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. . ,--, -- Geotechnical Consuftation Services Page 7 - 93-1397 Hannabrook Rock Wall - Lots 39 through 45 July 26, 1993 We also believe that it is important to draw the owner's attention to the safety aspects of the constructed rock wall. Because the wall provides an"attractive"place on which children may • climb, we recommend that the owner make it ctear that such activity is not, and will not be, tolerated. Such activRy can, and in some instances has, resulted in severe and fatal injury and should be avoided. Use of FabNc There are wide variations of opinion regarding the use of fabric in rock wall construction to "prevent" fines being flushed from the protected soil face out tnrough the rock filter layer. In our opinfon, and aRer detailcad discussions with several fabric manufacturers representatives, fabric should not be used in pro;active rock wall cons!ruction of this nature. For a geotechnical drainage fabric to function as designed, the manufacturer recommends that the interface between the soil face, fabric and backfill (the rock wall filter rock in this case) should be such that the fabric is very tightly sandwiched between the soil and backfill. This sandwiching effect keeps the filter cloth f;at and in close contact which is what prevents soil particles from moving. Unfortunately, it is usually difficult, if not impossible, to achieve this form of contact in rock well construction. As a result, it is often possible for soil particies to be flushed from the face of the soil into the fabric. Over time, and this is often a short period, large portions of the fabric become clogged and this leads to buildup of hydrostetic pressure behind the rock wall. Naturally, the wall cannot wkhstand such prassures, and it moves and/or fails. In our opinion, this scenario can be avoided if the filter rock material is placed carefully so that the soil face is suitably protected. Closure The recommendations contained in this lerier pertain specifically to the subject protective rock wall and are for the exclusive use of Colony Craft, and their other consultants and subcontractors only. The recommendations have been developed in a manner consistent with that ievel of care, skill and competence ordinarily exercised by other members of the profession in good standing currently practicing under similar conditions in this area. No other warranty is expressed or implied. The information is provided as a service to the client, but CEO, Inc., does not intend that it should be construed to mean that w�a take any responsibility for site safety measures,