Laserfiche WebLink
60 <br />~rJ_, =friction angle of fabric to soil <br />~,_, =Friction angle of soil itself <br />E, =varies from 0 to I <br />E, =varies from 0 to I <br />Designing with Geotextiles Chap. 2 <br />2.?.2.3 Anchorage Type <br />Anchorage reinforcement is similar to the shear type just described, but now the <br />soil acts on both sides of the geotextilt as a tensile force tends to pull it out of the soil. <br />The laboratory modeling of this t}'pe oC mechanism is similar to detect shear except that <br />now soil is in both halves of the shear box and the Fabric extends out of the shear box at <br />its center. Here it is gripped extemalh• and pulled, while normal svtsses act on the soils <br />and fabric within the shear box. Section 2.1.3.9 described [he situation and also govt <br />typical values in terms of shear svength parameters by themselves and efficiencies as <br />just discussed. An additional approach could be to express the efficiency as a (unction of <br />the amount of mobilized fabric strcn~th. \Vide-width tensile values should be used in <br />this case. As with the other types of mechanisms of geotextilt reinforcement, this catt- <br />eon of fabric anchorage is used quirt often. The applications mentioned in Chapter I <br />illustrate the poim. ~ <br />2.2.3 Filtration <br />Tht etotc.cult function of filtration involves the movement of water throu~,h the fabric <br />itscl((i.t., across its manu(acturcd plant). At the same time, the fabric sears the pur- <br />pose of retaining the soil on its upstream side. Both adequate ptnntabilit}' (requiring <br />an open fabric structure) and soil retention (requiring a tight fabric structure) arc <br />required simultaneously..4 third factor is also involved, that being the long-teem soil-to- <br />fabric compatibility that will not deitrioraie (or complete)}' clog) dunne the hl'etime of <br />the sesttm. Thus a dcgnition of filtration is: <br />_ Filrranon: the equilibrium labric-m-sod s}'seem which allows (or irec «~aicr Oow (bw not <br />:~' sod loss). across the plane of the (abnc over an indefinitely long lime ptrind. <br />I <br />This function of (ikrauon is a mayor one (recall the applicauon arras presented in <br />Section I.2.J) (or the geotexule industn• and. when properly desi~•ned and constructed. <br />^.' I offers a practical rcmcdy to ntuny gmtechnital problems. <br />2?.J.I Pcrmcability <br />This particular discwsion of fabrc permeability refers to cross-plant ptnnatbilrt} <br />when water Oow is pcrpcndicular w the plan:: of [hc labnc. ,blam~ of the fabrics used <br />for this purpose are rclativcly thick and compressible. For this reason the thickness <br />- is included in the permeability cotiiiaent and is used as a "pennittivny." which is ~ <br />defined as <br />k, <br />~y = - (2.16) <br />~. r <br />