Recently Susan Pastor with the U.S. Environmental Protection Agency wrote an article in the Spring 2012 edition of the Fox River Current titled “Latest Technology Guides Hydraulic Dredge”. The article was about the use of a Real Time Kinematic Global Positioning System (RTK-GPS) to aid the dredge operator in removing contaminated sediments from the Fox River in Green Bay, WI. In the article she writes about the use of the system and how it improves the accuracy in which a dredge operator can remove targeted sediments to designated depths. These operators can view their progress in real time using pricey, high accuracy equipment.
The reason a system like this is so beneficial to environmental dredge projects is because it can substantially reduce the overall cost. Due to the high cost of treatment and disposal of contaminated sediments, it is imperative that the quantities be minimized. Taking clean, underlying soils with the contaminated sediments will only inflate the overall cost of the project because once mixed, it all needs to be treated. The RTK-GPS system used in combination with customized software, positioning sensors, and an experienced operator are necessary to effectively remove all the contaminated sediments, while minimizing removal of clean sediments.
This theory goes against the grain of the entire concept of dredging. Since its inception, the goal has always been to remove as much material, as fast as possible. It is known as maximizing production. However, to maximize production in environmental dredging, one must surgically remove these sediments as efficiently as possible. High-accuracy equipment, such as RTK-GPS, and an experienced operator are the best ways to accomplish this extremely difficult task.
Preplaced aggregate concrete (PAC) is not a new concept. In fact it is a method of concrete placement that has been around since the late 1930’s. However, it is often overlooked as an option to repair dams and bridge piers. In fact, it is one of the most effective forms of underwater concrete repair.
What’s the difference?
Conventional concrete is placed as a composite aggregate and cement-grout mixture. This means the aggregate and cementitious grout components are combined before the concrete is placed into formwork. PAC is different than conventional concrete methods because its components are placed in separate steps. Like the name implies, the aggregates are placed before the grout mixture. This leads to several advantages.
Advantage #1
Because the aggregate is washed and placed into the formwork before the grout is injected, the aggregate-to-cement ratio is maximized. According to the American Concrete Institute this reduces shrinkage which can lead to higher bondability with existing concrete surfaces. Higher bondability and less shrinkage results in less cracking!
Advantage #2
Another advantage is that PAC disallows material separation when being placed, especially when the formwork is partially or fully submerged in water. Once the aggregate is placed, grout injection begins at the bottom of the formwork, and progresses vertically at separate injection points. Any water in the formwork is displaced as the grout fills all the voids between the aggregate, creating a homogenous mixture. A homogenous mixture leads to a stronger repair!
Advantage #3
Finally, when placing PAC, there is little need for heavy equipment. The aggregate can literally be washed into place using a sluice pipe. Then grout can be injected using a grout pump. This is especially beneficial on small bridge pier or dam repair projects because most of the equipment can be left onshore. Materials are transported to the repair site through temporary PVC sluice pipes and grout hoses. Fewer pieces of equipment will lead to a lower cost repair!
It is inevitable. Over time a river will dig out the land over which it flows. That’s why we have valleys, coulees, and scour problems on every structure we place in its path. As James Eads would mostly likely attest, rivers cannot be fully tamed and scour repair will always be a constant struggle for anything set in their way. Bridge piers are one of the most vulnerable structures to scour problems.
This leads to the periodic ritual of performing underwater inspections to ensure the bridge’s structural integrity remains intact. Traditionally completed by trained divers, the process can be frustrating because underwater visibility is often very limited. Scour damage and voids can be missed easily, or even worse, miscommunicated by the diver. Also, areas covered in rip rap can hide critical problems developing underneath. There is a solution that can create a detailed image of the underwater portions of the bridge pier and any scour problems around it.
A sector scan can capture an acoustic image of the pier that will most often show any areas of concern. This image will help pinpoint areas that require diver concentration. It can be included in inspection reports to show potential problems and potentially can eliminate the need for a full diver inspection altogether.
Sector scans can be carried out easily with a two-person crew and small work boat. The images can be captured quickly and digitally combined with above-water photos to create a composite image of the entire structure. The next time you are thinking about a bridge pier inspection, consider a sector scan.
Can you guess what's wrong with this bridge???
Posted by
Ryan Olsen on Fri, Apr 27, 2012 @ 08:21 AM
One of the key elements that all construction companies will face is how to prepare their crews for potential emergency situations at remote worksites. As a
Health and Safety manager, an everyday important component for managing the safety of its crews, regardless of their size, is preparing them for potential emergency situations. There are many considerations that go into to each unique job and each must be analyzed separately.
Therefore, it’s important to be
involved in every stage of the work activity. Get involved during preconstruction meetings and during job startup to become more familiar with the scope of work and the environment. It’s important to visit the jobsite during the initial stages of construction to analyze what types of emergency scenarios can be predicted. After that, regular site visits and updates from the site will help identify new or existing concerns and issues. Below are three key elements to consider when preparing for emergencies at remote worksites.
1. Identify and anticipate potential hazardous conditions relevant to the site
- Adverse Weather – Is there likelihood for tornadoes, temperatures extremes, strong winds, flooding, snow storms?
- Air quality or Visibility issues – will this play a factor and increase the danger of the tasks being performed?
- Potentially hazardous tasks being performed – Is the work being performed in a dangerous environment or one that has various exposures?
- Size of the crew and worksite – Is the site large and spread out and are there enough people around to know if someone is missing or needs emergency care?
- Methods of communication – if emergency assistance is needed, how will you contact responders or other crew members? Are 2-way radios available or do cell phones have service?
- Response time – In remote locations, the time it takes for responders to arrive might be lengthy. Are you able to respond to an emergency until responders arrive?
- Difficult access to worksite – Accessibility for emergency responders may be an issue. Are you familiar with the area and can direct responders to your location if needed and no address is available?
2. Analyze each situation that might lead to an emergency
- What emergency supplies may be needed in this scenario?
- What is the likelihood and severity of the potential incidents?
- Do they have a safe storm shelter or a place to hide from the elements?
- What are the surrounding conditions? Does the worksite present additional chemical or biological hazards?
- What type of emergency evacuation equipment should be available?
- How should we respond and where do we go in case of a fire?
- Talk to the crews and get input about what concerns they may have.
3. Prepare the site and workers with the appropriate training and supplies
- Have crews trained in CPR/AED and First Aid
- Locate an emergency shelter or safe location close to the work area
- Make the necessary equipment readily available - Fire extinguishers, spill kits, first aid kits, trauma kits, backboards, stokes basket, emergency rescue equipment.
- Identify phone numbers of local emergency responders, the closest hospital and an emergency plan if something occurs.
- Lastly, prepare crews for emergency situations and provide them with the appropriate tools to respond to various situations.
Due to their importance, the condition of water-based structures should never be taken for granted, nor should the methods in which they are inspected. Periodic underwater inspections are crucial to keeping your structure safe and dependable. Make certain that the dive teams you work with have the experience and know-how to provide you with all the information you need to ascertain current conditions of your structures by keeping three simple things in mind:
1. Divers need to be more than just divers - they need to have underwater construction experience
2. Reports must be clear, concise, and transparent - use a combination of options to analyze the condition of your structure.
3. There is always more than one solution to every problem - your dive team should be able to suggest a few effective solutions.
1. Divers need to be more than just divers
Have you ever had an inspection done by a diver who was not familiar with the structures in which he or she was inspecting? This is not an unusual experience for many railroads, utilities, or paper mills. Often times, to give clients a bit more confidence, many firms put a licensed PE in the boat to oversee the underwater inspection. This does not translate to a higher quality inspection, only a more detailed analysis of available information. To ensure you are getting the most for your investment, make sure that the divers have the necessary experience to conduct a thorough investigation of each area of concern.
How do you know when you may be relying on an inexperienced diver? Simple! There are several things you can look for during the interview and bidding process. First, if you are dealing directly with a dive firm, ask them about their construction experience. Do they only focus on inspections and salvage, or can they actually carry out the underwater repairs? An inexperienced diver may see a large void, but could have trouble discerning areas of weak and degraded concrete and masonry.
Second, ask the dive firm or engineer you are working with to provide credentials. Are they certified to carry out the inspection? Have they done this type of work in the past? How long have they been inspecting structures? This seems like an easy step, but is often overlooked when working with an engineering firm. In this case divers are usually subcontracted to perform the inspection. Remember, the PE is typically in the boat, not doing the inspection.
Finally, although price is always a factor, do not forget about value. If you are getting a PE and dive crew for fraction of your budget, red flags should be going up. This is usually a sure sign that the divers are temporarily subcontracted to carry out the inspection and have little experience to back up their methods. As the old saying goes, “You get what you pay for”.
2. Reports must be clear, concise, and transparent
Unless you are doing your own diving, you could be at the mercy of the diver inspecting your structure. He or she is your “eyes underwater” and must provide you with the information you need to effectively repair your structure. Don’t be left with just a short description of the dive, make sure you have video, drawings, photos, etc.
Also, make certain you or your engineer has access to the dive operation while it is underway. If the water is clear enough you should have a live video and audio feed to see what the diver sees. You should be able to talk with the diver and the attendant and be part of the process.
Finally, an underwater inspection should not only be confined to just diving. There are several tools that can complement a dive to provide a complete picture of the current condition of any structure. For instance, sector scans can provide underwater imaging in even the most turbid conditions, ROVs can access hard-to-reach areas or be used in hazardous conditions, and finally bathymetric surveys can be used to model channel bottoms and submerged structures. Confirm whether or not your dive firm is offering you several options.
3. There is always more than one solution to every problem
As any engineer will tell you, there is always more than one solution to every problem. However, make certain you have the information to determine which one is BEST! This is where a diver with underwater construction experience becomes so important. When the inspection is complete, and you have the report in hand, does it have a section outlining recommended solutions? A diver with construction experience can provide you with a few suggestions on how to fix the problem, and usually recommend one that will be the most cost effective.
Reduce the number of unknowns by using a diver that can actually carry out the repairs. So many dive firms have experienced divers, but not individuals with underwater construction experience. Save yourself the time and headaches and select a firm that specializes in not only diving, but underwater construction and inspection.