in the finalstate

INTRODUCTION Past flood events induced by long-lasting heavyrainfalls in the Piedmont region have promptedthe Interregional Agency for the Po River (AIPo)to plan a flood detention reservoir in Alpignano,northern Italy. As the Dora Riparia river crossesthe densely populated city of Turin beforejoining the Po River, it carries a high destructivepotential in the case of flooding. The project istherefore a key element in the flood protectionof Turin. AIPo has elaborated a flood detentionreservoir (Fig. 2) in the preliminary projectphase consisting of an inlet structure, lateralearth dam and an outlet structure, also known

as spillway, which is the focus of the analysis.

Foto

Diplomand

Graduate Isabel Sara Bohren

Examiner Professor Dr. Carlo Rabaiotti

Co-Advisor Engineer Gianluca Zanichelli, Agenzia interregionale per il fiume Po (AIPo), Collecchio

Subject area Geotechnics

SPILLWAY OF A FLOOD DETENTION RESERVOIR IN ALPIGNANO

GEOTECHNICAL ANALYSIS OF THE FOUNDATION AND SLOPE STABILISATION IN THE PRELIMINARY PROJECT PHASE

OBJECTIVEThe primary focus of the thesis is:

• the geotechnical verification of the officialspillway variant by AIPo according to Italian andEuropean standards

• implementation of optimisation proposalsbased on the findings if applicable

Experience abroadIt was a great honour to be able to work with ahighly knowledgeable and capable team ofengineers in the AIPo Torino office whilstexperiencing life in the beautiful country Italy,full of culture, history and last but not least,delicious food.

APPROACH• In an initial step, subsoil investigations areevaluated and subsoil properties conservativelyestimated• Subsequently, possible hazard scenarios anddesign situations are identified• Following, geotechnical stability analyses arecarried out numerically and analytically• Based on the results, potential optimisationproposals are applied and verified

Fig. 2: project site in Alpignano (source: AIPo, modified: author)

Fig. 1: picture of the Dora Riparia river in Alpignano, personallytaken on the 15/06/2021

Fig. 4 proposal of spillway foundation consisting of reinforcedbored pile walls (elaborated jointly with AIPo)

Fig. 3: morainic amphitheatre of Rivoli-Avigliana(source: WebGIS Arpa Piemonte, modified: author)

Fig. 5 proposal of the downstream slope stabilisation duringconstruction (shear force on micropile wall calculated in Optum)