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Back to Basics (plus a little extra) on Geotechnical ...

Back to Basics (plus a little extra) on Geotechnical Engineering: Ground Compaction Alan Parrock 1971 - 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 2015 - Convenor SABS TC98 SC006 responsible for drafting the new SA Geotechnical design code and reliability based design approach COMPACTION in the beginning TMH1-1979 Test Mass (kg) Drop height (m) Number of blows Layers Input energy (kNm) Volume (m3) Energy/Volume (kNm/m3) Mod AASHTO 55 5 2415 NRB 25 5 1098 Proctor 55 3 531 Impact roller Five sided 20 1 * 132 Three sided 20 1 * 224 Ram compaction* 7*7*5 11500 20 1 170 5*5*5 11500 20 1 334 5*5*4 11500 20 1 417 Vibratory compaction Bomag 212 300 1 ** 323 * = 1m depth ** = depth, 10 passes, and 30 vibrations/second RIC 12 000 45 1 16 200 441 RIC 12 000 45 1 16 200 441 y = R = 100 1000 10000 80 85 90 95 100 105 Energy (kNm/m3) Density as a percentage of Mod AASHTO Vs=1935/2700= Vv= Vw= E=Vv/Vs

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 ...

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Transcription of Back to Basics (plus a little extra) on Geotechnical ...

1 Back to Basics (plus a little extra) on Geotechnical Engineering: Ground Compaction Alan Parrock 1971 - 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 2015 - Convenor SABS TC98 SC006 responsible for drafting the new SA Geotechnical design code and reliability based design approach COMPACTION in the beginning TMH1-1979 Test Mass (kg) Drop height (m) Number of blows Layers Input energy (kNm) Volume (m3) Energy/Volume (kNm/m3) Mod AASHTO 55 5 2415 NRB 25 5 1098 Proctor 55 3 531 Impact roller Five sided 20 1 * 132 Three sided 20 1 * 224 Ram compaction* 7*7*5 11500 20 1 170 5*5*5 11500 20 1 334 5*5*4 11500 20 1 417 Vibratory compaction Bomag 212 300 1 ** 323 * = 1m depth ** = depth, 10 passes, and 30 vibrations/second RIC 12 000 45 1 16 200 441 RIC 12 000 45 1 16 200 441 y = R = 100 1000 10000 80 85 90 95 100 105 Energy (kNm/m3) Density as a percentage of Mod AASHTO Vs=1935/2700= Vv= Vw= E=Vv/Vs= DOS= Vw/Vv= = 70% Air voids= = CBR CBR = Stiffness plate load test E= r(1- 2)/2 Bearing capacity for derivation of shear strength Tested at Medupic (kPa) ( )

2 D = 2021 OMC = some theory Effect of moisture on stiffness Effect of moisture on stiffness-practical considerations Effects on hyperbolic parameters So how do we know if materials are going to compact easily Attributes of field rollers and stiffness achieved after compaction Eccentric masses Vibratory roller compaction Input cells Centrifugal force 530 kN Frequency 1560 Vibrations/minute Amplitude mm Operating speed m/sec Roller width m Layer thickness 2 m Energy input kNm Volume in 1 second m3 Energy input/volume kNm/m3 Number of passes for 90% 29 93% 45 95% 61 98% 97 100% 131 Actual optimum derived from field trial was 32 0 2 4 6 8 10 12 0 100 200 300 400 500 600 700 800 Depth (m) Vs (ms/) CSW-1 CSW-2 CSW-3 CSW-4 CSW-5 CSW-6 Go= Vs2 Go=2000x3002 Go=180 MPa Eo= Eo=486 MPa E insitu=49 MPa Vibration Compaction Vibration compaction Vibration replacement Impact compaction DC, RIC and Impact rolling Comparison DCRICMass (tonne) Height (m) (kJ/blow)1764-211688-176 Momentum (tm/s)214-23440-65 Blow Rate (blows/min)<140-60 Compaction Depth (m)6-83-4 PropertyCompaction MethodRIC Speed Safety Mobility Portability Applications of RIC Foundation support Stone columns Floor slab strengthening Liquefaction mitigation Waste stabilisation 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 Theory cont.

3 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 4m2 for 5, 10, 20 and 40 blows Theory cont. Comparison of compacted area under different ram masses Comparison of compacted areas under different drop heights Theory cont. Comparison of compacted area under different masses and drop heights Theory cont. The compacted area is defined by: Depth and radius of compacted area are given by the following expressions: Theory Cont. Relationship between compacted area momentum and energy 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. (mvN) b + a = ZZZlog(mvN) b + a = RRRlogOshima and Takada (1997:1641) 2gH = v Dr (%) az bZ aR bR 40 20 minmaxminmax d d ddd dr.

4 = DSpreadsheet to calculate the increase in relative densityTaken from the equations as given on page 31 of "Soil Mechanics"by TW Lambe and RV Whitman (1969)DepthMaximum dry density1800 Relative density100 Minimum dry density1350 Relative density0 Insitu dry density1521 Relative density45 Required dry density1700 Relative density82 Change in relative density37=InputMass and fall properties of Dynamic Compaction HammerMass =9tonnesRadialFall =1metresVel = from Oshima A and Takada N - Relation between compacted areaand ram momentum by heavy tamping - 14th ICSMFE Hamburg pp 1641-1644 Depth calculationFor DR = 20%For DR = 40% us look at some numbers .. Test Mass (kg) Drop height (m) Number of blows Layers Input energy (kNm) Volume (m3) Energy/Volume (kNm/m3) Mod AASHTO 55 5 2415 NRB 25 5 1098 Proctor 55 3 531 Impact roller Five sided 20 1 * 132 Three sided 20 1 * 224 Ram compaction* 7*7*5 11500 20 1 170 5*5*5 11500 20 1 334 5*5*4 11500 20 1 417 Vibratory compaction Bomag 212 300 1 ** 323 * = 1m depth ** = depth, 10 passes, and 30 vibrations/second RIC 12 000 45 1 16 200 441 Impact rolling Speed Safety Mobility ?

5 Portability ? Impact roller 30kNm Impact roller 15kNm Impact rolling -theory Theory suggests depth of compaction is some after 30 passes, Tests conducted indicate this is very dependent on material being compacted. Case Study - Dorsfontein Construction of a tunnel housing a conveyor system underneath a coal slot, Conveyor system very sensitive to movement. Dorsfontein Stone column layout 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 Design parameters E value determined by Continuous Surface Wave (CSW) tests Material strength parameter determined from shearbox and triaxial tests Dorsfontein cont. Site conditions: 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 Dorsfontein cont.

6 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 190 120 Piled raft, no culvert 48 80 Culvert, no piled raft 100 70 Piled raft, culvert (joints) 47 43 Piled raft, culvert (no joints) 45 8 Case Study Richards Bay Construction of container yard Typical profile: : Hydraulic fill 9m: Very soft silty clay 11m: Residual calcarenite 13m: Cretaceous siltstone t90 = 15 months preloaded with a 3m fill Installation of stone columns using Rapid Impact Compaction suggested as a manner of reducing t90 Case Study Richards Bay Case Study Richards Bay Case Study Richards Bay Richards Bay Cont. Four trials were conducted in test area: Two trials with compaction of in situ material with a diameter foot only One trial with a stone column spacing of 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 Richards Bay Cont.

7 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 spacing Improvement in DPSH results however no improvement in CSW results for 5m spacing t90 reduced to between 2 and 8 months Case Study Midfield Terminal Comprised construction of a 6 8m fill over site The site was divided into three zones: Midfield Terminal cont. Material properties: AreaCBR @ 90%E (MPa)Ferricrete126 Swampy-<2 Seepage1-22 Midfield Terminal 4 5m soft clay layer. E value = 6 MPa Founding solutions considered Do nothing Remove and replace Stone column installation Columns increase in-situ stiffness thus reducing settlements from 400mm to 200mm Stone columns provide reduced drainage path length 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 Midfield Terminal Cont.

8 Recommendations were given to construct stone columns in combination with high strength geosynthetic and gravel raft to provide a piled raft solution 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 10-15 blows RIC stone columns installed using 8 passes with 20-35 blows per pass Midfield Terminal cont. Midfield Terminal Cont. 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 Midfield Terminal Cont. Results obtained Stone columns exhibited an elastic modulus of approximately 50 60 MPa Material around stone columns increased in stiffness from 6 MPa to approximately 14 MPa 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 The site Measuring points Measured settlement -120 -100 -80 -60 -40 -20 0 20 Settlement (mm) Time (Date) Settlement vs.

9 Time Plate 1 Plate 2 Plate 3 Plate 4 Piezometer levels -8 Piezometer reading (m) Time (Days) Piezometer readings Piezometer 1 Piezometer 2 Piezometer 3 Piezometer 4 Piezometer 7 Piezometer 8 Midstream Hospital In-cab instrumentation CSW testing CSW Testing CSW in the Alps-John Rigby Jones Midstream hospital CSW results 0 2 4 6 8 10 12 14 16 18 20 0 200 400 600 800 1000 Depth (m) Vs (m/s) CSW1 CSW2 CSW3 CSW4 CSW5 CSW6 Midstream Hospital CSW testing The magic number is 160m/sec, As Go = V2 x , This would translate into Go=46 MPa, As E = 2(1 + ) x G, This would generate an Eo value of some times G ie Eo = 124 MPa, But using the softening coefficient of this generates an insitu E value = 37 MPa For a 2m x 2m base loaded to 150kPa = giving a relative rotation of 1:900 OK Softening function for soils Stiffness from Packard 0 20 40 60 80 100 1400 1500 1600 1700 1800 1900 2000 2100 10 15 20 25 30 35 Unload/reload E value (MPa) Dry density (kg/m3) Moisture content (%) Zero air voids dry density E value Poly.

10 (E value) And a little further from In Kenya In Israel In Israel RIC in action in Dubai Dubai Calcareous Sand Trials Dubai 2m above sea level 3m above sea level Thank you ladies and gentlemen


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