<p><p><figure id='attachment_3403' style='max-width:1024px' class='caption aligncenter'><img class="wp-image-3403 size-large" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of the completed overpass at the intersection of Glen Road and U.S. Highway 61 in Newport, MN." width="1024" height="653" /><figcaption class='caption-text'> Photo courtesy of Minnesota DOT</figcaption></figure></p><p><div><h2>Project Summary/Scope:</h2>Reconstruction of the Glen Road Intersection in the SE corner of the Minneapolis/St. Paul metro area. The project involved replacing three at‑grade intersections with a bridge overpass.</p><p>Subsurface Conditions: The site consists of sandy soils with mixed bearing properties overlying dolostone bedrock. Up to 23 meters of soft cohesive soils were present in an area where it appears that bedrock was eroded and later in-filled. The width of this clay feature was about 200 meters. Between 100 and 300 mm of total and differential settlements were predicted. The total settlement tolerance for the project was 25 mm. Consequently, DMM was used to reduce the total and differential settlements of the embankment and cast-in-place retaining walls.</p><p>The highest embankment for the bridge overpass was located above the clay feature. Two strengths were used for the DMM, one below footings for a wall with a 28-day compressive strength of 1 MPa (150 psi) and another below the embankment fills of 0.7 MPa (100 psi). Minimum strengths were set at 70% of the average strength. A triple-shaft wet mix system was used with the Cement Deep Soil Mixing method (CDSM). The diameter of the DMM columns was 1 meter and spacing and overlap depended on the location. Several mixes were used with cement weights of 180 to 200 kg/m³ of treated soil. Water-cement ratios ranged from 1.0 to 1.45.</p><p>A performance-based specification was developed by the Mn/DOT Foundations Unit and included in the contract provisions. Pre-qualification requirements for the ground improvement work were included in a statement of qualifications. DMM work took place from December 2002 to December 2003. The intersection was opened to traffic in September of 2004.<br><h2>Alternate Technologies:</h2>Considered technologies included pile supported mat foundations, excavation and replacement, surcharges, lightweight fills, and ground improvement techniques (stone columns, jet grouting, and deep mixing). Deep mixing was ultimately selected because of the need to minimize costly revisions to plans required to change the foundation construction, address tight project working conditions and a heavily-traveled adjacent rail line, and reduce impact to structural systems of the bridges and walls.<br><h2>Performance Monitoring:</h2>Wet grab samples and drilled cores were used in conjunction with visual observation and mix specific gravity analysis. Advance rates, cement-slurry injection rates, torque, and other parameters were monitored and adjusted in real-time by the operators to ensure proper and complete mixing. Specimen strengths were generally much higher than required. In-situ instrumentation consisted of four earth pressure cells, three embedded strain gages, and a soil extensometer. In-situ instrumentation confirmed assumptions regarding stresses applied to the columns. The deep mix columns are performing within the required tolerances as of 2005.</p><p>Problems with large cobbles and boulders in the near surface soils resulted in an extensive removal of surface materials to allow the deep mixing to proceed.<br><h2>Cost Information:</h2>Total cost of the interchange reconstruction was $32M. Original bid price for the deep mix columns was $58/m³ for a project cost of $5.25M.<br><h2>Case History Author/Submitter:</h2>Derrick Dasenbrock, P.E.<br>Mn/DOT Office of Materials<br>1400 Gervais Ave<br>Maplewood, MN 55109<br><a href="mailto:derrick.dasenbrock@dot.state.mn.us">derrick.dasenbrock@dot.state… Technical Papers:</h2>Dasenbrock, D. (2004). “DMM Implementation Challenges at the Glen Road Interchange: Lessons Learned,”<em> Geotechnical Engineering for Transportation Projects</em>, American Society for Civil Engineers, Geotechnical Special Publication 126, Eds. M.K. Yegian and E. Kavazanjian, pp. 1347-1355.</p><p>Dasenbrock, D. (2005). “Application of deep mixing method to a challenging bridge construction projects: the Glen Road Interchange,” GeoFrontiers, American Society of Civil Engineers, GSP No. 136, Austin, TX.<br><h2>Date Case History Prepared:</h2><strong> </strong>November 2012</p><p></div></p></p>