05-28-1991 Council Packet - Laserfiche WebLink

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An Overview of Geosynthetica Chap. 1 1.1 BASIC DESCRIPTION OF GEOSYNTHETICS Lost in the pages of histor>‘ are the initial attempts to reinforce soils with dissimil... materials possessing properties that would enhance the behavior of the soil itself. It seems reasonable to assume that it was attempted to stabilize swamps and marshy soils using tree trunks, small bushes, and the like. These soft soils would accept the fibrous material until a mass was formed that had adequate propenies for the intended purpose. It also seems reasonable to accept that continued use of such a facility was possible due to the properly stabilized nature of the now-reinforced soil (probably by a trial-and-error procedure), or impossible due to a number of factors, among which were: Insufficient reinforcement materials for the loads to be carried Pumping of the soft soil up through the reinforcement matenal Degradation of the fibrous matenal with time, leading back to the original unsuit able conditions Such stabilization attempts were undoubtedly continued with the development of a more systematic approach in which timbers of nearly uniform size and length were lashed together to make a mattressed surface. Such split-log "corduroy*' roads over peat bogs date back to 3000 B.C. [1]. This art progressed to the point where the undulating surface was filled in smooth and some of these svstems were surfaced with a stabilized soil mix- ture or even paved with stone blocks. Here again, however, time deterioration of the timber and its lashing was an obvious problem. The concept of reinforcing poor soils has continued until nearly the present day. The first use of fabrics made from natural fibers to reinforce roads was attempted by the South Carolina Highway Department in 1926 [2] They used a heav> i.otton fabric on a primed earth base, applied hot asphalt on the fabnc. and covered this with a thin layer of sand. They published their work in 1935. describing eight separate field experiments. Until the fabric deteriorated, the results showed that the roads were in good condition and that the fabric reduced cracking, raveling, and localized road failures. This project was certainly the forerunner of the separation-reinforcemen. function of geosynthetic materials as we know it todav. Another major topic area for the purpose of this book is that of providing an inter mediate barrier between two dissimilar materials for the purpose of water drainage and soil filtration. When requiring water flow across this barrier it must obviously be porous, yet not so much as to lose the retained soil — thus the necessity of using some sort of intermediate material. Again the historical development of attempts at filtration are important to set the stage for the work to follow. Run-of-bank gravel which was found to be naturally well graded had been used as filter material since ancient times. Purification by means of runni.ng polluted water '‘.u-ough soil is an outmoded concept but still apparently used on occasion. The idea of systeman.ring the process seems to have been originated by K. Terzaghi and A. Casagrande in the 1930s and brought to use by Bertram [3] shortly thereafter. This idea of soil filters, even multiple-graded soil filters, is a target area for the matenals described in this book — not for reasons of degradation, however, but for cost efficienev.