1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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.

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