Deep Replacement Presented by: M. Taromi Principles and Practices of Ground Improvement Deep Replacement Presented by: M. Taromi Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 1 - 28

CHAPTER 5: DEEP REPLACEMENT Introduction Ch. 5.2 Principles Ch. 5.3 Design Considerations Ch. 5.4 Design Parameters and Procedure Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 2 - 28

Deep Replacement Method 5.1. Introduction Deep Replacement Method Increase bearing capacity Increase density Decrease of settlement Provide lateral stability Increase resistance to liquefaction Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 3 - 28

Excavation of Geomaterials from Ground in Two Method: 5.1. Introduction Excavation of Geomaterials from Ground in Two Method: by injecting water into the ground, turning the geomaterial into slurry, and flushing it out from the hole. by drilling a hole in the ground Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 4 - 28 Page 3 - 50

Displacement of Soils in the ground in four Method: 5.1. Introduction Displacement of Soils in the ground in four Method: by injecting water/air into ground. Vibro – replacement Vibro - displacement by driving a steel casing into the ground Sand compaction column Encased granular column Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 3 - 50 Page 5 - 28

5.1. Introduction Displacement of Soils in the ground in four Method: by driving a reverse auger. Controlled stiffnes column by dropping a tamper to penetrate into ground. Dynamic replacement Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 3 - 50 Page 6 - 28

5.2. Principles The Vibro Replacement Technique (Vibro Stone Columns) The stabilization of soils by displacing the soil radially with the help of a depth vibrator, refilling the resulting space with granular material and compacting the same with the vibrator is referred to as Vibro Replacement and was developed by Keller in the 1950’s. The resulting matrix of compacted soil and stone columns has improved load bearing and settlement characteristics. Basic principle of the vibro replacement technique Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 3 - 50 Page 7 - 28

The Vibro Replacement Technique (Vibro Stone Columns) 5.2. Principles The Vibro Replacement Technique (Vibro Stone Columns) Principle Reinforcement and Drainage Applicable soils Mixed deposits of clay, silt and sand, Soft and ultra soft silts (slimes) Soft and ultra soft clays, Garbage fills Effects Increased shear strength, Increased stiffness, Reduced liquefaction potential Common applications Airport, Storage tanks,, Bridge abutments and Offshore bridge abutments and land / offshore applications Maximum depth 10-15 m Particle size distribution illustrating applicability of Vibro-Compaction and Vibro-Replacement Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 3 - 50 Page 8 - 28

The Vibro Replacement Technique 5.2. Principles The Vibro Replacement Technique Schematic of wet top feed method Schematic of dry bottom feed vibrocat method Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 9 - 28

5.2. Principles 3-50 The Vibro Replacement Technique Page 10 - 28 Mechanisms of load transfer for (a) a rigid pile and (b) a stone column ó – Stress óf - Mat/Pile Cap Pressure óp – Stress Induced to Piles ó – Stress óf - Mat/Pile Cap Pressure óc – Stone Column Stress ós – Soil Stress Idealized stress distribution pattern for deep foundation systems (piles) Idealized stress distribution pattern for stone column systems Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 10 - 28 3-50

The Vibro Replacement Technique 5.2. Principles The Vibro Replacement Technique Advantage Installation is fast and easy Higher strength and stiffness than sand compaction columns Disadvantage Installation of stone columns by bottom feeding does not generate spoil; however, that by top feeding generates spoil, which is not environmentally friendly. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 11 - 28 3-50

The Vibro – Concrete Columns 5.2. Principles The Vibro – Concrete Columns Vibro Concrete Columns (VCCs) are an innovative piling technique developed to provide enhanced load bearing capacity at shallow depths through use of enlarged bases. They are often used where weak organic soils overlie granular deposits. VCC columns are classified and designed as unreinforced piles. For the construction of VCC columns pump able concrete is generally used the strength classification C20/25. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 12 - 28 3-50

The Vibro – Concrete Columns 5.2. Principles The Vibro – Concrete Columns Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 13 - 28 3-50

The Vibro – Concrete Columns 5.2. Principles The Vibro – Concrete Columns Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 14 - 28 3-50

The Vibro – Concrete Columns 5.2. Principles The Vibro – Concrete Columns Advantage Higher strength and stiffness because of the use of concrete. The installation process is quick Disadvantage They are more expensive than granular column. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 15 - 28 3-50

The Controlled Stiffness Columns 5.2. Principles The Controlled Stiffness Columns A specially designed auger, powered by equipment with large torque capacity and high static down thrust, displaces the soil laterally, with virtually no spoil or vibration. During the auger extraction process, a column is developed by grouting under controlled limited pressure (less than 5 bars) through the stem of the displacement auger to achieve a predetermined stiffness ratio with the surrounding soil. The result is a composite soil/cement ground improvement system. Current practice is to install columns with diameter varying between 250 and 450 mm. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 16 - 28 3-50

The Controlled Stiffness Columns 5.2. Principles The Controlled Stiffness Columns Application CMCs can be applied to various soil conditions. The technology works well in loose sands, soft loams, organic soils (peat, aggradate mud, gyttjas) with a moisture content above 100% and anthropogenic soils (uncompacted fills, heaps). Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 17 - 28 3-50

The Controlled Stiffness Columns 5.2. Principles The Controlled Stiffness Columns Advantages can have strength and modulus according to project needs. Their strengths and moduli are higher than those of granular columns. They are installed fast with real-time monitoring and without any vibration and spoil. There is no issue of hole collapse. It has a low mobilization cost. Disadvantages However, they are more expensive than granular columns. Installation may be difficult in soils with rocks and boulders. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 18 - 28 3-50

The Rammed Aggregate Columns 5.2. Principles The Rammed Aggregate Columns Basic Function Aggregate Piers are a ground improvement method that uses compacted aggregate to create stiff pier elements. Aggregate Piers help increase bearing capacity, shear strength, rate of consolidation, and liquefaction resistance; and reduces settlement. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 19 - 28 3-50

The Rammed Aggregate Columns 5.2. Principles The Rammed Aggregate Columns 600 to 900 mm diameter holes are drilled into the foundation soils. The holes normally reach depths of 2 to 9 m below grade. This lifts of well-graded aggregate are rammed into the holes. The subsequent compacted lifts are typically 25 cm deep. A high-energy beveled tamper mounted on excavator equipment is used to compact the aggregate. Design parameters include pier length, spacing, pier stiffness, and stress concentration ratio. Pier spacing is from1.5 to 2.5 m center to center of the piers. Load capacities range from 222 to 445 kN. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 20 - 28 3-50

The Rammed Aggregate Columns 5.2. Principles The Rammed Aggregate Columns Geologic Applicability Soft organic clays, loose silt and sand, uncompact fill, stiff to very stiff clays, and medium dense to dense sands. Elevated water tables and cohesion less soils complicate the installation. Advantages Rapid installation Cost effective compared to other foundations options Creates additional drainage Allows for high level of compaction. Efficient QC/QA procedures Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 21 - 28 3-50

The Rammed Aggregate Columns 5.2. Principles The Rammed Aggregate Columns Disadvantages Limited treatment depth. Lack of bending resistance. Difficult to install in clean sands when the groundwater table is above the bottom of the pier. Not applicable of wide heavy load applications. Usually only effective to a depth of 2 to 9 m below foundation. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 22 - 28 3-50

The Dynamic Replacement 5.2. Principles The Dynamic Replacement The Dynamic Replacement technology consists in construction of large diameter aggregate columns in cohesive soil. The columns are formed by a heavy pounder with a weight ranging from 15 up to 30 tons which is dropped from a height ranging from 10 up to 30 m. Large diameter columns (ranging from 1.6 m up to 3.0 m) are driven to a depth ranging from 4.0 m up to 7.0 m. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 23 - 28 3-50

The Dynamic Replacement 5.2. Principles The Dynamic Replacement Geologic Applicability The Dynamic Replacement columns can be constructed both in loose non-cohesive and firm soils, soft cohesive soils as well as in organic deposits. Advantages High bearing capacity high shear strength and low deformation capacity of columns formed in weak soil. Comprehensive improvement Environmentally friendly The Dynamic Replacement columns can be formed of recycled material (concrete rubble, coarse grain rubble, Gravel, etc.). Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 24 - 28 3-50

The Geosynthetic-encased granular columns 5.2. Principles The Geosynthetic-encased granular columns Encased granular column technology is used for very soft soils and organic soils with undrained shear strength as low as 5 kPa. The typical depth of the columns is 5–10 m. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 25 - 28 3-50

The Geosynthetic-encased granular columns 5.2. Principles The Geosynthetic-encased granular columns Advantages Impart lateral confinement Increase the load capacity & stiffness Stresses are transferred to deeper strata. Higher lengths of stone column are possible. Higher degree of compaction can be achieved. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 26 - 28 3-50

The Geosynthetic-encased granular columns 5.2. Principles The Geosynthetic-encased granular columns Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 27 - 28 3-50

The Geosynthetic-encased granular columns 5.2. Principles The Geosynthetic-encased granular columns Geosynthetic-encased granular columns can be used in very soft soil with undrained shear strength lower than 15 kPa and as low as 5 kPa. Geosynthetic encasement increases the stiffness of columns as compared with granular columns. However, geosynthetic-encased columns are more expensive and slower to install as compared with granular columns without geosynthetic. Islamic Azad University – Islamshahr Branch Department of geotechnical Engineering Page 28 - 28 3-50