DESIGN OF A BULKHEAD OF MICROPILES AND PASSIVE TIE-RODS TO SUPPORT THE REALIZATION OF AN EXCAVATION WITHIN A RESIDENTIAL RENOVATION IN PADUA

CLIENT: Indgeo Due S.r.l, Via del Pozzo, 10 – S. Giuseppe di Comacchio (FE)
INTERVENTION LOCATION: Padua
SERVICES RENDERED: executive project
BEGINNING/END OF WORKS: 2008
CONSTRUCTION COMPANY: Eurocostruzioni S.p.a, Via Uruguay, 20 – Padua

PROJECT DESCRIPTION

This description concerns the design of a bulkhead of micropiles and passive tie-rods of provisional nature executed to support the construction of an excavation in the renovation of a residential complex in Via Locatelli, Padua.
The geometric configuration of the bulkhead of micropiles is as follows:

• Depth from ground level: 8.00 m
• Real length of the bulkhead: 8.00 m
• Diameter made micropiles: 200 mm
• Reinforcement micropiles: ø114 sp. 8 mm
• Micropiles pitch: pitch 330 mm
• Passive tie-rods: micropiles dia 200 arm ø88.9 sp. 9 mm
• Position of passive tie-rods: at 1.50 from the ground level

The existing building is located with its foundation at 50 cm from the bulkhead, at a depth of m. 1.0 and discharges, for a length of m. 1.0 a pressure equal to 120 kPa. In order to carry out this computational analysis taking into proper account the pre-existence of the building, the finite element calculation program Plaxis was used in version: Version 8.6; Update pack: (Build 608); Options: Full package.

The soil was modeled considering a hardening behavior of the same, i.e. implementing a HS model in Plaxis.
The substantially sandy soil allowed to find all the model parameters using the CPT tests provided and making use of a modeling analysis performed with a program designed by Teleios that takes into account the most recent bibliography on the subject.

In performing the calculation, the phases of construction of the bulkhead, excavation, laying of the passive tie-rod and the presence of the load behind were correctly considered, taking care to insert this load as pressure on the ground but not as displacements because these displacements are considered already stabilized (reset displacement to zero option). We also considered the lowering of the water table and calculated the safety coefficient of the bulkhead which was equal to 1.41.

The following are the most significant results in terms of displacements and stresses on the ground; displacements and stresses on the bulkhead.

The study and calculation of the configurations of the bulkhead runs through the operational and theoretical phases of calculating the excavation. Therefore, we will briefly illustrate, for each typical section, the calculation phases considered.

Phase 1 – operational and calculation phase
Activation of the foundation and loading of the existing structure.

Phase 2 – operational and calculation phase
Activation of vertical bulkhead and reset displacements of phase 1.

Phase 3 – operative and calculation phase
Excavation at q. -1.50

Phase 4 – operative and calculation phase
Tie rod application

Phase 5 – operative and calculation phase
Lowering of the water table to -4.0

Phase 6 – operative and calculation phase
Excavation at -4.0

Phase 7 – operative and calculation phase
Fi-ci reduction for safety coefficient calculation.