CID STREET INFRASTRUCTURE ASSESSMENT

Transcription

1 ABSTRACT An evaluation of the street infrastructure in Foxberry Estates Phase 1, including pavement condition, verification of construction techniques, and subgrade quality. Recommendations and costs for maintenance are provided. CID STREET INFRASTRUCTURE ASSESSMENT City of Lake Lotawana, Missouri Daniel G. Miller, P.E. Larkin Lamp Rynearson 9200 Ward Parkway, Suite 200 Kansas City, MO November 11, 2015 LLR PN

2 City of Lake Lotawana, Missouri CID Street Infrastructure Assessment LLR PN Contents Executive Summary... 2 Study Objectives... 3 Review of as constructed Roadway Plans Street Sections... 3 Structural Pavement Section... 5 Street Condition Inspection... 5 Methodology... 5 Pavement Structural Inspection... 7 Curb and Sidewalk Condition Previous Repairs Recommended Repairs Cost Estimate for Repairs Figure 1 - Street Sections, 128th Street... 4 Figure 2 - Street Sections, Primary and Secondary Streets... 5 Figure 3 - Pavement Condition Index Values... 6 Figure 4 - Subgrade Soil Properties... 9 Table 1 - Individual Sample Unit Inspections... 7 Table 2 - Pavement Inspection Results... 7 Table 3 - Core Thicknesses... 8 Table 4 - Subgrade CBR Values Table 5 - Cost Estimate for Repairs Appendix A Foxberry Estates Phase 1 Record Plans (Streets Only) Appendix B Pavement Coring Appendix C Sample Unit Maps Appendix D Pavement Inspection Forms Appendix E Pavement Condition Index Calculations Appendix F Full Depth Repair Location Recommendations 1 P a g e

3 City of Lake Lotawana, Missouri CID Street Infrastructure Assessment Executive Summary The City of Lake Lotawana is interested in the condition of the street infrastructure in the Foxberry Estates Phase 1 subdivision. The City may be asked to assume maintenance of the infrastructure and needs information about the streets to understand how they were constructed and to assess potential repairs that might be needed. Larkin Lamp Rynearson performed an inspection of the pavement condition and found that several of the streets have accelerated aging relative to their actual age of about 9 years. The combined Pavement Condition Indexes for the street segments ranged from 41 to 80 on the 100 point scale (100 is perfect). Individual sample units surveyed had PCIs as low as 14. Pavements, of this age, constructed with 8 of asphalt on unmodified dirt subgrade should generally be expected to have PCI ratings of at least 60 to 75. The deterioration is a result of several issues: Poor subgrade on which the asphalt was placed. Inadequate asphalt thickness and potentially substandard asphalt materials. Lack of maintenance since construction, specifically no crack sealing of the pavement, and failure to adequately repair alligator cracking. Continued construction traffic damaging the pavement, particularly at turning movements and directly in front of homes under construction. The infrastructure needs immediate maintenance to delay continued deterioration. This maintenance should include crack sealing, full depth base and subgrade repairs, and a chip seal surface treatment. The order of magnitude cost of these repairs is $114,000. This infrastructure will continue to require maintenance at shorter intervals, compared to streets constructed with adequate subgrades, proper asphalt pavement thicknesses, and construction material controls. It is recommended that the City institute more comprehensive design and construction controls on infrastructure that will be publically maintained, including increased design standards and construction observation to ensure that the design, materials, and construction techniques are suitable for assumption of long term maintenance of the facilities. 2 P a g e

4 Study Objectives The City of Lake Lotawana retained Larkin Lamp Rynearson to perform an assessment of the Foxberry Estates Phase 1 street infrastructure. Objectives of the study are as follows: Review as constructed plans for roadway elements of the CID. Inspect the streets, generally in accordance with Corps of Engineers PAVER standards, and estimate major areas of repair. Core the pavement at six locations to verify pavement thickness, and conduct soil testing at each core to estimate subgrade stability by the California Bearing Ratio (CBR) method. Prepare an inventory of all inspected elements in electronic format, identified according to the original construction plans. Identify immediate repair needs for all inspected elements and provide order of magnitude project cost estimates for street repair. Review of as constructed Roadway Plans. The subdivision plans were prepared by Whitehead Consultants, Inc. in August, The subdivision infrastructure was apparently constructed during the period, although there is no date on the as constructed plans. Appendix A contains the record plans for the Foxberry Estates Phase 1 infrastructure. Street Sections As shown in Figures 1 and 2, generally the streets were designed as 28 residential streets, with Foxberry Trail being a wider 36 section, typical of a collector standard. The west portion of 128 th Street, the entryway to the subdivision, was designed as dual 28 divided roadways with a 20 median. The eastern portion of 128 th Street is dual 16 divided roadways with a 20 median. There is a residential roundabout at the intersection of 128 th Street and Foxberry Trail. The main street infrastructure elements are pavement area, comprising 19,580 square yards, and 13,444 linear feet of 2 concrete curb and gutter. 3 P a g e

5 Figure 1 - Street Sections, 128th Street 4 P a g e

6 Figure 2 - Street Sections, Primary and Secondary Streets Structural Pavement Section According to the construction plans all street sections were to be constructed with 8 of asphalt concrete pavement placed on compacted soil subgrade. The plans did not call for any subgrade modification, which is not unusual practice for residential streets in many areas of the metropolitan region. No information was provided to the study team regarding any field testing of the subgrade compaction, the asphalt mix designs, or construction material testing. Street Condition Inspection Methodology The subdivision street pavements were inspected in accordance with Corps of Engineers PAVER standards. The inspection process is standardized by ASTM D The PAVER inspection system s purpose is to categorize and quantify all surface defects in the pavement and estimate 5 P a g e

7 the condition of the pavement on a point scale, with 100 being a perfect pavement. The general condition of the pavement sections on this scale are as shown: Figure 3 - Pavement Condition Index Values Using this methodology, each street pavement was divided into approximately 2,400-2,500 square foot segments. On a typical 28 residential street with 24 of pavement, each PAVER section is 100 in length. To ensure adequate sampling of the overall pavements, approximately 25% of the total pavement area was sampled and inspected. As shown on Table 1, this resulted in 23 sample units being inspected. 6 P a g e

8 Table 1 - Individual Sample Unit Inspections Results of the inspections are as shown on Table 2. The pavements inspected are about nine years old. Well-constructed residential pavements should last for at least 10 years without major maintenance, with the exception of crack sealing. The results of the pavement inspection show that most of the subdivision pavements are aging at an accelerated rate compared to what might be expected. Additionally, the pavement surface has raveling and pitting that might be a result of inadequate asphalt cement in the mix, and/or excessive shale in the aggregates used in the paving mix. Table 2 shows a summary of the street segment PCI ratings. Street Name Street Name No. of Sample Units Inspected No. of Sample Units Total Fox Den 2 6 Howard Drive 3 9 Laci Circle 5 17 Lake Point Drive 2 6 Foxberry Trail - North 3 9 Foxberry Trail - South th Street 5 18 Table 2 - Pavement Inspection Results Inspected Section No. PCI Inspected Section No. PCI Inspected Section No. PCI Inspected Section No. PCI Inspected Section No. PCI Total PCI Fox Den Howard Drive Laci Circle Lake Point Drive Foxberry Trail - North Foxberry Trail - South th Street Pavement Structural Inspection Larkin Lamp Rynearson contracted with Geotechnology, Inc. to perform physical inspection of pavement thicknesses in the Foxberry Estates Phase 1 subdivision. As noted previously, the pavements were designed as 8 thick asphalt concrete on compacted subgrade. The physical inspection procedure included advancing 4 diameter cores through the asphalt with removal for inspection. Subsequent to coring, the soil subgrade stiffness was determined by the use of a dynamic cone penetration procedure. The purposes of the coring were: Confirm as constructed pavement thickness Visually evaluate the condition of the lower portions of the pavement section 7 P a g e

9 Provide access to the soil subgrade to perform condition testing Appendix B contains the complete report from the subconsultant. Highlights of the core structural inspection are noted below: None of the cores contain asphalt concrete pavement in accordance with the subdivision design. The core depths range from with an average depth of Core Example B-6, 5.5 Thickness Inspection of the cores reveals that the surface lift is a reasonably consistent 1 ¾ to 2. The base layers differ considerably in thickness. In some of the cores, the middle base layer of asphalt appears to be moisture susceptible, indicating a lack of asphalt cement in that layer. Table 3 - Core Thicknesses The subgrade inspection determined the stiffness of the soils beneath the street sections at the coring locations. The stiffness and suitability for pavement subgrade can be represented by 8 P a g e

10 equating stiffness on a scale known as the California Bearing Ratio (CBR). While a number of soil parameters affect performance of the pavements upon which they are placed, CBR is a good indicator of the ability of the soil subgrade to support the pavement section. Figure 4 indicates the ranges of CBR relative to soil types and suitability for pavement subgrades. Medium and High plasticity clays typically have CBR values below 9, and are classified as having poor subgrade characteristics. Figure 4 Subgrade Soil Properties The CBR values for soils at the six boring locations, within about 18 of the bottom of pavement, are as shown on Table 4. 9 P a g e

11 Table 4 - Subgrade CBR Values Core # CBR within 18 of paving The CBR values obtained with the Dynamic Cone Penetration testing in the top 18 of subgrade were generally in the 2-8 category, with one outlier at about 10. In all cases, except B-4, the CBR in the top one foot of subgrade is less than 4. These values are clearly well below the desired values for pavement subgrades, and can significantly impact the long-term performance of the pavement section. Curb and Sidewalk Condition The subdivision curbs and sidewalks, where present, were visually inspected. For the most part, the curb and gutter sections show good workmanship and materials. The concrete used in this construction included limestone coarse aggregate, which can be very susceptible to material failures. Generally those material failures are a result of one, or both: D-Cracking, which is caused by excessive absorption of moisture by the limestone aggregate. During freeze-thaw cycles the rock expands due to the presence of moisture and breaks apart over time. ASR, or Alkali-Silica Reaction. In this case, the cement reacts with silica in the fine aggregate producing a gel. The gel increases in volume by absorbing water, expanding and causing pressure in the concrete, resulting in a map cracking failure. Fortunately, neither of these failure modes was observed in the concrete curb and gutter. Some of these failure modes may appear, however, over time. Neither D-Cracking nor ASR will likely be a major failure mode of the curb and gutter during its service life since none is present 9 years into the life of the curb. The major issue with the curb and gutter is damage by construction traffic. Home building in the subdivision has cracked and otherwise damaged curb segments in most of the locations. Most of this damage is cosmetic and is not affecting the primary purpose of the curb section, i.e. to carry water to the inlets. 10 P a g e

12 Previous Repairs There have been a number of pavement patches previously performed in the subdivision. They appear to be concrete of unknown depth underlying an inch or two of asphalt concrete. The patches are of variable quality, with some performing adequately, while others are not holding up as well. Other than the patches, no maintenance of the streets appears to have been performed since construction. Home construction in the subdivision continues to deteriorate the pavements as heavy truck traffic stresses the pavements. This is significantly occurring in turning areas, such as the roundabout and intersections, and directly in front of homes under construction. Recommended Repairs There are several repairs that should be performed immediately on the paving infrastructure to reduce the rate of deterioration. These include: The pavement should be crack sealed with a quality material, including cleaning out and crack sealing the joint between the pavement and curb and gutter. At numerous locations vegetation is growing in this joint, which will accelerate water penetration and deterioration of the pavement edge. Additionally, the large amount of block cracking is allowing water to penetrate the mat, and left unsealed, will propagate to alligator cracking. Alligator cracking indicates complete base failure and is a major source of low PCI ratings. Vegetation in Curb Curb and gutter sections should be replaced where they are impeding drainage from the street traveling to the curb inlets, or where they show signs of vertical displacement. Other cracked curb sections are not recommended to be replaced unless they meet the above criteria. Fortunately, the sections to be replaced are a relatively small quantity. 11 P a g e

13 Damaged Curb The worst areas of alligator cracking and potholes in the pavement should be removed and replaced full depth with at least 6 of quality asphalt. If major subgrade issues are found below the removal, those areas should be removed to stable material and aggregate base material should be compacted to the bottom of the asphalt patch. Base Repair Required The pavement should receive a surface treatment to seal the cracks that cannot be crack sealed, and to preserve the surface from further oxidation. An option would be to mill and overlay the pavement; however, due to cost considerations and the continued presence of construction traffic, that option is not recommended at this time. The mill and overlay would cost at least five times the cost of a chip seal surface treatment without appreciable benefit beyond that gained with a quality surface treatment. 12 P a g e

14 Crack and Chip Seal Required Cost Estimate for Repairs Table 5 - Cost Estimate for Repairs Item Units Quantity Unit Cost Mobilization Lump Sum Crack Seal LB Base Repairs (8") Tons Subgrade Base Aggregate (6") Tons Concrete Curb/Sidewalk LF Chip Seal SY $ 5, $ 1.50 $ $ $ $ 2.50 Total Cost $5,000 $17,622 $14,403 $3,320 $2,000 $48,950 Construction Subtotal Contingencies (20%) Construction Total $86,295 $17,259 $103,554 Plans, Specs, Const. Eng. (10%) Total Project Cost $10,355 $113,909 The repair cost estimate was prepared from 2015 public bids on projects that contained larger quantities of materials for the work. Adjustments were made in an effort to reflect the smaller amounts of work in an individual subdivision, but Larkin Lamp Rynearson recommends that additional estimates be obtained from qualified contractors to verify the anticipated cost of repairs. 13 P a g e