Back to Basics (plus a little extra) on Geotechnical Engineering: Ground Compaction

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1 Back to Basics (plus a little extra) on Geotechnical Engineering: Ground Compaction

2 Alan Parrock First exposed to soil mechanics at university 1973 Natal Roads Department 1976 Professional engineer 1976 NITRR of the CSIR 1978 BKS now Aecom 1982 First exposed to rock mechanics 1993 Founded ARQ 2007 Fellow of SAICE 2010 Geotechnical Division Gold Medal 2011 Keynote address 15 ARC in Maputo 2013 Keynote address Geo Africa Ghana Convenor SABS TC98 SC006 responsible for drafting the new SA geotechnical design code and reliability based design approach

3 COMPACTION in the beginning TMH1-1979

5 Test Mass (kg) Drop height (m) Number of blows Layers Input energy (knm) Volume Energy/Volume (m 3 ) (knm/m 3 ) Mod AASHTO NRB Proctor Impact roller Five sided * 132 Three sided * 224 Ram compaction* 7*7* RIC 3.5x3.5x *5* *5* Vibratory compaction Bomag ** 323 * = 1m depth ** = 0.15m depth, 10 passes, 3.6m/sec and 30 vibrations/second

6 Energy (knm/m 3 ) y = e x R² = Density as a percentage of Mod AASHTO

7 Vs=1935/2700=0.72 Vv=0.28 Vw=1935x0.101=0.195 E=Vv/Vs=0.28/0.72=0.40 DOS= Vw/Vv=0.195/0.28 = 70% Air voids= =8.50%

8 CBR

9 CBR =5.5/13.344=41

10 Stiffness plate load test E=πσr(1-ν 2 )/2δ

12 Bearing capacity for derivation of shear strength

14 Tested at Medupi c (kpa) φ( ) γd = 2021 OMC = 11.1

15 Now some theory

18 Effect of moisture on stiffness

20 Effect of moisture on stiffnesspractical considerations

26 Effects on hyperbolic parameters

31 So how do we know if materials are going to compact easily

34 Attributes of field rollers and stiffness achieved after compaction

35 Eccentric masses

41 Vibratory roller compaction Input cells Centrifugal force Frequency Amplitude Operating speed Roller width Layer thickness 530 kn 1560 Vibrations/minute 2.85 mm 0.5 m/sec 2.13 m 2 m Energy input knm Volume in 1 second 2.13 m 3 Energy input/volume knm/m 3 Number of passes for 90% 29 93% 45 95% 61 98% % 131 Actual optimum derived from field trial was 32

43 Depth (m) Vs (ms/) Go=ρVs 2 Go=2000x300 2 Go=180MPa Eo=2.7xGo Eo=486MPa E insitu =49MPa CSW-1 CSW-2 CSW-3 CSW-4 CSW-5 CSW-6

45 Vibration Compaction Vibration compaction Vibration replacement

47 Impact compaction DC, RIC and Impact rolling

Comparison Property Compaction Method DC RIC Mass (tonne) 12.5 9-12 Drop Height (m) 15-18 1-1.

48 Comparison Property Compaction Method DC RIC Mass (tonne) Drop Height (m) Energy (kj/blow) Momentum (tm/s) Blow Rate (blows/min) < Compaction Depth (m)

49 RIC Speed Safety Mobility Portability

50 Applications of RIC Foundation support Stone columns Floor slab strengthening Liquefaction mitigation Waste stabilisation

centrifuge models at the Osaka City University in Japan Testing was

51 Theory Method of calculating effect of heavy tamping was refined in the early 90 s by Takada and Oshima Testing was conducted in centrifuge models at the Osaka City University in Japan Testing was aimed at determining relationship between compacted area and ram momentum

52 Theory cont. Testing was conducted under field stresses of 100g Typical example of the propagation of compacted area for a mass of 20t, drop height of 20m and tamper area of 4m 2 for 5, 10, 20 and 40 blows

53 Theory cont. Comparison of compacted area under different ram masses Comparison of compacted areas under different drop heights

54 Theory cont. Comparison of compacted area under different masses and drop heights

55 Theory cont. The compacted area is defined by: Depth and radius of compacted area are given by the following expressions:

56 Theory Cont. Relationship between compacted area momentum and energy

57 Theory Cont. Findings of the analyses: Compacted area is governed better by ram momentum rather than ram kinetic energy, Depth and radius of the compacted area are in proportion to logarithm of total ram momentum.

58 Oshima and Takada (1997:1641) Z = a Z +b Z log(mvn) R= a R +b R log(mvn) v = 2gH ΔD r (%) a z b Z a R b R D r = d max d. d d - max - d min d min

59 Spreadsheet to calculate the increase in relative density Taken from the equations as given on page 31 of "Soil Mechanics" by TW Lambe and RV Whitman (1969) Maximum dry density 1800 Relative density Depth Minimum dry density 1350 Relative density 0 Insitu dry density 1521 Relative density 45 Required dry density 1700 Relative density Change in relative density 37 = Input Mass and fall properties of Dynamic Compaction Hammer Mass = 9 tonnes Fall = 1 metres Radial Vel = 4.4 metres/second Taken from Oshima A and Takada N - Relation between compacted area and ram momentum by heavy tamping - 14th ICSMFE Hamburg pp Depth calculation For DR = 20% For DR = 40%

60 Let us look at some numbers..

61 Test Mass (kg) Drop height (m) Number of blows Layers Input energy (knm) Volume Energy/Volume (m 3 ) (knm/m 3 ) Mod AASHTO NRB Proctor Impact roller Five sided * 132 RIC 3.5x3.5x Three sided * 224 Ram compaction* 7*7* *5* *5* Vibratory compaction Bomag ** 323 * = 1m depth ** = 0.15m depth, 10 passes, 3.6m/sec and 30 vibrations/second

62 Impact rolling Speed Safety Mobility? Portability?

63 Impact roller 30kNm

64 Impact roller 15kNm

71 Impact rolling -theory Theory suggests depth of compaction is some 1.3m after 30 passes, Tests conducted indicate this is very dependent on material being compacted.

72 Case Study - Dorsfontein Construction of a tunnel housing a conveyor system underneath a coal slot, Conveyor system very sensitive to movement.

73 Dorsfontein

74 Stone column layout

75 Options Remove about 5m of weak material and replace with G6 quality material compacted to 93% Mod AASHTO density Installing stone columns which greatly reduces costs

76 Design parameters E value determined by Continuous Surface Wave (CSW) tests Material strength parameter determined from shearbox and triaxial tests

77 Dorsfontein cont. Site conditions:

78 Dorsfontein cont. Stone columns installed using the RIC technique suggested to mitigate differential settlement Analysis conducted using Rocscience s Phase2 with Duncan Chang Hyperbolic material properties

79 Dorsfontein cont. Results obtained: Noticeable reduction in settlement Spacing of columns varied to combat differential settlements effectively Reduced time of consolidation Scenario Settlement (mm) Expected Differential No culvert, no piled raft Piled raft, no culvert Culvert, no piled raft Piled raft, culvert (joints) Piled raft, culvert (no joints) 45 8

81 Case Study Richards Bay Construction of container yard Typical profile: m: Hydraulic fill 2.5 9m: Very soft silty clay m: Residual calcarenite m: Cretaceous siltstone t 90 = 15 months preloaded with a 3m fill Installation of stone columns using Rapid Impact Compaction suggested as a manner of reducing t 90

82 Case Study Richards Bay

83 Case Study Richards Bay

84 Case Study Richards Bay

85 Richards Bay Cont. Four trials were conducted in test area: Two trials with compaction of in situ material with a 1.5m diameter foot only One trial with a stone column spacing of 7.5m with one in the middle One trial with a stone column spacing of 5m with one in the middle Testing was conducted before/after compaction and installation of stone columns Testing conducted included: Continuous Surface Wave (CSW) tests and Dynamic Probe Super Heavy (DPSH) tests

86 Richards Bay Cont. Results revealed the following: No change for the areas not treated with stone columns Improvement in CSW results however no improvement in DPSH results for 7.5m spacing Improvement in DPSH results however no improvement in CSW results for 5m spacing t 90 reduced to between 2 and 8 months

87 Case Study Midfield Terminal Comprised construction of a 6 8m fill over site The site was divided into three zones:

88 Midfield Terminal cont. Material properties: Area 90% E (MPa) Ferricrete 12 6 Swampy - <2 Seepage 1-2 2

89 Midfield Terminal 4 5m soft clay layer. E value = 6MPa Founding solutions considered Do nothing Remove and replace Stone column installation

90 Columns increase in-situ stiffness thus reducing settlements from 400mm to 200mm Stone columns provide reduced drainage path length

91 Midfield Terminal Cont. Construction of fill to induce a bearing pressure of approximately 160kPa Settlement over seepage and swampy area expected to range between 130 and 400mm Time of consolidation expected to be approximately 4-5 years

92 Midfield Terminal Cont. Recommendations were given to construct stone columns in combination with high strength geosynthetic and gravel raft to provide a piled raft solution

93 Midfield Terminal Cont. Piled Raft constructed using combination of RIC and DC DC used in the soft swampy area RIC used in the stiffer seepage area DC stone columns installed using blows RIC stone columns installed using 8 passes with blows per pass

94 Midfield Terminal cont.

95 Midfield Terminal Cont.

96 Case Study Midfield Terminal Quality assurance testing of the RIC stone columns included: Plate load tests to verify stiffness Excavation of stone column to verify structural integrity

97 Midfield Terminal Cont. Results obtained Stone columns exhibited an elastic modulus of approximately 50 60MPa Material around stone columns increased in stiffness from 6MPa to approximately 14MPa Settlements would be reduced to between 100 and 200mm Time of consolidation reduced from 4-5 years to just 7 months Construction time expected to be 8 months therefore settlements will be built out during construction

98 The site

99 Measuring points

100 Settlement (mm) Measured settlement Settlement vs. Time Plate 1 Plate Plate 3 Plate Time (Date)

101 Piezometer reading (m) Piezometer levels Piezometer readings Piezometer 1 Piezometer 2 Piezometer 3 Piezometer 4 Piezometer 7 Piezometer Time (Days)

102 Midstream Hospital

103 In-cab instrumentation

104 CSW testing

105 CSW Testing

106 CSW in the Alps-John Rigby Jones

107 Depth (m) Midstream hospital CSW results Vs (m/s) CSW1 CSW2 CSW3 CSW4 CSW5 CSW6

108 Midstream Hospital CSW testing The magic number is 160m/sec, As Go = V 2 x ρ, This would translate into Go=46MPa, As E = 2(1 + ν) x G, This would generate an Eo value of some 2.7 times G ie Eo = 124MPa, But using the softening coefficient of 0.3 this generates an insitu E value = 37MPa For a 2m x 2m base loaded to 150kPa δ = 5.5mm giving a relative rotation of 1:900 OK

109 Softening function for soils

110 Dry density (kg/m 3 ) Unload/reload E value (MPa) Stiffness from Packard Moisture content (%) Zero air voids dry density E value Poly. (E value)

111 And a little further from home

112 In Kenya

113 In Israel

114 In Israel contd.

115 RIC in action in Dubai

116 Dubai Calcareous Sand Trials

117 Dubai 2m above sea level 3m above sea level

118 Thank you ladies and gentlemen

Evaluation the Effectiveness of Rapid Impact Compaction (RIC) as a Ground Improvement Technique

Evaluation the Effectiveness of Rapid Impact Compaction (RIC) as a Ground Improvement Technique Bashar Tarawneh, Ph.D, P.E Assistant Professor Civil Engineering Department The University of Jordan Amman,