§ 40-185. Street structural thickness design.

(a)

Engineered design of street structural section. Except as provided by subsection (b) of this section, the developer shall have an engineer registered in the state design the street structural sections (structural thickness) in accordance with:

(1)

Portland Cement Association, Rigid Pavement Design Method;

(2)

American Association of State Highway & Transportation Officials (ASSHTO), Flexible-Pavement Design Method;

(3)

Asphalt Institute Design Method;

(4)

Any other design methods not specifically mentioned in this article may be used, with prior approval of the city engineer.

(b)

Standard pavement design. Where the proposed development consists exclusively of R-1 or R-2 street sections the developer may elect to use a standard pavement thickness. The standard pavement thickness for each pavement type are:

(1)

Flexible Pavement-8 inch compacted base with two-inch HMAC surface course.

(2)

Full Depth HotMix-4 inches of HMAC base with two inches HMAC surface course.

(3)

Reinforced Concrete-6 inches of 3,000 psi concrete reinforced with #3 rebar at 18-inch centers, both ways.

(c)

Structural street section design. The street structural section design shall be based on the total number and weight (plus configuration) of the axles expected to go over the street section during a design life of 20 years. The concept of "Equivalent Axle Loadings" shall be used to express the total number and mixture of loadings that will occur during the street section's expected life. If a roadway is proposed, it will be designated as an arterial, collector, or local, and the street structural section design shall be based on the loadings shown in Table 40-7: Street Design by Equivalent Axle Loads.

(d)

Alternative design standards for low density residential development in the city's extra-territorial jurisdiction (ETJ). The developer may, with approval of city council, provide non-curbed and gutter streets, as provided in Figure 40-9, in subdivisions in the city's ETJ subject to the following:

(1)

All lots must meet the estate lot standards as provided in subsection 40-132(b) of this chapter.

(2)

All lots shall be provided with full public water and sanitary sewerage service.

TABLE 40-7
STREET DESIGN BY EQUIVALENT AXLE LOADS
(20-YEAR DESIGN LIFE)

Street Classification	Description	Axle Loads Equivalent to 18,000 Pounds
A-1	Arterial	5,000,000
A-2	Arterial	5,000,000
C-1	Collector	400,000
LC-1	Local commercial	400,000
R-1 and R-2	Residential	9,000

 

(e)

Soils testing and subgrade stabilization.

(1)

The developer shall submit to the city a soil test report for each 1,000 square yards of paved surface proposed or for each type of soil encountered in the subgrade.

(2)

The developer shall submit to the city the following data as part of the soil test report:

a.

Soil classification;

b.

Optimum moisture/density (Modified Proctor, ASTM D 1557);

c.

Atterberg Liquid Limits and Plasticity Index (P.I.);

d.

Stabilization requirements for subgrade soil (percent lime for clay or percent cement for sandy soils), if street structural section is to be designed by an engineer;

e.

All tests shall be performed by a certified testing laboratory approved by the city.

(3)

The developer shall stabilize all subgrade soils with a P.I. of 20 or more:

a.

If the standard structural section design for paved local streets is used, five percent lime by weight may be used; otherwise,

b.

The developer shall have a certified testing laboratory conduct lime (or other approved material) series test to determine the percent of stabilizing agent necessary to lower the P.I. below 20.

(4)

Native soils with a P.I. of less than 20 may be used as subgrade material as long as they can meet the city's compaction requirements (see subsection (c)(1) of this section). The developer may add a stabilizing agent (lime, cement, etc.) as recommended by soils analysis, to such low P.I. soil to aid in compaction.

(5)

Subgrade soils evaluation shall generally apply to the top six inches of soil measured down from the proposed subgrade surface.

(f)

Other basic criteria.

(1)

The developer shall compact all subgrade and individual layers of base and paving materials to 95 percent relative density, plus or minus three percent optimum moisture, Modified Proctor Test.

(2)

The total design thickness of the street structural section shall be rounded up to the nearest whole inch.

(3)

The surface course for flexible pavement shall be a minimum of two inches of Type "D" HotMix Asphaltic concrete as specified in Item 340 of the TxDOT Standard Specifications for Construction of Highways, Streets and Bridges, 1993.

(4)

The base material for flexible pavement shall be Grade 2, Type "A" as specified in Item 247 of the TxDOT Standard Specifications for Construction of Highways, Streets and Bridges, 1993.

(5)

The developer shall completely clear and grub the area within the street right-of-way prior to construction of any street improvements.

(6)

Any other design methods not specifically mentioned in this chapter may be used with prior approval of the city.

(7)

The design requirements set forth in this section are minimum design standards. The city reserves the right to require additional precautions or treatments consistent with sound engineering practice to provide for conditions not specifically covered in this section.

(Ord. No. O-24-07, § I, 9-24-2007)