05-12-1997 Council Packet - Laserfiche WebLink

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» _ Mr. Steven Spartz GME Project No. 6721 - . — . • .. ■ I »r- • fnJ .2 February 18, 1997 As an additional component of the project, you have placed 3 foot diameter boulders approximately 4 to 5 feet behind the existing rock riprap along the level bench in the slope at the toe of the hillside. These boulders were placed for erosion control at the toe of the slope. This spring, you plan to fill the voids between the boulders with soil to establish a vegetative growth. Scope of Services Our scope of services for this project, as outlined in our contract, is limited to providing design and construction recommendations for the proposed granite block retaining wall, and also to present our evaluations concerning the suitability of the boulders for erosion protection. Our scope of services do n^ include a global stability analysis of the hillside. Our wall recommendations will only be provided with respect to local stability of the wall system and erosional stability of the boulder facing zone. Recommendations 1 information is not available, therefore, we have had to make ceistiin assumptions for our design. We assume that the foundation and -lined soil will consist of stiff sandy clay till havino . moist unit we.yht of 130 pounds per cubic foot, a drained frictic.r' v of 27®, and a remolded undrained shear strength of 250 pounds per square foot. The walls should be embedded at least one block course (6.5 inches) below final grade in front of the wall. We recommend that the lowest block layer bear on a compacted gravel or crushed stone base having minimum dimensions of 6 inches deep by 18 inches wide. The gravel should conform to Mn/DOT 3149.2B. The gravel or crushed stone base should be compacted to at least 95% of the maximum Standard Proctor dry density, ASTM: D 698. Prior to constructing the granular base, the exposed clay subgrade should be observed for soft or loose zones. These zones would require additional subcutting and replacement with compacted granular fill. A 1 foot wide piece of filter fabric (Mn/DOT 3733, Type 1) should be placed on top of the gravel base course, beneath the joint between the lowest block course and the granite walkway slab in front, to minimize pumping of the base course through the joint. The fabric should not extend beneath the entire width of block. We recommend that the block wall be constructed with a slight batter of 6® (3/4 inch setback per block) back into the retained embankment. We recommend that the backfill within at least 6 inches of the back of the wall consist of free draining granular fill such as Mn/DOT 3149.2H. At the base of the drainage layer, we recommend placing a 4 inch diameter slotted pipe (Mn/DOT 3278) wrapped with a Type I filter fabric (Mn/DOT 3733). The drain pipe should allow gravity drainage of accumulated water away from the walls. Therefore, the pipe should daylight down slope. GME CONSULTANTS. INC.