GEOTECHNICAL DESIGN OF THE BULKHEADS OF SUPPORT EXCAVATION AND FOUNDATIONS OF THE METAL WALKWAY FOR THE EXPANSION OF THE NURSING HOME “VILLA CHIARA” – CASALECCHIO DI RENO (BO)

CLIENT: HBC
INTERVENTION LOCATION: Casalecchio di Reno (BO)
SERVICES RENDERED: Design of bulkheads, both tie-barred and not, to be executed to support the realization of the important excavations necessary for the realization of the hospital extension. Design of the foundations of the new metal walkway that will connect the existing building and the new extension.
BEGINNING/END OF WORKS: 2015/2016

PROJECT DESCRIPTION

Three bulkheads have been designed to support the excavations within the realization of the extension of the nursing home “Villa Chiara”, located in the municipality of Casalecchio di Reno in Via Porrettana, 170. They were also designed the foundations of the newly built metal walkway to connect an existing building of the hospital with the new extension.

1. Bulkhead geometry
The three bulkheads designed have the following characteristics
a. Bulkhead 1: bulkhead with Ø500 mm bored piles, via Porrettana side. Permanent geotechnical ties.
b. Bulkhead 2: bulkhead with Ø250 mm micropiles adjacent to building A; it is subdivided into bulkhead 2A and 2B according to the height of the excavation to be supported and, therefore, the length of the micropiles. Temporary geotechnical tie-rods, definitive restraint of the bulkhead to the horizontal displacements carried out by the ground floor slab of the newly built extension.
c. Bulkhead 3: bulkhead in drilled piles Ø500 mm, Reno river side. Shelved bulkhead in provisional phase, final restraint of the bulkhead to the horizontal displacements carried out by the ground floor slab of the new realization extension.

Bulkhead 1

• Poles: Ø500 mm
• Pitch: 70 cm
• Bulkhead length: 12.00 m
• Excavation height: 6.50 m
• Head Retainers: permanent geotechnical tie rods
  Brand: TTM tension technology s.r.l.
  Model: TPE 02 SP
• Length of passive tie rod section: 13.00 m
• Active tie rod length: 9.00 m
• Diameter of the active tie rod section. 150 mm
• Pretension force: on the tie rod 150 kN – on the strand 25 kN
• Strands: n.ro 6 strands of 0.6″ (15.2 mm)

Bulkhead 2A

• Poles: Ø250 mm
• Pitch: 40 cm
• Bulkhead length: 8.00 m
• Excavation height: 4.30 m
• Head Retainers: temporary geotechnical tie-rods
  Brand: TTM tension technology s.r.l.
  Model: TPR 01
• Length of passive tie rod section: 11.00 m
• Active tie rod length: 8.00 m
• Active tie rod section diameter 150 mm
• Pretension force: on the tie rod 80 kN – on the strand 14 kN
• Strands: n.ro 6 strands of 0.6″ (15.2 mm)

Bulkhead 2B

• Poles: Ø250 mm
• Pitch: 40 cm
• Bulkhead length: 11.00 m
• Excavation height: 5.80 m
• Head Retainers: temporary geotechnical tie-rods
  Brand: TTM tension technology s.r.l.
  Model: TPR 01
• Length of passive tie rod section: 11.00 m
• Active tie rod length: 8.00 m
• Active tie rod section diameter 150 mm
• Pretension force: on the tie rod 80 kN – on the strand 14 kN
• Strands: n.ro 6 strands of 0.6″ (15.2 mm)

Bulkhead 3

• Poles: Ø500 mm
• Pitch: 70 cm
• Bulkhead length: 11.00 m
• Excavation height: 5.10 m

The bulkhead analysis was performed using a numerical finite element approach with the geotechnical FEM program Plaxis 2D.
In particular, the constitutive model HS SMALL was used, a hardening soil model in which it is possible to consider the non-linearity of the behavior of the soil as deformations increase but also the increased stiffness at small deformations.
The retaining structures were sized mainly in terms of deformability, containing the horizontal displacements but also the vertical ones generated on the back. This is very important since bulkhead 2 is built adjacent to the existing body A with the very function of preserving the safety and functionality even during the construction phases.
All this in the static field, considering also all the transitory configurations during the construction phases, and in the seismic field, considering that the projected work is designed in use class IV (Constructions with important public or strategic functions) and that, therefore, the seismic verifications are quite heavy.
As an example we report the most significant results obtained from the analysis of the bulkhead 1.

3. Footbridge foundations project
As part of the extension project of the Villa Chiara nursing home, the foundations of the new metal walkway that will be built to connect the existing building to the extension have also been designed.

The plinths have been designed to respect the numerous geometric constraints present (presence of existing foundations, plants, etc.), and to respect the geotechnical verifications both as regards resistance (bearing capacity to the axial and transversal actions of the piles, structural verifications of the reinforced concrete sections of the piles and plinths) and deformability (failure of the single pile, failure of the group of piles, differential failures and angular distortions between the different plinths), in the static and seismic fields.