EXTERNAL FLUSH METHODS WITH GROUT FOR MICROPILE INSTALLATION-PPT Presentation

PPT Presentation

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The subsurface profile is approximate, based on interpolation between widely spaced explorations. Fill extends to about 10–13.5 ft, underlain by upper sand to 36–52 ft, silt/clayey silt to 41–55 ft, and lower sand to 43–55 ft. Hartland Formation schist bedrock begins at approximately 70–75 ft. Surface grade varies around Elevation 12 ft; groundwater is around Elevation -1 ft, and the excavation bottom is Elevation -17.7 ft.<br /><br />Upper sand N-values range from 5 to 100 blows per foot (including refusal). Lower sand N-values are 13–23 blows per foot, with an allowable bond strength of 25 psi. Bedrock recovery is 85–88%, RQD is 54–80%, allowable bond strength is 200 psi, and allowable bearing strength is 60 ksf. Bond values apply to Type B pressure grout installed through casing during withdrawal.<br /><br />The design includes minipiles with soil sockets bearing in upper sand and minicaissons with rock sockets bearing in lower sand or bedrock. Minipiles have 6,000-psi grout, compression capacities of 10–45 tons, uplift capacities of 4–10 tons, and total depths of 30–65 ft. Minicaissons use 7.5- or 11.5-in. socket diameters, with compression capacities of 20–180 tons, uplift capacities of 20–115 tons, and total depths of 80–100 ft.<br /><br />Test Pile TP-1 was a bedrock-socketed minicaisson with 6,000-psi grout, a 13.375-in. × 1.03-in. casing, a 12-in. socket, one #18 reinforcing bar, and a 30-ft socket length. Its design compression capacity was 105 tons; the allowable bond stress was 200 psi. A maximum test load of 210 tons produced 0.58 in. of deflection.

Keywords

subsurface profile

fill layer

upper sand

silt clayey silt

lower sand

Hartland Formation schist

groundwater elevation

minipiles

minicaissons

bedrock socket testing