1. Vertical harbour quay rehabilitation using ground anchors
Hi! My name is Liliana Ribeiro. I’m a trainee at General Directorate of Natural Resources, Security and Maritime Services (Portugal). For the last two years I’ve being participating in some challenging projects related to harbor rehabilitation and slope stability. Today I’m going to show you, in Pinhão harbor case, how issues related to structural design can affect safety of future users and higher economic costs, resulting in overrunning initial budgets. Here’s how I’m going to do that:
Liliana Ribeiro and Alexandre Santos-Ferreira

2. Introduction Objectives:
Case study, monitoring of the works and vertical harbour quay pre-design using ground anchors for rehabilitation.
Stage 1
Works completed;
Ground anchors failure.
Stage 2
Rehabilitation:
Study & proposal of a new design approach
Work
monitoring
Theoretical
pre-design
FEM to
new design
Comparison
stage 1 vs. stage 2
Why the ground
anchors failed
in stage 1?
In this presentation Pinhão harbor case is divided in two stages. Stage 1 is the initial project where the work was completed and the ground anchors collapsed. Stage 2 is the harbor rehabilitation. At this stage the objective is to show you how we proceeded to the study and the new design approach. In this new design approach, we monitor closely the works; we did a theoretical pre-design in which we’ve applied the Finite Element Method and a slope stability study. Finally we compared the obtained results in stage 1 with the ones obtained is stage 2 and tried to answer the question “Why did the ground anchors failed in stage 1?” .

3. Definition of the problem
Most of Douro region economic resources are related to tourism so building a docking station capable of supporting large ships was needed.
First of all I think it’s important to show you a bit of context by defining the problem. Most of Douro economic resources are related to tourism. So, in this particular case, to improve touristic conditions, as Pinhão is located in a bank of Douro River, building a docking station capable of supporting large ships was needed. Those ships are hotel ships like the ones presented on this picture.

4. Definition of the problem (cont.)
Location
Geology
Northern Portugal, on the right bank of Douro river (upstream junction of Douro and Pinhão rivers).
As said, Pinhão fluvial harbor is located on the right bank Douro River (upstream junction of Douro and Pinhão Rivers) in northern Portugal. Recent deposits compose its local geology – clay-shale embankment with shale pebbles and brownish silty-sandy clays alluvium (as we can see in this picture, from up to bottom). And two Paleozoic formations: Greyish clay-shale Ervedosa Formation and grayish clay-shale with greywacke intercalations called Bateiras Formation.

5. Definition of the problem (cont.)
Stage 1 – Vertical harbor quay components:
81 m sheet pile wall
Heading beam
steel bar tendons
16 m total length
Inclination of 25º
21 ground anchors
In stage 1, an 81 m long sheet pile wall, with 21 ground anchors spaced by 3m, composed the Pinhão fluvial harbor. Those ground anchors have 16 m of total length, inclination of 25 degrees and steel tendon bars. The ground anchors are embedded in a heading beam. Shortly after completion of works and before Port and Maritime Institute definitely accepted it, it was found out that in some ground anchors the tendon was bent, thus compromising the work integrity. Became clear that a rehabilitation work would be necessary.

6. Methodology - Pinhão vertical harbour quay
Stage 2 – Vertical harbor quay components:
81 m sheet pile wall
Heading beam
steel strand tendons
19 and 21 m total length
Inclination of 20º
19 ground anchors
(interspersed between the preexisting)
Demolish the harbor was out of question because the problem was not related to the harbor structure itself. Port and Maritime Institute decided that the harbor would remain intact, and the collapsed ground anchors wouldn’t be removed. Instead new ground anchors would be designed, disregarding the collapsed ones. So the new approach was to design new ground anchors equally spaced by 3 m, interspersed between the collapsed ones, as shown in the picture. For a spacing of 3 m between the new ground anchors a total of 19 new anchors were required. These ground anchors consists of steel strand tendons (instead of steel bar tendons as the collapsed ones), they have 19 and 21 m of total length and 20 degrees of inclination. Next I’m going to show you how these values were obtained.
New
Failed

7. Methodology - Pinhão vertical harbour quay (cont.)
Stage 1
Analytical method: Eurocode 7
Computational method: FEM (Larix 3)
Stage 2
Analytical methods: Terzaghi-Peck diagrams, Bustamante & Doix (1983), Eurocode and EN 1537
Computational methods: FEM and slope stability software (Sigma W and Slope W)
Materials mechanical characteristics
Materials
Unit weight
(γ)
kN/m3
Choesion
(c)
kN/m2
Friction angle
(φ)
º (degrees)
Earthfill (bulk) 18
30º
Earthfill
Submerged 10
Saturated 20
Rockfill (bulk)
45º
Rockfill
Shale formation (bedrock) 60
40º
In stage 1 were used 2 methods for the design, one analytical method (Eurocode 7) and a computational method (Finite Element Method). Let us focus on stage 2. Here it was used a new design approach. We also used analytical methods, but here we divided the two main components of the ground anchor and design them separately. For the bond length we used the Bustamante e Doix’s method. For the free length we used Eurocode 7 and EuroNorm We also used computational methods to study the overall structural behavior (as Finite Element Method) and slope stability software. In this table are presented the material mechanical characteristics used in the design.

8. Methodology - Pinhão vertical harbour quay (cont.)
Stress-strain analysis – Finite Elements Method (FEM)
This was the model used in the Finite Element Method software, for the stress-strain analysis. From which we obtained:

9. Methodology - Pinhão vertical harbour quay (cont.)
Maximum total stresses
As we can see in this image the maximum total stresses values vary in the range of 200 and 1400 kPa.

10. Methodology - Pinhão vertical harbour quay (cont.)
Maximum shear strains
Maximum shear strains vary in the range of 0,2 to 8 millimeters.

11. Methodology - Pinhão vertical harbour quay (cont.)
Horizontal displacements
The horizontal displacement varies from 0,5 to 5,5 millimeters.

12. Methodology - Pinhão vertical harbour quay (cont.)
Limit equilibrium slope stability analysis
Morgenstern-Price Method (pseudo-static analysis )
Monte Carlo’s method: results
2,5176
Failure probability 0%
SF min.
2,126
SF max.
3,0027
Iterations
5000
To study the slope stability it was used the Morgenstern-Price limit equilibrium method. We used the probabilistic method with 5000 tests in a pseudo-static analysis. From which we obtained the results presented on the table.

13. Methodology - Pinhão vertical harbour quay (cont.)
Limit equilibrium slope stability analysis
Morgenstern-Price Method (static analysis )
Monte Carlo’s method: results
7,5817
Failure probability 0%
SF min.
5,7906
SF max.
10,079
Iterations
5000
Next, with the same method we did a static analysis. The values obtained were:

14. Results discussion - Pinhão vertical harbour quay
Design results (stage 1 vs stage 2)
Stage 1
(Failure)
Stage 2
(Rehabilitation)
Bibliographic recomendations
Bond length
4,0 m
3,0 m
(actualy used 6,0 m)
> 3,0 m
Tendon free length
12,0 m
15,0 m
> 4,5 m
(FHWA-IF , 1999)
Active pressures
158,9 kN/m
159,83 kN/m
N.A.
Anchorage load design
571,7 kN
575,38 kN
Global slope stability (SF)
3,2
7,562 (static analisys)
2,604 (pseudo-static analisys)
> 1
Distance to potential slope failure plan
Without information
8,0 m
Outside of the potential slope failure plan
This table shows a more focused comparison of both design stages. As we can see in the first row it’s presented both stages results for bond length. However the results doesn’t differ so much; in stage 1 was used 4 m for bond length and in stage 2 the design result was 3 m, but to be on the safe side we actually used 6 m. In the second row it’s presented the tendon free length. Here is where we can se the major difference between both stages. This can mean the difference between the bond lengths is inside or outside of the potential slope failure plan. As in stage 1 free length is 12 m and in stage 2 is 15 m. In third row are presented the active pressures. Although both values present a slight difference, it’s not very significant as stage 1 the active pressure is 158,9 kN/m and stage 2 we’ve obtained 159,83 kN/m. In both stages the anchor load design was no significant difference, as we can see in fourth row. The Safety Factor in both stages is superior to one, as required. And last, in the sixth row is presented the distance to potential slope failure plan. In stage 1 we have no information of that value, and in stage 2 we access a value of 8 m.

15. Conclusions Ground active pressures may be underestimated;
In stage 1 the tendon free-length was short (bond length may be within the potential slope failure plan);
SF values both (stage 1 and stage 2) within required;
Stress-strain analysis (stage 2) show a long term structural good behavior.
Although ground active pressures are not significant different they may have being underestimated. In stage 1 the tendon free length was short, and this may indicate that bond length may be within the potential slope failure plan, thus contributing to the ground anchors collapse. In a joint analysis for both stages it can be said that both safety factor is in the safe side as required. And finally for stress-strain analysis for stage 2 it shows a long-term structural behavior.

16. Thank you!