Reinforcement Stone Columns Method 1 What is Stone Column? stone columns are a ground improvement technique to improve the load bearing capacity of the soil. The stone column consists of crushed coarse aggregates of various sizes. The ratio in which the stones of different sizes will be mixed is decided by design criteria.
4 What is Stone Column? (Cont.) Vibro-Replacement Stone Columns extends the range of soils that can be improved by vibratory techniques to include cohesive soils. Densification and/or reinforcement of the soil with compacted granular columns or stone columns is accomplished by either topfeed or the bottom-feed method. Cohesive, mixed and layered soils generally do not densify easily when subjected to vibration alone. The Vibro-Replacement Stone Column technique was developed specifically for these soils, effectively extending the range of soil types that can be improved with the deep
vibratory process. With Vibro-Replacement Stone Columns, columns of dense, crushed stone are designed to increase bearing capacity, reduce settlement, aid densification and mitigate the potential for liquefaction, and improve shear resistance. 5 The Vibro-Replacement Stone Column Process! 1. Reduces shallow foundation settlement. 2. Increases bearing capacity, allowing reduction in footing size. 3. Mitigates liquefaction potential.
4. Provides slope stabilization. 5. Permits construction on fills. 6. Permits shallow footing construction. 7. Prevents earthquake-induced lateral spreading. 6 Stone Column Construction methods! The two primary methods of Vibro Stone Column construction are: 1. Wet, Top Feed Method (Replacement and
Displacement). 2. Dry, Bottom Feed Method (Displacement). 7 Stone Column Construction (cont.) **Wet, Top Feed Method (Replacement and Displacement): In this technique, jetting water is used to remove soft material, stabilize the probe hole, and ensure that the stone backfill reaches the tip of the vibrator. This is the most commonly used and most cost-efficient of
the deep vibratory methods. However, handling of the spoil generated by the process may make this method more difficult to use on confined sites or in environmentally sensitive areas. 8 Stone Column Construction (cont.) **Top-Feed Construction Method: 9
Stone Column Construction (cont.) **Dry, Bottom Feed Method (Displacement): This technique uses the same vibrator probes as standard Vibro-Replacement Stone Columns, but with the addition of a hopper and supply tube to feed the stone backfill directly to the tip of the vibrator. Bottom Feed Vibro-Replacement is a completely dry operation where the vibrator remains in the ground during the construction process. The elimination of flushing water in turn eliminates the
generation of spoil, extending the range of sites that can be treated. Treatment is possible up to a depth of 80 feet and is not inhibited by the presence of groundwater. 10 Important Stone Columns Parameters? 1. Ground conditions. 2. Relative density (RD). 3. Degree of saturation. 4. Permeation.
Control! 1. Stone column location ( the spacing between the stone column usually 1.5-3 m c/c). 2. Resistance level as measured by amp meter (Vibrator draws more current in denser sols). 3. Quality and quantity of stone added -- friction angle and size of stone columns. 13 Stone Columns Design Steps: 1. Perform site investigation
Soil type, gradation, consolidation, and strength important. 2. Calculate predicted improvement. (Problem understood) 3. Establish requirements of ground improvement (What settlements, factor of safety, etc., are allowable). 4. Design Vibro-Replacement scheme (Number of stone columns, diameter of stone column and/ or performance requirements required to achieve desired results). 5. Establish testing criteria (Load test, SPT, area of stone columns). 14
Fig. Step Construction procedure of aggregate pier element! Drill cavity using augers, install casing IF cave-ins occur. Place crushed stone at the bottom of the cavity. Ram bottom stone with beveled tamper to produce bulb. densify crushed stone
in layers of 30cm with tamper. Preload top of rap element. 15 Method to Estimate Settlement Reduction Using Stone Columns in Cohesive Soils !! 16 Vibroflotation and stone
column?? Vibroflotation is a technique for in situ densification of thick layers of loose granular soil deposits. It was developed in Germany in the 1930s. Stone column can be used instead of sand drains and it is the same as Vibroflotation. From Das, 1998
17 Pictures for stone column? 18 Pictures for stone column (cont.) 19 Pictures for stone column
(cont.) 20 Expected Stone Columns Results!! 21 22 DO YOU HAVE
ANY QUESTIONS?? 23 THANK YOU FOR YOUR ATTENTION! 24
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