Microtunnel
H. Hessing, P.E.
INRODUCTION
STV Incorporated (STV) has been involved with a $200,000,000 utility restoration program being performed at Co-op City, Bronx, New York for River Bay Corporation and New York State Housing Finance Administration. The work spanned a period of twelve years. STV provided comprehensive mechanical, electrical, structural, and civil engineering services for in-depth investigations and testing of all underground utilities, mechanical and electrical systems, and subsequent design and construction support services for the upgrade of systems and complete rehabilitation at the site.
Detailed investigations of all building systems and utilities on the 350-acre site were performed to de-termine existing conditions and the extent of damage due to the settlement of structures of up to three feet. The complex consists of 35 hi-rise buildings ranging from 24 to 33 stories with 15,372 apartments and seven groups of 472 townhouses presently housing 60,000 people.
The “Co op City Housing Project Repair Program” consisted of replacing the dual temperature and high temperature hot water distribution system; electric ductbank distribution system; reconstruction and repairs to underground utilities and appurtenant structures including gas, water, sewer; site settlement repairs including grading, drainage, paving and landscaping; and miscellaneous repairs to building interior mechanical and electrical systems, structure, and interior finishes, and replacement or repairs to building envelops and roofs.
The Hutchinson River and the Hutchinson River Parkway separate the southern section of the site from the power plant. STV Incorporated prepared a study to bring the new dual temperature system and electrical system to the south site.
Soil borings were taken and STV prepared plans and specifications entitled “TES-221” for installing five tunnels consisting of 54 “ reinforced concrete casing pipe under the Hutchinson River Parkway in the vicinity of the intersection of Bartow Avenue. The work included excavating and backfilling of jacking and receiving pits and temporary surface restoration in the work areas. The Contractor was not limited as to the method to accomplish the installation other than the fact that open cut and cover was not permitted because traffic could not be interrupted on the Parkway. The size and type of equipment was the Contractor’s choice.
Study Report
The heating, cooling hot water and electrical power for Co-op City’s housing complex are supplied to the buildings through three central underground sys-tems that emanate from the central Power Plant lo-cated at the northeast quadrant of the intersection of Bartow Avenue and Co-op City Boulevard. The power plant services both the North and South sites of Co-op City.
Heating or cooling, depending on the season is supplied through a two-conduit (supply and return) Dual Temperature (DT) system. Similarly, hot water is supplied through a two-conduit High Temperature (HT) system. Electrical power is supplied through cables in multiple conduits, encased in concrete forming an electrical duct bank (EDB) system.
For over a decade, severe problems had been ex-perienced with all three systems resulting in frequent service disruptions, efficiency degradation, exces-sive maintenance repairs costs and general incon-venience to the tenants and the administration. The decision was made to reconstruct all three systems.
STV prepared a report entitled “The Routing of the Dual Temperature, High Temperature and 15 kV Duct Bank Systems from MH #1 to the South Site” in April 1993. The purpose was to identify alternate routes and determine the most suitable and acceptable alternative for reconstruction of a portion of the systems, namely, from MH # 1 to the beginning of the South site east of the Hutchinson River Parkway (HRP).
The need for the study was precipitated by the lack of a clear unimpeded corridor to construct the new systems while the existing systems remained in ser-vice. The roadway bed of Bartow Avenue/HRP east is highly congested with various underground utilities including the existing DT/HT/EDB systems. The northerly shoulder area of Bartow Avenue/ HRP East (area north of the northerly curbline) is limited in width and is immediately followed by the bank of Hutchinson River. The southerly shoulder area of Bar-tow Avenue/HRP east is extremely narrow and is con-stricted at the Hutchinson River Parkway’s bridge abutment and embankments. The physical restraints dictated the need to consider various alternative routes and to perform careful research, study, assessment and evaluation before a selection was made.
Three corridors were identified as suitable for the crossings of the HT/DT/EDB systems. Within the cor-ridors, four possible schemes were possible. Based on the findings of the study an above ground scheme along the shoulder area requiring steel support struc-tures was recommended.
Plans & Specifications
The study recommendation was not approved. There were many meetings and discussions with several agencies including but not limited to: the New York State Parks Department, New York State Department of Transportation, New York State Department of Environmental Protection, New York City Department of Transportation, New York City Department of Environmental Protection, New York City Department of Parks and recreation and the U.S. Coast Guard. It was decided that microtunneling would be permitted to be constructed through the embankment of the Hutchinson River Parkway.
STV prepared plans and specifications for the mi-crotunnel project. The drawings indicated the layout of piping, size, dimensions, grades and other details. Coordinates of the center tunnel were given with horizontal offsets shown for the remaining tunnels. Preliminary specifications were prepared in Febru-ary 1994 and final specifications completed in April 1996. Research entailed obtaining literature from di-verse sources including New York City Department of Environmental Protection- Bureau of Sewers, New York State Department of Transportation Stan-dard Specifications, ASTM C76 – 85a Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe. Design requirements determined that Class IV Reinforced Concrete Pipe would be specified.
Subsurface Investigations at the Hutchinson River Parkway
A subsurface investigation program was performed by Warren George, Inc. for Riverbay Corporation between September 18, 1995 and October 18, 1995. Ten soil borings were taken. Nine were directly on top of the embankment of the Hutchinson River Parkway Bridge and one on Bartow Avenue near the southwest abutment of the bridge. The depth of borings into bedrock ranged from 53 feet at Boring B-40 on Bartow Avenue to 70 feet at Boring B-43 on top of the embankment. Ground water readings were not recorded. The ground water table fluctuates with rainfall. It is higher or lower based on a dry or wet season.
There were five basic layers of soil strata encountered. They are as follows: A) Embankment Fills, overlaid by B) Gray, c-f Sand, little to some Silt, with Cobbles, overlaid by D) Gray, weathered rock (Mica), overlaid by E) Gray Schist with Quartz Lens.
Embankment Fills
The embankment fills ranged from a depth of 27 feet on the southbound side to 19 feet on the northbound side of the HRP. The soils consisted of a brown c-f Sand with little to some silt, containing pieces of cinder ash, brick chips, glass, uniformly distributed. The material may have been placed in concurrent lifts from the same stockpile. The fill is essentially a medium dense soil as per the blow counts. Some blow counts were higher because the split spoon sampler may have hit pieces of cobble causing a higher reading. These cobbles could be penetrated using a roller bit. In one instance a large cobble had to be cored. This occurred at a depth of 10.0 feet at Boring B-50. The toe of the embankment on the southbound side is at approximate elevation 8.0 feet and on the northbound side it is at approximately 12.0 feet.
Gray, c-f Sand, little to some Silt, Cobbles
These soils underlay the embankment fills and are nine feet in thickness on the southbound side. On the Northbound side of the HRP, this soil was approximately ten feet thick. The soil may be considered Medium density. Cobbles of Mica were encountered; however, the cobbles could be penetrated using a roller bit.
Gray Clayey Silt
This soil underlies the Gray c-f Sand, little to some Silt with Cobbles. Based on the N value, (number of blow counts per foot) the Clayey Silt is very stiff. The soil was essentially Silt turning to clay.
Gray Weathered Rock (Mica)
This stratum is under the Gray Clayey Silt. The soil consisted of medium density soil of weathered mica and cobbles.
Gray Schist with Quartz Lens
Bedrock was encountered at a depth of 48 feet below Bartow Avenue, Boring B-40. Core recovery ranged between 49 inches and 60 inches. Due to the high percentage of Clear Quartz found in the rock, it may be considered a soft through hard rock.
Observations
Although clusters of cobble were found during observations, it seemed feasible that concrete pipe could be installed in the Gray c-f Sand with little silt, underlying the embankment fills. No borings had to be moved due to an inability to penetrate cobble. One boring had to be moved due to equipment failure.
54" RCP JACKING PIPE (3)
STV performed a plant inspection at the pipe manufacturer’s facility on September 16, 1997. Vianini Pipe, Inc. is located in Somerville, New Jersey. STV witnessed the manufacturing of 54-inch diameter reinforced concrete jacking pipe required for the Microtunneling project at Co-op City. On the day of inspection weather conditions were sunny and 80 F.
STV met the plant production manager who showed us the areas used for manufacturing the 54" RCP. He introduced us to the inspection staff and Mr. Kevin Brown who was a great source of information.
It was explained that Vianini Pipe, Inc. has production and engineering divisions. Quality control is part of engineering.
Quality control of the manufactured pipe follows the procedures submitted for approval on 7/21/97. The inspector uses the form entitled "Quality Assurance Jacking Pipe Report." A form is completed for each pipe and cross-referenced by production number and date cast. The inspector marks the pipe with the appropriate designation. The form is filled out as the pipe goes through the various stages of construction. It can not be completed at one time or in one day.
Quality control (QC) has a testing laboratory on site. They have the capability to test aggregate, run sieve analysis, take concrete slump and concrete cylinder samples. They have curing boxes. They can break the cylinders to determine compressive strength. They have separate steel tapes of each diameter pipe to measure circumference.
Aggregates are stockpiled. Certain clients such as New York State Department of Transportation (NYSDOT) require separate stockpiles labeled for their use only. The stockpile next to it may be the same material but they are separated just the same.
Woven wire fabric (WWF) reinforcement arrives at the site in rolls. In one plant it is unrolled through a machine and set in the shape and required diameter. The Class D round pipe required for the TES 221 Project had two layers of reinforcement which were two different diameters.
The inner reinforcement is placed around an inner steel form. The form and WWF are set vertically on a round, level plate in an outdoor, open area by a Manitowoc crane. The outer cage reinforcement is lifted and lowered into place. Spacers are used to maintain the required cover. The outer form is lifted and lowered into place. Vibrators are permanently attached to the outside jacket. The entire assembly is checked for alignment before the pour.
A preset computer controls the aggregate, cement and water. An operator can adjust the mix based on his experience and his observations of the water content of the aggregate as it enters the hopper. The material goes into a mixer and then onto a conveyor belt. The concrete mixture is placed into a crane bucket, placed in the forms from the top and vibrated. Two men climb on top to verify the height of the pour. Two pipes are poured in the morning and two in the afternoon after which the crane places a tent over them. On site steam generation allows for curing. The allowable ambient temperature range is 90 to 130 degrees. The setting was 110 degrees.
After the initial set the forms are removed. The pipe is transferred to another area. Excess concrete is removed from both ends of the pipe. The inspector takes preliminary measurements of the wall thickness and inside radius. These are not recorded as it is performed just to eliminate any pipe which is out of round or otherwise does not meet the specification.
Tremendous effort is made to ensure that the bell and spigot ends are flush, round and manufactured to the required depth and tolerances of the acceptance criteria. Each man has a square (tool) to measure the depth of the bell and spigot ends. A hand held jackhammer is used to get the bell and spigot to the correct depth. A smooth section is roughened in the same manner. Sika 123 is applied by hand trowel to prepare a smooth surface. This can only be done in 1/8 of an inch layers. Excess material is removed. Half the pipe is done and then the pipe is rolled so the other half can be done. Air holes are patched. Exterior "gate" refers to the area where the forms come together. If it is greater then 1/8 of an inch it is ground smooth. The inspector uses a caliper, a square, and a tape to verify acceptance of all of the above and then places a check mark on the form for each item.
When the results from the concrete cylinder breaks come back they are recorded on the inspector's form.
The ends of the pipe are sounded with a Swiss hammer. This is done to check for voids, which are not observable. A weak section is cause for pipe rejection. Rejected pipe is removed from the production line and stored in a separate location. I did not see this test performed on the day of my inspection but I was shown a pipe rejected on that basis.
External load crushing test is performed by the three-edge-bearing method in accordance with ASTM C76-85a, 11.3.1. The three-edge bearing test machine is located in another area. This is a destructive test in which a load is applied on the top of the pipe. A crack usually develops on the bottom inside radius. A feeler gauge is used until 1/100th of an inch can be measured. The reading on the pressure gauge indicates the strength of the pipe. If the ultimate strength is required the pressure is continued until the pipe destructs. This test was not performed the day STV visited the production site.
Gaskets are sent with the pipe for the Contractor to install.
STV asked Kevin Brown if there was an independent quality assurance person or group who implements the quality control program and sees to it that QC is being performed correctly. He said that this is not done for reinforced concrete pipe in the industry. It does exist for pressure pipe and Vianini follows the same quality control procedures with RCP as they do for pressure pipe with the only difference being the material. He said that they are the only manufacturers in the northeast who has an independent agency perform quality assurance of their quality control program. The independent QC auditor is Lloyd's Register Quality Assurance. STV asked for and received copies of this certification.
STV was told that NYSDOT, NYCDOT, NYCDCC as well as NJDOT have approved the plant.
In conclusion, the fabrication facility and the QC exercised in the plant met all the requirements of the TES 221 Specifications.
Concurrent Projects
Although not all inclusive, the following is a listing of the major work whose time frame spanned the same time the Housing Project Repair Program was underway at Co-op City. The Contractor for the microtunnel project was expected to coordinate his work with these and other work contracts.
RIC/EDB-250
Under this contract, the thermal systems and electric distribution system servicing the entire north site was replaced. This included Buildings 1 through 25 as well as townhouses and shopping centers in the area. A limited amount of surface restoration was performed under this contract.
SIT-207
Under this contract, the domestic water, fire, gas, storm and sanitary sewer lines were replaced in the vicinity of Buildings 12, 13 and 14 of the north site. Surface restoration was performed in the area following this work.
SIT-205
Under this contract, the domestic water, fire, gas, storm and sanitary sewer lines were replaced on the eastside of the north site, except for Buildings 12, 13 & 14. Surface restoration was performed in the area following this work.
TES-220
Under this contract, the thermal and electric distribution system servicing the entire south site was replaced, except for work performed under contract TES-222. The domestic water, fire, gas, storm and sanitary sewer lines were replaced. This included Buildings 26 through 35, except Building 29, as well as townhouses in the area and Shopping Center 3. Surface restoration in the work area was performed under this contract.
TES-222
Under this contract, thermal and electric lines were run from the proximity of the Power Plant through the casing pipes installed under contract TES-221 and into the south site and Building 29. Surface restoration in the work areas will be performed under this contract.
ASB-252
Under this contract, asbestos abatement to support all construction work within the north was performed, except for asbestos abatement within Buildings 12, 13 & 14.
ASB-SOU
Under this contract, asbestos abatement to support all construction work within the south site was performed.
GARAGE REHABILITATION
Contracts were to be issued for the repair, renovation and/or replacement of garages. The work scope was unknown at the time. A garage consultant was engaged to do all investigation and engineering work to accomplish this work.
EMERGENCY/PRIORITY REPAIRS
Repair work to the existing piping and electrical systems servicing Co-op City. This work was ongoing throughout the life of the Housing Project Repair Program.
POWER PLANT WORK
The Power Plant required various contracts to rehabilitate the facility. Some of the work entailed roof replacement and exterior brickwork to the existing facility.
MICROTUNNELING PROJECT
Microtunneling is a term used to describe methods of horizontal earth boring. It can be subdivided into two groups: slurry method and auger method. The tunnel boring machine is laser guided, and remotely controlled to permit precise line and grade installation to an accuracy of +/- 1-inch.
The low bidder was disqualified as he submitted an improper bid. He had tried to qualify his bid by tying it into his anticipated production rate. This was unacceptable. The second low bidder for the TES 221 Contract was Northeast Construction Inc. (NCI) of New Jersey. Their bid was accepted. They chose the Microtunneling method to install the casing pipe. The boring span of each tunnel was 230 feet. Work was started in January 1998 and completed in March 1998. One bidder chose the jacking method rather then microtunneling but his bid was not competitive.
Based on his interpretation of the boring data NCI chose the Harrenknecht AVN 1200 tunnel-boring machine (TBM) which utilizes the slurry method. As it was known that there were boulders in the fill, NCI was questioned about the capability of the TBM to bore through the anticipated soil layers. NCI gave verbal assurances of the same. The slurry method involves jacking pipe and simultaneous cutting of soil at the face of the machine by a cutting head. The tunnel was supported at the face by pressurized slurry. The spoil was removed hydraulically in the form of slurry. The conveying fluid is simultaneously used to counteract hydrostatic forces created by ground water pressure at the face of the as well as spoil removal.
Construction Procedure
1 A reinforced concrete jacking pit was constructed on the southwest side of HRP. The back wall was thicker then the other walls, as it had to absorb and distribute the thrust of the jacking reaction force into the surrounding ground. For the 54 inch RCP with a factor of safety of 3.2 the jack-ing force required was 583 tons.
2 The Contractor used a Grove RT635C cherry picker to place the jacking equipment, discharge pump in the pit and pipe into the pit.
3 An entrance ring with rubber seal was placed on the wall around each bore location to form a seal against groundwater and slurry penetration into the shaft.
4 Slurry settling tanks were placed at grade near the shaft. Piping between the tanks and the shafts make a circuit for the slurry. A charge pump is set near the slurry tanks.
5 A control cabin was set up at grade. The electrical equipment and operation board was set up with power and control cables. The main power supply was a diesel-operated generator.
6 Hydraulic hoses between the power pack and the jacking equipment were connected.
7 The Harrenknecht shield was lowered into the jacking pit and set on the guide rails.
8 Flexible hoses for slurry lines were connected to the TBM shield from the pit by-pass unit, the power and control cables were connected to the machine and the slurry tanks were filled with wa-ter. Bentonite was added via a separate pump.
9 The system was tested, adjusted and retested.
10 The hydraulic jacks were engaged to push the TBM close to the work face through the entrance rubber seal.
11 The pit by-pass unit and the slurry pumps were op-erated to circulate the slurry between the TBM shield and the slurry tank.
12 The cutter head of the TBM shield is rotated, and the jacks extended to push it forward and start the excavation.
13 During driving, the operator controls the jacking speed, the torque of the cutter head, the slurry flow rate, the slurry pressure at the work face, the earth pressure and the inclination of the TBM.
14 After the TBM shield is driven into the earth, the operation of the machine and slurry pumps are stopped and the jacks are retracted. The electric ca-bles and slurry lines are disconnected in the jacking pit, in order to allow placing of the first 54 “ RCP onto the rails.
15 The hydraulic jacks are extended to push the pipe forward until it fits to the tail of the TBM shield.
16 The pipe joint with the shield tail was checked for fit. The electric cables and slurry lines were recon-nected to the TBM shield. The laser and target were checked.
17 The microtunneling operation was resumed with the restart of the slurry pumps, the pit by-pass unit operated, the cutter head rotated, and the hydraulic jacks extended.
18 This microtunneling process is repeated to jack each pipe, one after another.
19 While the pipe jacking operation is carried out, a lubricant is pumped continuously to the periphery of the concrete pipe to reduce jacking friction.
20 The receiving pit is constructed at the same time the jacking pit is. It is used to recover the TBM shield on completion of the drive.
21 When the shield was within one foot of the re-ceiving pit the TBM was stopped and the timber sheeting removed as the jacks pushed the pipe ahead. The TBM was recovered and brought back to the jacking pit. The equipment was aligned to begin the next tunnel.
22 The TBM was checked and the shield cleaned. It was lowered into place and the electric cables and slurry hoses reattached.
Actual Experience
Microtunneling worked well on the first two tunnels but encountered difficulty on the third. The head could not advance beyond approximately the halfway point. This meant the head of the TBM was directly under the median of the Parkway. NCI stated that the TBM was not advancing and was obstructed by solid sheeting, oil tank, or excessive timber bulkhead.
To recover the TBM, NCI constructed a jacking pit on the opposite side of the Hutchinson River Parkway. They installed 1” thick, 84” diameter steel casing pipe. Excavation was done by hand from inside the steel casing pipe. Rail was placed and a cart was utilized so that the excavated material could be removed. The steel pipe was advanced using hydraulic jacks. No obstruction was found when the head of the TBM was reached.
Ears were welded on the TBM and cable attached. The TBM was hauled out as the 54 “ RCCP was pushed in place from the opposite side. The TBM was dismantled and cleaned. The intake port was clogged. Small steel bolts nails and debris was found in the bottom of the cone section. It was hypothesized that the steel disturbed the turbulent flow required to make the operation work. Thereafter, hose, pipe, and pumps were cleaned and flushed more often. The next two tunnels were completed without any problems.
Monitoring points indicated no settlement to the Parkway. The next contract required that the Contractor install the carrier pipe from the power plant to the south site through the five, 54” RCCP tunnels under the Hutchinson River Parkway.
THE CLAIM
NCI filed a claim with the construction manager based on differing site conditions. Throughout the claim NCI stated they relied on the test boring information and they were part of the Contract documents. In fact, the borings were part of an appendix and marked “For information only, not part of contract documents”.
As noted earlier, NCI stated at the pre-award meeting that they had no concern about any material other than encountering bedrock. Several interested parties attended the pre-award meeting. Everyone understood those words. The claim attempted to put a different twist on what was said. The owner, construction manager and engineer were unwilling to accept new interpretations.
It was pointed out to NCI that they were not the low bidders. The low bidder put forth-unacceptable conditions with the regard to extras in the event that certain materials were encountered. The owner paid a premium based on NCI’s assurances. The award was recommended based on these assurances.
The claim expressed the contractor’s view as to the responsibilities of the engineer. He ignored to mention his responsibility to read the entire contract documents and abide by the pre-award understanding.
The remainder of the claim dealt with the title of the specification, selection of the equipment, definition of microtunneling and their interpretation of the “intent” of the Contract. These were put forth to justify the claim.
During the bidding stage questions were asked about jacking, were responded to in an addenda which, by definition, were made an integral part of the contract. Language in the specifications permitted jacking and/or boring. At least one bidder intended to do jacking.
It was interesting that the contractor sought 100 % compensation, when retrospectively “solid sheeting, oil tank, or excessive timber” as anticipated by him did not obstruct the TBM when the TBM was not advancing. There was no mention at that time of bolts, nails or debris. Their opinion was that it had to be a total blockage until it was discovered there was none. Then it became a question of the validity of borings, miscellaneous small hardware, title of the specification, intent of the specification, etc. Accordingly, the claim was rejected.
REFERENCES
Urbahn/Seelye, 1993. Report on: The Routing of the Dual Temperature, High Temperature and 15KV Duct Bank Sys-tems from MH #1 to the South Site
SSV&K, 1995. Draft Report of Subsurface Explorations
Hessing, H. 1997. Inspection report prepared for SSV&K.
