Ground Improvement Tehnique: Issues, Methods and their Selection Dr. J.N.Jha, Professor and Head (Civil Engineering), Guru Nanak Dev Engineering College, Ludhiana, Punjab-141006

Present Day Scenario Best buildable lands not available for construction Available sites are having low strength because : Filled up sites, Low lying water logged, Waste lands, Creek lands with deep deposits of soft saturated marine clays Another problem: Design loads are high and the site is situated in seismic zones

What are the options? Traditional foundation techniques sometimes costlier than the super structure and in many situations can’t be built when a poor ground exists at the project site, designer faces following questions: Should the poor ground be removed and replaced with a more suitable material? Should the weak ground be bypassed laterally by changing the project’s location or vertically by the use of deep foundations? or Should the design of the facility (height, configuration, etc) be changed to reflect the ground’s limitations?

Development of ground improvement, gives the designer/bulder has a fourth option To “fix” the poor ground and make it suitable for the project’s needs Now the designer/builder faces new questions: Should the problematic ground at the project site be fixed instead of bypassed? What are the critical issues that influence the successful application of a specific fixing tool? And Which fixing tool to be used from comprehensive and diversified set currently available in the tool box?

What are the major functions of Ground improvement in soil ? To increase the bearing capacity To control deformations and accelerate consolidation To provide lateral stability To form seepage cut-off and environmental control To increase resistance to liquefaction Above functions can be accomplished : by modifying the ground’s character - with or without the addition of foreign material

The current state of the practice: Densification Consolidation Weight reduction Reinforcement Chemical treatment Thermal stabilization Electrotreatment Biotechnical stabilization

Ground Improvement by Densification Methods of Application :  Vibrocompaction Dynamic Compaction Blasting Compaction Grouting Key Issues affecting densification: Percent of fines in the soil, Ability of the soil to dissipate excess pore water pressure, Energy felt by the soil, Presence of boulders, utilities and adjacent structures, and Mysterious phenomenon of ageing.

Vibrocompaction Loose granular soils are densified at depth by insertion of vibrating probes into the ground Compaction is achieved by impact and vibration, Compaction is achieved by with or without the use of a water jet or compressed air, addition of granular material. Densification can be achieved to up to 30 m in depth

Schematic View and Equipment Used Vibrofloatation Schematic View and Equipment Used 1.Vibrofloat 2. Crane for Suspending Vibrofloat 3. Power Supplying Unit (75-150 KW)

Real Time Photos

Vibrofloat Nose Cone Lower Most Part helps in Penetration in to the soil Eccentric Weight Provides Weight, helps in lowering Vibrofloat Water Jet Creats a Quick Condition facilitating the vibrrofloat unit to sink Electric Motor Develops a huge Centrifugal Force by its Rotational Motion Vibration Insulator Prevents the vibration s to reach Hollow Tube Follow Tubes Facilitates the Vibrating Unit to Reach Desired Depth Diameter and Length Diameter- 300-400mm Length- 2-3m.

Procedure-Step Step-1-Jet at the bottom of Vibrofloat is turned on and is gradually lowered into the ground Step-2- Water Jet creats a quick condition in the soil thus facilitating the vibrating unit to sink under its own weight

Step-3-Granular material is poured from the top into the hole through the annular space between the hole and vertical pipe. Water from the lower jet is transferred to the top of Vibrating unit which carries the granular material down to the hole. Step-4- Vibrating unit is raised gradually in lifts (1 feet) and held for vibration for 30 seconds. This process is continued which compacts the soil to the desired density

Grain Size Distribution Zone-B Most suitable for Vibroflotation since Quick condition can easily be created Zone – C and Zone –D Contains excessive amount of Fines, Difficult to compact and requires considerable effort Zone- A Appreciable amount of Gravel, Compaction by Vibroflotation is uneconomical

Suitability of the Backfill Suitability NumberSN = 1.7 {3/(D50)2 + 1/(D20)2 + 1/(D10)2}1/2 Where D50 ,D20 ,D10 are particle sizes corresponding to 10, 20 and 50 % finer of the backfill material Range Of SN Rating of the Backfill Material 0-10 Excellent 10-20 Good 20-30 Fair 30-50 Poor >50 Unsuitable

Comparison of CPT Test CPT Test Performed Before Densification of Sand Fills CPT Test Performed After Densification of Sand Fills

Dynamic Compaction Repeated lifting and Dropping of Weight at a location Tamping Weight (Concrete/Cast iron/Steel)- 80 to 120 kN Ht. of Drop- 10 to 15m No. of drops (same location)- 8 to 12 times Formation of Crater like Depression-Filled with Extra Soil Process Repeated- Grid Pattern at a spacing of 2-4 m Densification of Soil- 4-8m below GL

In-Situ Dynamic Compaction

Blasting Weight of Charge(Rough Guideline)- W= 164CR3 W = Weight of Explosive (N) C = Coefficient (0.0025 for 60% detonator) R = Radius of influence (m) Arrangement of Explosive- Grid Pattern Firing Pattern – From outside to inside First Blast- At the corner of Periphery Line of First Grid from outside Second Blast – At the Centre of Periphery Line of First Grid from outside Third Blast - At the corner of Periphery Line of Second Grid from outside Spacing – 3 to 8 m (Less than 3 generally avoided) Depth of Stratum to be densified – 10m or less Depth of Explosive- 2/3 of depth Compaction - In one tier only Depth of Stratum to be densified – More than 10m Depth of Charge – Greater than Radius of Sphere of Influence (R) Compaction- More than one Tier

Materials & Equipments Dynamite sticks. Electric detonator. Drilling equipment. Backfill material (Sand). Waterproof packets.

Method Series of boreholes are drilled and Pipe of 7.5 to 10 cm is driven to the required depth Dynamite sticks and detonator are wrapped in a water proof bundle and is lowered through casings Casing is withdrawn and a wad of paper or wood is placed against the charge of Explosive (To protect it from misfire) Boreholes are backfilled with sand to obtain full force of blast Electric circuit is closed to fire the charge The charge is fired in definite pattern For deeper deposits blast is done in stages Repeated shots are more affective than single larger one Each successive blast in a given area will cause less densification than the one preceding Top 1m surface get disturbed and needs surface compaction

Compaction Grouting Step -1 Predrilled Compaction Grouting hole to desired depth Step-2 Insert Compaction Grouting Casing in Predrilled hole Step-3 Begin Pumping Low Slump Compaction Grout Mix in Stages and withdraw at Controlled rate Step-4 Withdraw casing as stages are complete until the hole is complete

Key Issues Affecting Densification Percent of fines in the soil, Ability of the soil to dissipate excess pore water pressure, Energy felt by the soil, Presence of boulders, utilities and adjacent structures, and Mysterious phenomenon of ageing.

Presence of Fines Fines act as lubricants reducing the frictional resistance between the rearranged soil particles of the densified mass. In vibrocompaction, a fines content of 20 percent renders the process ineffective. The amount of fines in the soil also affects drainage properties (A key factor when the densified soil is in a saturated state)

Pore Pressure Dissipation In a saturated cohesionless material, during densification a micro- liquefaction process takes place allowing the soil particles to rearrange themselves If excessive fines or cohesive soils are present, dissipation of the excess pore water pressure generated by the densification process is slowed down (or maybe prevented) thus affecting the feasibility of the applied method

Level of Energy Factors affecting Level of Energy: Characteristics of the equipment (Vibrating frequency, Tamper weight, amount of explosives, etc) Configurations of application (probe spacing, drop height, depth of charge, etc) Ground characteristics, effectiveness of the applied procedures and the experience of the equipment operator Degree of saturation and the way weight is dropped (a crane drop is less efficient than a free drop) Presence of soft cohesive layers or peat has a damping effect on the dynamic forces penetrating the soil, and thus the depth of influence is reduced

Proximity to Structures The impact of the process 9 vibrocompaction or dynamic compaction) on adjacent structures - A major concern with no set criteria in present practice as to how close can it be implemented next to an existing structure A recent project involving vibrocompaction of hydraulic fill adjacent to a bulkhead structure: Horizontal deflection less than 10 mm when the vibroprobe was 3 m away from the bulkhead Horizontal deflection increases to more than 50 mm as the probe got within 2 m of the bulkhead

Ageing Mechanism Increase in strength and deformation modulus with time to the possible action of silica bonding between grains Rearrangement of the sand particles during secondary compression, resulting in gradual increase in particles interlocking Example Ageing: Strength increase of 35% from the second to the sixth week after a major vibrocompaction application in Hong Kong On a recent project in Norfolk, Virginia, USA, a 15-30 percent increase in the relative density of a hydraulic fill, approximately 20 days after vibrocompaction was measured due to ageing

Ground Improvement by Consolidation Methods of application: Preloading with or without vertical drains Electro-osmosis Vacuum consolidation

Preloading with or without vertical drains Preloading is usually accomplished by placing surcharge fills To accelerate consolidation, vertical (sand or prefabricated wick) drains are often used with preloading

Principle and Mechanism Coefficient of Surcharge: Ratio of weight used in preloading and wt. of the final structure to be constructed on the improved soil Using a surcharge higher than work load, soil always remains in an overconsolidated state secondary compression for overconsolidated soil is much smaller than that of normally consolidated soil Increasing the time of temporary overloading or size of the overload, secondary settlement can be reduced /eliminated.

Electro-osmosis The process of dewatering assisted by the application of a direct electric current is known as electro- osmosis thus resulting in consolidation soft clays whose moisture content cannot be reduced by conventional dewatering methods. In Electro-osmosis method, Electrodes are installed in the soil and a DC current supplied which results water movement from anode to the cathode A wellpoint system or ejector well system used as cathode which collects and removes the water from the ground.

Mechanism Electro-osmosis transports water of the clay pore space to the cathodically charged electrode When these cations move toward the cathode, they also bring water molecules along with them These water molecules clump around the cations as a consequence of their dipolar nature Macroscopic effect of this process is reduction of water content at anode and an increase in water content at the cathode Free water appears at the interface between the clay and the cathode surface

Molybdenum Electrodes Graphite Electrode Metallic Electrodes Shapes of Electrodes

Connecting Wires Electrodes Before Installation DC Current Source

Flow of Water under Electro-osmosis

Advantages and Limitations Practical application limited since very costly. Before actual application on site Laboratory tests and site tests are imperative. Huge amount of electricity. needed Highly skilled labour needed Electrodes replacement needed from time to time. Method becomes ineffective If the moisture content of the soil is extremely low Can be used for dewatering of silty and clayey soils which are difficult to drain by gravity. Method is fast and instantaneous. Environment-friendly method Equipments required are few in number and easy to carry to the site. Method useful for all types of soils. Efficiency of this method is very high. Less man-power required to implement this method.

Vacuum consolidation Vacuum consolidation, Both liquid and gas (water and air) are extracted from the ground by suction This Suction is induced by the creation of vacuum on the ground surface and assisted by a system of vertical and horizontal drains Vacuum is applied to the pore phase in a sealed membrane system The vacuum causes water to drain out from the soil and creates negative pore water pressure in the soil This leads to an increase in effective stress to the magnitude of the induced negative pore water pressure, without the increase of total stress

For rapid pre-consolidation, vertical drains (Prefabricated Vertical Drains) along with the vacuum preloading are used Vertical drains helps to distribute the vacuum pressures to the deeper layers and drain out water from the sub soil Vacuum preloading with PVD substantially reduces the lateral displacement and potential shear failure Maximum achievable vacuum pressure in the field is only about 80kPa Schematic view vacuum consolidation technique

Advantages of Vacuum preloading technique over the Surcharge preloading technique Ground improvement with vacuum preloading does not require any fill material and there is no need of heavy machinery Construction period is generally shorter The increase in effective stress under vacuum preloading is isotropic. Therefore, the corresponding lateral displacement is in the inward direction and there is no risk of shear failure Application of Vacuum Preloading improves Bearing capacity of soil by 100% in the case of soft clays and eliminates 70% of the total estimated settlement of design load The overall cost of vacuum preloading is only about 2/3rd of that with surcharge preloading

Ground Improvement by Consolidation Key Issues associated with consolidation: Stability during surcharge placement, Clogging of vertical drains, and Maintenance of the vacuum.

System Stability To safeguard against stability problems, the surcharge loads are often placed in stages Each stage of loading is added only after the soil has acquired sufficient strength under the influence of the previous stage to support the new load Build up and dissipation of the excess pore water pressure and the accompanying soil deformations are monitored to pinpoint the time for stage placement In case of electro-osmosis or vacuum consolidation no stability problem is anticipated

Clogging of Drains Clogging of the vertical drain is a key issue affecting the feasibility of the system of ground improvement Major advantage of the plastic wick drains over sand drains is their flexibility and ability to sustain large deformations of the consolidating cohesive soil, which may otherwise shear and clog the sand drains, rendering them ineffective The hydraulic conductivity of the wick drains is influenced by the potential crimping of the material when large deformations take place or clogging of the drainage channels due to an ineffective filter jacket A non-wooven geotextile fabric is usually used to provide filtering and ensure the hydraulic conductivity of the prefabricated drains

Maintenance of the Vacuum Maintaining the vacuum by providing an all-around seal is critical for the successful application of vacuum consolidation Resistance of the membrane to tear during and after placement is an important factor Membrane is covered by a layer of soil or by water ponding to prevent its tear by vehicles, animals or birds attacks, or vandalism Vacuum is generated by circulation of air through a series of specially designed drains, installed to the depth of the layer to be consolidated (new system developed recently in France eliminated the need for the membrane)

Ground Improvement by Weight Reduction Methods of Application: Placing lightweight materials over the native soil in one of three ways: Spread in a loose form, then compacted Cut in block forms, then stacked according to a certain arrangement, or Pumped in a flowable liquid form

Lightweight material used for ground improvement Fill Material Source/Process Dry Unit Weight (kg/m3) Wood fibers Sawed lumber waste 550 – 960 Shredded tire Mechanically cut tire chips 600 – 900 Clam shells Dredged underwater deposits 1100 – 1200 Expanded shale Vitrified shale or clay 600 – 1040 Fly ash Residue of burned coal 1120 – 1400 Air-cooled slag Blast furnace material 1100 – 1500 Flowable fill Foaming agent in a concrete matrix 335 – 770 Geofoam Block molded expanded polystyrene 12 – 32

key Issues (Weight Reduction Method) Placement of the lightweight material, Longevity and long-term performance

Material Placement When fly ash is wet during placement, it may become spongy and difficult to compact; and when dry it may become too dusty and environmentally unacceptable Crushing and knitting of the shells during compaction, and contamination of the shell embankment with the generated fines, may significantly affect its gradation and performance.

Longevity Flotation of the geofoam, its susceptibility to fire and to deterioration from gasoline spills or insect borrowing, are long- term longevity problems that require special measures Continued crushing and knitting of the shells under the influence of vehicular traffic may reduce the drainage potential of the embankment resulting : Ponding of water at the surface May reduce the frictional angle of the material, thus, increasing its lateral pressure on supporting structures

Ground Improvement by Chemical Treatment Cement, lime, fly-ash, asphalt, silicate and others are used to stabilize weak soils (bind the soil particles resulting in higher strength and lower compressibility) Lime stabilization, an ion exchange reduces the soil’s plasticity and improves its workability. The ion exchange is then followed by a chemical reaction that increases the shear strength In surface stabilization, the chemicals are mixed with the soil and an appropriate amount of water, and then compacted using conventional compaction equipment and procedures In deep mixing methods chemicals are applied at depth by injection

Methods of Application Permeation grouting Jet grouting Deep soil mixing Lime columns Fracture grouting

Permeation grouting Cement, lime, bentonite or chemical grouts (silicates, etc.) fill the voids in the soil to increase and cohesion and reduce permeability, with no change in the volume or structure of the original ground Microfine cement grout is the latest addition to permeation grouting Grout additives may be used to enhance penetrability and strength, and to control setting time Grouting is performed by drilling holes in the ground and injecting slurry grouts through the end of a casing, or through specialized equipment such as a tube-a-manchette

Jet grouting Uses high-pressure fluids, applied through a nozzle at the base of a drill pipe, to erode the soil particles and mix them with cement grout as the drill bit is rotated and withdrawn, forming hard, impervious columns The grouted columns can be formed vertically, horizontally or at an angle. A row of overlapping columns forms a wall. Jet Grouting is used mainly for excavation support, underpinning, tunneling and groundwater cut- off

Deep Soil Mixing Technique consists of mixing in-place soils with cement grout or other reagent slurries using multiple-axis augers and mixing paddles to construct overlapping stabilized-soil columns By arranging the columns in various configurations, the system can be used for strengthening of weak soils, for groundwater cut-off, or liquefaction control When used for liquefaction control, the DSM system is performed in a block or lattice pattern to resist the stress from embankment or surcharge loading when loose cohesionless soils liquefy during seismic ground shaking If needed, steel reinforcement is inserted in the column to provide bending resistance

Lime Columns Lime columns method is a variation of deep soil mixing, in which unslaked quicklime is used in lieu of, or mixed with, the cement The lime columns are suitable at best for stabilization of deep soft clay deposits A pozzolanic reaction takes place between the lime and the clay minerals resulting in substantial increase in the strength and reduction in the plasticity of the native material The heat generated by hydration of the quicklime also reduces the water content of the clayey soils, resulting in accelerated consolidation and strength gain Lime columns can be used for load support, stabilization of natural and cut slopes, and as an excavation support system

Installation step of Lime Column

Protection of pile structure with lime column Stabilisation of light structure with lime column Stabilisation of cuts with lime column

Fracture grouting Fracture grouting, is also known as Compensation Grouting. It is the injection and hydro fracturing with grout slurry of the soil between the foundation to be controlled and the process causing the settlement Grout slurry is forced into soil fractures, hence causing an expansion to take place counteracting the settlement that occurs or producing a controlled heave of the foundation. Multiple injections and multiple levels of fractures create a complementary reinforcement of the area. Fracture grouting is used to increase the shear strength so that the resultant bearing capacity could act as resistance of soils and to raise structures. Fracture Grouting Applications Elimination/Prevention of the settlement of buildings Reduction or reversal of total settlement Prevention of the settlement of tunnels Reduction or reversal of differential settlement

Key Issues involved in Chemical Treatment Soil-grout compatibility and reactivity, Operational parameters, Column verticality, and Weathering effects

Soil-grout compatibility and reactivity The type of grout used and the make-up of the grout mix are dependent on the properties of the ground In permeation grouting, the principal parameter affecting permeation is the size of the intergranular voids, usually represented by the soil’s coefficient of permeability Success of jet grouting is influenced by ground characteristics such as the size and frequency of boulders, and the presence of peat or organic materials In lime columns, the feasibility of stabilization and the amount of lime needed for pozzolanic reaction are influenced by the type of soil being treated

Operational parameters All deep chemical treatment methods are operator-sensitive and their success depends on operational parameters controlled by the construction crew Both the strength and the permeability of the treated mass are influenced by Net amount of cement in the ground (controlled volumes of cement, water and additives mixed at the grout plant or at the top of the deep mix auger) By the level of the soil-grout mixing achieved in situ In deep soil mixing, the grout flow is usually adjusted constantly to accommodate varying drill speeds in different soil strata Diameter of the column is a function of operating parameters, such as injection pressure, grout flow, and rod withdrawal and rotation rates In case of fracture grouting the grout mix is adjusted by the operator to provide the required performance(performance-type specifications)

Column verticality The verticality of the constructed column is an important issue in jet grouting, particularly when used to construct fluid barriers Multiple rows of overlapped columns are usually designed when used for construction of a cut-off wall, on the basis of the assumed permeability of the jet grouted column When two adjacent columns deviate from their vertical alignments in opposite directions, the required column overlapping may not materialize, and voids may develop in the jet grout wall rendering it ineffective as a cut-off wall The verticality and overlapping of columns are less of an issue in deep soil mixing since the columns are constructed to fixed diameters and the overlapping is ensured by the construction process

Weathering effects Long-term behavior of the chemically-treated soil structure is influenced by weathering, particularly if it is continuously exposed to weathering elements such as water, wind or temperature Lime-treated soils absorb less water with time and also dry faster Frost heave in lime-stabilized soils is more particularly if the soils are frozen within one month after compaction Resistance against frost-thaw effects, however, increases rapidly with curing time as the strength of the stabilized soil is increased Resistance of the chemically treated soils to weathering effects is tested through durability tests involving wet-dry or freeze-thaw cycles

Ground Improvement by Reinforcement Methods of Application: Mechanical stabilization Soil nailing Soil anchoring Mirco piles Stone columns Fiber reinforcement Key Issues Affecting Soil Reinforcement: Load transfer to the reinforcing elements, Failure surface of the reinforced soil mass, Strain compatibility between the soil and the reinforcement, Arrangement of the reinforcing elements, Durability and long-term behavior of the reinforcements.

Ground Improvement by Thermal Stabilization Methods of Application: Ground freezing Vitrification Key Issues of thermal stabilization Degree of saturation of the soil, Rate of groundwater movement, Creep potential of the frozen ground, Post thawing behavior, Heat transfer in the melted soil and Impact of heat on utilities and adjacent structures.

Ground Improvement by Electrotreatment Methods of Application: Electrokinetic remediation Electroheating Electrokineting fencing Bioelectrokinetic injection Key Issues in Electrotreatment Soil’s electrical conductivity, Ionic characterization of the contaminants, and Impact on buried objects and utilities

Ground Improvement by Biotechnical Stabilization Methods of Application: Brush layering Contour wattling Reed-trench layering Brush matting Live staking and others key issues affecting biotechnical stabilization Development of artificial cohesion in the ground, Effects of evapotranspiration, and Durability of the vegetation

Factors affecting the selection of a ground improvement method Groundwater Construction considerations including schedule, materials, accessibility, right-of- way, equipment and labor (d) environmental concerns, (e) durability, maintenance and operational requirements (f) contracting, politics and tradition, (g) cost

Thankyou...............

Waste Containment with Geosynthetics Large quantities of waste are being produced since 1990 due to Rapid industrialisation and Excessive urbanisation Waste needs to be disposed off and only disposal bin is ground and it occupies large chunk of land. One million ton of municipal solid waste occupies approximately one million square meter (One square kilometer of land area when waste is spread uniformly with a thickness of one meter)

Other problem associated with waste disposal Another problem with the disposal of waste : Source of pollution Contaminates the soil beneath the waste Contaminates the ground water as contaminants travel from the solid waste to the subsurface environment

Other sources of subsurface contamination Ponding or impoundment of Liquid Waste : Slurry type liquid waste Leakage from storage of liquids in underground tanks Leakage from pipelines that transport liquid Accidental spills of toxic liquid Application of fertilizers , pesticides on large agricultural areas

How to tackle and minimise this damage Design and implementation of solution for detection, control, remediation and prevention of subsurface contamination Protection of uncontaminated land Analysis of the fate of contaminants on and in the ground including transportation through geomedia Use of waste material on and in the ground for geotechnical construction

Pollution:MSW/ISW Municipal solid waste/Industrial solid waste place on the ground: two most significant source of subsurface contamination Water infiltrates into waste and reacts physically, chemically and biologically to produce leachate Leachate infiltrates into the ground causing subsoil and ground water contamination Solid waste continues to stay at the location where it is placed for years Therefore the process of leachate infiltration into subsurface environment continues , slowly but surely for several yearss

Control and Remediation Clean up of soil involves - Treatment of three phases in soil:Solid soil particle, Liquid pore fluids and Pore gases Methods Controlling the spread of polluted zone by installing impermeable vertical barriers (cut-off walls) all around and horizontal cover above the contaminated site Removing the source of contamination and placing it in designed facility Excavating the affected soil, washing it or teating it and placing it back after treatment

Pumping out the contaminated ground water by using a set of tube wells installed in the Contaminated zone , treating the ground water and the injecting the purified waterback (Pump and Treat Method) Pumping out pore gas from the unsaturated zone using gas wells and allowing air to enter through injection wells Using micro-organism to biomediate the sub soil and ground water by transforming or immobilzing the contaminants Using thermal treatment e.g. incineration

Control of subsurface contamination for new facility For solid waste: Providing impermeable flexible liners at the base and covers on top of all Solid waste disposal facilities to minimize leachate formation For slurry type waste: Providing storage in ponds and impoundments having incrementally raised embankments and impermeable flexible liners at the base For liquid: providind storage in ponds with impermeable flexible liner For underground liquid storage facility: Providing double walle tanks with leakage detention system placed between the walls