Agenda - Public Works Committee - 04/16/2024

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Longitudinal cracking are cracks parallel to the pavement centerline or laydown direction. These can be caused by poor joint construction, reflective cracking from an underlying layer, fatigue cracking or top -down cracking resulting from the age of the pavement or due to expansion and contraction of the pavement surface or increased loads/traffic on the pavements. Transverse cracking are cracks perpendicular to the roadway centerline or laydown direction. These are often caused by shrinkage of the pavement surface, reflective cracking from an underlying layer or top - down cracking. Alligator or fatigue cracking can be symptomatic of poor subgrade soils and/or inadequate pavement thickness. Aggregate Base An aggregate base layer was observed below the pavements at each boring location. Laboratory testing indicated that most of the samples tested did not meet the range of MN/DOT gradation specifications for Class 5 aggregate base. It is possible that the aggregate base was initially placed as new or virgin Class 5 aggregate base but has degraded over time possibly due to vehicle traffic and freeze -thaw cycles. Fill and Possible Fill The origin of the Fill or Possible Fill encountered in the borings is unknown but is likely associated with construction of the roads and/or any underground utilities. The Fill or Possible fill was mostly composed of silty sand and clayey sand soils which are generally suitable for pavement support. However, these soils are frost susceptible materials and can heave if they become saturated and freeze. Additional details are presented in the "Subgrade Soil " paragraph below. Organic Soils Buried topsoil/ swamp deposits were encountered in boring SB-1 and SB-2 at about 7 and 9 1/2 feet, respectively, below the ground surface. The buried topsoil/swamp deposits extended to about 9 1/2feet at borg SB-I. Boring SB-2 terminated in the buried topsoil at about 11 feet below the ground surface. Organic contents ranged from about 21/2to 61/2. Soil with organic contents between 2 and 5 percent are considered slightly organic. Soil with organic content between 5 and 10 percent are considered organic. Organic soils are poor quality for pavement support and we typically recommend removing organic soil from below the proposed pavement areas. Based on the soil borings, soil corrections to remove the organic soil will likely extend to depths ranging from about 10 to 11 feet, or deeper, below the ground surface. Excavations to depths greater than about 3 to 4 feet below the pavement section may not be cost effective for the benefit gained. In addition, the buried topsoil has likely been in -place for several years and has likely reach an equilibrium so that the potential for significant additional settlement is low, especially if there will be no significant raise in site grades. For these reasons, it is our opinion, that the buried topsoil does not necessarily need to be removed. If this option is selected, you must be aware that some settlement due to long-term consolidation of the buried topsoil could occur. The use of geogrid reinforcing along this section of the roadway could aid in mitigating the effects of potential long-term settlement. Subgrade Soils Below the pavement section the borings encountered both sandy and clayey subgrade soils. Soil identified as poorly graded sand (SP) and poorly grades sand with silt (SP- SM) are well suited for pavement and/or pipe support and are considered non -frost susceptible soils and are also free draining materials. The silty and clayey (ASTM classification SM, SC, SC-SM, CL, CL-CH) are generally suitable for pavement and/or pipe support. However, these soils are frost susceptible materials and can heave if they become saturated and freeze. These soils can also loose strength when they thaw which can result in cracks in the pavements, additional maintenance costs and reduced pavement 9