vertical drains

1. CE-464 Ground Improvement VERTICAL DRAINS PRELOADING TECHNIQUE MAY NOT WORK SOMETIMES ALONE DUE TO A THICK UNIFORM SOFT CLAY LAYER OR PERMEABILITY OF THE CLAY IS VERY LOW SO THAT TIME FOR PRECOMPRESSION (TSR) IS VERY LONG AND NOT PRACTICAL OR SURCHARGE WILL BE VERY HIGH FOR REASONABLE WAITING PERIODS. SOMETIMES RATE OF UNDRAINED SHEAR STRENGTH GAIN IS VERY SMALL WITH TIME SO THAT RAPID PLACEMENT OF A HIGH FILL WILL CAUSE FAILURE.

2. CE-464 Ground Improvement TO ACCELERATE THE RATES OF SETTLEMENT HENCE TO DECREASE THEPRELOADING TIMES, VERTICAL DRAINS ARE INSTALLED TO SHORTEN THE DRAINAGE PATHS. IT IS ESPECIALLY EFFECTIVE IN PRIMARY CONSOLIDATION. PORE WATER PRESSURES DISSIPATE QUICKLY, T a Hdr2 , IN MOST DEPOSITS kh>kv . IT IS NOT EFFECTIVE IN ORGANIC SOILS AND PEATS IN WHICH COMPRESSIONS ARE DOMINATED BY SECONDARY COMPRESSION.

3. CE-464 Ground Improvement THEORY OF CONSOLIDATION FOR RADIAL FLOW AND BOTH RADIAL-VERTICAL CONSOLIDATION (COMBINED) HAVE BEEN DEVELOPED FOR A LONG TIME (BARREN I948;CARILLO. 1942). CONSOLIDATION TIME IS MAINLY AFFECTED BY THE DRAIN SPACING RATHER THAN THE DRAIN DIAMETER. EFFICIENCY OF DRAINS: IS THERE A SIGNIFICANT DIFFERENCE IN THE PRIMARY CONSOLIDATION RATE WHEN DRAINS ARE USED? FOR SUCCESSFUL PROJECTS : 1. (svo’+Pf)>svo’ (PRECONSOLIDATION PRESSURE) (FIgure 7) 2. MUST BE LARGE. 3. THERE SHOULD NOT BE NATURAL DRAINAGE LAYERS.

4. CE-464 Ground Improvement

5. CE-464 Ground Improvement FIELD MEASUREMENTS FROM 5 SITES INDICATE THAT SATISFACTORY e VALUES RANGE BETWEEN 0.6 AND 0.8. THE NEED AND EFFICIENCY OF DRAINS ARE LARGELY DEPENDENT ON SOIL CHARACTERISTICS, SOIL PERMEABILITY AND COEFFICIENT OF CONSOLIDATION. RECENT ALLUVIAL DEPOSITS CONTAIN FREQUENT HORIZONTAL BANDS OF SAND OR GRAVEL ETC. THESE ARE USUALLY THIN AND VERY PERMEABLE COMPARED TO CLAYS. 1. HIGHLY PERMEABLE BANDS OR SEAMS GREATLY INCREASE EFFICIENCY OF DRAINS SINCE THEY ACT AS HORIZONTAL DRAINS CONNECTED TO MAIN ARTERIES. 2. CONTINUOUS AND FREQUENT SEAMS OR BANDS OF HIGH PERMEABILITY SOILS OFTEN MAKE VERTICAL DRAINS UNNECESSARY OR GREATLY REDUCE THEIR REAL EFFECTIVENESS (FIGURE 8).

6. CE-464 Ground Improvement 3. SOIL INVESTIGATIONS ARE VERY IMPORTANT CONTINUOUS SAMPLING K FIELD AT LOW HEADS LARGE DIAMETER (25-30 CM) LABORATORY CONSOLIDATION TESTS.

7. CE-464 Ground Improvement A NUMBER OF DRAINS AVAILABLE : SAND DRAINS CARD BOARD DRAINS SAND WICKS PLASTIC DRAINS SOME FACTORS AFFECTING THE DRAIN PERFORMANCE : 1. SMEAR AND DISTORTION OF DRAIN WALLS WHICH REDUCE DRAIN PERMEABILITY. 2. DISTURBANCE AND LATERAL DEFORMATIONS OF SOFT GROUND RESULTING FROM DRAIN INSTALLATION. PERMEABILITY DECREASES, UNDRAINED SHEAR STRENGTH DECREASES AND PORE WATER PRESSURES INCREASE (ROWE, 1968)

8. CE-464 Ground Improvement SAND DRAINS THEY WERE WIDELY USED BETWEEN 1930 -1980 WITH DIAMETERS CHANGING BETWEEN 20 -60 CM AND WITH 1.5 TO 6 M SPACING. CLOSED MANDREL METHOD : APPLIED BY PERCUSSION OR VIBRATION OR JETTING. THE TUBE IS PUSHED DISPLACING THE SOIL. THERE IS A LOOSE CAP AT THE END WHICH IS DETACHED AFTER PUSHING IS COMPLETE. THEN THE TUBE IS FILLED AND EXTRACTED. IN THIS METHOD THERE IS DISPLACEMENT AND DISTURBANCE WHICH RESULTS IN A DECREASE OF UNDRAINED SHEAR STRENGTH, PERMEABILITY DETECTED BY MEASURING PORE WATER PRESSURES, EU AND SURFACE HEAVE. OPEN MANDREL METHOD : IN THIS METHOD THE SOIL IN THE TUBE IS REMOVED BY JETTING OR ANGERING. THE PROBLEM OF SMEAR STILL EXISTS. AUGER METHOD USING SOLID STEM OR HOLLOW STEM AUGERS WHICH IS A NON-DISPLACEMENT METHOD MAY BE CONSIDERED AS THE BEST AS COMPARED TO THE OTHERS. ROTARY JETTING METHOD MAY ALSO BE APPLIED. SAND DRAIN APPLICATIONS ARE COMING TO AN END IN THE WESTERN COUNTRIES.

9. CE-464 Ground Improvement CARDBOARD DRAINS THEY ARE FIRST TRIED IN 1937 AND 1948 BY KJELLMAN. THERE ARE DYNAMIC AND STATIC METHODS OF INSTALLATION. CARDBOARD DRAINS ARE DRIVEN INTO THE GROUND BY PURPOSE-MADE MANDREL WHICH IS THEN REMOVED. THE ADVANTAGES CAN BE LISTED AS FOLLOWS: THEY ARE EASY TO INSTALL THEY CAN BE SPACED CLOSELY THEY HAVE LONG LIFE THEY HAVE THE ABILITY TO RESIST LARGE DEFORMATIONS. CARDBOARD WICK DRAINS VISUALLY CONSIST OF A CORE PLASTIC AND FILTER SLEEVE OF PAPER, FIBROUS MATERIAL OR POROUS PLASTIC.

10. CE-464 Ground Improvement

11. CE-464 Ground Improvement PLASTIC DRAINS THESE ARE THE NEW GENERATION DRAINS WHICH ARE VERY SIMILAR TO CARDBOARD DRAINS. THERE ARE SEVERAL COMMERCIAL BRANDS IN THE MARKET AT PRESENT LIKE ALIDRAIN, GEPDRAIN, CASTLEBOARD, COLBONT, MEBRADRAIN AND PVC DRAIN. SEE FIGURE 10 FOR GEODRAIN.

12. CE-464 Ground Improvement SAND-WICKS THESE ARE READY-MADE SMALL DIAMETER SAND DRAINS WHICH ARE CONTAINED IN LONG CANVAS BAGS (APPROXIMATELY 10 CM IN DIAMETER). THEY ARE USUALLY INSTALLED BY CLOSE MANDREL TECHNIQUE. THEY ARE RELATIVELY CHEAP AND FIRST USED IN INDIA BY DASTIDAR ET AL. (1969) AND THEN BY SUBBARAJU ETAL. (1973).

13. CE-464 Ground Improvement DESIGN OF VERTICAL DRAINS THE MAIN ASSUMPTIONS MADE FOR THE DESIGN OF VERTICAL DRAINS ARE ; EACH DRAIN IS INDEPENDENT AT THE CENTRE OF A CYLINDRICAL SOIL MASS AND IS ONLY AFFECTED BY THE DRAINAGE OF THE SOIL IN IT. INSTANTANEOUS LOADING OF THE HOMOGENEOUS SOIL RESULTS IN SOLELY RADIAL CONSOLIDATION (AND THEREFORE RADIAL FLOW) UNDER CONDITIONS OF CONSTANT PERMEABILITY (kh ) AND RADIAL CONSOLIDATION COEFFICIENT (ch) .

14. CE-464 Ground Improvement THE EQUATION WHICH GOVERNS THE RELATIONSHIP BETWEEN PORE PRESSURE, U, RADIAL DISTANCE FROM THE DRAIN , r, AND TIME, t,(IN FACT kh=f(t) AND ch=f(t) ) IS GIVEN BELOW. DRAIN EFFECTS, SMEAR DISTURBANCE, WELL RESISTANCE, LOADING RATE, CREEP EFFECTS, APPROPRIATE HYDRAULIC FLOW FORMULATION CAN BE ALL INCLUDED IN THE ANALYSES.

15. CE-464 Ground Improvement SOLUTIONS MAY BE OBTAINED FOR TWO TYPES OF BOUNDARY CONDITIONS. UNIFORM SURCHARGE ON THE GROUND SURFACE (FREE STRAIN) UNIFORM VERTICAL DEFORMATION OF THE SURFACE (EQUAL STRAIN) BOTH SOLUTIONS ARE SIMILAR BUT UNIFORM VERTICAL STRAIN CONDITION IS SIMPLER. ASSUMING THAT THE VERTICAL FLOW IS NEGLIGIBLE, THE EXPRESSION FOR RADIAL (HORIZONTAL) DEGREE OF CONSOLIDATION IS ;

16. CE-464 Ground Improvement HANSBO(1979);F = F(n) + Fs + Fr WHERE; F(n) : DUE TO SPACING OF DRAINS Fs : SMEAR EFFECT Fr : WELL-RESISTANCE TIME FOR CONSOLIDATION IS; WHERE Uh, IS THE AVERAGE DEGREE OF RADIAL CONSOLIDATION USUALLY n>12 AND F(n)= m = ln(n) - 0.75 MAY BE USED.

17. CE-464 Ground Improvement

18. CE-464 Ground Improvement VARIATION OF Uh WITH HORIZONTAL TIME FACTOR FOR VARIOUS n VALUES (EQUAL VERTICAL STRAIN) IS SHOWN IS FIGURE 12. THE EQUATIONS OF Cv AND t FOR VERTICAL AND RADIAL CONSOLIDATION ARE AS FOLLOWS;

19. CE-464 Ground Improvement

20. CE-464 Ground Improvement CONSOLIDATION OF THE CYLINDRICAL BODY OF SOIL AROUND A VERTICAL DRAIN IS, IN FACT, THREE DIMENSIONAL AND IS GOVERNED BY THE EQUATION ; OVERALL (THREE DIMENSIONAL) DEGREE OF CONSOLIDATION, U=1-U=(1-UH).(1-UV) WHERE UV IS THE AVERAGE VERTICAL DEGREE OF CONSOLIDATION. THE ABOVE CONSIDERATIONS ARE FOR ALL TYPES OF VERTICAL DRAINS. THE EQUIVALENT DIAMETER DW OF A BAND SHAPED DRAIN OF WIDTH B, AND THICKNESS T, IS CALCULATED BY USING THE RELATIONSHIP GIVEN BELOW.

21. CE-464 Ground Improvement

22. CE-464 Ground Improvement REVIEW - DESIGN CONSIDERATIONS THE COEFFICIENT OF CONSOLIDATION FOR VERTICAL COMPRESSION AND HORIZONTAL FLOW DOMINATES THE DESIGN OF SAND DRAINS.

23. CE-464 Ground Improvement Ch IS PRINCIPALLY DEPENDENT ON kh BECAUSE mv IS LESS VARIABLE. ONE WAY OF ESTIMATING kh, IS TO CONDUCT SPECIAL LABORATORY TESTS FOR RADIAL DRAINAGE IN UNIFORM SOILS USUALLY kh>kv (HANSBO(1960), ROWE(1964), BERRY AND WILKINSON(1969), PAUTE(1973). MITCHEL AND GARDNER NOTED THAT THE BEST WAY IS TO MEASURE AV OR MV IN THE LAB AND KH, IN THE FIELD(USUALLY CH/CV RANGES BETWEEN 2- 10).

24. CE-464 Ground Improvement FIELD CONTROL OF THE CONSTRUCTION IT IS VERY IMPORTANT TO CHECK WHAT IS GOING ON AFTER THE DESIGN HAS BEEN DONE AND THE LOADING STARTED. MEASUREMENTS ARE INTEGRAL PART OF THE DESIGN PROCESS AND IT MAY NOT BE POSSIBLE TO COMPLETE A PRELOADING-DRAINS PROJECT WITHOUT FIELD INSTRUMENTATION. THE SIMPLEST WAY IS TO MEASURE THE SURFACE SETTLEMENTS. PIEZOMETERS AT THE CENTRE AND OTHER ELEVATIONS OF THE SOFT CLAY AT THE MID-DISTANCE OF THE DRAINS AND THE SETTLEMENT GAUGES AT VARIOUS DEPTHS (BOREHOLE GAUGES) ARE USUALLY USED TO ASSESS AND TO CHECK THE DESIGN ASSUMPTIONS. NECESSARY CHANGES ARE MADE IF REQUIRED.

25. CE-464 Ground Improvement VARIOUS CASE HISTORIES INVOKING VERTICAL DRAINS TO SPEED UP THE CONSOLIDATION PROCESS WERE DESCRIBED BY JOHNSON (1970B), BJERRUM (1972) AND PILOT (1981). VERTICAL DRAINS ARE GENERALLY EFFECTIVE EXCEPT IN ORGANIC CLAYS, HIGHLY STRATIFIED SOILS OR IN SOILS WHERE SEVERE STABILITY PROBLEMS EXIST. THESE SOILS ALREADY SETTLE IN A SHORT TIME. THE METHOD OFTEN SAVES LARGE SUMS OF MONEY AND CAN BE USED IN VERY POOR SUBSOIL CONDITIONS. LARGE POST CONSTRUCTION SETTLEMENTS MAY BE ELIMINATED, COSTS OF SURCHARGE AND/OR VERTICAL DRAINS AND PRELOADING PERIODS SHOULD BE COMPARED.

26. CE-464 Ground Improvement PLASTIC DRAINS ARE INCREASINGLY BEING USED. BEST METHOD IN THE INSTALLATION OF SAND DRAINS IS AUGERING. OPEN MANDREL METHOD RESULTS IN MORE EFFICIENT DRAINS THAN CLOSE MANDREL METHOD. TIMES FOR CONSOLIDATION CHANGES FROM MONTHS TO A YEAR OR MORE. IF Pf < sc' DO NOT USE SAND DRAINS.

27. CE-464 Ground Improvement FIELD TESTS (ESPECIALLY FIELD PERMEABILITY) IN STRATIFIED SOILS MAY BE REQUIRED TO DECIDE EFFICIENCY OF THIN PERVIOUS SOILS AS DRAINAGE LAYERS. IN MANY CASES CONSOLIDATION RATES ARE MUCH FASTER THAN USUALLY PREDICTED DUE TO CONVENTIONAL LABORATORY APPROACHES AND THERE MAY NOT BE ANY NEED FOR DRAINS IN SOILS HAVING CONTINUOUS PERMEABLE BANDS. ON THE OTHER HAND PREDICTIONS OF RATES OF CONSOLIDATION WHERE DRAINS ARE INSTALLED CAN NOT BE MADE RELIABLY BECAUSE OF THE DIFFICULTIES IN DETERMINING A REPRESENTATIVE VALUE OF ch , AND ACCOUNTING FOR THE EFFECTS OF THE DRAIN INSTALLATION (DISTURBANCE AND SMEAR). SITE INVESTIGATION EFFORTS MUST BE OF GOOD QUALITY.

28. CE-464 Ground Improvement WELL RESISTANCE DISCHARGE CAPACITY OF THE DRAINS = qw PERMEABILITY OF THE SOIL = kc WHERE l = LENGTH OF THE DRAIN WHEN OPEN AT ONE END ONLY (HALF LENGTH OF THE DRAIN WHEN OPEN AT BOTH ENDS) z = DISTANCE FROM OPEN END OF DRAIN (0 < z < 21) WHEN qw / kc < 3000 m2 WELL RESISTANCE CAN NOT BE IGNORED.

29. CE-464 Ground Improvement SMEAR DISTURBANCE WHERE s=ds / dw ds = DIAMETER OF THE DISTURBED ZONE kc' = PERMEABILITY OF THE DISTURBED ZONE

30. CE-464 Ground Improvement CHAPTER 2DEEP COMPACTION THE MAIN PURPOSE OF TREATING OR IMPROVING THE SOILS IS TO ELIMINATE THE DANGER OF EXCESSIVE SETTLEMENTS. LOOSE COHESIONLESS SOILS DO NOT POSE SERIOUS PROBLEMS IN TERMS OF STABILITY AND SETTLEMENT. LIQUEFACTION IS THE MAIN CONCERN FOR LOOSE COHESIONLESS SOILS UNDER WATER TABLE. OTHER DYNAMIC LOADS ALSO AFFECT THESE SOILS. METHODS FOR COHESIONLESS SOILS : - VIBROCOMPACTION TECHNIQUES - COMPACTION PILES

31. CE-464 Ground Improvement 1. VIBROFLOATATION THIS IS NOT A NEW METHOD. (50 YEARS OLD). THE EQUIPMENT HAS THREE ELEMENTS. A) THE VIBRATOR OR VIBROFLOT B) EXTENSION TUBES C) CRANE (-T-WATER JET SUPPLY WATER, PUMP+GENERATOR, CABLES). VIBROFLOT IS A CYLINDRICAL PROBE WHICH PENETRATES INTO THE GROUND WITH THE AID OF VIBRATION (VERTICAL AND/OR HORIZONTAL) AND ITS OWN WEIGHT AND JETTING (WATER MOSTLY, FOR DEEP PENETRATIONS AIR OR AIR AND WATER).

32. CE-464 Ground Improvement VIBROFLOT DIAMETERS ARE IN THE RANGE OF 0.35 - 0.50 m, LENGTHS 2-6 m. AN ECCENTRIC MASS IS AT THE LOWER PART OF THE VIBRO PROBE WHICH IS A HOLLOW STEEL TUBE WEIGHTS OF VIBROFLOTS ARE USUALLY IN THE RANGE OF 20 - 40 kN (2-4 ton) AND THEY DEVELOP HORIZONTAL CENTRIFUGAL FORCES OF 80-160 kN. VIBRATION AMPLITUDES ARE UP TO 20-25 mm AND USUAL OPERATING FREQUENCIES ARE 30-50 Hz (1800 - 3000 rpm) (35-100 kW POWER) WATER JETS MAY BE APPLIED AT TOP AND/OR BOTTOM.

33. CE-464 Ground Improvement

34. CE-464 Ground Improvement TYPICAL VIBROFLOT PENETRATION RATES: 1-2 m/mIn, VIBROFLOT WITHDRAWAL / COMPACTION RATES : 0.3 m/mIn. WATER JETTING PRESSURES UP TO 800 kN/m2, FLOW RATES UP TO 3000 lt/mIn (50 lt/sec). SAND BACKFILL IS SUPPLIED AT A RATE UP TO 1.5 m3/m RADIUS OF INFLUENCE, R FROM THE VIBRATOR DEPENDS ON THE TYPE OF VIBRATOR AND SOIL TYPE 0.6–0.9 m FOR 20 % OR MORE SMALLER THAN NO. 200 SIEVE AND 2 m FOR CLEAN SANDS.

35. CE-464 Ground Improvement MOST EFFECTIVE IN CLEAN SANDS, HOWEVER WEBB & HALL (1968) REPORT GOOD SUCCESS IN SOILS CONTAINING APPRECIABLE PORTIONS OF SILT AND CLAY AS MUCH AS 30%. CAQUAT - KERISEL (1966) RECOMMEND COARSE SAND, GRAVEL OR COBBLES AS FILLING MATERIAL. WHEN DENSIFYING FINE SANDS AND SILTY SAND COARSE PARTICLES ARE MORE EFFECTIVE TO IMPROVE TRANSMISSION OF VIBRATION TO SURROUNDING SOIL BETTER. THERE ARE ALSO CASES ON RECORD WITH VERY FINE SAND, FINE SAND WITH LENSES OF MUD, FINE SAND WITH BALLS OF CLAY AND SILTS AND SANDS WITH CLAY LAYERS UP TO A METER.

36. CE-464 Ground Improvement

37. CE-464 Ground Improvement RELATIVE DENSITY, Dr,OF AT LEAST 70 % CAN BE OBTAINED BETWEEN CENTERS. INCREASE IN RELATIVE DENSITY IS BETWEEN 20% - 40%. qall AFTER TREATMENT IS USUALLY AROUND 2 - 3 kg/cm2 (COST ROUGHLY 2- 4 $/m3 USA RATE). THE DESIGN OF A VIBROFLOATATION TREATMENT REQUIRES SPECIFICATION OF THE DESIRED RELATIVE DENSITY AND THE PATTERN AND SPACING OF VIBROFLOT HOLES. A RELATIVE DENSITY OF AT LEAST 75 % HAS BEEN A FREQUENTLY USED REQUIREMENT TO INSURE AGAINST EXCESSIVE SETTLEMENT OR LIQUEFACTION, HOWEVER THE VALUE SPECIFIED IS A FUNCTION OF THE TYPE OF PROJECT AND THE LOCAL CONDITIONS.

38. CE-464 Ground Improvement D'APPOLONIA, MILLER AND WARE (1955) SUMMARIZE SOME OF THEIR FINDINGS; TRIANGULAR PATTERN PREFERRED DUE TO GREATEST COMPACTION EFFORT OVERLAP. D, IS NOT INCREASED ABOVE 70% AT POINTS MORE THAN 1 m FROM A SINGLE VIBROFLOT COMPACTION. THE OVERLAPPING EFFECT FOR SPACINGS GREATER THAN 2.4 m IS SMALL. SPACINGS LESS THAN 1.8 m SHOULD GIVE Dr HIGHER THAN 70 % WITHIN THE COMPACTED AREA. THE EFFECT OF ADJACENT COMPACTIONS CAN BE SUPERIMPOSED. A PROCEDURE FOR DETERMINING VIBROFLOT SPACING REQUIRED TO OBTAIN A SPECIFIED Dr (mIn.) IS PRESENTED.

39. CE-464 Ground Improvement WEBB & HALL (1968) ALSO DESCRIBE A SIMILAR METHOD FOR SILTY AND CLAYEY SAND. A SPACING OF 2.1 – 2.4 m IS OFTEN CHOSEN. CLEAN COARSE SANDS AND COARSER SOILS MAY REQUIRE 2.4 m OR MORE. FINER MATERIAL AND MATERIAL CONTAINING CLAY INCLUSIONS MAY REQUIRE MUCH CLOSER SPACINGS. RANGE (1.5 -3M) DEPENDS ON; - TYPE OF SOIL AND BACKFILL - PROBE TYPE AND ENERGY - LEVEL OF IMPROVEMENT REQUIRED

40. CE-464 Ground Improvement 2. VIBRATING PROBES VIBRATORY PIPES OR PROBES MAY BE PUSHED INTO THE SOIL TO DENSIFY THE SOIL LAYERS WITHOUT ADDING MATERIAL AT DEPTH, ONLY SURFACE ADDITION IS DONE. ANDERSON(1974) USES PILE VIBRO-DRIVER HAMMER ON TOP OF A 0.76 m DIAMETER PIPE PILE (3-5 m LONGER THAN THE DEPTH OF TREATMENT). TYPICAL APPLICATION CHARACTERISTICS ARE; FREQUENCY 15 Hz, VERTICAL AMPLITUDE 10-25 mm, APPROXIMATELY 15 Probes /hr, 1-3 m SPACING, UPPER FEW METERS ARE NOT EFFECTIVELY DENSIFIED. SAITO (1977) USES AGAIN VIBRATORY PILE DRIVING HAMMER AND VIBRO-RODS

41. CE-464 Ground Improvement

42. CE-464 Ground Improvement 3. VIBRO - COMPOZER METHOD COMPRESSED AIR IS USED INSIDE THE CASING TO HOLD SAND IN PLACE WHILE WITHDRAWING THE CASING MURAYAMA (1958)

43. CE-464 Ground Improvement 4. SOIL VIBRATORY STABILIZING METHOD (SVS) IN SVS VERTICAL VIBRATION AND HORIZONTAL VIBRATION ARE APPLIED. SIMILAR TO VIBROFLOT SAND BACKFILL USED, WATER IS NOT USED.

44. CE-464 Ground Improvement 5. COMPACTION PILES DENSIFICATION FROM TWO EFFECTS DISPLACEMENT OF SOIL VIBRATION DURING DRIVING A CASING WITH DETACHABLE (LOST POINT) END PLATE OR WITH A SPECIAL OPENING MECHANISM AT THE TIP IS DRIVEN BACKFILL IS FILLED AS THE CASING IS WITHDRAWN. USUALLY 0.9 - 1.5M SPACING IS USED. BETTER IN FULLY SATURATED OR DRY SANDS.

45. CE-464 Ground Improvement FRANKI MACHINES AND TECHNIQUE ARE ALSO VERY SUITABLE TO FORM SAND OR GRAVEL PILES. IF THE PERMEABILITY OF THE SOIL IS NOT HIGH, SAND OR GRAVEL PILES ALSO ACT AS DRAINAGE COLUMNS SAND DRAINS TO ACCELERATE SETTLEMENTS ARE DIFFERENT CONCEPT AS WE HAVE DISCUSSED PREVIOUSLY HORIZONTAL EXTENT OF THE COMPACTED ZONE ALONG THE SHAFT IS ABOUT 5 RADII. FRANKI TECHNIQUE IS MORE EFFECTIVE THAN A DRIVEN PIPE, MEYERHOF (1959).

46. CE-464 Ground Improvement SUITABILITY OF SOILS AND METHODS SOIL TYPE, GRADATION, FINES CONTENT ETC. DEGREE OF SATURATION, LEVEL OF G.W.T INITIAL DR s’V0 , s’H0 (OCR, sVMAX) INITIAL SOIL STRUCTURE, CEMENTATION, AGE ETC. SPECIAL CHARACTERISTICS OF THE METHOD USED VIBROCOMPACTION METHODS ARE BEST SUITED TO CLEAN COHESIONLESS SOILS WITH 20-25% MAXIMUM FINE CONTENT DUE TO LOW PERMEABILITY AND COHESION IN LOESS, SILTY SANDS WHERE FINES ARE HIGH IN %, TRY OTHER TECHNIQUES LIKE HEAVY TAMPING (DYNAMIC CONSOLIDATION)

47. CE-464 Ground Improvement EVALUATION OF THE TREATED GROUND MAY BE DONE BY ONE OR TWO OF THE FOLLOWING METHODS; SURFACE SETTLEMENT MARKERS VOLUME OF ADDED SOIL (CRATERS OR VIBROCOMPACTION DISP.) STANDARD PENERATION TEST, SPT. CONE PENETRATION TEST, DUTCH CONE, CPT PRESSUREMETER TEST, PMT SEISMIC SHEAR WAVE VELOCITY DETERMINATIONS, VS PILE DRIVING RESISTANCES PLATE LOADING TESTS DOWN - HOLE DENSITY METERS.

48. CE-464 Ground Improvement

49. CE-464 Ground Improvement VIBROCOMPACTION GRIDS ARE SQUARE OR TRIANGULAR ASSUMING DENSIFICATION ONLY IN LATERAL DIRECTION (D<80CM)SQUARE TRIANGULAR (CONSIDER AVERAGE De)

50. CE-464 Ground Improvement

51. CE-464 Ground Improvement BROWN (1977) HAS DEFINED A SUITABILITY NUMBER FOR VIBROFLOATATION BACKFILLS. D10, D20 and D50 ARE MM PARTICLE SIZES CORRESPONDING % PASSING. SUITABILITY NUMBERS AND BACKFILL CLASSES

52. CE-464 Ground Improvement DYNAMIC CONSOLIDATION OR HEAVY TAMPING (POUNDING) FIRST APPLICATIONS 1970 - 1973 BY MENARD. IT IS REPEATED DROPPING OF A HEAVY WEIGHT ON TO THE SURFACE OF THE SOIL TO COMPACT IT. WEIGHTS (OR POUNDERS) USED MAY BE CONCRETE BLOCKS, TOUGHENED STEEL PLATES BOLTED TOGETHER OR THICK STEEL SHELLS FILLED WITH CONCRETE OR SAND AND MAY RANGE BETWEEN 1/2 - 200 TONS. DURABILITY OF THE WEIGHT IS IMPORANT BECAUSE OF LARGE NUMBER OF DROPS. DROP HEIGHTS (H) ARE UP TO 40 M AND SQUARE OR CIRCULAR SHAPES IN PLAN ARE USED.

53. CE-464 Ground Improvement B(WIDTH) OR D (DIAMETER) IS FEW METERS AND DEPENDS ON WEIGHT REQUIRED MATERIAL BEARING CAPACITY OF THE SOIL A TYPICAL APPLICATION H = 20 M AND W = 15 - 20 TON DEPTH OF COMPACTION = 10 M. USUALLY LARGE AREAS (NOT VERY CLOSE TO POPULATED AREAS) ARE SELECTED TO APPLY HIS METHOD. USUALLY RECTANGULAR GRID POINTS 5-10 M APART ARE USED, 5-10 BLOWS OF THE TAMPER ARE APPLIED AT EACH POINT. THE NUMBER OF BLOWS AT A POINT IS CONTROLLED PRIMARILY BY THE OBSERVATION OF THE DEPTH OF DEPRESSION CREATED.

54. CE-464 Ground Improvement A TYPICAL TREATMENT : AVERAGE 2-3 BLOWS /m2 2 OR 3 COVERAGES OF AN AREA MAY BE REQUIRED. THE TIME INTERVAL BETWEEN COVERAGES DEPENDS ON THE RATE OF DISSIPATION OF EXCESS POREWATER PRESSURES AND STRENGTH REGAIN. EXAMPLE FOR COARSE SAND DAYS AND FOR FINE GRAINED SOIL WEEKS MAY BE NECESSARY. GROUND SURFACE IS USUALLY LEVELLED BETWEEN COVERAGES BY IMPORTED GRANULAR MATERIAL. BEFORE FURTHER PASSES OF TAMPING, MEASUREMENTS ARE DONE AFTER LEVELLING TO ASSESS AVERAGE FORCED SETTLEMENT ( DS : 2 - 5 % PER COVERAGE). TO ASSESS THE TRUE VOLUME COMPRESSION MEASUREMENTS AND CALCULATIONS ARE DONE AT SELECTED POINTS.

55. CE-464 Ground Improvement

56. CE-464 Ground Improvement BEFORE STARTING TAMPING A SURFACE BLANKET OF UNSATURATED GRANULAR MATERIAL I M THICK OR MORE IS SPREAD OVER THE AREA TO BE TAMPED IF THIS DOES NOT OCCUR NATURALLY TO LESSEN LOCAL SHEAR & TO ALLOW EFFECTIVE COMPACTION. "IRONING" IS FULL COVERAGE OF THE AREA BY SMALL IMPACTS. IT COMPACTS THE SURFACE LAYERS (H = 2-3 M). IT CAN BE DONE BY SURFACE ROLLING.

57. CE-464 Ground Improvement

58. CE-464 Ground Improvement

59. CE-464 Ground Improvement ECONOMIC DEPTH BELOW BLANKET: 3-10 M. S(NO IMPROVEMENT) / S(AFTER TAMPING) = 4-5 NOTE THAT IMPROVEMENT IS NOT UNIFORM WITH DEPTH. PRELIMINARY TESTS (TRIAL) ARE NECESSARY. A SUITABLE METHOD OF CONTROLLING THE COMPACTION IS ESSENTIAL (PRE&POST TESTS) GENERALLY IT IS BELIEVED THAT PLASTIC SATURATED CLAYS ARE NOT SUITABLE FOR TAMPING. LOW PLASTICITY COHESIVE SOILS MAY BE SUITABLE.

60. CE-464 Ground Improvement

61. CE-464 Ground Improvement BLASTING PRINCIPLE OF THE METHOD: BY BLASTING BURIED EXPLOSIVES (DYNAMITE, TNT, AMMONITE ETC.) LONGITUDINAL AND SHEAR DETONATION WAVES ARE PRODUCED. APPLIED TO MAINLY LOOSE, COHESIONLESS, SATURATED SOILS (MOST SUITABLE) BLASTING CAUSES LIQUEFACTION, AND THEREFORE SOIL STRUCTURE IS BROKEN AFTER BLASTING, WATER AND GAS IS EXPELLED. DENSIFICATION OCCURS SAND BOILS AT THE SURFACE (CRATERING IS AVOIDED)

62. CE-464 Ground Improvement PROCEDURE : PIPE IS INSTALLED TO THE DESIRED DEPTH (BY JETTING, VIBRATING ETC.). CHARGE IS PLACED IN THE PIPE. PIPE IS WITHDRAWN AND THE HOLE IS BACKFILLED (SOMETIMES PIPES ARE LEFT IN PLACE AND FIXED LATER ON). THE CHARGES ARE DETONATED ACCORDING TO THE PRE-ESTABLISHED PATTERN.

63. CE-464 Ground Improvement MAJOR SETTLEMENT FOLLOWS THE BLAST, SMALLER SETLEMENTS LAST FOR THE NEXT FEW MINUTES. PIEZOMETERS ARE USUALLY INSTALLED. DENSER (STRONGER) THE SAND AND HIGHER DR AND GREATER THE REQUIRED DEPTH FOR DENSIFICATION NEEDS GREATER AMOUNTS OF EXPLOSIVES (BLAST) TO BE USED (I.E. HIGHER ENERGY REQUIRED). SUITABILITY AS FAR AS GRAIN SIZE DISTRIBUTION IS CONCERNED IS SAME AS VIBROFLOATATION. LYMAN REPORTS EFFECTIVENESS IN SILTY SOILS. WILD & HASLAM FOUND THE METHOD EFFECTIVE IN A MICACEOUS SAND (75 % OF THE PARTICLES SMALLER THAN NO: 200 SIEVE). PRUGH FOUND THAT CLAY POCKETS REDUCE THE EFFICIENCY DRASTICALLY.

64. CE-464 Ground Improvement PARTLY SATURATED SOILS MAY BE SATURATED ARTIFICIALLY. NO GENERALLY ACCEPTED DESIGN PROCEDURES ARE AVAILABLE. CONDUCT FIELD TRIALS AND/OR FOLLOW GENERAL GUIDELINES FROM PREVIOUS EXPERIENCES AND STUDIES FOR A GOOD APPLICATION. IVANOV (1967) EXPERIENCES UP TO 20 M DEPTH. CHARGE SIZE : < 1 - 12 kg DEPTH OF BURIAL ‘D’ (CENTER OF CHARGE) D> H/4 - D=H ANOTHER RECOMMENDATION D = 0.67 H

65. CE-464 Ground Improvement CHARGE SPACING IN PLAN : 3-15 m NUMBER OF COVERAGES : 1-5 (2-3 usual) EACH COVERAGE CONSISTS OR A NUMBER INDIVIDUAL CHARGES. TOTAL EXPLOSIVE USE : 8-150 g/m3 (10-30 g/m3 typical) SURFACE SETTLEMENT : 2-10 % of layer thickness DEPTH OF TREATMENT : VARIABLE, APPLICATIONS UP TO 30-40 m ARE QUOTED;PRACTICAL LIMIT: TO PLACE THE REQUIRED CONCENTRATED CHARGES TO THE REQUIRED DEPTH.

66. CE-464 Ground Improvement AS 'H' INCREASES s0 AND Dr ALSO INCREASE WITH INCREASING ENERGY REQUIRED, DECREASING RADIUS OF INFLUENCE. IVANOV 1987 where ; Pmax IS THE MAGNITUDE OF SHOCK WAVE PRESSURE (kg/cm2) C IS THE SIZE OF CHARGE, (kg of TNT) R IS THE DISTANCE FROM CENTRE OF CHARGE (m) m1, m2, k1, k2 ARE EMPIRICAL COEFFICIENTS. ‘I’ IS THE IMPULSE PER UNIT AREA (kg.sec/cm2). SOMETIMES THE RATIO IS CALLED HOPKINSON'S NUMBER.

67. CE-464 Ground Improvement EVEN SMALL % GAS CAUSES DAMPING OF P - WAVE PRESSURES. DENSIFICATION UP TO 75-80 % DR HAS BEEN POSSIBLE, SOMETIMES ERRATIC RESULTS OCCUR, INITIALLY DENSE LAYERS MAY BE LOOSENED. UPPER 1 - 2 m NOT EFFECTIVE AND COMPACTED BY SURFACE ROLLERS.

68. CE-464 Ground Improvement LYMAN, 1942 GIVES THE FOLLOWING RELATIONSHIP BETWEEN WEIGHT OF CHARGE, C, IN LBS AND RADIUS OF SPHERE OF INFLUENCE, R(ft), C = a * R3 a = 0.0025 (0.062 m/ kg) for 60% Dynamite THE SIZE OF THE CHARGE ‘C’ (IN KG TNT) CAN BE TAKEN AS, ACCORDING TO IVANOV, 1978; C = 0.055 * d3ch where d3ch IS THE DEPTH OF CHARGE PLACED. KOK & TRENSE, 1979 BASED ON PRACTICAL EXPERIENCE THE EFFECTIVE RADIUS, Reff (IN m) OF THE INFLUENCE OF BLASTING (DEFINED AS THE RADIUS WITHIN WHICH FAIRLY UNIFORM COMPACTION OCCURS AND APPROXIMATES THE BASE OF THE SETTLEMENT SAUCER) CAN BE EXPRESSED AS; where K=2-5

69. CE-464 Ground Improvement AS A RESULT OF BLASTING, LIQUEFACTION OCCURS WHICH IS THE POTENTIAL FOR DENSIFICATION. LIQUEFACTION COEFFICIENT Du/s’0 Du : EXCESS POREWATER PRESSURE s’0 : EFFECTIVE OVERBURDEN PRESSURE PRIOR TO BLASTING IF DEPTH EFFECT IS DISREGARDED : KOK & TRENSE, 1979 LIQUEFACTION OCCURS WHEN Du/s’0 APPROACHES TO UNITY.

70. CE-464 Ground Improvement

71. CE-464 Ground Improvement BARENDSEN & KOK (1983): IF THEN NO BOILING.

72. CE-464 Ground Improvement THE MINIMUM DISTANCE R OF THE CHARGE CAN BE DEDUCED

73. CE-464 Ground Improvement ACCORDING TO IVANOV (I983) OPTIMUM VALUE OF SUCH CHARGES WOULD BE AT THE ORDER OF ABOUT 10 KG TNT. HOPKINSON NUMBER IS ALSO A MEASURE OF SETTLEMENT OF THE SOIL LAYER, WITH INITIAL THICKNESS H, WHEN TREATED WITH EXPLOSIVES;

74. CE-464 Ground Improvement AFTER BLASTING PENETRATION RESISTANCES IN LOOSE SOILS DO NOT INCREASE IMMEDIATELY BUT GRADUALLY ! VERY DENSE LAYERS MAY BE LOOSENED OR WEAKENED BY BLAST BUT OVERALL EFFECT IS POSITIVE. REPEATED SHOTS ARE MORE EFFECTIVE THAN A SINGLE LARGE ONE OR SEVERAL SMALL ONES DETONATED SIMULTANEOUSLY. DELAYED BLASTING (1-5 SEC) IS MORE EFFECTIVE THAN ORDINARY BLASTING. WHEN A SERIES OF COVERAGES ARE USED THE SURFACE SETTLEMENT ACCOMPANYING EACH COVERAGE IS USUALLY LESS THAN THE ONE PROCEEDING.

75. CE-464 Ground Improvement DEPTH SHOULD BE GREATER THAN R IF SURFACE CRATERING IS TO BE AVOIDED. MOST WIDELY USED EXPLOSIVES ARE 60 % DYNAMITE, 30% SPECIAL GELATINE DYNAMITE AND AMMONITE. USING EXPLOSIVES FOR COMPACTION RELATIVE DENSITIES DR OF LOOSE SAND LAYERS CAN BE IMPROVED BY AN AVERAGE OF DDr = 15% UP TO 30% IF INITIAL DENSITY IS LOW ENOUGH (E.G. Dr <50%). FOR MEDIUM DENSITIES WHICH SURPASS FOR INSTANCE Dr = 60 % A NOTICABLE IMPROVEMENT IS OFTEN VERY DIFFICULT.

76. CE-464 Ground Improvement

77. CE-464 Ground Improvement