Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support

CHAPTER 8. CONTRACTOR PROCUREMENT

This chapter describes the types of contracting approaches that are generally used for developing DMM project specifications. Contractual responsibility should be divided equitably between the owner and the general contractor (GC) (or their specialty subcontractor, the DMM contractor), dependent on the experience of the owner with DMM technology, availability of qualified contractors, and the criticality of the application. The terms "owner's representative" and "engineer" in chapters 8 and 9 refer to the design professional who may be an employee of the owner or may be a subcontractor or subconsultant.

A hybrid approach between conventional method performance specifications is recommended in section 8.1. Typical measurement and payment items are listed in section 8.2, other potential contractual vehicles are presented in section 8.3, and contractor qualifications are discussed in section 8.4.

Method specifications and performance specifications lie at the opposite ends of the spectrum of contracting approaches with regard to allocation of responsibility (see figure 136).

Figure 136. Graph. General allocation of responsibility between owner and GC or DMM contractor based on contracting approach.

In a purely performance approach, the owner specifies the minimum performance requirements of the project, and the GC or DMM contractor develops the design and installation method for the DMM system to meet these specifications. The owner/engineer prepares documents that define the loading requirements of the structure (including groundwater containment) and performance requirements of the foundation (including factors of safety or load and resistance factors) and settlement tolerances. The bid quantities are obtained from specified pay limits noted on the plans, although the contractor determines the amount, arrangement, and properties of the deep mixed ground necessary to satisfy the performance requirements. The owner/ngineer identifies the basis for detailed designs through calculations and working drawings in a special provision. The special provision must clearly identify the required submittals and schedule to be prepared by the GC including construction control and monitoring. These submittals must be reviewed and approved by the owner/engineer

In a purely method approach, the owner/engineer performs the design and specifies the scope of work, installation, and QC/QA requirements of the DMM system. The owner/engineer develops a detailed set of plans and specifications, which are incorporated into the project bidding documents. The equipment, materials, and installation techniques for the DMM are prescribed to meet the embankment or structure foundation support requirements. In this approach, the contractor is not responsible for performance of the DMM system or any of its components. For example, in a purely method approach, the DMM contractor is not responsible for the strength of the deep mixed ground. During the bidding process, GCs develop a firm price proposal based on the owner's detailed plans and specifications.

Regardless of the approach used, the owner must have in-house engineers or consultants experienced in DMM design and construction to review these bids and submittals.

8.1 Recommended Contracting Approach

The most appropriate approach is one that equitably distributes the responsibilities and risks between the owner and contractor. For deep mixing projects, the recommended approach is a hybrid or combination method in which the owner performs the overall design but relies on the contractor to define the means for achieving the required deep mixed material strength. As in a method approach, the owner conducts the design of the deep mixed embankment or foundation support in accordance with the procedure outlined in chapter 6 and specifies the strength of the deep mixed ground and the layout and geometry of the deep mixed elements, as outlined in table 16. Similar to a performance approach, the contractor proposes the means, materials, and methods to construct a DMM foundation that meets the requirements of the design. This approach is used with a design-bid-build contract. Typical allocation of responsibilities of the owner and contractor for DMM work is outlined in table 18.

Table 18. Typical allocation of responsibilities of owner and contractor for DMM work.

Typically, the owner provides the following project-specific information in the bidding documents:

• Geotechnical reports and data, including results from all precontract testing.
• DMM design parameters, including geometry, strength, modulus, and permeability,
  as appropriate.
• Existing utility plans.
• Site limitations, including information about access limitations, right-of-way, scour potential, liquefaction potential, noise requirements, vibration requirements, and potential for hazardous or contaminated materials.
• Requirements for DMM contractor qualifications.
• Minimum and maximum values of geometry and layout of DMM elements.
• Requirements for DMM contractor working drawings and submittals, including schedule and information on penalties.
• Material specifications.
• Testing requirements.
• Instrumentation requirements (if any).
• DMM acceptance criteria.
• Method of measurement and payment.

After the contract is awarded, the DMM contractor prepares and provides the following submittals to the owner via the GC (construction begins after the owner reviews and approves these submittals):

• Evidence of DMM contractor qualifications.
• Plan and results of preproduction laboratory and/or field tests conducted by the GC or DMM contractor.
• DMM program plan demonstrating compliance with the project specifications, including working drawings and descriptions of binder storage and mixing equipment, DMM equipment, materials, methods to be used, and supporting calculations. The plan should include proposed mix design details and drawings showing the center coordinates, size, bottom elevation, and top elevation of every DMM element, which should each be uniquely numbered.
• QC/QA plan demonstrating compliance with the project specifications, including binder and mixing parameters to be controlled and monitored, sampling methods, sampling depths, sampling frequency, testing frequency, testing methods, and documentation.

Provided effective specifications are developed and qualified contractors are used, there are advantages to both the owner and the contractor in this hybrid approach. The owner obtains detailed knowledge of the project and its requirements by reviewing technical alternatives, completing the detailed design, and developing the specifications. The owner is therefore able to evaluate the bids effectively because all of the contractors propose solutions based on the same overall design. Being more familiar with the production and capabilities of their mixing systems, the DMM contractors have the flexibility to use their expertise to propose a system of equipment, mix design, and operation procedure capable of constructing a DMM foundation that complies with the owner's design. As a result, the owner likely receives a more cost effective solution.

In the hybrid approach, more of the risk is transferred to the contractor, who is more familiar with his/her own methods and techniques than the owner. This contrasts with a method approach in which the owner accepts responsibility for the design and performance of the DMM product, provided the elements are constructed in accordance with the plans and specifications. Additionally, any changes to the design that are required after encountering actual field conditions during construction are also the owner's responsibility.

8.2 Measurement and Payment

Suggested pay items are outlined in table 19. In general, measurement and payment may be made on a lump sum basis if the number and depth of DMM elements are fully detailed by the owner. Including add/deduct unit costs (per foot (meter)) is suggested to accommodate increases or decreases to the specified quantities (numbers of elements and/or depths) without requiring contract revisions. The same approach may be used for QC/QA testing, where a fully defined testing program may be bid as a lump sum item with additional/omitted individual tests being added/deducted on a per-test basis. Measurement and payment of DMM work using the hybrid approach is typically made on a lump sum basis.

Table 19. Suggested pay items and units of measure for DMM contract items.

8.3 Other procurement methods

Performance specifications may be used dependent on the level of experience of the owner with DMM technology, the availability of qualified contractors, and the criticality of the application. Purely method specifications are virtually never used for DMM projects. Other types of procurement methods may also be used as appropriate. The procurement approach should be selected based on consideration of both price and technical proposal. Design-build contracts are used with purely performance specifications.

A best value approach to contractor procurement may have advantages on projects that are technically challenging or involve relatively greater risk, where success may be more dependent on the technical approach than on price. A best value approach involves the contractors submitting separate price and technical proposals, which are reviewed independently and scored proportionately (price proposal = a portion of x points, where x is a positive number less than 100, and technical proposal = a portion of 100 − x points). The scoring allocation (x) is defined based on the relative importance of price and technical approach. The contract is awarded to the bidder with the highest combined score.

Financial incentives may be used on projects with tight schedules. Typically, the owner is responsible for establishing the overall project schedule, and the GC is responsible for establishing and achieving interim milestones that lead to achieving the overall project schedule. An incentive for the GC to accelerate production may involve a monetary bonus for certain quantities of the production work completed by milestone dates. Conversely, disincentives such as liquidated damages may be levied if the GC misses clearly defined interim and final schedule milestones. Other disincentives may be included that discourage poor quality such as payment at a reduced rate for QC/QA results that do not meet specified requirements.

ECI methods are attractive due to the contractor-driven nature of DMM work. ECI methods involve the owner's solicitation of technical input from qualified contractors for use in developing the project solution. All contractors involved in the ECI process for a project should be able to submit a bid of the project; that is, contractors involved in the ECI process should not be precluded from bidding. ECI provides the owner with a contractor's perspective on constructability, sequencing, and other project construction challenges. ECI has been used successfully on the U.S. Army Corps of Engineers (USACE) Tuttle Creek Dam project and the LPV 111 earthen levee project.^(123,124)

Value engineering proposals are submitted by the GC after contract award and contain price proposals for alternative foundation designs that meet the specified requirements at a significant cost savings. After contract award, with concurrence from the owner, the contractor redesigns the project and submits revised working drawings and design calculations that demonstrate that the proposed solution meets the intent of the design as outlined in the original specifications at a lower price. The engineering costs for the GC's redesign work are included in the revised price proposal for the foundation work. Often, the owner and GC divide the cost savings in mutually agreed proportions.

8.4 contractor Qualifications

Selecting an experienced and qualified DMM contactor is critical to the success of a project because the quality of the DMM material depends on an understanding of the ground conditions and the use of specialized equipment, techniques, and workmanship. Contractor prequalification, although prohibited in some States, is acceptable and reasonable for DMM projects because it assists GCs in identifying subcontractors who have the expertise required for the project. On projects located in areas where prequalification is prohibited, the use of the best value approach, which includes both price and technical proposals, may be advantageous to ensure that the technical approach selected is sound and reliable.

Regardless of whether pre-qualification of contractors is used on a project, requirements of the technical qualification of the DMM contractor and his/her staff must be established. The following personnel are typically involved in a DMM project:

• The project manager is the contractor representative responsible for the overall direction of the DMM project including site operations, technical acceptability, project billing, and reporting. The project engineer and the project superintendent ordinarily report to the project manager.
• The project engineer is responsible for supervising the QC technicians' work, providing technical support to the QC technicians, and reviewing production records and QC/QA data to ensure the quality of the DMM work.
• The project superintendent oversees construction operations, equipment, and material supply; collects and compiles daily production reports; and ensures QC activities are conducted in accordance with project requirements. The project superintendent and the project engineer may work together on QC activities and documentation.
• The DMM equipment operator is responsible for operating the equipment
  during construction.
• On large, complex, or critical deep mixing projects, the contractor or the owner (sometimes both) employs a deep mixing specialist or a review board to provide advice, review, and assistance with dispute resolution.

Contract documents for DMM work should clearly define contractor qualification requirements, submittal procedures for the qualification documentation, and means by which the owner will enforce the requirements. The following minimum requirements (and associated documentation) for the DMM contractor are recommended:

• The DMM contractor must have previous successful experience with DMM projects for soil conditions and project scope similar to that of the project being bid (contractor provides project description(s) and reference list).
• The DMM contractor must assign a project manager who has had significant experience on at least five DMM projects (contractor provides the number of years/projects, project description(s), and reference list).
• The DMM contractor must assign a project engineer to supervise the technical engineering and quality aspects of the DMM work. The project engineer must have had significant experience on at least five DMM projects (contractor provides the number of years/projects, project description(s), and reference list). For a design-build project, the DMM contractor must assign a professional engineer who is registered in the jurisdiction in which the project is located to supervise the design and preparation of the drawings and to review QC/QA records and as-built drawings to confirm that the DMM work meets the design intent.
• The DMM contractor must assign a full-time project superintendent with at least five projects and at least 130,000 yd³ (100,000 m³) of total treatment volume in DMM construction (contractor provides the number of years/projects, project description(s), and reference list).
• The DMM contractor must provide at least one DMM equipment operator with at least 1 year of experience with the equipment and DMM construction (contractor provides the number of years/projects, project description(s), and reference list).

The GC must provide a written request and supporting documentation for substitutes of these key personnel prior to making any personnel changes. Documentation must include evidence that the substitute meets the qualification requirements listed in the specifications. Substitutions may not be made without written approval from the owner.