geomembranes Use geosynthetic materials for filters, erosion control, water barriers, drains, or soil reinforcing (see Art. 6.11) Effective filters for all soils; reinforcement often used for soft soils Widely used to accomplish a variety of tasks; commonly used in conjunction with other methods (e.g., strip drain with surcharge or to build a construction platform for site access) Source: M. P. Rollings and R. S. Rollings, Geotechnical Materials in Construction, McGraw-Hill Publishing Co., New York. TABLE 6.21 Site Improvement Methods (Continued) Method Technique Principles Suitable soils Remarks FIGURE 6.47 Site improvement methods as a function of soil grain size. (Reproduced from M. P. Rollings and R. S. Rollings, Geotechnical Materials in Construction, McGraw-Hill Publishing Co., New York, with permission of McGraw- Hill, Inc.) than foundation underpinning, and it can be used to relevel the structure. The disadvantages are that analyzing the results is difficult, it is usually ineffective near slopes or for near-surface soils because of the lack of confining pressure, and the danger exists of filling underground pipes with grout. Thermal. As indicated in Table 6.21, the thermal site improvement method consists of either heating or freezing the soil in order to improve its shear strength and reduce its permeability. Figure 6.47 presents a summary of site-improvement methods as a function of

Over 5 to 8 incl. 63 42 A992 Shapes only 65 50 Heat-treated low-alloy steels A514 To 3/4 incl. 115135 100 Over 3/4 to 21/2 115135 100 Over 21/2 to 4 incl. 105135 90 *Yield stress or yield strength, whichever shows in the stress-strain curve. Minimum tensile strength may not exceed the higher value. 7.2.1 Grades of Steel Structural steel grades are referred to by their corresponding ASTM designation. For example, the most commonly used grade of structural steel is A36, which is produced to meet the requirements of the ASTM A36 specification. This grade offers a good mix of strength, weldability, and cost. In many designs, this specification alone will satisfy designers needs. Other specifications, such as A53 for pipe, provide an equivalent grade of steel for that type of product. However, as loads on the structural elements becomes larger, other grades of steel may become more economical because of dimensional limitations or simpler fabrication. These grades provide greater strength levels at somewhat higher costs per unit weight. AISC recommends certain grades of steel, all of which have desirable characteristics, such as weldability and cost-effectiveness, for use where higher strength levels are required. The specifications covering these grades are listed in Table 7.2. Several steels have more than one level of tensile strength and yield stress, the TABLE 7.3 Symbols for Structural Shapes

Sometimes a dispute may arise as to whether or not the work is part of the contract documents and hence the obligation of the contractor. Such a dispute may result in FIGURE 17.19 Change-order proposal submitted by a contractor to an owner to request issuance of a change order. a claim on the part of the contractor. In making a claim, the contractor may request that a change order be issued prior to proceeding with the work. Or the contractor may nevertheless proceed with the work so as not to delay the job, but request that a change order be issued. Such a request is made in the form of a change-order proposal (Fig. 17.19). Depending on the size of the claim and the attitude of the owner or architect, the contractor may decide whether to continue with the extra work or to press for a decision on the claim, through either arbitration (Art 17.14.4), or some other remedy available either under the contract or at law. Dispute Resolution. The American Institute of Architects Forms, which are widely used in the construction industry, now provide for an additional means of settlement of claims between contractors and owners. AIA Form A-20 1, 1997 Edition, General Conditions of the Contract for Construction, for the first time features a mediation clause requiring parties to resort to mediation prior to instituting litigation or arbitration. This expanded approach to dispute resolution will empower the parties to work out any problems in an informal and expedient way. (See Art. 17.14.4.) The new edition of A-201 continues the practice of making the architect the first arbitor of construction claims, except for those involving aesthetic effect. However, a new section, 4.5, adds mediation as the next step in the dispute resolution process. The new A-201 retains the Arbitration Clause which provides that claims not resolved by mediation shall be decided by arbitration. These methods of claim resolution are available in any construction contract that includes, as part of its terms, the AIA General Conditions A-201. 17.14.3 Who Pays for the Unexpected? A well-drafted construction contract between contractor and owner should always contain a changed-conditions clause in its general conditions. (See General Conditions of the Contract for Construction, AIA A201, Art. 4.3.4, Claims for Concealed and Unknown Condition, American Institute of Architects, 1735 New York Ave., NW, Washington, DC 20006.) This clause should answer the question: If a contractor encounters subsurface conditions different from what might normally be expected or from what is described in plans, specifications, or other job information provided by the owner or owners agents, resulting in increased cost, should the contractor absorb the increased cost or should the owner pay it? A properly drafted change-conditions clause should contain the following elements: A requirement that the owner pay for the unexpected. Arrangements so that the owner will not be the arbiter of whether the unexpected