305.01 DESCRIPTION. Subgrade layer is primarily used for new
roadway construction. Treat subgrade soil materials with portland cement, portland-pozzolan blended hydraulic cement, or a combination of portland cement and lime, or construct a subgrade layer of stone, recycled portland cement concrete, blended calcium sulfate, or asphalt concrete in accordance with plan details or as directed. When requiring traffic to be placed on the completed, unsurfaced subgrade layer, or when the subgrade layer falls below natural ground, blended calcium sulfate will not be allowed. When not specified, the subgrade layer may be composed of any of the types of materials listed above, at the option of the contractor. Use the same subgrade layer throughout the project unless otherwise approved by the project engineer. The plans may limit the types of subgrade layer allowed. These specifications set forth the minimum requirements for construction of the subgrade layer; however, construct a subgrade layer that will provide adequate support for construction equipment and processes. Quality assurance requirements shall be as specified in the latest edition of the Department’s publication titled Application of Quality Assurance Specifications for Embankment and Base Course. Submit a dust control plan to address weather, sight clearance, operational procedures, traffic control, and any other project specific concerns. Failure to maintain sight clearance will result in the engineer stopping contractor operations. The Department will identify the dust-sensitive areas on the plans. In order to meet air quality standards, the contractor may be required to use central plant mixing of cement or cement and lime treated mixtures in dust sensitive areas at no direct pay.
305.02 MATERIALS. Materials shall comply with the following
sections and subsections: Geotextile Fabric 203.11 & Section 1019 Asphalt Concrete Section 502 Portland Cement 1001.01 Blended Hydraulic Cement 1001.02 Emulsified Asphalt Section 1002 Stone 1003.01 & 1003.04.1 Recycled Portland Cement Concrete 1003.01 & 1003.04.1 Blended Calcium Sulfate 1003.01 & 1003.04.2 Water 1018.01 Lime 1018.02 Sample blended calcium sulfate in accordance with the requirements for stone in Section 302 of the Materials Sampling Manual. Asphalt concrete shall meet the requirements of Section 502 base course. When the contractor elects to use blended hydraulic cement, the rate of cement shall be determined in accordance with 303.02.1.3 at no expense to the Department. The design compressive strength criteria for cement treated subgrade layer shall be 100 psi as determined in accordance with DOTD TR 432, Method B or C.
305.03 EQUIPMENT. Furnish and maintain equipment necessary to
produce a finished product meeting specification requirements. The equipment must be approved prior to use.
305.04 Construction Requirements.
305.04.1 Treated Subgrade Layer: Materials to be treated shall
be existing or placed under other pay items.
305.04.1 1 Subgrade Soils: Subgrade soils to be treated shall
be no more than 79 percent sand or 69 percent silt, when tested in accordance with DOTD TR 407, and shall have a Plasticity Index (PI) not exceeding 35 when tested in accordance with DOTD TR 428. Do not blend to adjust the percents sand or silt for subgrade layers for Class I base course. Do not blend or treat to reduce PI.
305.04.1 2 Treatment: Treat subgrade soils by mixing with
portland cement or a combination of portland cement and lime conditioning, and compact, finish, and cure. In-place treatment with portland cement shall be in accordance with Section 303. When central plant mixing is used, conform to Section 301. Treatment with lime shall be in accordance with Section 304 for Type C treatment. Use the minimum quantities of portland cement and lime in accordance with Table 305-1. Table 305-1 Minimum Quantities of Portland Cement and Lime
P.I. Percent by Volume 0 – 15 6% cement 16 – 25 6% lime and 6% cement 26 – 35 9% lime and 6% cement The engineer has the option of increasing or decreasing the percentages of cement and lime based on field conditions. The contract unit price for Subgrade Layer will be adjusted for the actual percentages of cement and lime required.
305.04.1 3 Pulverization: After treatment the pulverized
mixture shall conform to the gradation requirements in Table 305-2 when tested in accordance with DOTD TR 431. Table 305-2 Gradation Requirements for Treated Subgrade Layer
U.S. Sieve, Inches Percent Passing By Weight 3/4 95 No. 4 50
305.04.2 Aggregate Surface Layer: Unless otherwise specified,
furnish stone or recycled portland cement concrete. Place the aggregate subgrade layer and compact, finish, and protect in accordance with Section 302. If using an aggregate subgrade layer, furnish and place a Class D geotextile fabric to separate the aggregate subgrade layer from untreated soil.
305.04.3 Asphalt Concrete Subgrade Layer: Construct asphalt
concrete subgrade layer in accordance with Section 502.
305.04.4 Blended Calcium Sulfate: Blend calcium sulfate with an
approved aggregate prior to placement. Uniformly mix and sample the blended calcium sulfate material from dedicated stockpiles. Add water or use other suitable means to prevent dust during the transport and placement of dry blended calcium sulfate. Place, spread, and compact blended calcium sulfate to produce layers not exceeding 12 inches compacted thickness. Place each layer for the full width, bring to optimum moisture content, and compact to at least 95 percent of maximum dry density before the next layer is placed. Determine optimum moisture and maximum dry density in accordance with DOTD TR 415 or TR 418 Method G, modified to include a maximum drying temperature of 140°F. Provide a forced draft type oven capable of maintaining the temperature for field moisture content determination for density control. Do not place blended calcium sulfate within 10 feet of metal pipe. Protect and cure blended calcium sulfate in accordance with 301.12.2.
305.05 MEASUREMENT. The quantities of subgrade layer for payment
will be the design areas as specified in the plans and adjustments thereto. Design quantities will be measured in square yards based on the horizontal dimensions of the completed subgrade layer shown on the plans. Design quantities will be adjusted if the engineer makes changes to adjust to field conditions, plan errors are proven, or design changes are necessary. DOTD TR 602 measurements for width and thickness will not be made, but the width and thickness will be checked by the engineer during construction. When using aggregate, blended calcium sulfate, asphalt concrete, or central mixing, the removal of existing soil materials from the subgrade will not be measured for payment. Geotextile fabric used beneath the subgrade layer will not be measured for payment.
305.06 PAYMENT. Payment for subgrade layer will be made at the
contract unit price per square yard which includes lime, lime treatment, cement, cement treatment, water, stone, recycled portland cement concrete, blended calcium sulfate, asphalt concrete, geotextile fabric, and asphalt curing membrane or prime coat, subject to the payment adjustment provisions of Section 1002 for specification deviations of asphalt materials and 303.11.1 for density deficiencies of cement treated materials. Adjustments in pay for increase or decrease in the percent cement ordered by the engineer will be in accordance with 303.13. Adjustments in pay for increase or decrease in percent lime ordered by the engineer will be based on the price of lime shown on paid invoices (total of all charges). The Materials and Testing Section will provide the payment adjustment percentage for properties of asphalt materials. Payment will be made under: Item No. Pay Item Pay Unit 305-01 Subgrade Layer ___ in Thick Square Yard
Referenced in this section
Sections that cite this one
Get an email when 305 changes
Louisiana revises spec sections through supplementals and new editions. We check this one every week and email you the day it changes. Free, no account.
Source: Standard Specifications for Roads and Bridges, 2016 Edition. Pages 223–227 of 1,145. View official source ↗