This article will address the role of a geotechnical site investigation for a successful trenchless project. First let’s define what is meant by a trenchless project. Trenchless construction is a group of pipeline construction methods that are an alternative to traditional continuous open cut. Trenchless does not mean no excavation as the first thing that will show up on a construction site is an excavator or backhoe. Trenchless pipeline construction methods are commonly classified as new construction methods, online methods and pipeline renovation methods.

New construction methods include auger boring, pipe ramming, jack and bore, horizontal directional drilling (HDD) and microtunnelling. Not included is large diameter and high-cost (tens of million dollar) tunnelling projects such as transportation project (subways, railways, roads, etc.) or hydro projects. Online replacement construction methods use an existing pipe as a pathway to install a new pipe. Pipe bursting or pipe splitting are trenchless online methods. Pipeline renovation methods use the existing pipeline as a form to construct a new pipe within a pipe. Cured in Place Pipe (CIPP) and slip lining are common trenchless pipeline renovation methods.

You can see from the above that the term “trenchless project” is an all encompassing term and that the geotechnical considerations will be completely different for a new construction, online and renovation project. For this article, I will only focus on the geotechnical considerations for trenchless new construction projects.

Now that we have a better understanding of what is a trenchless project, we need to make sure we have a clear understanding of the reasons for obtaining geotechnical information for a trenchless new construction project.

The first reason is so the engineer of record can design the project to meet the owner’s requirements and specifications, i.e., a gravity sewer, low pressure forcemain, or watermain. For a typical engineer designed and tendered, project the engineer must establish the pipeline location within the subsurface, prepare the tender documents and design drawings, and provide the owner with expected project bid costs–the engineer’s estimate–so sufficient funds can be allocated by the owner to complete the project. Project construction costs will depend significantly on the site’s ground conditions (i.e., excavation of bedrock or soil, site dewater requirements) and the pipeline trenchless construction method, e.g., microtunnelling cost per metre will be significantly high than auger boring and pipe ramming.

Case law also requires that the engineer of record must also ensure the design and project is constructible. For example in the 1979 decision by Manitoba Queen’s Bench: Trident Construction Ltd. v. W.L. Wardrop and Assoc. et al. it highlights the need for the engineer to properly specify the design. In this case the judge sympathizes with the contractor, and rules that engineers have far more time to prepare initial specifications than contractors have to ensure that a reasonable interpretation of vague specs is accurate enough when bidding. It should also be noted that the Engineering Act requires the engineer of record—the engineer that stamps the design drawings and tender specifications—to be an expert in the area of practice. This means the engineer of record must be able to establish themselves as an expert in trenchless construction design.

The second reason for geotechnical site investigation is so the contractor can bid the tendered project at an reasonable cost. The contractor bid cost will mainly depend on the means and methods required to complete the project as designed and estimation of the number of work hours. Contractors also price project risk. For example, in a lump sum contract if there is no geotechnical data the contractors will provide a high contract price to cover uncertainty and risk in the means and methods required to complete the project. Having no geotechnical investigation will also produce scatter in contractors’ submitted bids. If good geotechnical data is provided in the tender that can reduce contractor uncertainty and risk, then submitted contractor bids will be lower and have less scatter. In 1984 the Subcommittee on Geotechnical Site Investigations, U.S. National Committee on Tunneling Technology (USNCTT), published a report “Geotechnical Site Investigations for Underground Projects”.

In this report the committee reviewed original data from 87 case study projects. Figure 1 shows the Contractor’s Bid as a percentage of the completed project versus the boreholes in linear foot per route foot of tunnel alignment.

This report states that the ascompleted cost can differ significantly (±50 per cent) when the level of effort or funds devoted to geotechnical site investigations are low. The deviation between as-completed and the estimated costs decreases as exploration increases and the engineer estimate becomes a more reliable tool for predicting actual costs when sufficient exploration has been completed, more than 0.6 linear foot per route foot. At this point a substantial reduction is reflected in the frequency and degree of scatter in the estimate.

The reason for the high variation is that the contractor is pricing risk and uncertainty in the project. You will note that for one project where very little geotechnical data was provided and the contract bid was approximately 172 per cent greater than the completed cost.

This means for a USD 1,000,000 project, the owner paid the contractor USD 1,720,000 which is USD 720,000 over the actual project cost. In cases where the contractor bid is significantly lower than the actual cost there is an increased probability of a contractor claim and litigation in an attempt to recoup the loss. Although the USNCTT 1984 report cases are for mined tunnels the same construction issues and processes will apply to trenchless projects–these are also underground projects.

So let’s recap. The engineer of record needs geotechnical data to design and estimate the project cost and the contractor needs geotechnical data to determine means and methods and to prepare an accurate bid price which is often lump sum.

The ultimate cost of projects can be estimated accurately and controlled or moderated without sacrificing fair compensation to the contractor. These are attainable when the site investigation program is conducted at a sufficient level to permit a thorough evaluation of the subsurface by all parties to the construction process and according to their specific needs. It should be noted that a geotechnical investigation can not predict every problem that may be encountered, and attempts to do so generally result in projects that are disproportionately expensive for the value received. For every underground project, cost-benefit is a key element. Increasing the level of effort and funds for exploration is demonstrably beneficial and cost-effective to ensure accurate tender bids, reduced claims and litigation, and for the projects to be completed on time and on budget.

Sufficient Geotechnical Investigation

In mined tunnel projects the cost to complete a sufficient level site investigation typically ranges from one to two per cent of the total project cost. In some complex projects the site investigation cost may be increased to five per cent of the total project cost. In projects where a sufficient body of information is available to understand the site conditions the site investigation cost can be less than one per cent. The cost to complete a sufficient level of site investigation is very low and as shown above it will be money well spent generating cost savings.

Since there is no universal project there is also no universal amount for site investigations that need to be completed. The geotechnical site investigation must be proportionate to the project size and expected trenchless construction methods, i.e., auger boring, pipe jacking, directional drilling or microtunnelling. A good guide for practitioners is the recently updated Standard Design and Construction Guidelines for Microtunneling, Standard ASCE/CI 36-15, which covers the planning, design, materials, and construction. New sections in this standard have been added on sustainability; regulations; detailed site investigations, especially geotechnical aspects; microtunnelling design elements and operations; construction support services; and aspects of measurement and payment.

Another good document for consideration is ASTM Standard F1962 Standard Guide for Use of Maxi-Horizontal Directional Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles, Including River Crossings. This document states the following, with respect to test borings’ locations, “boreholes should be located at a sufficient lateral distance (to either side) from the proposed bore path to avoid boring into the test hole, and the holes should be sealed with grouting to avoid potential leakage paths for drilling fluid during the actual installation.” This is very different to an open cut project where boreholes are often constructed on the pipeline alignment.

Data collection should be aimed at identifying earth materials at the site and exploring subsurface stratification (including identification of the boundary between rock and other strata, presence of cobbles or boulders and other anomalies such as old tree stumps and fill debris), soft ground conditions, rock conditions, mixed face conditions, groundwater conditions, potential buried objects, potential for naturally occurring gas such as methane and hydrogen sulfide, contaminated groundwater or ground and man-made and environmentally sensitive features. If bedrock is near or within the tunnel design invert bedrock must be proven by coring and testing completed to determine equipment constructability at, near or within the bedrock/soil interface. Geotechnical testing should also be completed to classify the rock strength. The investigation should also focus on identification of potential show stoppers – boulders, cobbles, running/flowing soils, artesian pressures, wood, fill, debris and or old foundations.

For large projects the engineer of record should consider having a Geotechnical Baseline Report (GBR) provided with the tender document. Details on how to prepare a GBR are provided in ASCE 2007 Geotechnical Baseline Reports for Construction: Suggested Guidelines. This book examines the role of the GBR as a means of allocating and managing subsurface risks associated with subsurface construction. It discusses the importance and benefit of ensuring compatibility between the GBR and other contract documents, as well as, the importance of involving experienced firms and individuals in the preparation and review process.

Legal Concerns

Over the past numbers of years, I have been retained as an expert in numerous trenchless litigations cases in Canada and the US. Based on this experience I have developed a list of top reasons why lawyers get involved in construction projects.

1. Project size and claim – the bigger the project the higher the probability of a bigger claim. The project needs to be big enough to cover the cost of lawyers and litigation. Litigation is expensive with lawyer rates being USD 750 per hour or higher. Compare this to a senior engineer whose upper limit is USD 250 to 300 per hour. Litigation costs can easily exceed hundreds of thousands of dollars before going to trial.

2. Polarization between parties – Projects have many different players: owner, design engineers, contractor and its subcontractors, and quality assurance/project engineer. If polarization happens between these parties, the potential for litigation increases especially with payment hold backs.

3. Bad/poor design – I have reviewed many tendered designs that are not constructible. One contractor told me that “if I only bid projects that are constructible I would have no work. I bid the job knowing I have to change them to make them constructible.” Getting the design changed is not an issue when all parties are working together to get the project done.

4. No resolution process or not following the resolution process – Many tender specifications have no dispute resolution mechanisms or if they do they are not followed. If this is the case the contractor has no other option but to get a lawyer involved.

5. “The God Syndrome” – This is a common issue where a technician or engineer thinks they know more than the contractor. Trenchless projects are completed successfully every day by specialist trenchless contractors. These people are very experienced. Engineers and technicians on the other hand often have limited experience or do a couple projects a year. I have seen cases where the inspector, who knows nothing, actually believed they knew everything and that the contractor knew nothing. This is not a good formula for a successful project.

6. Poor or no geotechnical site investigation – ground conditions are nothing like what was expected. More often than not someone decided to save money and not to do a proper geotechnical site investigation by not drilling deep enough, not getting the drill rig on, near or in the creek or river bed, not probing bedrock, etc. Thus, they hope the boreholes on the roadway or some other convenient location will represent the ground conditions adjacent to the roadway but they do not.

7. Engineers/owner do not want to admit they made an error. I have seen this many times. The engineer of record does not want to admit, especially in front of their client, that they made a mistake in the design or specification. If the case goes to litigation rest assured that error will be highlighted, so it is best not to dig your heels in, and get the project corrected for everyone’s sake.

8. False belief you can write everything into a tender document and hold the contractor to it. Here are some classics.

  • Contractor is not to rely on the geotechnical report for bidding. If the geotechnical report was good enough for the engineer of record to design the project, complete a construction feasibility and the engineer’s estimate, then why is it not good enough for the contractor to use in preparing their bid? This clause most likely will not stand up in court.
  • Contractor is responsible for doing their own geotechnical site investigation. Most projects are tendered with the contractor required to provide a detailed bid submission in as little as three to 15 days. In this time period, it is impossible to get access to the site and if required to obtain permits. Once again this clause will most likely not stand up in court.
  • I can specify everything in the geotechnical report and the tender documents to cover everything that could possibly happen. Once again this is not engineering as it should be and will drive costs up for the client. What happened to fair and reasonable risk sharing?

9. Your lawyer says you have a strong case. Lawyers get paid for their services and have no incentive to tell you that you have no case. I have seen the this happen many times, especially in cases where it was obvious that the other side messed up. In fact, it is often in the best interest for a lawyer to drag it out as long as possible to maximize their fees and to see if the other side will screw up. You need to remember you need to be only 50.1 per cent correct to win in court. In the end a judge must decide whom they believe the most, from which comes the 50.1 per cent.

In summary trenchless pipeline projects are very different than traditional open-cut pipeline projects and are more similar to mined tunnel projects. These projects require experienced and specialized design engineers to make constructible designs and prepare reasonable tender specifications. The work also needs to be completed by an experienced, specialized trenchless contractor. Without a proper and complete site investigation the engineer of record cannot properly design the project and the contractor cannot properly determine the means and methods and prepare a realistic bid price.

The key to having a successful project – done on time and on budget – requires all parties to understand that there are unforeseen construction risks in all trenchless projects, to have a proper risk sharing model, and a fair and reasonable way to resolve contractor claims and disputes.

Please remember that a geotechnical site investigation will save you in construction bid and claims and is the best 1 to 2 per cent of the total project cost you can spend, as it is a lot cheaper than lawyers and litigation.