The National Academies Press

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Pages 96-128

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From page 96... ... Sill Settlement and Angular Distortion • The settlement of the sill was much smaller in the Amoco test section than in the Mirafi test section. Under an applied pressure of 200 kPa, the average sill settlement was 40 mm and 72 mm in the Amoco test section and the Mirafi test section, respectively. Read the entire page →
From page 97... ... This would render the Amoco test section only "marginally acceptable" and the Mirafi test section "unacceptable" under a design pressure of 200 kPa. The measured data from the Founders/Meadows abutment (with a soil friction angle of 40 deg from the standard direct shear tests) Read the entire page →
From page 98... ... , the pullout safety factors in the top two reinforcement layers were less than 1.0 for both test sections, with the lowest value of pullout safety factor of 0.2 occurring at the very top layer. Trial and error revealed that a pullout safety factor of 1.0 would occur at an applied pressure of 33 kPa. Read the entire page →
From page 99... ... Step 2: Establish engineering geotechnical properties (including unit weight and internal friction angle of the reinforced fill and the retained earth and allowable bearing pressure of the foundation soil and the reinforced fill) Read the entire page →
From page 100... ... The allowable bearing pressure for the selected sill width is equal to the allowable pressure determined in Step (1) multiplied by the correction factor. Read the entire page →
From page 101... ... , especially the analysis results of allowable bearing pressures. Special emphases have been placed on the applied pressure at short-term sill settlement = 1 percent of lower abutment wall height and on the applied pressure corresponding to the condition in which the critical shear strain has just reached a triangular distribution extending through the height of the load-bearing wall (for details, see Load-Carrying Capacity Analysis) Read the entire page →
From page 102... ... , in which H2 is the height of the upper wall; and γ is the unit weight of reinforced fill. The safety factor against bearing failure is evaluated by dividing the average foundation contact pressure, pcontact, by the allowable bearing pressure of the foundation. Read the entire page →
From page 103... ... . It is recommended that the resistance at tensile strain of 1.0 percent be taken as the reference strain for specification of the required reinforcement stiffness. Read the entire page →
From page 104... ... is the maximum lateral stress in the reinforced fill and s is the vertical reinforcement spacing. For non-uniform reinforcement spacing, s = (1/2 distance to reinforcement layer above) Read the entire page →
From page 105... ... should be observed to avoid potential facing failure. The interface strengthening effect will be more effective if the facing blocks are interconnected after all the facing units are in place. Read the entire page →
From page 106... ... If the GRS abutment is in a stream environment, scour/abrasion/channel protection measures should be undertaken. • Establish trial design parameters: – Sill width, B (a minimum sill width of 0.6 m is recommended) Read the entire page →
From page 107... ... On the other hand, if a single set of tests shows that a soil has a friction angle of 35°, then the "design friction angle" will be taken as 34°. • Establish retained earth parameters: – Friction angle of the retained earth – Wet unit weight of the retained earth – Coefficient of active earth pressure of the retained earth • Establish foundation soil parameters: – Friction angle of the foundation soil – Wet unit weight of the foundation soil – Allowable bearing pressure of the foundation soil, qaf Step 3: Establish design requirements • Establish external stability design requirements: – Factor of safety against reinforced fill base sliding ≥ 1.5 – Eccentricity ≤ L/6 (L = length of reinforcement at base of the reinforced zone) Read the entire page →
From page 108... ... Conditions: Fill: φdesign = 34° (note: φtest = 34.8° from a single set of standard direct shear tests) Reinforcement spacing = 0.2 m Isolated sill, sill width = 0.9 m Allowable bearing pressure: (1) Read the entire page →
From page 109... ... . • Check allowable bearing pressure of the reinforced fill; the applied contact pressure on base of the sill should be ≤ qallow determined in Step 4. Read the entire page →
From page 110... ... s where σh(max) is the maximum lateral stress in the reinforced fill, and s is the vertical reinforcement spacing. Read the entire page →
From page 111... ... . The abutment settlement, under the recommended allowable bearing pressure determined in Step 4, can be estimated conservatively as 1.5 percent of H1 (H1 = height of the loading bearing wall) Read the entire page →
From page 112... ... . – For abutment walls less than 10 m high, unless the ground surface is level and the foundation soil is stiff, a leveling pad should be constructed under the first course of the facing blocks. Read the entire page →
From page 113... ... – Placement of the reinforced fill near the front should not lag behind the remainder of the structure by more than one lift. – Backfill should be placed, spread, and compacted so as to prevent the development of wrinkles or movement of the geosynthetic reinforcement and the wall facing units. Read the entire page →
From page 114... ... Other Flexible Facings For a flexible facing differing from the segmental concrete block facing, the following construction guidelines about the facing should be observed: Wrapped-Faced Geotextile Facing • If the geotextile is wide enough for the required reinforcement length, it can be unrolled parallel to the wall (i.e., in the longitudinal direction) Read the entire page →
From page 115... ... Length of concrete approach slab 4.25 m Trial design parameters: Sill width, B 1.5 m Clear distance, d 0.3 m Sill type integrated sill Facing modular concrete blocks Facing block size 200 mm x 200 mm x 400 mm Batter of facing 1/35 (6 mm setback for each block) Reinforcement spacing 0.2 m Note: As the batter of 1/35 corresponds to an angle of 1.6°, less than 8°, the abutment wall is to be designed as a vertical wall, and the coefficient of earth pressure is to follow the general Rankine case, per Section 4.2d, NHI manual. Read the entire page →
From page 116... ... Integrated sill, sill width = 1.5 m (1) From Table 3-1, for φ = 34° and reinforcement spacing = 0.2 m, allowable bearing pressure = 180 kPa. Read the entire page →
From page 117... ... /134.53 kN/m = 0.11 m B/6 = 1.5 m/6 = 0.25 m e < B/6 (OK) Check allowable bearing pressure of the reinforced fill: psill = applied pressure from the sill psill = 134.53 kN/m/[1.5 m − (2 0.11 m) Read the entire page →
From page 118... ... pcontact = 264.40 kN/m2 < qaf = 300 kN/m2 (OK) Step 8: Evaluate internal stability at each reinforcement level With geosynthetic reinforcement, the coefficient of lateral earth pressure is constant throughout the entire wall height, per Section 4.3b, NHI manual. Read the entire page →
From page 119... ... Step 10: Design of back/upper wall Reinforced fill: Same as that of the loadbearing wall Reinforcement: Same as that of the loadbearing wall Reinforcement length: 4.25 m (length of approach slab) + 1.5 m = 5.75 m (see The Recommended Design Method Step 10) Read the entire page →
From page 120... ... Front batter 1/35 Sill type integrated sill Sill width 1.5 m Sill clear distance 0.3 m Embedment 200 mm (one facing block height) Reinforcement: Minimum stiffness at =1.0 percent, T@=1.0 percent = 12.0 kN/m Minimum ultimate strength, Tult = 65.8 kN/m Length in load-bearing wall = 7.0 m Read the entire page →
From page 121... ... Reinforcement spacing 0.2 m Note: As the batter of 1/35 corresponds to an angle of 1.6°, less than 8°, the abutment wall is to be designed as a vertical wall, and the coefficient of earth pressure is to follow the general Rankine case. The configuration of the initial trial design for the GRS abutment is shown in Figure 3-8. Read the entire page →
From page 122... ... = tan2 (45° − φre/2) = 0.33 Foundation soil: φfs = 30°, γfs = 20.0 kN/m3, qaf = 300 kN/m2 Step 3: Establish design requirements External stability design requirements: – Sliding ≥ 1.5 – Eccentricity ≤ l/6 – Sill pressure ≤ allowable bearing of the reinforced fill qallow = 345 kPa (as determined in Step 4 below) Read the entire page →
From page 123... ... /79.25 kN/m = 0.01 m B/6 = 0.6 m/6 = 0.10 m e < B/6 (OK) Check allowable bearing pressure of the reinforced fill: psill = applied pressure from the sill p Va B esill = − Σ 2 ' e B M M Va RA OA = − − 2 Σ Σ Σ FS Va LL Fasliding rf = −( ) Read the entire page →
From page 124... ... Step 7: Check external stability of reinforced fill with the preliminary reinforcement length established in Step 5 The forces needed to evaluate the external stability of the abutment are shown in Figure 3-8. These forces are calculated as follows: V4 = (L × H1) Read the entire page →
From page 125... ... = 0.38 m L/6 = 2.4 m/6 = 0.4 m e < L/6 (OK) Check allowable bearing pressure of the foundation soil: Calculate the "influence length" D1 at the foundation level and compare with the effective reinforcement length, L. Read the entire page →
From page 126... ... pcontact = 138.14 kN/m2 qaf = 300 kN/m2 (OK) Step 8: Evaluate internal stability at each reinforcement level With geosynthetic reinforcement, the coefficient of lateral earth pressure is constant throughout the entire wall height, per Section 4.3b, NHI manual. Read the entire page →
From page 127... ... Step 10: Design of back/upper wall Reinforced fill: Same as that of the load-bearing wall Reinforcement: Same as that of the load-bearing wall Reinforcement length: 1.3 m (without an approach slab, the back wall reinforcement length is to be flush with the reinforcement in the load-bearing wall) Reinforcement layout: Vertical spacing = 0.2 m 127 Read the entire page →
From page 128... ... Abutment configuration: Load-bearing wall height, H1 2.4 m Back wall height, H2 0.6 m Facing modular concrete blocks (200 mm x 200 mm x 400 mm) Front batter 1/35 Sill type isolated sill Sill width 0.6 m Sill clear distance 0.3 m Embedment 200 mm (one facing block height) Read the entire page →

From page 96...

... Sill Settlement and Angular Distortion • The settlement of the sill was much smaller in the Amoco test section than in the Mirafi test section. Under an applied pressure of 200 kPa, the average sill settlement was 40 mm and 72 mm in the Amoco test section and the Mirafi test section, respectively.