Transcript DESIGN OF VERTICAL DRAINS - Middle East Technical University

DEEP COMPACTION
THE MAIN PURPOSE OF TREATING OR IMPROVING THE
SOILS IS TO ELIMINATE THE DANGER OF EXCESSIVE
SETTLEMENTS. LOOSE COHESIONLESS SOILS GENERALLY
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
- BLASTING
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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).
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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
HORIZONTAL
20 - 40 kN (2-4 ton) AND THEY DEVELOP
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.
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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.
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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.
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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.
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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
SUPERIMPOSED.
ADJACENT
COMPACTIONS
CAN
BE
THERE ARE PROCEDURES FOR DETERMINING VIBROFLOT
SPACING REQUIRED TO OBTAIN A SPECIFIED Dr (mIn.) .
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WEBB & HALL (1968) ALSO DESCRIBE A 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
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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
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3. VIBRO - COMPOZER METHOD
COMPRESSED
AIR
IS
INSIDE
USED
THE
CASING
TO
HOLD SAND IN
PLACE WHILE
WITHDRAWING
THE
CASING
MURAYAMA
(1958)
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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.
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5. COMPACTION PILES
DENSIFICATION FROM TWO EFFECTS
1.
DISPLACEMENT OF SOIL
2.
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.
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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).
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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)
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EVALUATION OF THE TREATED GROUND MAY BE DONE BY
ONE OR TWO OF THE FOLLOWING METHODS;
1.
SURFACE SETTLEMENT MARKERS
2.
VOLUME OF ADDED SOIL (CRATERS OR
VIBROCOMPACTION DISP.)
3.
STANDARD PENERATION TEST, SPT.
4.
CONE PENETRATION TEST, DUTCH CONE, CPT
5.
PRESSUREMETER TEST, PMT
6.
SEISMIC SHEAR WAVE VELOCITY DETERMINATIONS, VS
7.
PILE DRIVING RESISTANCES
8.
PLATE LOADING TESTS
9.
DOWN - HOLE DENSITY METERS.
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VERY
LOOSE
LOOSE
MEDIUM
DENSE
DENSE
VERY
DENSE
SPT- N
VALUE
<4
4-10
10-30
30-35
>50
CPT QC
(KG/CM2)
<50
50-100
<15
15-35
35-65
65-85
85-100
DRY UNIT
WEIGHT
(KN/M3)
<14
14-16
16-18
18-20
>20
FRICTION
ANGLE
<30
30-32
32-35
35-38
>38
EQUIVALENT
DR (%)
>200
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VIBROCOMPACTION GRIDS ARE SQUARE OR TRIANGULAR
ASSUMING
DENSIFICATION ONLY IN LATERAL DIRECTION
 (1  e0 )
 (1  e0 )
(D<80CM)
S
e0  e
d
SQUARE
S  1.08
e0  e
TRIANGULAR
(CONSIDER AVERAGE De)
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d
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BROWN (1977) HAS DEFINED A SUITABILITY NUMBER FOR
VIBROFLOATATION BACKFILLS.
Suitabilit y Number  1.7
3
1
1


( D50 ) 2 ( D20 ) 2 ( D10 ) 2
D10, D20 and D50 ARE MM PARTICLE SIZES CORRESPONDING % PASSING.
SUITABILITY NUMBERS AND BACKFILL CLASSES
0-10
EXCELLENT
10-20 GOOD
FASTER THE
VIBROFLOT TAKEN UP
20-30 FAIR
30-50 POOR
> 50 UNSUITABLE
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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.
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B(WIDTH) OR D (DIAMETER) IS FEW METERS AND DEPENDS ON

WEIGHT REQUIRED

MATERIAL

BEARING CAPACITY OF THE SOIL
A TYPICAL APPLICATION H = 20
DEPTH OF COMPACTION = 10 M.
M AND W = 15 - 20 TON
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.
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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
COVERAGES BY IMPORTED GRANULAR MATERIAL.
BETWEEN
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.
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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.
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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.
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wave propagation under impact (after R.D.WOODS)
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BLASTING
PRINCIPLE OF THE
EXPLOSIVES
LONGITUDINAL
METHOD:
BY
(DYNAMITE,
AND
SHEAR
TNT,
BLASTING BURIED
AMMONITE
DETONATION
WAVES
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)
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ETC.)
ARE
PROCEDURE :
1. PIPE
IS
DESIRED
INSTALLED
TO
DEPTH
JETTING,
(BY
THE
VIBRATING ETC.).
2. CHARGE IS PLACED IN THE PIPE.
3. PIPE IS WITHDRAWN AND THE
HOLE IS BACKFILLED (SOMETIMES
PIPES ARE LEFT IN PLACE AND
FIXED LATER ON).
4. THE CHARGES ARE DETONATED
ACCORDING
TO
THE
PRE-
ESTABLISHED PATTERN.
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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.
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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
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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.
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AS 'H' INCREASES s0 AND Dr ALSO INCREASE WITH
INCREASING ENERGY REQUIRED, DECREASING RADIUS OF
INFLUENCE.
 C

 k1 

R


3
IVANOV 1987
where ;
Pmax
m1
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  k2
 C

C 

 R 
3
3
m2
‘I’ IS THE IMPULSE PER UNIT AREA (kg.sec/cm2).
3 C
SOMETIMES THE RATIO 
 R

 IS CALLED HOPKINSON'S NUMBER.


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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.
Sand Below GWT
Gas Content (%)
k1
0.35
0.85
1
4
600
450
250
45
Moist 8-10 % water
Moist 2-4 % water
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m1
k2
m2
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;
Reff  K .3 C
where K=2-5
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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.
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Du/s’0 VALUES
3
C
1.53  0.77
R
3
C
1.65  0.64
R
MIN
MEAN
3
C
2.15  0.74
R
MAX
This gives a mean value for the radius of liquefaction
2.0 C 
3
MIN
Rliqu
4.7 C 
 2.8 C 
3
MEAN
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3
MAX
BARENDSEN & KOK (1983):
IF 3 C / R  0.15 THEN NO BOILING.
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THE MINIMUM DISTANCE R OF THE CHARGE CAN BE DEDUCED
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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;
Ds  H . ( C / R)
3
EXPERIMENTALLY FOR AMSTERDAM HARBOUR:


Ds  2.73  0.9 ln( 3 C / R)
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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.
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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.
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HYDRO-BLASTING TECHNIQUE HAS BEEN USED VERY
SUCCESFULLY IN USSR IN LOESS DEPOSITS (COLLAPSIBLE)
THERE ARE MAINLY TWO PROBLEMS ASSOCIATED WITH BLASTING.
•EFFECTS ON ADJACENT STRUCTURES
•EFFECTS ON PEOPLE
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