Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 James H. Brace, Francis Mason, and S. H. Woodard Informative Summary

Overview:

This 1910 paper from the Transactions of the American Society of Civil Engineers focuses on the construction of the New York Tunnel Extension of the Pennsylvania Railroad, specifically the East River tunnels. The authors, James H. Brace, Francis Mason, and S. H. Woodard, delve into the various engineering challenges and unique construction methods employed during this ambitious project. The paper highlights the importance of compressed air and shield technology in tunneling through soft ground and rock formations.

The paper details the construction process, starting with the sinking of temporary and permanent shafts on both sides of the East River. It describes the different excavation methods used in various geological conditions, including all-rock sections, mixed earth and rock, and all-earth sections. The paper also discusses the use of shields, compressed air, and the innovative approach to tunneling in compressed air without a shield. Key challenges and solutions like blow-outs, settlements, and the innovative use of a clay blanket are covered in detail. The paper concludes with a discussion of the concrete lining, electric conduits, and the final grouting process.

Key Findings:

• The use of compressed air and shield technology was crucial for tunneling through soft ground and rock formations.
• The East River tunnels faced unique challenges like blow-outs and settlements, requiring innovative solutions like a clay blanket.
• The paper provides detailed insights into the various excavation methods employed in different geological conditions.
• The authors highlight the importance of careful planning, engineering expertise, and adaptability in overcoming construction hurdles.

Learning:

• Compressed Air and Tunneling: Readers will learn about the critical role of compressed air in tunneling, particularly through soft ground and underwater. The paper details how air pressure was used to control ground conditions, prevent water influx, and facilitate excavation.
  • Air Pressure: The authors discuss the various air pressures used during different stages of the project, highlighting the importance of balancing the hydrostatic head and minimizing air loss.
  • Blow-outs: The paper analyzes the causes and effects of blow-outs, which occurred when air escaped through porous ground, and explores the innovative solution of using a clay blanket to mitigate the problem.
  • Air Supply: The paper examines the complexities of air supply, including the size and capacity of compressors, the impact of air consumption on different tunnel sections, and the challenges of maintaining adequate air pressure during high-demand periods.
• Shield Technology: The paper explains how shields were used to excavate the tunnels, providing details on their construction, operation, and challenges.
  • Shield Design: The paper delves into the different shield designs, including those with fixed and sliding hoods and extensions, highlighting their strengths and weaknesses in various geological conditions.
  • Shoving: The paper explains the process of shoving the shields through the ground, including the use of jacks, the pressures applied, and the challenges of maintaining proper alignment and grade.
  • Excavation Methods: The paper explores various excavation methods employed within the shield, including bottom headings, full-face methods, center headings, and the use of shutters. It examines the effectiveness of each method in different geological conditions.
• Clay Blanket: Readers will learn about the unique and crucial role of the clay blanket, which was used to control air pressure and minimize blow-outs. The paper explores how the blanket was created, its effectiveness, the challenges of maintaining it, and its ultimate impact on the success of the project.
  • Clay Blanket Design and Placement: The paper explains the selection of suitable clay, the methods of dumping and redepositing it, and the importance of monitoring its integrity.
  • Impact on Air Pressure: The paper demonstrates how the clay blanket significantly reduced air loss and blow-outs, ultimately enabling continuous work in the tunnels.
  • Challenges of Maintaining the Blanket: The paper discusses the challenges of maintaining the blanket against erosion and the need for prompt action to address blow-outs.

Historical Context:

This paper was written in 1910, during a period of rapid industrial and urban development in New York City. The Pennsylvania Railroad, known for its ambitious projects, was expanding its infrastructure to accommodate the growing demand for transportation within the city and beyond. The East River tunnels represented a major engineering feat, pushing the boundaries of tunneling technology and demonstrating the innovative solutions required to overcome the challenges of excavating beneath a major waterway.

Facts:

1. East River tunnels were part of the New York Tunnel Extension of the Pennsylvania Railroad. The tunnels connected Long Island City to Manhattan, offering a new route for the railroad.
2. Construction began on May 17th, 1904 and was completed on May 17th, 1909. The project took five years to complete.
3. The project involved two permanent shafts on each side of the East River and four single cast-iron tube tunnels. Each tunnel was approximately 6,000 ft long.
4. The contract for construction was awarded to S. Pearson and Son, Incorporated. They used a profit-sharing model with the railroad company.
5. The project utilized three different construction sites. Work was carried out from permanent shafts near the river, two similar shafts at the Long Island City riverfront, and a temporary shaft near East Avenue, Long Island City.
6. A temporary shaft was sunk at East Avenue, Long Island City, to a depth of 55 ft. This shaft was used for excavating the land section of the tunnels.
7. Compressed air was initially used to drive the tunnel headings through soft ground. However, it was discontinued after the headings reached solid rock.
8. A novel method of tunneling in compressed air without a shield was successfully employed in Tunnel B. This method proved to be as cost-effective as using a shield.
9. The iron lining of the tunnels was constructed in short lengths, typically four rings or less. This allowed for the gradual transfer of weight from the timbering to the iron lining.
10. Grout dams were placed behind the iron lining to retain grout and prevent its loss. This ensured the stability and water-tightness of the tunnels.
11. The Long Island shafts were constructed using pneumatic caissons, which were sunk to a depth of 78 ft. below mean high water. This involved sinking 54 ft. through solid rock.
12. The shafts consisted of two steel caissons, each 40 by 74 ft. in plan, with walls 5 ft. thick filled with concrete. They were divided into two wells, each directly over a tunnel.
13. Circular openings for the tunnels, 25 ft. in diameter, were provided in the sides of the caissons. These openings were closed by bulkheads during the sinking process.
14. The average rate of lowering the caissons through earth was 0.7 ft. per day, and through rock, it was 0.48 ft. per day in the south caisson and 0.39 ft. per day in the north caisson. The sinking process was a complex operation involving hydraulic jacks and blocking.
15. The Manhattan shafts were similar to the river shafts in Long Island City, each located across two lines of tunnels. The west portions of the shafts were later used by the contractor for the cross-town tunnels.
16. The excavation of the south shaft was started on June 9th, 1904. A 16 by 16-ft. test pit was sunk to a depth of 20 ft. to evaluate the rock conditions.
17. The north shaft was sunk in a very restricted area, with one side of the caisson clearing an adjoining building by only 1 ft. This presented significant challenges for the sinking process.
18. The shields used for the river tunnels were 23 ft. in outside diameter and were driven through the rock section in pairs. They were equipped with working chambers and air locks.
19. The tunnel materials encountered included Hudson schist, Fordham gneiss, and a variety of sand and gravel formations. The paper provides a detailed description of the geology of the East River.
20. The shields were equipped with sliding hoods and extensions to support the roof and sides during excavation in mixed earth and rock sections. These proved to be less effective than fixed hoods.

Statistics:

1. The total length of the four East River tunnels was approximately 6,000 ft. This included 3,900 ft. under the river and 2,000 ft. in Long Island City.
2. The temporary shaft at East Avenue was 127 by 34 ft. in plan. It was sunk to a depth of 55 ft. through earth and rock.
3. Compressed air was used at a pressure of about 15 lb. per sq. in. to drive the headings through soft ground. The use of compressed air was then discontinued.
4. The contractor’s plant for the project was rated at 25,000 cu. ft. of free air per minute. However, this proved to be inadequate for driving four tunnels simultaneously.
5. The total quantity of free air compressed for the tunnels and the Long Island caissons was 34,109,000,000 cu. ft. This includes 10,615,000,000 cu. ft. compressed for power purposes.
6. A maximum loss of about 220,000 cu. ft. of free air occurred in 10 min. during a blow-out. This represents a significant loss of air pressure.
7. The average rate of rock excavation in the Long Island caissons was about 44.5 cu. yd. per day. This was significantly slower than the rate of earth excavation.
8. The average rate of lowering the caissons through earth was 0.7 ft. per day. This was significantly faster than the rate of lowering through rock.
9. The concrete cradles used in the East Avenue tunnel averaged 1.05 cu. yd. per ft. of tunnel and cost $6.70 per cu. yd. This cost included labor and top charges.
10. The hand-packed stone used in the East Avenue tunnel averaged 1-1/2 cu. yd. per ft. of tunnel and cost $2.42 per cu. yd. This cost also included labor and top charges.
11. The total cost of placing and removing the clay blanket was $304,056. The clay blanket was a crucial element in controlling air pressure and minimizing blow-outs.
12. The total quantity of grout used on the project was equivalent to 249,647 bbl. of 1 to 1 Portland cement grout. The majority of the grout was ejected through the iron lining of the tunnels.
13. The average cost of grout ejected outside of the river tunnels was 93 cents per bbl. for labor and $2.77 for top charges. The cost of grouting was a significant expense in the overall project.
14. The number of broken plates occurring in the river tunnels was 319, or 0.42% of the total number erected. Broken plates were a common issue, particularly in the bottom segments.
15. The average labor cost chargeable against caulking the joints between segments was 12 cents per lin. ft. This was in addition to the top charges.
16. The total leakage in each tunnel was reduced to about 0.002 cu. ft. per sec., an average of 0.00000051 cu. ft. per sec. per lin. ft. This was achieved through a rigorous repair process.
17. The sump and pump chambers were constructed to drain the tunnels. Each pair of tunnels had its own sump and pump chamber.
18. The concrete lining of the tunnels was placed using a mixing plant in each of the five shafts. The concrete was placed in normal air.
19. The cost of labor directly chargeable to concrete was $1.80 per cu. yd. Top charges, excluding material costs, amounted to $3.92 per cu. yd.
20. The cost of labor in the tunnels chargeable to duct laying was $0.039 per ft. of duct. Top charges brought the cost up to $0.083 per ft.

Terms:

1. Compressed air: Air that is compressed to a higher pressure than atmospheric pressure. In tunneling, it is used to control ground conditions, prevent water influx, and facilitate excavation.
2. Shield: A large, cylindrical structure used in tunneling to support the surrounding ground and prevent cave-ins. It is equipped with working chambers and air locks.
3. Blow-out: An event where air escapes from a tunnel through porous ground, causing a sudden drop in air pressure and potential damage.
4. Clay blanket: A layer of clay placed over the tunnel to control air pressure and minimize blow-outs.
5. Hood: A protective structure attached to the front of a shield, used to support the roof and sides during excavation in mixed earth and rock sections.
6. Shutters: Panels used in the face of the shield to facilitate excavation in soft ground. They help to control the flow of material and minimize air loss.
7. Caisson: A watertight structure used to sink shafts through earth and rock. It typically has a working chamber and air locks.
8. Grout: A mixture of cement, sand, and water used to fill voids and seal spaces in tunnels and shafts.
9. Caulking: A process of sealing the joints between segments of the tunnel lining using materials like iron filings, sal ammoniac, or lead wire.
10. Sump: A pit or chamber at the lowest point of a tunnel to collect water for drainage.

Examples:

1. Trial of a shield in Tunnel C without compressed air. This attempt proved unsuccessful as the shield flattened due to the lack of support from the surrounding material.
2. Tunneling in compressed air without a shield in Tunnel B. This novel method proved successful and cost-effective, demonstrating the adaptability of the engineers.
3. The use of concrete cradles in the East Avenue tunnel to support the iron lining. This was a cost-effective solution compared to filling the voids with grout.
4. The sinking of the Long Island shafts using pneumatic caissons. This involved sinking through 54 ft. of solid rock, presenting a unique challenge.
5. The use of a clay blanket to control air pressure and minimize blow-outs. This proved to be a crucial element in the success of the project.
6. The use of English Blue Lias lime as a grouting material. While initially promising, it proved unsuitable for supporting the tunnel and was replaced with a modified quick-setting natural cement.
7. The repair of broken plates in the tunnel lining. This involved the use of steel segments, long bolts, and twisted steel rods.
8. The construction of special junctions at the meeting points of the shields. This involved using a rolled-steel ring and special cast-iron rings to connect the tunnel lining.
9. The placement of concrete lining in the tunnels. This was done using a mixing plant in each of the five shafts and involved multiple stages.
10. The laying of electric conduits in the tunnel walls. This involved careful placement and sealing to prevent grout and mortar from entering the duct openings.

Conclusion:

The construction of the East River tunnels was a remarkable feat of engineering, pushing the boundaries of tunneling technology at the time. This paper provides valuable insight into the complex challenges faced and the innovative solutions employed. Readers gain a deeper understanding of the critical role of compressed air, shield technology, and the ingenious use of a clay blanket in overcoming these challenges. The paper serves as a testament to the resilience and adaptability of engineers in pushing the limits of construction. The lessons learned from this project are still relevant today, highlighting the importance of careful planning, meticulous execution, and creative problem-solving in large-scale construction projects.

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