Jet grouting underpinning of a building on a marl embankment platform (Portugal) Cláudia Santos Trainee at IPTM, IP./post-graduate student at FCT – UNL, Portugal Ana Paula Silva CICEGe/Dept. Ciências da Terra, FCT – Univ NOVA of Lisbon, Portugal Alexandre Santos Ferreira CICEGe, FCT – Univ. NOVA of Lisbon /IPTM, IP., Portugal

Introduction Jet grouting underpinning of a building on a marl embankment platform (Portugal) In an industrial plant near Coimbra, Portugal, the study area local facilities were comprised of a pit and a reinforced concrete building. The earthworks included: a 10.7m deep excavation for the pit and its contention structures, an embankment for the building’s foundation According to the project specifications: - the filling materials included marls and clayey marls from the cuttings in site Due to inadequate compaction, after an heavy rainfall period, unacceptable settlements occurred, requiring the reinforcement of the foundations

Site location and geological map Geotechnical characterization Jet grouting underpinning of a building on a marl embankment platform (Portugal) Local geology (top to bottom): Clayey silts with scattered pebbles superficial deposits Carrascal sandstones Formation (Cretacic) Marls and marly limestones Formation (Jurassic) Prior geotechnical investigation: - percussion boreholes trial pits. The results allowed a geotechnical zoning: GU1 to GU3 zones, from the most favourable to the least favourable mechanical characteristics, respectively. This zoning served as guide to the design of earthworks, namely the slopes gradient and the foundation strata for the pit and the adjacent embankment platform. Site location and geological map

S1 and S3 boreholes location Geotechnical characterization Jet grouting underpinning of a building on a marl embankment platform (Portugal) Geotechnical investigation: Percussion boreholes (S1 and S3) SPT with undisturbed soil sampling Laboratory tests: soil identification, compressibility and mechanical (direct shear, edometric and triaxial) S1 and S3 boreholes location Soil identification results: Unified Soil classification: SC - clayey sand AASHTO classification: A-6(2) Depth (m) S1 S3 NSPT 1.5 6 28 3 17 25 4.5 24 49 60 (3) 7.5 23 9 20 10.5 60 (13) S1 and S3 boreholes’ SPT results

Embankment and building’s structural behaviour Jet grouting underpinning of a building on a marl embankment platform (Portugal) The building is almost 20m high and occupies an area of circa 57x28m. The building’s foundation consists in footings. Shortly after the embankment and the building’s main structure completion, following a severe rainfall period, differential settlements of the earthfill occurred. Due to the structure rigidity, its structural elements got under excessive stress and as a consequence, elements as beams, foundation beams linking footings and some inner walls cracked or even broke. Structural elements cracking details

Topographic monitoring survey Jet grouting underpinning of a building on a marl embankment platform (Portugal) Monitoring system: - 22 survey marks in 6 alignments A1 and A11 alignments monitoring: rapid settlements due to heavy rainfall - differential settlements

Foundation reinforcement solution Ground reinforcement Jet grouting underpinning of a building on a marl embankment platform (Portugal) Inadequate filling materials Wrong reference value for the compaction control Excessive differential settlements Excessive deformation in structural elements Foundation reinforcement solution Several solutions were considered as: Micropiles Reinforced concrete piles Jet grouting columns Total demolition of the structure and the embankment reconstruction A jet grouting solution was adopted as the most suitable geotechnical approach and time and cost effective

Underpinning by jet grouting (1) Jet grouting underpinning of a building on a marl embankment platform (Portugal) Jet grouting solution 96 vertical jet grouting columns (4 per footing) - 600mm of diameter 4 to 9m length (according to the depth of the stiffer in situ formations) Design jet grout columns mechanical characteristics Resistance to compression σ ≥ 4.0 MPa (ultimate limit state) σ ≥ 2.0 MPa (design service value) Modulus of deformability Es ≥ 1.0 GPa

Underpinning by jet grouting (2) Jet grouting underpinning of a building on a marl embankment platform (Portugal) Prior to construction works 2,5m length test columns were performed to set the drilling and the jet parameters and to support the grout mix specification Jet grouting column’s specimens were submitted to uniaxial compressive strength tests .the drilling of each footing in four points was necessary to set the correct location of the jet columns, underneath the shallow foundations During jet grouting execution the adoption of an alternating sequence in terms of the isolated footings and of each footing corner allowed to distribute the stress and the uniform gain of ground strength the short implementation period (less than a month) assured the beginning of exploration within the deadline.

Concluding remarks Jet grouting underpinning of a building on a marl embankment platform (Portugal) The presented case is related to the mitigation of post embankment construction unexpected settlements and the damages induced to a building founded upon it. Some remarks can be pointed out from this study as: A new site investigation enabled assessing the cause of the bad behaviour of the compacted soils Insufficient sampling and testing of the filling soils at the design stage led to inadequate reference values for the compaction control during construction - The implementation of underpinning by jet grouting columns (d=600mm) of marly soils has proven to be an effective technical alternative to reinforce footings, and also a rapid and cost effective solution, allowing to mitigate the described situation - A quality control program that comprised all construction stages ensured successful geotechnical performances.

Thank You for your attention Jet grouting underpinning of a building on a marl embankment platform (Portugal) Thank You for your attention