Category HIGHWAY ENGINEERING HANDBOOK

As previously indicated, states must perform a VE analysis on all federal-aid-funded projects on the National Highway System having an estimated total cost (design, construction, right-of-way, and utilities) of $25 million or more. However, additional projects should be selected for study, based on providing the maximal opportunity to improve the public investment by quality enhancement or life cycle cost savings. AASHTO has identified the following typical characteristics of potential VE projects:

• Projects substantially exceeding initial cost estimates

• Complex or multipart projects or processes providing unique, but costly functions

• Items using critical or high-cost materials

• Items requiring difficult construction or fabrication procedures

• Items performing a questionable function

• Items appearing too costly to build, operate, or maintain

• Projects that have grown complex, possibly by development over a long period of time

• Major structures

• Projects with complicated or costly traffic control or detours

For optimal results, VE should be applied as early as possible after basic design elements and preliminary cost information have been developed. This way, design rec­ommendations can be more readily incorporated; the earlier VE is applied, the greater the potential for savings. With proper timing and planning, the VE administrator can ensure that specific VE studies are accomplished without conflicting with the project schedule.

The main benefit of a VE program is improvement of the benefit-to-cost ratio throughout state transportation programs. Other perceived benefits are as follows:

• Design, construction, and maintenance standards are constantly being reviewed through VE team activities.

• The structured, functional approach using a job plan (see Arts. 10.3 and 10.4) provides trained employees with a new method of approaching problems.

• VE team members develop an appreciation for the concerns and issues of other functional areas or disciplines, and communications are often improved.

• Team work skills and team dynamics are enhanced in the design process.

• Designers improve or develop their skills in preparing and delivering to management logical, organized presentations supporting their views.

• After gaining VE experience, many designers find it comparatively easy to apply the principles in the regular design process.

• Implementing a VECP program has a potential for improving state/contractor relations through more cooperative processing of change proposals.

• Proven VE designs or techniques and VECP-accepted changes often have applica­tions for numerous future projects or contracts, thereby providing continuing savings and other benefits.

10.2.2 Training

AASHTO recommends that orientation and training be provided at nearly every level within the organization, including team members, team leaders, and management. Executive management must understand and support the fundamentals and principles of VE for the program to be successful. VE administrators, team leaders, and team members need basic and subsequent training to ensure success of the VE process and the implemen­tation of recommendations. An overview of the procedures and the benefits of VE should be provided to staff not directly involved to encourage understanding and support.

Training in VE is available from various sources, including the National Highway Institute and consultants. A combination of VE theory and hands-on experience is desirable. SAVE International (formerly Society of American Value Engineers) offers several forms of VE certification. (See www. value-eng. com.) To become certified, one must meet all of the employment, VE performance standards, formal training, pro­fessional growth, and professional contribution requirements established by SAVE. The following certifications are available:

• A value methodology practitioner. Individuals who are familiar with VE but whose primary occupation is not VE.

• An associate value specialist. Individuals familiar with VE, but who have not acquired enough points to become a certified value specialist.

• A certified value specialist (CVS). Individuals whose principal occupation is VE.

To become a CVS, one must attend a 40-h SAVE-certified Mod I VE workshop and a 24-h SAVE-certified Mod II VE workshop, have 50 percent or more of the job description relate to VE, perform a number of VE studies as a team member and as a team leader, write a paper on VE, and take a test. Normal time to become certified is 4 to 5 years.

To assist state DOTs in the application of VE, the AASHTO Task Force on Value Engineering, originally organized in 1985, has developed the publication, Guidelines for Value Engineering, already cited. Portions of the publication[22] are summarized in Arts. 10.2.1 through 10.2.6. The AASHTO value engineering technical committee maintains a useful website, www. wsdot. wa. gov/partners/AASHTOVE. Also, a VE engineering conference is sponsored every 2 years.

AASHTO has taken the position that every member state should establish an ongoing VE program to improve design excellence and achieve cost and quality control. VE is seen as a means for addressing the problem of rising costs and diminishing resources through applications in many areas such as project development, construction, traffic operations, and maintenance.

10.2.1 Elements of a Successful VE Program

AASHTO suggests the following as important elements of a successful VE program:

• A firm commitment of resources and support by executive management is the most important element for ensuring the success of a VE program.

• All levels of management must understand and support VE.

• A state VE program requires the development of a policy directive describing where, when, how, and to what specific areas of work the VE effort should be directed.

• It is essential to provide some degree of VE training and program familiarization at every level within the state organization.

• For optimal results in the project development phase, VE should be performed as follows:

Early in the planning-design process to maximize potential product improvement and cost savings.

On high-cost and/or complex projects.

By a multidisciplinary team of professionals trained in VE techniques.

• A value engineering change proposal program to encourage contractors to develop construction VE proposals allows the state to benefit from a contractor’s design and construction ingenuity, experience, and ability to work through or around bureaucrat­ic restrictions. Some important elements of a successful, ongoing VECP program are the following:

Processing of proposals must be kept simple and done quickly.

Cost savings are shared with the contractor.

Change proposals become the property of the state, and the concept may be used on future projects.

Change proposals should not compromise any essential design criteria or preliminary engineering commitments.

Change proposals cannot be the basis for a contract claim. The state agency has the option to reject, with good justification, contractors’ proposals.

• It is essential that all VE team recommendations and contractor proposals be fairly reviewed and expeditiously evaluated for implementation.

• VE techniques can also be used to improve productivity in other areas of a state’s transportation program, including traffic operations, maintenance processes, proce­dures and operations, standard plans and specifications, and design criteria and guidelines.

• VE programs within the state organization should be closely monitored, evaluated, and modified to ensure the program’s effectiveness.

It is also emphasized that understanding and support of VE by top management are the most important factors in a successful VE program. Such support is needed initially to ensure adequate funding for training of staff and establishment of the program. Once the VE program is established, the continuing active involvement of top management is needed to create and maintain positive attitudes.

The FHWA has developed the following federal-aid policy guide that provides much useful information for the application of VE:

1. PURPOSE. To provide policy guidance on the application of value engineering in

the federal-aid highway program.

2. AUTHORITY.

a. Section 106(e) of Title 23, United States Code provides: “For such projects as the Secretary determines advisable, plans, specifications, and estimates for proposed projects on any Federal-aid system shall be accompanied by a value engineering or other cost reduction analysis.”

b. Section 106(g) of Title 23, United States Code provides: “The Secretary shall establish a program to require States to carry out a value engineering analysis for all projects on the National Highway System [NHS] with an estimated total cost of $25,000,000 or more.” The Federal Highway Administration published its regulation establishing this program on February 14, 1997.

c. Paragraph 6b(2) of DOT Order 1395.1A, Use of Value Engineering in the Department of Transportation, dated May 8, 1992, provides: “Each DOT Operating Administration should strongly encourage the use of VE in its grant awards or Federally assisted programs for major transportation projects throughout the planning, design and/or construction phases. This may include the use of VE proposals as a result of VE studies/analyses as well as VE incentive clauses in construction contracts.”

d. Paragraph 9 of the Office of Management and Budget’s (OMB) Value Engineering Circular A-131, dated May 21, 1993, provides: “Each agency shall report Fiscal Year results of using VE annually to OMB, except those agencies whose total budget is under $10 million or whose total procurement obligations do not exceed $10 million in a given fiscal year.” The Circular also describes what VE data must be submitted and the format for submitting the data to OMB.

3. DEFINITIONS.

a. Life cycle cost: The total cost of an item’s ownership over its life cycle. This includes initial acquisition costs (right-of-way, planning, design, construction), operation, maintenance, modification, replacement, demolition, financing, taxes, disposal, and salvage value as applicable.

b. Project: A portion of a highway that a state proposes to construct, reconstruct, or improve as described in the preliminary design report or applicable environ­mental document. A project may consist of several contracts or phases over several years.

c. Product or service: Any element of a highway project from concept through maintenance and operation. In all instances, the required function should be achieved at the lowest life cycle cost consistent with requirements for perfor­mance, maintainability, safety, and aesthetics.

d. Value engineering: The systematic application of recognized techniques by a multidisciplinary team to identify the function of a project or service, establish a worth for that function, generate alternatives through the use of creative thinking, and provide the needed functions to accomplish the original purpose of the project, reliably, and at the lowest life cycle cost without sacrificing safety, necessary quality, and environmental attributes of the project.

e. Value Engineering Change Proposal (VECP) clause: A construction contract provision that encourages the contractor to propose changes in the contract requirements which will accomplish the project’s functional requirements at less cost or improve value or service at no increase or a minor increase in cost. The net savings of each proposal is usually shared with the contractor at a stated reasonable rate.

4. POLICY. The FHWA will ensure that a VE study is performed on all federal-aid – funded NHS projects with an estimated cost (includes design, right-of-way, and construction costs) of $25 million or more, and on other federal-aid projects where its employment has high potential for cost savings. In addition, FHWA will strongly encourage state departments of transportation to use VE throughout high­way project development, design, and construction.

5. CHARACTERISTICS. To be considered VE, the analysis process should incorporate each of the following characteristics:

a. A multidisciplinary team approach

b. The systematic application of a recognized technique (VE job plan)

c. The identification and evaluation of function, cost, and worth

d. The use of creativity to speculate on alternatives that can provide the required functions (search for solutions from new and unusual sources)

e. The evaluation of the best and lowest life cycle cost alternatives

f. The development of acceptable alternatives into fully supported recommendations

g. The presentation/formal reporting of all VE recommendations to management for review, approval, and implementation.

6. APPLICATION.

a. A VE analysis shall be applied to all federal-aid-funded NHS projects with estimated costs of $25 million or more; however, VE should not be limited to only projects of this scope. It can also be highly effective when used on other projects when there is potential for a significant ratio of savings to the cost of the VE study or substantial improvements in project or program effectiveness.

b. For maximum benefit, VE should be employed as early as possible in the pro­ject development/design process so valid VE recommendations can be imple­mented without delaying the progress of the project or causing significant rework of completed designs. States should schedule VE routinely into the project development/design process. While all projects will not necessarily benefit from the application of VE, the review process should be set up to con­sider all projects and a VE analysis should be applied to those projects offering the greatest potential for improvement and/or savings.

c. Recommendations from VE studies and VECPs should receive prompt reviews by state officials to determine their acceptability. States should also develop procedures for implementing accepted recommendations.

7. BACKGROUND INFORMATION. The FHWA’s text “Value Engineering for Highways” provides further details on the VE technique and its applicability to high­way projects and functions. It has been widely distributed as a part of FHWA’s train­ing effort and a copy should be available in each state DOT and FHWA office. Additional copies may be obtained from the FHWA VE coordinator. The American Association of State Highway and Transportation Officials (AASHTO) Guidelines for Value Engineering (AASHTO, Washington, D. C., 2001) also pro­vides an excellent description of VE.

8. FHWA RESPONSIBILITIES.

a. Division office

(1) Designate a VE coordinator and encourage state to host VE training provided by the FHWA, a qualified VE consultant, and/or develop its own VE training.

(2) Encourage state to use VE by actively participating in VE studies and advising it that VE study costs are eligible (as preliminary engineering costs) for federal-aid participation.

(3) Ensure all applicable NHS projects receive a VE analysis and encourage additional studies of other projects.

(4) Ensure the state has an active VE program and encourage it to include a VECP clause in its construction contracts.

(5) Summarize the state’s VE activity on all federal-aid projects annually and provide the information to the FHWA VE coordinator.

b. FHWA VE coordinator

(1) Promote VE and serve as the technical expert on VE matters for FHWA, state, and local highway agencies.

(2) Provide VE briefings to FHWA, state, and local executives and upper management.

(3) Provide VE training and technical expertise to FHWA, state, and local highway agencies. Assist states to develop VE programs.

(4) Coordinate VE with other FHWA activities aimed at cost reduction or product improvement.

(5) Compile VE activity data received from the division offices and prepare annual report for DOT.

(6) Represent FHWA in VE forums with the U. S. DOT and other federal and state governmental agencies, including membership in SAVE International (formerly the Society of American Value Engineers). Serve as FHWA’s representative to the AASHTO VE Task Force.

9. STATE DOT RESPONSIBILITIES.

a. Each state shall establish a continuing VE program that ensures all applicable NHS projects will receive a VE analysis and provides for the review, approval, implementation, and documentation of the VE study recommendations. Individuals knowledgeable in VE shall be assigned the responsibility to coor­dinate and monitor the program. States should also develop a VE training pro­gram, a tracking and/or record keeping system, and a process to disseminate

and publicize their VE results. This work may include the use of qualified VE specialists on a consulting basis.

b. States should include a VECP clause in their construction contracts to encour­age contractors to propose changes in contract requirements which will do the following:

(1) Reduce project cost(s) or improve value or service at no increase or a minor increase in cost.

(2) Provide states with innovative contractor ideas or techniques to be considered when preparing plans, specifications, and estimates on future projects.

The net savings of each proposal should be shared with the contractor at a stated reasonable rate. Reimbursement for such share is eligible for pro rata reimburse­ment with federal-aid funds. States should retain the right to accept or reject all proposals and acquire all rights to use accepted VE proposals in current and future projects without restriction. An example VECP provision is contained in the AASHTO Guidelines for Value Engineering.

10. USE OF CONSULTANTS. States may employ qualified VE consultants to conduct VE studies on federal-aid projects or elements of federal-aid projects. Consulting firms should not apply VE to their own designs (the law prohibits persons involved in the project from being on the VE team). It is strongly recommended that consultants be qualified VE practitioners, be experienced in performing and leading VE studies (have participated in several VE studies as a team member and as a team leader), and have sufficient VE training, education, and experience to be recognized by SAVE International as meeting the requirements for certification.

11. REPORTING.

a. All VE studies and VECP conducted on federal-aid projects shall be used to pre­pare an annual VE summary report. At the end of the fiscal year, each division office and/or state DOT will prepare the annual VE summary report and submit it to the FHWA VE coordinator. Reports are due by November 10 of each year.

b. The FHWA VE coordinator shall prepare an annual report including an assess­ment of the effectiveness of efforts to encourage VE on federal-aid projects to the U. S. DOT by December 10 of each year.

The VE review process uses a team of individuals representing different disciplines who do not have a vested interest in the project. The teams break down a project into its basic functions and then use creativity to find different ways to perform these func­tions. The teams provide management with as many recommendations as practicable. The recommendations are then evaluated by staff offices in specialty areas that may be impacted. Management must then decide, based on all available information, whether or not to approve the recommendations.

The following steps are used in every VE review:

• Identify the major elements of a project.

• Analyze the functions these project elements perform.

• Use brainstorming to develop several design alternatives to perform those functions.

• Evaluate the alternatives to ensure they do not degrade the project.

• Assign costs (including life cycle costs) to each of the most promising alternatives.

• Develop the promising alternatives into acceptable recommendations.

The FHWA’s VE program applies to the federal-aid program under which authorized funds are distributed to states for state Department of Transportation (DOT) projects. According to the FHWA, the program is designed to (1) encourage state DOTs to use VE,

(2) ensure that National Highway System projects required by law and regulation (cur­rently greater than $25,000,000 for federal-aid highway projects or $20,000,000 for bridges) receive VE reviews, (3) encompass a variety of VE activities focused on edu­cation and training, technical assistance, liaison with industry and states, promotional activities, and active participation in studies, and (4) focus on training federal, state, and local highway employees through the National Highway Institute’s VE workshop.

Table 10.1 summarizes past VE savings in the federal-aid program over a 4-year period as reported by the FHWA. Savings in 2007 on highway programs totaled nearly $2,000,000,000. In addition to these savings, other federal departments generated significant VE savings.

Articles 10.1.1 through 10.1.4 are based on information excerpted from the website www. fhwa. dot. gov/ve. Further information is available in the FHWA text, “Value Engineering for Highways,” available in each state DOT or FHWA office or from the FHWA VE coordinator.

10.1.1 Goals and Objectives

The FHWA states the following regarding VE goals and objectives:

The goal of a VE study is to achieve design excellence. Its objectives are to improve qual­ity, minimize total ownership costs, reduce construction time, make the project easier to construct, insure safe operations, and assure environmental and ecological goals. The VE team is looking for the optimum blend of scheduling, performance, constructability, main­tainability, environmental awareness, safety, and cost consciousness. The VE process is not meant to criticize today’s designs or insinuate that the regular highway design process is not providing acceptable designs. This is not the case. The designs being prepared today are good designs, they can be built, and they will function as intended. Highway designers do not deliberately design poor value into a project; yet, it happens.

10.1.2 Reasons for Poor Quality

Reasons cited for poor quality in some highway designs are as follows:

Lack of information

• Failure to get sufficient facts before starting.

• Lack of knowledge or misunderstanding of the full requirements of the original project plan.

• Decisions based on “educated guesses.”

Wrong beliefs

• Erroneous interpretations or conclusions of the facts.

• Unfortunate experiences with past applications of materials, etc.

• Bias against proven technology.

Habitual thinking

• Doing things “the same way we’ve always done them.”

• Tendency to reuse what worked the last time.

• Copying standards of other agencies.

• Lack of attention to the current state-of-the-art.

Risk of personal loss

• Anything done over and over again minimizes risk through trial and error.

• Risk associated with trying something that you have not tried before.

• Decisions based on “nearly related” data, rather than the actual case.

Reluctance to ask for advice

• Designers are often very reluctant to seek advice from others in their field.

• Failure of designers to admit that they might not know all the answers.

Time pressures

• Need to provide a project design as quickly as humanly possible, sometimes even quicker.

• Pressure becomes so great that anything with a reasonable chance of working is designed into the project.

• Acceptance of the first workable solution in order to complete the design on time.

• No time to sit and contemplate.

• No time to sit and think up alternative approaches.

Negative attitudes

• Some people are reluctant to consider a change of any type regardless of its merit.

• Most designers feel they always provide the best, the first time, regardless of how much time they spend developing the design.

Rapidly changing technology

• Rapid strides taking place in the development of processes, products, and materials.

• Technology is constantly changing.

• No one person can be expected to be completely current in any field.

Strict adherence to “requirements”

• Requirements are often unrelated to required performance, materials, safety, or procedures.

• Assumed requirement when not specifically specified.

• Concentration on the development of a reliable system that exceeds all known and assumed requirements.

• Each unnecessary requirement that is met in a design costs money, but worse still, increases the chance of failure of the overall system.

Poor human relations

• Poor communications.

• Misunderstandings.

• Jealousy.

• Normal friction between human beings.

Harold G. Tufty, CVS, FSAVE

Editor and Publisher

Value Engineering and Management Digest
Washington, D. C.

Value engineering (VE) may be defined as a systematic method for identifying the function of a product or service, establishing its worth, and generating alternatives to provide the required function at the least life cycle cost. A discipline that evolved out of the necessity for finding alternative materials for manufacturing during the 1940s, it was originally applied to projects in the Department of Defense and in industry. First adopted for highways in California and Florida in the early 1970s, it has been used with increasing success for highway projects nationwide. Virginia’s pioneering VE legislation in 1990 set a standard that resulted in a savings of over $565,000,000 over the next 17 years.

The impetus for using VE increased in 1995 when Congress passed the National Highway System (NHS) Designation Act, which included a provision requiring the Secretary of Transportation to establish a program that would require states to carry out a VE analysis for federal-aid projects of $25,000,000 or more. The Federal Highway Administration (FHWA) subsequently published its regulation (23 CFR Part 627) establishing the program on February 14, 1997.

Life cycle costing, or least-cost analysis, is an integral part of VE. It provides a rational means of comparing the costs of alternatives in terms of today’s dollars, including the effects of initial cost, maintenance cost, and rehabilitation cost.

This chapter reviews the policies of the Federal Highway Administration on VE, and guidelines offered by the American Association of State Highway and Transportation Officials (AASHTO). It also explains the fundamentals of the process, provides detail on implementation methods, and cites examples of successful VE programs.

The following material is presented in the format of a typical specification used by one agency for the construction of noise barriers (noise walls). In addition to the type of wall included—timber wall with concrete posts—it can be adapted to walls of other types.

A. Miscellaneous Structure Removal

Abandoned structures and other obstructions shall be removed from the right-of-way and disposed of in accordance with DOT provisions except as modified below:

All debris resulting from the removal items and all other materials that become the property of the contractor and are not recycled into the project shall be disposed of outside the right-of-way in accordance with DOT provisions. This work shall be incidental to removal and salvage operations, and no direct compensation will be made therefor.

The contractor’s attention is directed to possible privately owned appurtenances adjacent to the construction site that may need to be removed. If the private appurte­nances are damaged, the contractor will be required to reinstate the appurtenances to satisfaction of owner. This work shall be considered incidental to the removal operations, and no direct compensation will be made therefor.

B. Clearing and Grubbing at Construction Site

The engineer shall have authority to limit the surface area of erodible earth material exposed by clearing and grubbing, excavation, and borrow and fill operations and to direct the contractor to provide immediate permanent or temporary control measures to prevent contamination of adjacent streams and other watercourses, lakes, ponds, and areas of water impoundment. Cut slopes shall be seeded and mulched as the excavation proceeds to the extent considered desirable and practicable.

The contractor will be required to incorporate all permanent erosion control features into the project at the earliest practicable time as outlined in his/her accepted schedules. Temporary pollution control measures will be used when needed to correct conditions that develop during construction but were not foreseen during the design stage, when needed prior to installation of permanent erosion control features, or when needed temporarily to control erosion that develops during normal construction practices; by definition, such temporary measures are not associated with the permanent control features on the project.

Where erosion is likely to be a problem, clearing and grubbing operations should be so scheduled and performed that grading operations and permanent erosion control features can follow immediately thereafter if the project conditions permit; otherwise, temporary erosion control measures may be required between successive construction stages. Under no conditions shall the surface area of erodible earth material exposed at one time by clearing and grubbing exceed 750,000 ft[21] (70,000 m2) without approval of the engineer.

C. Furnishing Concrete Post and Wood Noise Wall

This work shall consist of furnishing all materials for and constructing wood noise attenuator walls complete with concrete posts, and wood retaining wall, all in accor­dance with the plan details, the applicable DOT Standard Specifications, the required specifications for pigmented sealer and exterior wood surface stain, and the following:

1. General. All thickness and width dimensions of solid sawn wood for timber facing material indicated in the plans for wood wall construction shall be construed to be nominal dimensions unless otherwise indicated in the plans or these special provisions.

D. Preservative Treatment

All lumber shall be pressure-treated with a preservative in accordance with the provi­sions of AASHTO M133 and the American Wood Protection Association (AWPA)

manual.

1. All wall facings and battens shall be treated with a pressure preservative as approved by AWPA.

2. Wood materials shall be treated as required for aboveground installation, or for installation in contact with ground or water, in accordance with the applicable pro­visions of AASHTO M133 with a retention level of 0.60 lb/ft3 (9.6 kg/m3).

3. All southern pine materials shall be free of sap stain (blue stain).

4. All wood members shall be kiln-dried to a moisture content of 15 percent or less after preservative treatment.

5. After completion of the preservative treatment, all lumber materials shall be protected from any increase in moisture content by covering or any other approved method until incorporated into the wall.

6. The same preservative treatment shall be used to treat bolt holes, saw cuts, etc., if any, and for any additional dressing deemed necessary by the engineer.

7. All treated wood members shall be cared for in accordance with the applicable pro­visions of AWPA Standard for the Care of Preservative Treated Wood Products.

E. Construction Requirements

1. Construction of wood noise attenuator walls, together with appurtenant posts, etc., shall be accomplished in accordance with the plan details, the applicable DOT Standard Specifications, these special provisions, or as otherwise approved by the engineer.

2. Nailing and fastening shall be accomplished in a manner that will avoid splitting boards. A 4-mil (0.10-mm) polyethylene sheeting may be placed between the planks and the earth for added protection when fill is being retained.

3. Joints shall be constructed in a manner that will completely arrest the passage of light. No daylight shall be visible through the joints 120 days after completion of the wall. The contractor is advised to take whatever measures are necessary to avoid excessive shrinkage or shifting that would cause the passage of light. Where passage of light does occur, the contractor shall take corrective action, in the form of caulking, or other means to the satisfaction of the engineer, at his/her own expense.

4. Storage of materials within the right-of-way will be permitted only as approved by the engineer.

5. Debris shall be disposed of outside the right-of-way as specified by the engineer. Posts shall be plumb after installation.

6. The trench and trench backfill shall be compacted by the ordinary compaction method. The trench bottom shall be compacted to 90 percent of maximum density, and the bedding to 95 percent and 90 percent on each side of the footing. The den­sity control shall not apply to the topsoil. The layers of material to be compacted shall be placed and compacted simultaneously so that the backfill material will be raised uniformly throughout the entire embedment depth.

F. Noise Wall Measurement and Payment

1. Concrete posts of each size will be measured separately by the length of the posts furnished and installed complete in place as specified. Payment will be made at the contract bid price per linear foot, which shall be compensation in full for all costs relative thereto.

2. Noise wall construction will be measured by the total front face area of the wall constructed (i. e., the area between the centers of end posts, and between the top of the wall and 6 in (150 mm) below the tabulated ground line).

3. Payment will be made for noise attenuator wall at the contract bid price per square foot, which price shall be compensation in full for all costs of constructing the wall complete in place as specified, except the appurtenant concrete posts, which shall be compensated for separately under the appropriate contract item provided.

4. Instead of the hand-driven “full-head” nail as shown in the plan, a reduced-head power-driven nail may be used to meet one of the following modifications:

a. Use a nail one gauge heavier.

b. Increase the number of nails used in each pattern by a minimum of 50 percent.

For example, use 3 nails instead of 2, 5 instead of 3, 2 instead of 1.

5. In case of failure on the part of the contractor to control erosion, pollution, and sil – tation as ordered, the DOT reserves the right to employ outside assistance or to use its own forces to provide the necessary corrective measures. All expenses so incurred by the department, including its engineering costs, that are chargeable to the contractor as his/her obligation and expense, will be deducted from any monies due or coming due the contractor.

The capacity of the foundation soil should be determined using accepted engineering prin­ciples and measurement of material parameters such as cohesion and angle of friction, or on the basis of field data such as the standard penetration test or the shear vane test. (See Chap. 8 for pertinent information.) One agency uses the following for default values:

1. Use angle of friction ф = 30° for granular soils and a cohesion value of c = 1000 lb/ft2 (48 kPa) for plastic soils to determine post embedment. Water encountered in soils above embedment depths will require special designs.

2. Use 2000 lb/ft2 (96 kPa) for allowable bearing capacity unless higher values are approved by the soils engineer.

3. A maximum of 2 ft (600 mm) of unbalanced fill on one side of the noise wall will be allowed. Good compaction must be achieved on the low side of the wall prior to placing unbalanced fill.

The AASHTO Guide Specifications recommend the following safety factors for the design of spread footings that support noise walls:

For walls supported on two or more rows of piles, the design should follow procedures in Standard Specifications for Highway Bridges (AASHTO, Washington, D. C., 2004). For walls supported on a single row of piles, the pile must be designed as a column, considering both axial loads and bending. Also, the pile must be designed for the shear from the lateral loads.

For panel-and-post type walls, the embedment depth of the post can be determined using Rankine or Coulomb earth pressure theories. The following equation follows from static equilibrium analysis and applies for a pile or post on level ground:

applied ultimate lateral load, lb (N)

vertical distance from lateral load to top of embedment, ft (mm) (disregard upper 6 in (150 mm) of soil at ground surface)

net horizontal ultimate lateral soil pressure limit, lb/ft2 (Pa) per ft (mm) of depth required depth of embedment, ft (mm)

Note that both P and R are ultimate values. The design load must be increased by an appropriate load factor, and the resisting soil pressure decreased by an appropriate load factor.

Example—U. S. Customary units. P = 200 lb, h = 6 ft, and R = 600 (lb/ft2)/ft. Determine d.

By trial and error, it is found that d = 3.2 ft satisfies Eq. (9.3). The final trial gives

0 = 1638 – 427 – 7 – 1200 0 « 4 (close enough; OK)

The post should be embedded a distance of 3.2 + 0.5 = 3.7 ft below the ground surface.

The maximum moment in the pile or post can be expected to occur at a depth of

0. 25d. In this case, the maximum moment is

M = P(h + 0.25d)

= 200(6 + 0.25 X 3.2)

= 1360 ft • lb

Example—SI units. P = 890 N, h = 1830 mm, and R = 0.0287 Pa. Determine d. By trial and error, it is found that d = 975 mm satisfies Eq. (9.3). The final trial

gives

0. 0287(975)3 _ 2(890)(975) _ (890)2

12 3 3(0.0287)(975)

2,216,739 _ 578,500 _ 9,436 _ 1,628,700

103 (close enough; OK)

Noise barriers can be designed by working-stress design methods or load factor design. For the working-stress design method, the following load combinations should be considered:

Group I: D + E + SC

Group II: D + W + E + SC

Group III: D + EQD + E

Group IV: D + W + E + I

dead load

lateral earth pressure live load surcharge wind load seismic load ice and snow load

For load combination I, the stresses are limited to 100 percent of the basic allowable stresses. For load combinations II, III, and IV, the stresses are limited to 133 percent.

9.9.2 Design Criteria

The AASHTO Guide Specifications state that, for the design of noise barriers in concrete, timber, or steel, the design should conform to either the AASHTO Bridge Specifications or an industry-recognized design specification. Such sources may be referred to for allowable stress values and other details. For masonry walls, detailed design criteria are presented in the AASHTO Guide Specifications. Other materials can be designed using established engineering principles and appropriate industry specifications.