CHICAGO SANITARY AND SHIP CANAL AT LOCKPORT REHABILITATION CASE STUDY Brant Jones, P.E. 1 Thomas Mack, P.E. 2 Amy Moore, P.E. 3 ABSTRACT This paper will discuss the unique history and techniques for restoring portions of the Chicago Sanitary and Ship Canal (CSSC) to acceptable safety standards. The CSSC was constructed in the 1890 s to reverse the natural flow of the Chicago River preventing Lake Michigan pollution. Today, it is used for sanitary, hydropower, flood control, and navigation. The CSSC is a perched canal for 2 miles north of the Lockport Lock. Both banks combine with the Lockport Lock and the Hydro-Powerhouse and Controlling Works to form an intricate water retaining complex that was classified as the riskiest, high-hazard navigation dam in 2004. The west side water retaining structure is a zoned earth embankment. On the east side, water is retained by a concrete wall backed by rock fill. The 120-year-old system suffers from deterioration as evidenced in the canal walls by the visible deterioration, poor investigative cores, and numerous seepage areas. The opposite approach dike has experienced sloughing, sinkholes, and constant seepage. In 2004, a reliability assessment identified stability and pool loss concerns. Repair concepts required minimal impacts to canal operations. In 2007, contractors constructed a 4,300 foot slurry trench cut-off wall using hydromill technology in the earth embankment. Construction is underway for repair of the concrete canal wall under full pool. New precast concrete panels will be placed in a rock trench in the channel floor and tied back to an anchor wall. Infill concrete will then be placed, encapsulating the old wall. BACKGROUND AND HISTORY The Chicago Sanitary and Ship Canal (CSSC) is located in the greater Chicago area. Refer to Figure 1 for a location map. The concept of constructing the CSSC began in the mid-1880s, when Chicago was struck with a series of outbreaks of waterborne illness. Wastewater from metropolitan Chicago was discharged into the Chicago River, which flowed into Lake Michigan. The city drew its drinking water from Lake Michigan near 1 Structural Engineer, US Army Corps of Engineers-Rock Island District, P.O. Box 2004, Rock Island, IL 61204, brant.t.jones@usace.army.mil 2 Chief, Geotechnical Engineering Branch, US Army Corps of Engineers-Rock Island District, P.O. Box 2004, Rock Island, IL 61204, thomas.e.mack@usace.army.mil 3 Civil Engineer, US Army Corps of Engineers-Rock Island District, P.O. Box 2004, Rock Island, IL 61204, amy.r.moore@usace.army.mil Chicago Sanitary and Ship Canal 1123
the source of the Chicago River, causing the waste to be cycled into the drinking water system. In order to address this issue, it was decided that the flow of the Chicago River should be directed away from the drinking water supply. Figure 1. Lockport Lock and Dam Location Map Construction of the CSSC began in 1892 and the canal was opened in 1900. This was the first important work of the newly formed Sanitary District of Chicago (now the Metropolitan Water Reclamation District of Greater Chicago (MWRD)). The CSSC began at the South Branch of the Chicago River at Robe Avenue (now Damen Avenue) and continued to the Controlling Works at Lockport, IL, a distance of approximately 30 miles. The construction of the CSSC reversed the natural flow of the Chicago River. The river now flowed out of Lake Michigan, through the South Branch of the Chicago River, through the CSSC at Damen Avenue, through the Controlling Works and into the Des Plaines River at Lockport, ultimately flowing down the Illinois River to the Mississippi River. Between 1903 and 1907, the main channel of the CSSC was extended from the MWRD Controlling Works to the Upper Basin in Joliet, IL. The distance of the extension was approximately three miles. The location of this new reach extends from the confluence of the Des Plaines River and main channel (approximate River Mile 290.0) to the MWRD Controlling Works (approximate River Mile 293.2). This extension of the main channel is now considered to be part of the CSSC. Once the extension was complete, the CSSC had the ancillary benefit of providing a navigable connection between the 1124 Collaborative Management of Integrated Watersheds
Mississippi River and the Great Lakes. Five major features contain the downstream extension of the CSSC at Lockport, IL: the Lockport Lock at River Mile 291, the MWRD Lockport Powerhouse also at River Mile 291, the Approach Dike acting as the right descending bank between RM 291.2 and 292.1, the Controlling Works at River Mile 293.2, and the Concrete Canal Wall that forms the left-descending bank along this Reach. Refer to Figure 2 for an overview of the area. Approach Dike Controlling Works Des Plaines River Powerhouse & Dam Canal Wall Lock Figure 2. Overview of Lockport Pool Features The Lockport Pool, as defined for this paper, consists of the first three miles of the CSSC upstream of the Lockport Lock, from RM 291.0 to RM 294.1. The CSSC is a perched body of water in this reach, with canal water levels reaching approximately 38 feet above the adjacent Des Plaines River on the right and the Deep Run Creek on the left. Upstream of the river mile 294.1, adjacent ground elevations tend towards the top of canal elevations and the CSSC is no longer a highly perched canal. Thus, the risk of pool loss due to failure of the CSSC embankment or Concrete Canal Wall does not exist as a primary catastrophic consequence of unsatisfactory performance. However, in the subject three-mile Lockport Pool reach, the risk of catastrophic breaching of either an embankment or Concrete Canal Wall is prevalent, with significant economic consequences associated with such an event. In 1984, a memorandum of agreement (MOA) between the Department of the Army (DA) through the US Army Corps of Engineers (USACE), Rock Island District (District) and MWRD was created, transferring primary maintenance responsibility of the CSSC to USACE. This memorandum divided up responsibility between both organizations, specifically addressing features along the CSSC. It specifically addresses the Lockport Controlling Works and Protection Cells and the Lockport Dam and Powerhouse. The Chicago Sanitary and Ship Canal 1125
MOA states the DA will operate and maintain at no cost to MWRD, the currently used Lockport Lock, the remainder of the gravity structure, the cutoff wall, the right descending embankment from the gravity structure upstream to the southern-most sluice gate of the Lockport Controlling Works, and the left descending embankment and access road from the gravity structure upstream to River Mile 293.1. In short, the DA agreed to maintain any structure in the Lockport Pool area which retained water in the canal. EVALUATION PROCESS Given the age of the structure and the lack of routine maintenance, the CSSC structures needed repair. The District attempted a number of minor repairs, including a sandbentonite cap addition to the core of the Approach Dike. When these repairs were deemed unsuccessful, the District chose to evaluate the entire system for a major rehabilitation effort. This evaluation was accomplished in two phases, first an evaluation was performed followed by an in-depth risk assessment. Major Rehabilitation Evaluation Report In 2004, the District published the Lockport Pool Major Rehabilitation Evaluation Report (RER), which evaluated the economic feasibility of rehabilitating the Lockport Canal Walls, Approach Dike, Powerhouse, Controlling Works, and associated appurtenances. The purpose of the RER was to determine if construction was economically justified. As such, it documented the benefits of the project, both through actual benefits gained and avoidance of future negative outcomes (such as flood damage due to system failure) and compared it against the estimated cost of construction. Most of the benefits were obtained through the avoidance of estimated costs due to structural failure. Since this is difficult to quantify, expert elicitation was used to determine a range of failure scenarios for each component of the system and the estimated likelihood that the failure would occur over the evaluation period. Based on the projected impacts, the potential costs for each failure were determined. These costs included estimated emergency repair costs, loss of navigation revenue, and loss of hydropower production, as applicable. At the time of the RER, the likelihood of loss of life was deemed low enough that is did not need to be included in the analysis. However, further hydraulic modeling has since revealed a greater potential for loss of life downstream of the project if a full breach were to occur. These factors were then used to complete risk-based assessment plans, using reliability models and a range of repair and rehabilitation plans. To derive a benefit-cost ratio for the project, the cost impacts from a system failure had to be determined. First, an expert panel determined possible failure modes for project features, and the likelihood of each mode occurring over the next 25 years. Economic impacts for each failure scenario were derived, based on damage to the surrounding community, cost of emergency repair, loss of navigation benefits, and power generation revenues during the repair. Once these were determined, the likelihood of each scenario occurring combined with the impact costs were run through a Monte Carlo simulation to determine an overall cost of failure for the 25 year planning period. Future costs were 1126 Collaborative Management of Integrated Watersheds
converted to 2004 present worth dollars and compared against the estimated repair costs to determine benefit-cost ratio for project components. The RER found that major rehabilitation was economically justified. Repairing the Controlling Works would avoid $12.9M (2004 Dollars) in damages, including up to 30 days of lost navigation, yielding an estimated benefit-cost ratio of 5.39. Likewise, repairing the Canal Wall would avoid up to $50.4M in total damages, including up to 120 days of lost navigation, yielding an estimated benefit-cost ratio of 1.44. Finally, repairs at the Approach Dike would avoid up to $50.8M in total damages, including up to 120 days of lost navigation, yielding an estimated benefit-cost ratio of 1.20. Screening Portfolio Risk Assessment The Lockport system was evaluated using the Screening Portfolio Risk Assessment (SPRA) process in 2005. The SPRA process is a risk-informed management strategy for dam safety which utilizes uniform criteria to classify and rate all dams within USACE. With uniform rating criteria, the results are used to manage and reduce risk by sending resources to higher priority projects before lower priority projects. Project features were evaluated independently, with ratings given for each. The concrete throughout the Lockport Canal Walls, Controlling Works, and Approach Dike was rated Probably Inadequate. Probably Inadequate is defined as being judged not to perform well under specified loading with a low level of confidence and it requires additional studies and investigations to confirm. This rating was given based on observed deterioration and stability calculations. The earthen embankments associated with the Approach Dike were rated Inadequate, which is defined as judged not to perform well under specified loading with a high level of confidence; physical sights of distress are present and/or analysis indicates a factor of safety near the limit state. This rating was given based on the presence of sink holes and significant seepage found during the site investigation. A Dam Safety Action Classification (DSAC) rating was given to the system. The rating is based upon a combination of annualized loss of life or economic damages and the likelihood of poor performance. Based on the condition of the structure and the impacts of a failure, the Lockport system was given a DSAC 2 rating, defined as confirmed (unsafe) and unconfirmed (potentially unsafe) dam safety issues; failure could begin during normal operations or be initiated as the consequence of an event. The likelihood of failure from one of those occurrences, prior to remediation, is too high to assure public safety. The Lockport system received the highest (or most unsafe) rating of any dam in 2005 and is currently the Mississippi Valley Division s highest priority. The remainder of the report will address the modifications made to the Approach Dike and Canal Walls in order to restore the Lockport system to an acceptable rating. Chicago Sanitary and Ship Canal 1127
Pre-Construction Condition LOCKPORT APPROACH DIKE Original Embankment Construction: The approach dike forms the right descending bank of the CSSC in the area of the Lockport Pool. The embankment is approximately 4300 feet long and up to approximately 43 feet high. The crest width is around 30 feet wide with side slopes that are approximately 1.5 horizontal to 1 vertical. The embankment impounds up to 38 feet of water. Figure 3 shows a typical cross section of the dike. Figure 3. Existing Approach Dike Cross Section The dike foundation consists of silurian dolomite. The material beds are generally flat with only a small dip running north upstream of the project. The joints in the rock are generally vertical. The top three feet of rock is generally more fractured than rock deeper in the formation. The original embankment consists of a lime cement concrete core wall, surrounded by a clay buttress and a rock shell. The clay material consists of engineered clay material which is generally dense and impervious. The rock shell consists of rubble spoil from the excavation of the canal upstream of the Lockport Pool. The lime cement core wall was built prior to the use of Portland cement concrete. The material is relatively weak with compressive strength generally around 500 psi. It is somewhat permeable and water soluble. The extent of cracks or joints is also not known. The core wall was constructed on top of the bedrock, but the amount of unsuitable rock that was removed is unknown. The buttresses appear to be built generally of clay. The amount of engineering is unknown. It is also believed that the engineered-fill was placed on top of in situ material adjacent to the core wall. Thus the material is variable in permeability and strength. The rock fill is simply spoil from the channel excavation. It varies in size, but much of the material is greater than 12 inches. Some areas consist of sand material, but the material is variable. 1128 Collaborative Management of Integrated Watersheds
Distress Present in the Embankment: Through the years various sinkholes developed in the embankment. The first sinkholes were noticed between 1960 and 1972, but the documentation was poor. Between 1972 and 2002 at least 13 subsidence events were recorded with the largest being 18 feet deep. Table 1 shows the documented seepage events. Date Table 1: Historical Subsidence Events. Approximate Description Station 1960s-1970s Several Undocumented Settlements Dec 1972 42+90 Subsidence 1.5 x 1.5 x 2 deep Feb 1973 42+90 Subsidence 3 x 3 x 2.5 deep Mar 1973 42+90 Subsidence 6 x 6 x 2.5 deep Mar 1973 42+90 Large cavity (?) on Des Plaines side slope 1978 Cavity 18 deep noted Feb 1984 26+35 Subsidence 4 x 4 x 6 deep Feb 1985 41+15 Subsidence 15 x 7 x 6 deep May 1990 40+80 Subsidence 8 x 10 x 5.5 deep Jun 1990 40+80 Subsidence 8 x 10 x 1 deep Nov 1990 40+32 Subsidence 10 x 11 x 6 deep Mar 1991 46+00 Subsidence 1 x 2 x 3.5 deep Jul 1996 42+90 Subsidence 3 x 5 x 5 deep Oct 2001 43+35 Subsidence 8 x 8 x 10 deep Jan 2002 24+00 Subsidence 5 x 5 x 6 deep Feb 2002 8+98 Subsidence 1 x 2 x 2 deep In the 1980s, several geophysical surveys were conducted in an attempt to identify where seepage was occurring. Resistivity studies identified several areas of seepage. In ground penetrating radar studies, other possible seepage areas were identified, but there were no conclusive results for where, or at what elevations, the seepage was occurring. The prevailing thinking of the time was that the seepage was occurring over the top of the core wall and that the filter criteria between the engineered clay fill and the rock fill was not satisfied. Thus material was eroded from the internal structure of the dam causing the sink holes to form. In 1987, a trench was excavated in the top of the dike down to the top of the core wall. The trench was backfilled with a compacted mixture of bentonite and sand. The mixture was placed up to elevation 579. The height of water in the canal was approximately 576. After the formation of additional sinkholes in 1990, an investigation revealed that the top elevation of the sand-bentonite varied from 576 to 579. Thus it was thought that water was again flowing over the top of the sand-bentonite cut-off wall. Then in 1990, the cap was raised along the entire dike to an elevation of 581.5. Chicago Sanitary and Ship Canal 1129
In order to closely monitor the flow of water through the approach dike, three weirs were installed on the downstream side of the dike in 1992. A fourth weir was installed in 2007. This weir was installed to measure flow through the canal wall downstream of the project. Despite raising the sand-bentonite cap, additional sinkholes continued to develop. In 1997, a sheet pile cut-off wall was installed. The sheet pile cut-off consisted of 35 footlong sheet pile sections driven on the canal side of the cut-off wall into the engineered clay fill. The sheet pile was installed centered along an area where chronic sinkholes were occurring. While this appeared to solve the seepage in that area, other sinkholes developed at the ends of the sheet wall. With each of the repairs, the amount of the seepage across the weirs remained unchanged. Measured seepage averaged 65, 12 and 31 gallons per minute for the original three weirs. This indicated that the seepage through the dike was not limited to that occurring over the core. Other possible seepage paths include through the core wall and through the bedrock. A possible reason for seepage through the core wall is insufficient filter criteria. A proper filter criteria prevents material migrating through the dam from the water pressure which could lead to piping. Piping is a phenomenon caused by water pressure forcing fine particles through the coarser material particles until a void forms in the embankment leading to sinkholes. When the filter criteria is satisfied, the grains are close enough in size so that the smaller particles will not fit between the coarse materials. Therefore, water can pass from one material to the next without the migration of the finer material. Modern dam design material gradations would be sized so that filter criteria is satisfied, but it may not have been considered during the construction of the approach dike in the early 1900s. Another possible reason for seepage through the core wall is the possibility of fractures in the core wall itself. The joints and cracks in the core wall are not known. Modern dam joints would be treated with water stops to prevent migration of material through the joints, but this may not have been done during the original construction. It is also possible that cracks could allow piping of material leading to the formation of sinkholes. A possible reason for seepage through the bedrock is fractures in the bedrock. Current practices in embankment design would require treatment of fractures in the surface of the rock preventing the piping of fine particles through factures in the rock. It is unknown if rock fractures were treated during the dike s construction. Thus the potential exists for embankment material to be piped through fractures in the rock. Proposed Repair USACE decided to construct a seepage cut-off to stop the flow of water through the embankment and the upper portion of the heavily fractured rock. The seepage cut-off 1130 Collaborative Management of Integrated Watersheds
wall was proposed to be installed from the crest of the dam into the competent bedrock foundation. Figure 4 depicts the proposed repair. Figure 4. Proposed Seepage Remediation The specification of this project was performance-based. This allowed consideration of several types of cut-off walls. USACE felt that several methods could be utilized to accomplish this work. The seepage barrier had the following requirements: The barrier material needed to have a minimum strength of 200 psi. The strength was specified so that material would not have the ability to migrate under water pressure. In many cut-off walls the material is softer in consistency, but with the open-graded rock shell it was felt that some minimal amount of strength was required. During construction, the requirement was increased to 1000 psi to allow better recovery of the core samples. The minimum thickness of the barrier was specified to be 18 inches. USACE received several proposals that fell into two categories: slurry trench cut-off walls and secant pile walls. The selected contractor proposed a slurry trench cut-off wall. The final cost for the slurry wall was approximately $24M. Slurry Trench Cut-off Wall: The excavation was accomplished with a hydromill, a reverse circulation trench cutter. The cutter operated inside a bentonite slurry trench that maintained the trench stability during excavation. The milling head consisted of two horizontal axis cutting wheels operating in the opposite direction, while the cutter head grinds up the material. Between and just above the cutter head a large pump is used to extract the cuttings. The pump sends the cuttings (in bentonite slurry) to a separator unit to separate the cuttings from the slurry. The slurry is returned to the trench to maintain the level of the slurry in the trench. Figure 5 shows the cutting head of the hydromill. Chicago Sanitary and Ship Canal 1131
Figure 5. Hydromill Cutter Head and Pump The entire unit is mounted in a large frame that creates a pendulum effect so that the milling head naturally wants to make the cut vertically and straight. The frame is instrumented so that the operator can monitor the position of the cutter in all three dimensions. The frame also has large push plates on all sides that can be actuated to push the cutter head and maintain proper position. Thus, alignment can be achieved between panels. Figure 6 shows the hydromill frame. Figure 7 shows the operator controls that monitor many aspects of the machine position and operation. Figure 6. Hydromill Frame with Push Plates for Controlling Position of Cutter 1132 Collaborative Management of Integrated Watersheds
Figure 7. Operator Quality Control Report and Display The installation of the cut-off wall is accomplished by first installing a guide trench, next excavating the overburden with a slurry filled trench, then milling the underlying bedrock to key the wall into the trench, and finally placing the concrete wall. The final wall is a continuous wall the entire length of the dike, constructed via a series of primary and closing panels. The guide trench provides proper verticals, horizontal, pitch, roll, and yaw alignment for the excavation equipment. The concrete trench is a relatively shallow trench that acts as a guide for the excavation equipment. It also serves as slurry containment and allows easy access to the excavation for construction and quality control activities. Figure 8 shows a cross section of the cut-off trench. Figure 8. Guide Trench Detail (Courtesy BENCOR Corporation of America) Chicago Sanitary and Ship Canal 1133
In order to construct the wall, the primary panels, nominally 30 feet in length, are excavated and backfilled first. Figure 9 shows the primary panel excavation. Figure 9. Primary Panel Installation (Courtesy BENCOR Corporation of America) Closing panels are constructed by first excavating the material between primary panels. Although Figure 9 shows straight vertical ends on the primary panels, in reality the ends are irregular. Since the space between primary panels is nominally 9 feet and the width of the hydromill trench cutter is ten feet, the ends of the primary panels are trimmed as the closing panel is cut. This provides a clean surface to cast the closing panel concrete. Figure 10 shows the closing panel installation. Figure 10. Closing Panel Installation (Courtesy BENCOR Corporation of America) 1134 Collaborative Management of Integrated Watersheds
Post-Construction Status After the barrier was constructed, cores were taken periodically to verify that the wall was continuous and did not contain voids. Additionally, the contractor utilized slug-out or bail-out tests to evaluate the permeability of the cut-off wall. These tests consist of removing a slug of water from a core hole using a bailer or pump. The depth to water is measured prior to removing water from the core hole. After the slug is removed, water levels are measured at timed intervals as the water returns to the original static level. The hydraulic conductivity is measured as a function of the water level versus time. Table 2 shows the results. Any discrete cracks, lift joints, or voids would contribute to the overall measurement. The results indicated that very low permeability was achieved. Several holes were taken at joints between panels. The results also indicated tight interface between panel joints. Table 2. Core Hole Permeability Testing Results Core Hole Calculated Notes Permeability cm/sec AP-03 9.887 x 10-7 Core hole extended 5 feet into Bedrock AP-03/AC-04 2.454 x 10-5 AC-10/AP-11 5.337 x 10-8 AP-17/AC-18 8.632 x 10-6 AC-29/AP-30 6.629 x 10-7 AP-30 6.762 x 10-7 Core hole extended 5 feet into Bedrock AP-30 (B) 1.369 x 10-6 AC-24/TP-01 9.557 x 10-7 AP-76 3.068 x 10-7 BP-48 2.406 x 10-4 Core hole extended 5 feet into Bedrock P indicates a Primary Panel C indicates a Closing Panel C/P indicates interface between two panels Weir measurements were also taken during the life of the project. Prior to the project the Average weir readings dropped from 65, 12 and 31 gallons per minute prior to the project to 26, 15 and 16 gallons per minute after the project, respectively. While the results will be monitored, it is believed that the seepage has been effectively reduced. Seven lines of three piezometers were also placed along the project. In each line, one piezometer is on the canal side (upstream) of the old core wall and the others are located on the riverside (downstream) side of the core wall. On the downstream side of the core wall, one well is open to the embankment and the others extend into the bedrock. All piezometers are located on the downstream side of the new seepage barrier. The placement of piezometers can be seen in Figure 11. Chicago Sanitary and Ship Canal 1135
Figure 11. Piezometer Line Layout Water levels have generally dropped in the piezometers indicating the seepage reduction was achieved (as can be seen in Figure 12). USACE will continue to monitor the piezometer and well data to determine the long term effectiveness of the cut-off wall. USACE will also continue to monitor for the formation of sink holes. LP-07-04, LP-07-05, LP-07-06 585.0 LP-07-04 LP-07-05 LP-07-06 Adjacent Panels Closed 580.0 Well Water Elevation (Feet above Sea Level) 575.0 570.0 565.0 560.0 555.0 550.0 545.0 540.0 05-Dec-07 17-Dec-07 28-Dec-07 09-Jan-08 21-Jan-08 01-Feb-08 13-Feb-08 25-Feb-08 10-Mar-08 21-Mar-08 09-Jun-08 20-Jun-08 All three wells show a decrease in water level after the adjacent panels are closed, especially the two on the riverside. 02-Jul-08 16-Jul-08 11-Aug-08 22-Aug-08 17-Sep-08 29-Sep-08 10-Oct-08 22-Oct-08 03-Nov-08 Date Figure 12. Piezometer Readings One Line 14-Nov-08 26-Nov-08 08-Dec-08 19-Dec-08 09-Jan-09 23-Jan-09 04-Feb-09 18-Feb-09 02-Mar-09 16-Mar-09 08-Apr-09 22-Apr-09 04-May-09 15-May-09 29-May-09 10-Jun-09 22-Jun-09 08-Jul-09 1136 Collaborative Management of Integrated Watersheds
CANAL WALLS Pre-Construction Condition The Concrete Canal Wall (see Figure 13) forms the left descending bank of the Lockport Pool. The wall was constructed between 1890 and 1905 and placed in monoliths approximately 40 feet in length. The concrete wall extends down to bedrock (fractured dolomite) which slopes upward to the north. Thus, the height of the concrete wall increases in a downstream direction. The wall is believed to be keyed into the bedrock approximately 2 feet. The most critical section of the wall occurs immediately upstream of the Lockport Lock, where the canal water is perched nearly 38 feet. Figure 13. Existing Canal Wall Section Showing 1924 Rehabilitation The original concrete construction utilized lime cement without air entrainment. As a result, the canal wall lacks durability especially relative to freeze-thaw cycles. In response to significant concrete deterioration that was observed early in the wall s design life, rehabilitation was performed in 1924. The upper canal side face (approximately 15 feet) as well as the top 5 feet of the wall were re-constructed with reinforced Portland cement concrete (see Figure 13). Random rock fill, resulting from the excavation of the canal, forms the embankment behind the canal wall. The top width of the embankment is generally 40 to 100 feet, including the canal wall. An access road runs along the top of the embankment for one Chicago Sanitary and Ship Canal 1137
mile upstream of the Lockport Lock, providing the only vehicle access to the lock. The embankment separates the CSSC from Deep Run Creek upstream of the Lockport Lock. Deep Run Creek empties into the canal just downstream of the lock. Numerous areas of seepage are clearly evident through the free-draining embankment. Several of these seepage paths have flows in excessive of 300 gallons per minute. Since the Concrete Canal Wall provides a vertical canal-side face, it also serves as a guide wall to the navigation industry. This is especially true through narrow sections of the canal, around bends, and near the Lockport Lock. The canal has been in service since the extension of the CSSC to the Lockport Lock in 1905. Besides the major rehabilitation performed in 1924, maintenance has been limited to access road maintenance and occasional check-post repair. The wall is severely deteriorated as a result of age, heavy usage, and antiquated materials (see Figure 14). This is evidenced by the visible concrete deterioration, investigative coring, and the numerous areas of seepage. A structural reliability assessment created immediate concerns of wall stability and loss of pool. Figure 14. Typical Canal Wall Monolith Showing Deterioration and Concrete Loss Proposed Repair As part of the RER, it was determined that the 2.1 miles of canal wall immediately upstream of the Lockport Lock posed the greatest risk and should be repaired. Recall that the height of the wall decreases upstream as the depth to bedrock decreases. Near the lock, the wall is approximately 38 feet tall whereas 2.1 miles upstream it is only 20 feet tall. Additionally, the average elevation difference between the upstream pool and the downstream canal is 39.5 feet at the Lockport Lock. Original Concept: The RER recommended an anchoring concept that relied on the structural integrity of the original 1890s lime cement concrete (see Figure 15). This concept included removing the deteriorated concrete surface of the concrete that was 1138 Collaborative Management of Integrated Watersheds