The effects of test method and strain calculation method on strains from nominal 25 mm coarse gravel indentations are examined for a 1.5 mm thick HDPE geomembrane with full-scale physical modeling. Maximum principal strains were calculated using thin plate theory that considers lateral displacement effects and bending strain. Strains from index tests with no subgrade were found to be twice as large as those from performance tests with clay, while strains from index tests with rubber as the subgrade were only 40% of those with clay; neither index test is suitable for selecting protection layers to limit geomembrane strain. Strains from past index tests with idealized single-point loading need to be multiplied by a factor of at least 1.8 to reproduce the maximum strain from performance tests with coarse gravel. Limiting the average membrane strain to 0.25% was found to limit the maximum principal strain to less than 6%, but not to 3% as originally intended by the German standard. The maximum result of membrane plus bending strain of 3% was shown to be closer to a maximum principal strain of 4–6% because of large-displacement and three-dimensional effects. The geotextile protection layers tested (nonwoven, needle-punched, 1500 and 1800 g/m²) were only able to limit the strain to 6% at a vertical pressure of 250 kPa and were unable to limit strain below 3%.

通过全尺寸物理建模，检查了测试方法和应变计算方法对 1.5 毫米厚 HDPE 土工膜标称 25 毫米粗砾石压痕应变的影响。使用考虑横向位移效应和弯曲应变的薄板理论计算最大主应变。没有路基的指标试验应变是粘土性能试验的两倍，而以橡胶为路基的指标试验应变仅为粘土性能试验的40%；这两种指标测试都不适合选择保护层来限制土工膜应变。过去理想化单点载荷指数测试的应变需要乘以至少 1.8 的系数，才能重现粗砾石性能测试的最大应变。研究发现，将平均膜应变限制在 0.25% 可以将最大主应变限制在 6% 以下，但不能像德国标准最初预期的那样限制在 3% 以内。由于大位移和三维效应，膜加弯曲应变 3% 的最大结果更接近 4-6% 的最大主应变。测试的土工布保护层（无纺、针刺、1500 和 1800 g/m ² ）在 250 kPa 垂直压力下只能将应变限制在 6%，并且无法将应变限制在以下3%。