Design Guidelines for Increasing the Lateral Resistance of Highway-Bridge Pile Foundations by Improving Weak Soils (2011) / Chapter Skim
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Chapter 2 - Available Ground Improvement Case Histories and Approaches
Chapter 2 - Available Ground Improvement Case Histories and Approaches
Pages 5-13
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From page 5... ...
In connection with research studies, field load tests have been performed on two pile groups where the native clay soil was excavated and replaced with compacted granular soil. These studies were primarily undertaken to evaluate group interaction factors under lateral loading.
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From page 6... ...
to high Mod. to high In-Situ Densification Dynamic Compaction Densification to 25-ft depth from surface impact •Decrease in improvement with depth •Produces vibration and noise •Could produce downdrag in existing piles •Requires overhead clearance for dropping weight Low Low Vibro Compaction •Relatively uniform improvement with depth •Could produce downdrag in existing piles Low Moderate Stone Columns •Increased densification relative to vibrocompaction •Increased shear resistance of reinforced soil mass •Drainage provided by columns in the event of liquefaction concerns •Must install stone through entire layer to treat loose sand at depth •Could produce downdrag in existing piles Low Moderate Stone Columns with Wick Drains •Improved effectiveness with high fines content soils •Does not produce spoils •Increased cost and logistical effort of installing wick drains prior to stone column treatment Low Moderate Compaction Grouting •Can be used for retrofit below a pile cap •Can treat zones of interest without treating all soil above the zone •Does not produce spoils •Less effective at shallow depths where pressure is restricted •More difficult to evaluate improvement for retrofit conditions below pile Moderate Moderate Soil Mixing Deep Soil Mixing •Mixing can occur to 60- to 80-ft depths •Significant strength gain can be achieved • Can produce columns (3-ft dia.)
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From page 7... ...
• Creates extremely dense high- friction angle columns Low Low In-Situ Soil Mixing Vibro Replacement • Increases shear resistance of the reinforced soil mass • Can cause heave of surrounding ground Low Low Compaction Grouting • Can be used for retrofit below a pile cap • Can treat zones of interest without treating all soil above the zone • Does not produce spoils • Less effective at shallow depths where pressure is restricted • Can decrease the strength of sensitive clays • More difficult to evaluate improvement for retrofit conditions below pile Moderate Low Deep Soil Mixing • Mixing can occur to 60- to 80-ft depths • Significant strength gain can be achieved • Can produce columns (3 ft dia.) or wall panels at desired depths • Can decrease the strength of sensitive clays • Produces spoils Mod.
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From page 8... ...
Tests were conducted on a silty sand at two densities and on loose silty sand with a 1- to 2-m wide zone of dense compacted gravel immediately adjacent to the pile cap. The native clay in the tests performed by Mokwa and Duncan (2001)
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From page 9... ...
Crack patterns from the tests, shown in Figure 2-6 indicate that the compacted gravel zones increase the effective 9 Figure 2-3. Comparison of passive force provided by stiff, partially saturated clay and compacted sandy gravel against 1.1-m deep 1.9-m wide cap block.
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From page 10... ...
6 ft sandy gravel zone plus loose silty sand backfill 10 ft x 17 ft x 3.67 ft Pile Cap 2 ft x 2 ft Grid 10 ft x 17 ft x 3.67 ft Pile Cap 2 ft x 2 ft Grid Gravel Backfill Loose Silty Sand Figure 2-6. Plan view of crack patterns behind a pile cap after excavation and replacement of loose silty sand with (a)
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From page 11... ...
shaft that reacted against a group of four 0.324-m diameter driven steel pipe piles. Lateral load tests were first performed on the test foundations prior to treatment, then comparable lateral load tests were performed after treatment for comparison.
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From page 12... ...
12 x xx x x x x x x x xx x x xx o oo o o o o o o o o o o o x = Charges for first and second blast @ 3.5 m o = Charges for second blast only @ 3.5 m = Stone Column, 0.9 m Diameter, Installed to a depth of 6 m = 2 x 2 Pile Group = 0.6 m CISS Pile Limit of Excavation Limit of Densification Scale: 1m Figure 2-9. Layout of test foundations, stone columns, and explosive charges.
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From page 13... ...
Static load vs deflection curves before and after stone column treatment for (a) pile group and (b)
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