A dig into the past: the first tieback wall

Abstract

This is an investigative work by the authors, all of them former students and employees at Tecnosolo Ltd, the company founded by our late Professor Costa Nunes, to find and photograph the first tieback wall designed and built in 1957 by Tecnoloso under Prof Costa Nunes’ guidance.

Keywords
Tieback wall; Ground anchors; Tiebacks; Wedge method

1. Introduction

This is a story of digging into the past, which the Authors embarked on and eventually had a successful outcome on 26 June 2023.

In the late 60’s the first three Authors were undergraduate students at the Federal University of Rio de Janeiro, while the fourth Author, 10 years senior, was a practising geotechnical engineer working at Tecnosolo SA. This company was founded in the early 50s by the late Engineer and Professor Costa-Nunes (1917-1990) – researcher and pioneer in ground anchors.

In his classes, Costa Nunes (Figure 1) talked about the first tieback wall built in 1957. He mentioned it was built at the site of an old 19^th-century hospital named “Beneficiência Portuguesa” in the city centre of Rio de Janeiro, and 1958 in Germany.

Figure 1
Professor Costa Nunes.

Weatherby (1982) and Hunt & Costa Nunes (1978) reported that permanently tied-back walls have been the most common method of slope retention in Brazil since 1957. After 1958 tiebacks found their way into Europe in Germany (Jelinek & Ostermayer, 1966; Jelinek & Ostermayer, 1967) and later in Switzerland, England, and France (Ranke & Ostermayer, 1968; Dupeuble & Brulois, 1969; Descoeudres, 1969; Littlejohn, 1980).

The first permanent soil tiebacks in the United States took place in 1961 (Jones & Kerkhoff, 1961).

The Authors were engineers and colleagues at Tecnosolo since the early 70s and recently realized that no photographs of this early wall survived. This is the story of a quest to find this wall.

2. A quest to find a wall

The first Author contacted several old colleagues from Tecnosolo, but only the second Author, aka PH, knew exactly the wall location, as he had visited the site long ago. The other Authors shared information about this first wall.

Today it is located between an old and the recent hospital building (Figure 2 and Figure 3) and it is difficult to access, hidden between two buildings (Figure 4).

Figure 2
Site view, foreground: the old Beneficiência Portuguesa Hospital, at the back of the Gloria D’Or Hospital in Rio de Janeiro city centre.

Figure 3
19th Hospital (foreground) and the new hospital building (background).

Figure 4
Sketch of the tieback wall location, squeezed into the new hospital building.

3. Eureka

On 26 June 2023, the first (AO) and the second (PH) Authors visited the site. It did not take long for PH to find it hidden between two buildings (Figure 4). Eureka!

After conversations with the hospital management, permission was granted for this visit (Figure 5).

Figure 5
Evidence of this “archaeological” digging, left A Ortigao, right PH Dias.

4. Description

Figure 6 presents the 6 m high and some 50 m long wall sketches. Hunt & Costa Nunes (1978) described this innovative construction method taken from the top (Figure 7), replacing gravity walls which demanded a lot more excavation volume to be built.

Figure 6
Tieback wall sketch.

Figure 7
Tieback wall pictures.

Professor Costa Nunes once told in his classes that he designed the upper part of the wall with a concrete grid, given the high cohesion of this residual soil. Nevertheless, he changed his design of later walls and used a concrete slab, replacing the grid. “Concrete grid only for rock slopes”, he said.

The Authors found that the ground anchors were 20 mm in diameter, certainly CA-50 steel-grade, which became available a few years before. All anchors were tested to 90% of the steel yield load (170 kN), then reduced to the working load of about 100 kN.

5. Design method

It took a few years for Prof Costa Nunes to publish a paper on the design method of anchored walls, which he did in 1963 (Costa Nunes & Velloso, 1963). They devised a wedge method (Figure 8) and equations which were used in Brazil for the design of thousands of anchored walls, until the advent of computers and limit equilibrium specialized software.

Figure 8
Wedge method (Costa Nunes & Velloso, 1963).

6. Corrosion

Corrosion protection was certainly not an issue in this first tieback wall. Nonetheless, the corrosion level seems quite small (Figure 9), given its 60 years of ageing.

Figure 9
Corrosion is underway.

It was the first of its kind, followed by a series of developments which included corrosion protection, and higher load reduction factors, among others, thanks to Prof Costa-Nunes’ ingenuity.

The Authors are very pleased to re-discover this geotechnical engineering milestone and to remember our mentor, the late Prof Costa-Nunes.

Data availability

All data produced or examined in the course of the current study are included in this article.

• Discussion open until November 30, 2023.

References

• Costa Nunes, A.J., & Velloso, D.A. (1963). Estabilização de taludes em capas residuais de origem granito-gnaissica. In Associação Brasileira de Mecânica dos Solos (Org.), Proceedings of the Second Panamerican Conference on Soil Mechanics and Foundation Engineering (pp. 383-394). São Paulo: ABMS (in Portuguese).
• Descoeudres, J. (1969). Permanent anchors in rock and soils. In Sociedad Mexicana de Mecanica (Org.), Proceedings of the Seventh International Conference on Soil Mechanics and Foundation Engineering (pp. 195-197). London: ISSMGE.
• Dupeuble, P., & Brulois, J. (1969). Measurements and observations on the behaviour of anchorages in soils. In Sociedad Mexicana de Mecanica (Org.), Proceedings of the Seventh International Conference on Soil Mechanics and Foundation Engineering (pp. 147-155). London: ISSMGE.
• Hunt, R.E., & Costa Nunes, A.J. (1978). Retaining walls: taking it from the top. Civil Engineering, 48(5), 73-75.
• Jelinek, R., & Ostermayer, H. (1966). Verankerung von Baugruben Umschließungen. Vortrage der Baugrundtagung München Deutsche Gesellschaft für Erde und Grundbau.
• Jelinek, R., & Ostermayer, H. (1967). Zur berechnung von fangdämmen und verankerten stutz wanden. Die Bautechnik, 44.
• Jones, N., & Kerkhoff, G. (1961). Belled caissons anchor walls as Michigan remodels an expressway. Engineering News-Record, (May 11), 28-31.
• Littlejohn, G. (1980). Design estimation of the ultimate load-holding capacity of ground anchors. Ground Engineering, 13(8), 25-39.
• Ranke, A., & Ostermayer, H. (1968). Beitrag zur Stabilitätsuntersuchung mehrfach verankerter Baugruben Umschließungen. Bautechnik, 45(10), 341-350.
• Weatherby, D.E. (1982). Tiebacks: executive summary Federal Highway Administration. Report no. FHWA/RD-82/04 7.

Publication Dates

• Publication in this collection
  01 Sept 2023
• Date of issue
  2023

History

• Received
  20 June 2023
• Accepted
  21 June 2023