土工合成材料加固挡土墙(Geosynthetic Reinforced Retaining Wall)
1 引言
在《土钉支护的边坡稳定性(Stability of Slope Reinforced with Soil Nails)》中曾经提到，HYRCAN目前提供了5种支护型式：End Anchored, Grouted Tieback, Soil Nail, GeoTextile, Pile。这个笔记讨论了使用GeoTextile支护挡土墙的计算过程。
GeoTextile支护类型可用于模拟各种类型的边坡加固，例如网(meshes)、网格(grids)、条带(strips)等。这类支撑系统通常被称作土工织物或土工布、土工格栅、土工合成材料等。
2 问题陈述
该挡土墙拟使用9m长的土工合成材料进行支护，地基土有两层，上层为回填土(Backfill), 下层为冰川沉积土(Glacial till, 加拿大北部地区典型的土层)，支护区域单独划为一种材料。
地层的物理力学属性如下所示。
3 HYRCAN计算
根据上面的问题陈述依次设置外部边界，材料边界，材料属性，指定属性。
set("numSlice",50,"Method","GLE/M-P","on","Method","JanbuSim","on","Method","Spencer","on")extboundary(-23,-5,-14,-4.5,-12,-5.5,-1,0,0,0,0,8.3,9.1,8.3,16,7.5,19.5,6,24,6.5,24,-15,-23,-15,-23,-5)matboundary(-23,-7.5,-7,-7.5,-4.5,-8,-1.5,-7,24,-7)matboundary(0,0,9.1,0,9.1,8.3)definemat("ground","matID",1,"matName","Backfill","uw",21.7,"friction",33)definemat("ground","matID",2,"matName","Wall","uw",20.4,"cohesion",0,"friction",41)definemat("ground","matID",3,"matName","Till","cohesion",2,"friction",54)assignsoilmat("matid",1,"atpoint",5.73128,-4.02114)assignsoilmat("matid",2,"atpoint",6.28592,2.26478)assignsoilmat("matid",3,"atpoint",4.80688,-12.5256)
接下来增加支护。使用"属性(Properties)->定义支护(Define Support)"菜单打开支护属性对话框。目前程序有5种支护方式可以选择，在本例中，支护类型选择土工材料(Geotexile)，输入下图所示的参数。
Geotexile分三种类型，区别在于抗拉强度的不同。施力方式选择“被动",力的方向选择"平行于加固(Parallel to Reinforcement)",锚固类型选择"Slope Face"。
definemat("support","matID",1,"supportType","GeoTextile","matName","Type 1","forceApp","passive","stripTensile",111,"stripAdhesion",0,"stripFricAngle",41)definemat("support","matID",2,"supportType","GeoTextile","matName","Type 2","forceApp","passive","stripTensile",71,"stripAdhesion",0,"stripFricAngle",41)definemat("support","matID",3,"supportType","GeoTextile","matName","Type 3","forceApp","passive","stripTensile",42,"stripAdhesion",0,"stripFricAngle",41)
当GeoTextile 用于加固边坡时，材料被放置在一定宽度的条带中。条带覆盖率(Strip Coverage)指的是这些条带在平面外方向（即沿边坡）的间距。如果这些条带是连续铺设的，相邻条带之间没有空隙，那么条带覆盖率=100%。如果条带不是连续铺设的（即相邻条带之间有空隙），那么条带覆盖率将低于100%。例如，如果铺设4米宽的条带，每条带之间有2米的间距，那么条带覆盖率将等于67%(即4/(4+2))。
接下来添加Geotexile的布置方式，使用Support>Add Support Pattern分别设置三类支护,如下图所示。
addsupport("pattern","id",1,"matid",1,"orientation","anglefromhoriz","angle",0,"length",9,"spaced","along","dist",0.6,"frompoint",0,0.25,"topoint",0,3.9)addsupport("pattern","id",2,"matid",2,"orientation","anglefromhoriz","angle",0,"length",9,"spaced","along","dist",0.6,"frompoint",0,4.45,"topoint",0,6.5)addsupport("pattern","id",3,"matid",3,"orientation","anglefromhoriz","angle",0,"length",9,"spaced","along","dist",0.6,"frompoint",0,6.85,"topoint",0,8.3)
最后一步设定边坡限制。
definelimits("limit",-14,-1,"limit2",2,19.5)
每种方法计算的最小安全系数为:
Bishop Simplified Method: fos=1.459
GLE/M-P Method: fos=1.459
Janbu Simplified Method: fos=1.324
Spencer Method: fos=1.458
4 SLIDE计算
相同的数据在SLIDE下运行，每种方法计算的最小安全系数为:
Bishop Simplified Method: fos=1.483
GLE/M-P Method: fos=1.484
Janbu Simplified Method: fos=1.380
Spencer Method: fos=1.483
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