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THE PROBLEM/SOLUTION REPORT
The problem/solution report falls into two parts, with the emphasis on the latter. The first section presents a problem, and the second section presents a solution to that problem. The documentation in the report falls mainly in the solution section, since the problem stems from personal experience in a particular job and hence requires little documentation. Once the writer defines the problem, however, she defends the solution with all the documented information she can muster. The following article is an example of a problem/solution report.
Temporary Installation Reduces Sewer Failure Problems
Clarence W. Myrold, P.E.
An impermanent installation rescued the City of Detroit, Mich., when a major sewer that serviced more than 150,000 persons failed.
The failure of a major 11-ft. diameter sewer posed a serious health hazard to several communities and a military base northeast of Detroit. Because of this, the mayor requested urgent action. Detroit was declared a disaster area by the governor of Michigan, who demanded an accelerated, flexible, and integrated solution.
This major sanitary sewer services an area of approximately 55 sq. miles in the northeastern suburbs of Detroit, Mich., including the communities of Mt. Clemens, Fraser, Clinton Township, Harrison Township, and the northeast portion of the City of Sterling Heights. Emergency pumping operations were initiated by the owner. Further action included immediate restoration of the decommissioned and evacuated Hayes/18 Mile Pumping Station and reactivation of the existing Selfrige Air Force Base Treatment Plant to isolate a portion of the upstream flow, stabilization of the failed interceptor and surrounding subsoils utilizing a special grout mixture of water, cement, and flyash, and design and construction of a temporary bypass and pumping station with capacity to carry peak flows.
Considering the complexity of the Temporary Bypass and Pumping Station installation, it is unique that only 97 calendar days were required from design to activation. The temporary bypass was actually in operation earlier, accepting flow from the emergency pumps within the sewer.
SEWER BUILT ON A LAKE BED
Original construction of the existing 11-ft. inside diameter interceptor sewer consisted of a secondary lining of poured-in-place concrete, wall thickness of not less than I4 inches with a primary lining of rib and wood lagging, consisting of 4-inch thick boards set between typical 4-foot spaced ribs.
The mining machine utilized bore a tunnel 14.5 feet in diameter utilizing dewatering wells in advance of the mining the bulk of the mining operations air pressure. In general, the design invert is approximately 60 feet below ground surface.
The geologic setting in which this project is located consists of a glacial lake-bed environment. The lacustrine deposits of sand and clay are bordered by the Birmingham Moraine several miles to the west and the Mt. Clemens Moraine a short distance to the east. Both of these water-laid moraines trend in a northeast to southwest direction.
A Pleistocene age delta has been deposited by the predecessor of the present Clinton River, the Birmingham Moraine. This delta created large sand deposits along the north side of Clinton River. The area between the Clinton River and the project site appears to represent a transitional area between the deltaic deposits and the lacustrine deposits of sand and clay.
The cause of the failure has not established. Determination of such is not within the scope of this review. However, it is known that shortly after midnight July 29, 1978, officers on routine patrol noted that on 15 Mile Road, in the vicinity of Ha buckling and settling. Eventually, the 15 Mile Road was highly evident as lane ultimately settled approximately 3.5 feet the level of the westbound lane and open fissures developed along and adjacent to the sewer centerline. Later investigation indicated that the interceptor was completely filled with soil at one point.
EMERGENCY RELIEF IS PROVIDED
The initial main thrust of the owner, the Detroit Water and Sewerage Department (DWSD), was directed at the rapid construction of an emergency relief around the failed interceptor. However, it was recognized that this system would not provide adequate service for a sufficient period of time to effect repairs to the failed section of the interceptor. On this basis, the DWSD began preparations to build a major, although semi-permanent, pumping station together with its bypass and standby electrical protection, of sufficient capacity to carry peak flows. The design construction, and construction management during this time of stress provided numerous
examples of cooperation nationwide. To expedite delivery of sheet piling from North Carolina and Mississippi, men stood in front of weigh stations waving the trucks through. When requested by the consultants, pumps and other equipment from Connecticut, Texas, Indiana, and New York were diverted to the project. A major electrical control panel was designed in three days and subsequently constructed by the supplier in 12.
Around the clock construction included driving sheet piling at night utilizing emergency floodlights. This proved to be an extremely difficult task. Initially, it was considered feasible to drive the sheet piling utilizing a vibratory driver, possibly in conjunction with predrilling operations. However, due to the extremely compact nature of the subsoils found at the lower depths, the performance of the vibratory hammers was not satisfactory. The sheet piling was ultimately driven utilizing a Link-Belt 660 diesel hammer in conjunction with a program of augering and jetting adjacent to the piles as they were being driven.
Innovative features created by necessity include: 1) two 48-inch diameter wet taps into the existing sewer approximately 60 feet below grade, which are the largest known; and 2) the completed operational pumping station at the time of its construction was the largest submersible sanitary pumping station in the world. The magnitude of the project can be further shown in that the daily ground water discharge from the 51 wells required to dewater the area to construct the Temporary By-pass and Pumping Station and stabilize the failed sewer was calculated as sufficient to supply 20,000 homes.
The completed by-pass system is performing satisfactorily and is meeting or exceeding the requirements set forth by the DWSD. The Pumping Station includes six 6,000-gpm submersible pumps for a total capacity of 36,000 gpm, which are electrically sequenced to provide both conservation of electrical energy and to provide uniform wear of the pump units. In addition, two 750 kw emergency generators provide further stand-by protection.
CAN BECOME PERMANENT
The structures involved were designed in such a manner that although they are presently considered temporary (two to five year design life), certain additional expenditures would allow their designa-tion to be extended to that of a permanent facility.
The failed zone of the existing tunnel sewer was isolated and stabilized from the operational system by means of bulkheads constructed both upstream and downstream of the failed zone, installation of dewatering wells along the present tunnel sewer, and the injection of cementious grout into the fissured subsoils.
Based on records maintained during the grout stabilization program a total of 16,946 cu. ft. of grout was injected into the subsoils surrounding the inter-ceptor. This total represents an average application rate of approximately 30 cu. ft. of grout per lineal foot of sewer along the stabilized area west of Hayes Road and approximately 46.4 cu. ft. per lineal foot of sewer east of Hayes Road.
The site was restored to the point that 15 Mile Road may be reopened to normal traffic and permanent repairs to the tunnel sewer may be implemented as soon as plans and funding are available.
A potential disaster involving the health, welfare, and personal loss to more than 150,000 residents of several communities, as well as disruption of an established military base, was averted by the rapid application of engineering principals and prompt construction which minimized the effects of a major sanitary trunk sewer failure. The actual cost of approximately $12 million was also within the preliminary project estimate, not to exceed $13 million.
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