Avoiding Differing Site Conditions For A Microtunneling Project (Part 2) – The Contractor’s Responsibilities

The Introduction and Part 1 of this paper discussed the importance of including a Differing Site Conditions (DSC) clause in the Contract Document for an MTBM project and the responsibilities for the project Owner and its Designer to prepare the contract document in a manner that minimizes the possibility for encountering a DSC during construction. In concluding Part 1, it was stated that “when all is said and done, the Owner must assume that if the Contractor does everything as provided for in the contract document, then the project will be constructed for the cost and within the timeframe established by the Contractor’s bid.” Based on the above and the authors’ experience with designing and observing the construction of MTBM projects, the primary purpose of Part 2 is to discuss the Contractor’s responsibilities for preparing its bid based upon a “reasonable and prudent” interpretation of the work required to be accomplished as defined by the contract.

The contract document for a tunneling project typically consists of five parts as listed below:

  1. The General and Special Provisions,
  2. The Plans,
  3. The Specifications,
  4. The Geotechnical Data Report (GDR), and
  5. The Geotechnical Baseline Report (GBR).

The General and Special Provisions establish the framework for preparing a bid and it is beyond the scope of this paper to discuss all of the issues associated with those provisions. Foremost for this paper is consideration of the contractual status for the geotechnical reports, the DSC clause, the designer’s status during construction, the requirements for filing a claim, and the contractual provisions for the resolution of disputes. When reviewing the above contract provisions, it is necessary for the Contractor to decide if the Contract Document does, in fact, represent a desire on the part of the Owner to work together with the Contractor in a fair and equitable manner in order to produce a successful project outcome. Insofar as that is not the case, then the Contractor must think long and hard about how to prepare its bid based upon any perceived shortcoming in the contract. If necessary, the Contractor should be prepared to walk away from the tender if onerous language presents unbalanced risk.

Next on the list of Contractor responsibilities with respect to the purpose of this paper is to look at the project plans for the size, shape, depth, location and alignment of the underground openings that need to be constructed. Frequently, those drawings will also show the minimum requirements for supporting those openings in a safe and stable manner, which for a microtunnel will typically include the size and design assumptions for the pipe needed to advance the MTBM and for the minimum types of soil and rock supports required to construct the entrance and exit shafts as well as any needed ground improvements.

Having the above firmly in mind, the next and, without a doubt, most important evaluation that needs to be accomplished by the Contractor is a critical and thorough evaluation of the GDR; i.e. not the GBR. The GDR tells you everything that you need to know about the ground conditions that will be encountered during construction from a straightforward and factual perspective. The GDR should also include an “accurate” discussion of the geologic setting for the ground conditions revealed by the subsurface investigations. In essence, it is the subsurface investigation that sets the stage for all of the decisions that need to be made about how to construct the underground openings and about how much it will cost and how long it will take. It is from the GDR that the Contractor should evaluate:

  • MTBM production rates
  • Required jacking capacity and number of Inter-jacking stations
  • The cutterhead configuration of the MTBM
  • The type of casing or direct jacking pipe if the specifications allow
  • Lubrication; type, location and rate of injection
  • Evaluation of risks such as surface settlement, heave, and inadvertent returns

Sometimes the contract document will suggest and/or require the Contractor to retain the services of a geotechnical engineer or engineering geologist to help provide an “independent” assessment of the thoroughness and adequacy of the subsurface investigation and the authors of this paper see great benefit with that approach. As stated above, the GDR sets the stage for all decisions about what types of ground will be encountered and about how that ground will behave and/or interact with the MTBM being used to advance the tunnel but the Contractor may need some help in developing its own, independent opinion about how those encounters and/or interactions will unfold during construction.

Having accomplished the above, the Contractor can then turn its attention to the GBR and to the project specifications to see if those documents are 1) in accordance with the Contractor’s opinions about how the project should be constructed, and 2) if they provide a reasonable and prudent interpretation for those construction requirements. In essence, the GBR and the project specifications, combined, should provide one clear and consistent explanation of what the Contractor is obligated to accomplish during construction. Quite often the Owner will provide minimum requirements for various construction procedures and/or ground improvement activities that go beyond what the Contractor considers necessary, but that is OK as long as the Contractor will be paid for doing that work. At other times, the Owner will provide unit price or cash allowances for various activities that would be difficult for the Contractor to estimate.

No one wants to encounter a DSC on a tunneling project and very few contractors bid low on a project expecting to make up the difference with change orders or claims. More often than not, the Contractor is the low bidder for a project because he/she already owns the required equipment, is local and has favorable relationships with suppliers, has experienced crews available to do the work, and/or has completed other projects in similar ground conditions.

The next big issue that needs to be discussed as related to DSCs is contractor submittals. Project submittals are a mechanism to facilitate communication between the Owner and Contractor with respect to two important topics for a microtunneling project:

  1. The Contractor’s understanding of contract requirements, and
  2. The Contractor’s proposed means and methods for excavating and controlling the ground.

Upon the provision of a project submittal, it then becomes the Owner’s responsibility to review and “approve” that submittal with respect to contract conformance, i.e. does the submittal conform to the contract requirements as provided for in the project specifications. In general, and to accomplish the above, project submittals are divided into these subgroups: 1) Quality Control Plans and 2) Highly Technical Submittals.

The first type of submittals are the Quality Control Plans which are intended to explain how the Contractor intends to conform to the specified means and methods of construction such as:

  • Tunnel and Shaft Work Plans,
  • Water Control Plans,
  • Inspection and Testing Plans, and
  • Geotechnical Monitoring Plans

These plans can be used by the Owner’s CM team to oversee and manage the work being performed by the Contractor. Quality Control Plans will also reveal a lot about what type of ground reaction the Contractor believes will take place as a result of the specified means and methods of construction in the ground conditions indicated by the project GDR and GBR and very often it is those ground reactions that form the basis for a DSC claim on a microtunneling project. It is not possible to observe undisturbed samples of the soil or rock deposits being encountered during construction so the very first indication of a DSC will be how the MTBM is interacting with the ground. For instance,

  • The jacking force has increased dramatically,
  • The cutterhead torque has increased dramatically,
  • The rate of tunneling advance has decreased dramatically,
  • Pore water pressure has increased or decreased dramatically,
  • The MTBM is not responding to steering adjustments,
  • The type of soil or rock revealed by the excavated material has changed dramatically, or
  • The MTBM has been damaged dramatically by indication from the above points

If any of the above happens, then it is incumbent upon the Contractor to notify the Owner of a possible DSC and to begin assembling evidence in support of its claim, and it is at this point when the standard DSC clause reveals its limitations. As stated in Part I, it is typically not possible for either the Contractor or the Owner to actually observe the ground being encountered by the MTBM, unless it is a large MTBM with face access. Hence, the best indication of a DSC based on available project documents may be how the tunneling performance varies from the approved Tunnel Work Plan. Further confirmation of a DSC may only be possible based on additional subsurface explorations, but who should be responsible for doing those investigations based on the language contained within the DSC clause; the Contractor or the Owner?

Highly Technical Submittals are related to how the Contractor intends to control the ground either by the use of a specific piece of tunneling equipment or by the use of various ground improvement technologies such as construction dewatering, ground freezing, jet grouting, permeation grout, etc. These submittals also reveal a lot about how the Contractor expects the ground to behave and/or to react to a given tunneling technology. For instance, no one has performed a subsurface exploration in the ground that will be “improved” during construction so how should the Owner have provided a contract “indication” for ground that did not even exist prior to construction?

Another conundrum for microtunneling projects, is the status of a construction submittal after it has been “approved” by the Owner. Most of the published literature for construction submittals states that “approved” submittals do not become part of the Contract Document, but almost all of the published literature about project submittals is related to above-ground structures that do not come into contact with the ground. As an absolute minimum, when the Owner reviews and approves a Contractor submittal, then he/she has indicated that that submittal conforms to the contract requirements for each specified task. Hence, and if that tunneling procedure was performed in accordance with the submittal, then who becomes responsible for the resulting ground reaction?

The authors of this paper recognize that any bid for a tunnel project involves the evaluation of a huge number of logistical and risk assessments that have not been addressed in this paper. However, the primary objective of this paper is to address only those issues relating directly to the avoidance of a DSC claim both by the Owner during design and then by the Contractor during the preparation of its bid. It is possible, of course, than an actual DSC will be encountered during construction no matter what level of effort was expended during design and bidding, but it is still necessary for all parties to at least try, to the best of their ability, to keep that possibility to a minimum. Poorly performed subsurface investigations and/or poorly prepared contract documents, including the GBR, have no place in the procurement process for a microtunneling project.

One final issue that must be discussed is the contractual provisions for the resolution of DSC claims if one does occur despite all best efforts by all parties to avoid that possibility. Many tunneling contracts include provisions for the establishment of a Dispute Review Board (DRB) and the authors of this paper are in favor with that approach. Contractors must seriously evaluate an Owner’s past experience in working together with the Contractor in order to produce a successful project and Owners with a history of forcing every dispute into litigation should be approached with extreme caution. Litigation is very time-consuming, expensive, frustrating and replete with a variety of legal twists and turns that can never be fully anticipated in advance by the Contractor. In some cases the Owner is willing to spend enormous sums of money for attorneys and experts when a similar amount of money (or even less) could have be used to simply settle the claim and Owners with this type of mentality should be avoided.

Constructing tunnels is a risky business but only the Owner is able to benefit from its long-term investment in a tunneling project. Contractors that short circuit important project requirements and/or that do not perform in conformance with important contractual provisions should not be rewarded for their behavior; but it is best for all parties involved with a particular project to seek some middle ground. In conclusion, therefore, do everything in your power to avoid DSCs for a microtunneling project and then be prepared to work cooperatively in order to successfully complete each project.

Gary Brierley is President of Doctor Mole, Inc.; Todd Kilduff is President of Kilduff Underground Engineering, Inc.; and Becky Brock is President of Brock Geo-Consulting, LLC.

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