Design Guideline for the Reintroduction of Wood into Australian Streams

stable pile depth in the Snowy River study (SKM 2005) is outlined. The inputs used in the run of the LLP99 model were: • single soil layer, • very high flexural stiffness of pile (1,000,000 kN/m). • pile width = 0.3 m (i.e. wooden pile), • shear strength in the absence of lateral stress (for unconsolidated sand 150 kN/m was used), • effective unit weight of soil (15 kN/m), • active lateral effective stress coefficient (used 0.426 based on coefficient of earth pressure at rest for sand with = 35°), • neutral lateral effective shear stress coefficient (used default – 1), • passive lateral effective stress coefficient (= 1/ active lateral stress coefficient = 2.35), and • stroke displacement between active and passive stress (used default 0.02 m). Loading steps of 1 kN were applied at 1 m above the pile interception with the pre-scour bed level. The moment for each loading step is based on a maximum scour hole depth of 3.5 m, hence the moment arm is 4.5 m (i.e. moment = 4.5 kNm for each loading step).The depth of pile was varied in order to determine an effective pile depth for securing LWD. The pile deflection was limited for all pile depths considered (Table 7). For piles constructed 1 m below the maximum scour depth, the piles should not deflect more than 1 cm under the bankfull flow. In practice we would recommend that piles be driven an extra metre to account for any underestimation in maximum scour depth. The recommended pile depth is, therefore, the maximum depth of scour (3.5 m) plus 2 m, or 5.5 m from the pre-scour bed level for securing in-stream wood. Table 7. Pile displacement under alternative loads.