Amendment 0001 Report for the Determination of Ground Vibration Limits_Final.pdf

Report for the Determination of Ground Vibration Limits at Soo Locks

EXECUTIVE SUMMARY

Precision Blasting Services (PBS) has been requested to develop vibration level constraints for the Soo

Locks Expansion project. In this report, PBS has analyzed the critical structures and focused solely on the ground vibration that the structures can be subjected too, with the intent that any risk of damage be avoided. All residential structures will be limited to the modified U.S. Bureau of Mines Z‐Curve, the ground vibration at the location of the piers for the International Bridge and the CN railway bridge are recommended to be set at a conservative 5 in/s regardless of frequency. Massive concrete which has aged for at minimum 10 days will be limited to 10 in/s. The powerhouse at unit 10 will be limited to 1 inch per second regardless of frequency. The fish spawn area in unit 10 will be limited to 0.75 in/s.

RESIDENTIAL STRUCTURES

Residential structures have been thoroughly studied in the United States and elsewhere in the world for effects of damage due to ground vibration from blasting events. In the United States, the majority of this work was conducted by the U.S. Bureau of Mines (USBM) cumulating in the Report of Investigation (RI)

8507, which provided charts for damage criteria to typical residential structures. With residential structures, two classifications of damage exist:

1. Minor Damage

2. Major Damage

The damage to these structures was based on crack extension of previous cracks, which were monitored with strain gauges and in most cases not visible to the naked eye. This can be considered cosmetic damage and from a damage classification is considered minor damage – or damage which does not weaken the structural integrity of the structure. This damage is correlated to the peak particle velocity (or the maximum velocity of movement) from a blast and the frequency at which this vibration moves. At low frequency, much less vibration is required for minor damage whereas high frequency motion requires much higher levels of ground vibration in order to produce damage. The USBM issued a chart in RI 8507 which was correlated the ground vibration and frequency to understand the minimum levels required to induce damage from blasting ground vibration. This is known in the blasting industry as the Z‐Curve and is a standard in limiting ground vibration near residential structures. This will be the limit for all residential structures (and private corporate buildings) near the project. Figure 1 shows a map of the project with three of the critical buildings that will require this limit; however, this map is not all encompassing and the contractor must understand how their blasting may effect other structures in the area.

Figure 1 ‐ Residential Structures near Blasting

INTERNATIONAL BRIDGE

The International Bridge is a competent, rigidly built bridge that has piers anchored on bedrock on either side of the canal. The individual piers are likely to withstand any damage at blasting loads at 10 in/s which is the limit on this project for massive concrete. The bridge span currently functions with large amounts of traffic and is elevated well above the blasting area. The bridge span will likely experience less vibration from blasting than it experiences during normal daily activities due to the large attenuation of vibration through the bridge piers. This bridge poses minimal risk to the project; even with blasting occurring 15’ to

20’ away. However, due to its close proximity to the railway bridge a limit of 5 inches per second at any frequency is recommended.

CN RAILWAY BRIDGE

CN has exhibited large concerns of the railway bridge that is near the project and expressed concern over damage due to ground vibration levels of the bridge. In order to develop vibration criteria, seismographs where installed on the ground near the base of the bridge piers and then on the bridge tower to assess background vibration levels for both the bridge and the ground. Through two weeks of study, the maximum vibration levels have been compiled from hundreds of events and are shown in Table 1.

Table 1‐ Maximum Vibration Levels from Background Monitoring on CN Railway Bridge

MAXIMUM VIBRATION MAXIMUM DISPLACEMENT

BRIDGE TOWER 2.5 in/s 0.324 in GROUND NEAR PIER 0.15 in/s 0.003 in

As can be observed from table 1, the bridge naturally undergoes 2.5 inches per second of ground vibration from normal activities with a total displacement of 0.324 inches. While the blasting industry utilizes ground vibration as a measure of damage, it is important to understand that the true measure of damage is the displacement of a structure, or the strain of the structure. In this case the use of the bridge generated a displacement of 0.324 inches in the bridge; whereas typical blasting has displacement levels of 0.001 inches to 0.0001 inches. This is because the frequency of blast waves is high compared to normal vibrations leading to a higher velocity but lower displacement.

Additionally, major dampening can be observed between the ground and the structure. This works in both directions, not necessarily to the same magnitude, but when ground vibration is experienced by the bedrock and the bridge piers it will be dampened as it moves towards the structure. While it is impossible to know the true magnitude of dampening of a structure, it is significant. This would mean that the ground vibration would be significantly reduced from the ground to when it reaches critical areas of the structure.

Finally, the motion of the structure is considered quasi‐static when compared to blasting vibration. In many cases the vibration from train passing or bridge movement can last seconds to minutes whereas ground vibration typically lasts under two second. Material exhibits much higher strength when under dynamic, fast loading and in many cases can be subjected to 3 to 4 times the total load of a quasi‐static state.

With all these considerations, Precision Blasting Services feels that an extremely conservative limit for this structure is 5 inches per second.

CONCRETE

Two forms of concrete are possible to experience on a construction job that can be impacted by ground vibration. The first is green concrete, which depending on how long after it is poured, will exhibit different effects from ground vibration. Immediately after pouring, the concrete is still liquid and can withstand upwards of 2 inches per second of vibration. As it begins to harden, the concretes resistance to vibration is reduced until it eventually builds up to the limit of normal concrete. The table for green concrete vibration levels can be seen in Table 2, were frequency has no effect on the damage.

Table 2 ‐ Green Concrete Ground Vibration Levels

VIBRATION LEVELS FOR GREEN CONCRETE/SHOTCRETE

TIME AFTER POUR ALLOWABLE PPV (in/sec)

0 - 4 Hours 2.00 4 - 24 Hours 0.25 2 - 3 Days 1.00 4 - 7 Days 2.00 8 - 10 Days 5.00

Over 10 Days 10.00

Damage to cured concrete from ground vibration due to blasting has been extensively studied, including on projects which blasting is occurring directly in the concrete. In many cases cured, massive concrete has been known to withstand over 150 inches per second to 300 inches per second of ground vibration without problems. However, the typical limit placed on massive concrete is 10 inches per second. In addition to this, numerous other common structures have been studied and their ground vibration limits are shown below in Table 3.

Table 3 ‐ Concrete and Other Structures

STRUCTURE TYPE ALLOWABLE PPV (IN/SEC)

Standard Construction Timber Frame, Brick, and Concrete Buildings 2.0

Reinforced Concrete Structures 4.0 Steel Structures 4.0 Buried Utilities 2.0 Wells and Aquifers 2.0

Steel Pipelines 5.0

Massive Concrete Monoliths (Cured Concrete), Shotcrete 10.0

POWERHOUSE UNIT 10

The powerhouse in Unit 10 is in deteriorating condition and a full structural analysis has not been conducted. While this is likely built to withstand more ground vibration than a typical residential structure, it is in the best interest of the COR to protect this structure and without a structural study to determine current condition Precision Blasting Services would recommend that a ground vibration limit of 1.0 inches per second be placed on the Powerhouse. As the fish spawn is nearby with a lower vibration limit it is unlikely that this level would be controlling to the contractor and is highly unlikely to cause any damage.

FISH SPAWN UNIT 10

The fish spawn at unit 10 is a controlled structure to prevent the breaking of fish eggs which are laid in the gravel. As this is of major concern to the environmental groups near the project, a conservative limit has been placed of 0.75 inches per second. In a majority of situations, a vibration of over 5.2 inches per second was required in order to break Salmonid eggs. Lake Trout eggs have reported no problems to blast vibration as high as 1.1 inches per second. While some guidelines such as the 1992 Alaska Department of

Fish and Game have limited ground vibration to 0.5 in per second for salmon eggs, this has been viewed as an unnecessary limit with a factor of safety well over 10. However, with the critical nature of the spawning ground and environmental impacts Precision Blasting Services recommends that while eggs are present – especially in early stages of development – the ground vibration be kept below 0.75 inches per second which will not dramatically alter the course of the project but ensure protection of the eggs.

CONCLUSION

The Soo Lock expansion will have multiple ground vibration limits imposed based on the type of structure.

The structure(s) of concern which will limit the ground vibration at site may be constantly changing depending on the contractors work area. Multiple seismographs will be needed on‐site with, at minimum, one being located at each vibration concern. In addition, PBS would recommend that the contractor has at least two moving seismographs to be set up at the USACE discretion. PBS would also recommend that the contractor start the project by using a predicting equation for construction blasting to limit the initial weight of explosive per 8ms delay (and the scaled distance) and as the project progresses develop daily linear regression vibration reports to predict site specific ground vibration before the shot. This should be documented on the contractors Daily Blasting Plan submittal. The following list is the ground vibration limit recommendations for the blasting specification for the Soo Lock project:

Residential Structures – Follow USBM Z‐Curve

IBA Bridge at base of Piers – 5 inches per second

CN Railway Bridge at base of Piers – 5 inches per second

Unit 10 Powerhouse – 1 inch per second

Fish Spawn in Unit 10 – 0.75 inches per second

This report has been developed by Precision Blasting Services for the United States Army Corp of Engineers for the Soo Lock Expansion Project. Please direct any questions or concern to Anthony Konya at

Anthony@idc‐pbs.com.