Woodbridge Addition Driveway Separation

Transcription

1 City of Dilworth, Minnesota Woodbridge Addition Driveway Separation Study and Report mooreengineeringinc.com August 2014 Project No.18099

2 August 13, 2014 City of Dilworth Attn: Peyton Mastera 2 1 st Ave SE PO Box 187 Dilworth, MN RE: Woodbridge Driveway Separation Study/Report Moore No Peyton, Moore Engineering is pleased to provide the Dilworth City Council this study on the issue of driveways separating from the curb and gutter in the Woodbridge Addition. Please feel free to contact me if you have any questions or comments at Sincerely, Daniel R. Hanson, P.E. Senior Project Engineer Moore Engineering, Inc.

3 TABLE OF CONTENTS Letter of Transmittal Table of Contents A. Scope 1 B. Area and History 1 C. Possible Causes of Driveway Separation and Settlement 1 D. Potential Problems that could be Caused by the Separation 2 E. Recommended Corrective Actions 2 F. Special Assessment Policy 3 G. Recommendations 4 APPENDICES INDEX 5 Appendix A Area Map of Study Boundaries Appendix B Pictures of driveways displaying separation and settlement in need of corrective action.

4 Woodbridge Addition Driveway Separation A. Scope This study was focused on the issue of existing driveways within the Woodbridge Addition separating from the curb, creating a fault as well as a separation gap. B. Area and History The Woodbridge First Addition sewer/water and streets was originally constructed in the year 2001 and has expanded with future additions to Woodbridge 5 th Addition that was constructed in 2013 with the final wearing course being placed in the spring of Woodbridge First Addition consisted of 4 th Avenue from 7 th St. NE extending east to 12 th Street NE and also included Woodbridge Circle. The vast majority of driveway separation is occurring in this location which is where the study is focused. There may be additional driveways throughout the City of Dilworth, but they are outside the scope of this study. During construction, there was an abundance of rainfall, causing the clay soils to be saturated. According to interviews with City staff, the Contractor at the time had a very hard time making densities on the subbase of the roadway due to these wet conditions. This wet weather pushed the completion date back into the late fall and the City was allowing houses to be constructed prior to the roadways being completed to assist the Developer in selling lots and home owners to move in when they had sold their previous houses. C. Possible Causes of Driveway Separation and Settlement The heavy clay soils in the Fargo-Moorhead-Dilworth area are very subject to shrinkage, swelling and heaving. With different levels of wet weather, dry weather and freeze/thaw cycles, the clay soils can shrink, expand and heave upwards of 8-inches vertically. It is also not uncommon to see the soil surrounding structures and driveways pull away during dry periods. With the known moisture that was in the ground at the time of construction of the streets in Woodbridge First Addition, it is reasonable to assume that the soils were swollen. Over time and during dry conditions, as the moisture wicks out of the ground, the clay soils more than likely have shrunk, causing some driveways to pull away from the curb. With regards to some driveways settling, it should be noted that the curb fronting the driveways still seems to be generally on grade. It is a safe assumption that the roadway, to pass density tests for completion of the roadway project, was farmed, disked, dried and recompacted. This, along with a draintile installed underneath the curb to remove ambient subsurface water, would lend the street section including the curb and gutter to less settlement as it had less water in it to begin with. The aggregate base is a drainable base that sheds water 1

5 into the draintile, creating less frost heave than the abutting driveway. With this differential in heaving during freeze/thaw cycles, it is reasonable to assume that the driveways move differently than the curb section. Appendix A has a list of driveways that have been noted to either have separation, settlement or both. Appendix B has examples of driveways that have separation as well as settlement. D. Potential Problems that could be Caused by the Separation In areas where the driveway has either settled or separated from the curb, water being shed from the residential property is sheet flowing down the driveway and flowing into the crack created between the curb and the driveway. This water is basically being injected into the subbase of the roadway which can eventually lead to problems including but not limited to the following: 1. Potential washing out of the granular subbase which leads to voids and then potholes 2. Over saturation of the clayey soils leading to high plasticity which causes the subbase to lose stability and not be able to withstand the traffic loads and pavement failure 3. Additional moisture in the driveway areas of the roadway which can cause differential frost heave from one area to the next. This could result in failed pavement, cracking and frost boils. E. Recommended Corrective Actions It is recommended that the City take action to correct this issue in the near future to avoid future roadway damage. It is assumed that over the past 13 years, the soils have dried to what is considered to be normal moisture content and that any settlement that is going to occur has already occurred. Correcting the issue can be accomplished in several different ways. 1. In areas where the driveway has not settled, but has separated from the curb by ½ or less, a backer rod could be inserted with a joint filler compound covering it. a. This will prevent additional water from being allowed to flow into the subgrade, but it will not fill any existing voids that may have been created over time. This should be considered a temporary correction. If the driveway heaves during freeze/thaws different than the curb, the backer rod could be rendered useless after the first freeze thaw cycle. b. Estimated cost for backer rod and joint filler material is approximately $5.00 per Lineal Foot (LF) of curb. 2. In areas where the driveway has settled and has separated from the curb by ½ or less, the driveway could be mudjacked up to proper grade and a backer rod/joint filler could be inserted into the joint. This would theoretically fill any voids created in the past and would prevent the water being shed down the driveway from reaching the subbase. a. Estimated cost for mudjacking is approximately $25 per Square Yard (SY) of driveway concrete. 2

6 3. In areas where the driveway has separated from the curb over ½ but hasn t settled, it is recommended that a 3 wide strip of driveway be removed and replaced with the new concrete tied into the existing curb with deformed epoxy coated #4 rebar placed 18 on center across the driveway and also should be tied to the existing driveway concrete. Along with this, Expansion joint material should be installed along the back side of the curb. a. This would allow any voids created in the past to be filled with the new concrete and would be a more permanent solution. b. Estimated cost for driveway concrete removed and replaced is approximately $100/SY. 4. In areas where the driveway has separated from the curb over ½ and has also settled, and assuming the driveway concrete is in good shape, it is recommended that the curb be removed and replaced along the front of the driveway. The back of the curb could match the existing driveway concrete and the flowline would need to be poured at a straight grade across the driveway to maintain flow in the gutter. The new curb would need to be tied to the existing concrete driveway slab with #4 rebar placed 18 on center across the driveway as well as being tied to adjacent curb. It is recommended that a construction joint be sawcut approximately 3 into the driveway from the back of the new curb in the event that there is differential settlement between the driveway slab and the curb that the crack be controlled. a. This would allow any voids created in the past to be filled with new concrete. b. This option would reduce the bump that many in the Woodbridge First Addition experience as the back of curb height would be reduced. c. Estimated cost for curb and gutter removal and replacement is approximately $35 per LF of curb replaced. F. Special Assessment Policy According to the Special Assessment Policies for the City of Dilworth produced February of 2006, on page 7 under C.3 Driveway Approaches The assessable cost for driveway approaches both new and reconstructed, shall be 100% except when reconstruction is required by changes in street grade. If the option of replacing the curb is chosen, it should be noted that it isn t because of the deterioration or loss of functionality of the curb, it is being replaced due to the separated and settlement of the driveway. The purpose for removing and replacing the curb would be to correct the issues caused by the driveway and therefore, the recommendation of this report is that it should be considered 100% assessable to the abutting property. If the City does not have the funds in an account available for dedication to the corrections, it has the option of bonding for the project, however it is estimated that the cost of this project is considerably less than $100,000 which is not a desirable amount to bond. In lieu of bonding, the City can check with financial institutions regarding loans that could be taken out to pay for the project and assessed to the benefitting properties. 3

7 G. Recommendations The preferred method of corrective action should be on a driveway by driveway basis based on the amount of separation and settlement occurring. In any event, it is recommended that the City take action to correct the issues mentioned in this report before damage occurs to the street section. Respectfully submitted, Moore Engineering Inc. Municipal Consultant Engineers West Fargo, North Dakota 4

8 APPENDICES INDEX Appendix A Appendix B Area Map of Study Boundaries. Pictures of driveways displaying separation and settlement in need of corrective action. 5

9 APPENDIX A Area Map of Study Boundaries. Note: This area was generated from a list that was provided by City Staff who identified the driveways studied in conjunction with this report and is not to be considered comprehensive or final.

10 D C B A 1 N W E S Scale in Feet MEI PROJECT NO DRIVEWAY SEPARATION REPORT AUGUST 2014 WOODBRIDGE FIRST ADDITION DRIVEWAY SEPARATION AND SETTLEMENT CITY OF DILWORTH, MN 4TH AVENUE NE WOODBRIDGE CIRCLE LEGEND STUDY AREA PROPERTIES 7TH STREET NE

11 APPENDIX B Pictures of driveways displaying separation and settlement in need of corrective action.

12 Separation

13 Settlement

14 Separation

15 Settlement

16 Minor Separation, No Settlement