<p><p><h2>Summary of Example Specifications</h2><div class="grayed-title"><strong>Specification Name/Number:</strong> FHWA Ground Improvement Manual, Method Spec</div><strong>Reference(s):<br></strong><em>Elias et al. (2006b)</em></p><p>The specification found in the FHWA GI Manual contains some elements of method specifications and some elements of a performance specification. It is categorized as a combined performance/method specification in this assessment since it contains method elements (gradation requirements, maximum lift thickness, etc.) and performance elements (lift density measurement). It is focused on the select fill and reinforcement in the Load Transfer Platform (LTP). It does not include the construction of the columns or general embankment fill. Regarding the LTP fill, it does not prescribe the method of compaction or fill placement but specifies that it should be placed to 95% of the modified Proctor dry density at +/- 2% of the optimum water content. Since the specification requires measurement of design-related properties (density and water content), it is categorized as Performance Level 4. The specification is brief, outlining the basic requirements for CSE construction. Some elements are missing from this specification. For example, the document indicates that the test methods and frequency of fill density and moisture testing should be specified by the Owner.<br><div class="grayed-title"><strong>Specification Name/Number:</strong> FHWA Ground Improvement Manual, Performance Spec</div><strong>Reference(s):<br></strong><em>Elias et al. (2006b)</em></p><p>This specification is a performance specification relating to the load transfer platform and is suited to a design-build contract. The design method is left to the design-build contractor to select. The contractor should specify the number of reinforcement layers, strength, and vertical spacing, as well as the type and gradation of fill material(s). The specification includes requirements for a test section that consists of a minimum of four rows of columns in each direction with the geosynthetic reinforcement installed and embankment constructed on top. The performance is acceptable if the differential settlement is within the limits specified by the Owner. No recommendation for allowable differential settlement is given in this specification. The specification is categorized as Performance Level 1 since differential settlement is measured after<br><div class="grayed-title"><strong>Specification Name/Number:</strong> Draft MnDOT LTP for CSE</div><strong>Reference(s):<br></strong><em>Minnesota DOT</em></p><p>This specification is categorized as a combined performance/method approach specification. It specifies some method requirements such as a maximum lift thickness and some design-related properties such as minimum relative compaction. It is categorized as Performance Level 4. It is focused on successful installation of the load-transfer platform based on achieving 100% standard Proctor compaction of the fill material. This specification is clearly marked “DRAFT” but may contain some useful elements to be incorporated into a sample guide specification.<br><div class="grayed-title"><strong>Specification Name/Number:</strong> VCS Specification</div><strong>Reference(s):<br></strong><em>The Collin Group</em></p><p>This specification is categorized as a combined performance/method approach specification. It specifies some method requirements such as gradation of the select fill, maximum lift thickness, and minimum geosynthetic strength, as well as some performance requirements such as maximum total settlement of 2 inches and maximum differential settlement of 1 inch per 100 feet. It also contains a load test requirement on one column. It is categorized as Performance Level 1 since the CSE is paid on a lump sum basis and the final payment is based on successful completion of the settlement and monitoring program. Furthermore, the settlement and monitoring program is based primarily on the total and differential settlement requirements. The CSE designer must perform the design “in accordance with FHWA recommendation or using finite element analysis.” The methods listed in the FHWA Ground Improvement Manual are the Swedish Method, the Hewlett and Randolph Method, and the Collin Method.</p></p>