Session Report Pavements and Fills

Transcription

1 Session Report Pavements and Fills Dr Burt Look

2 Papers in Report Session Verification Of An Impact Rolling Compaction Trial Using Various In Situ Testing Methods Suggested QC Criteria for Deep Compaction Using the CPT A New Indirect Tensile Testing Setup to Determine Stiffness Properties of Lightly Stabilised Granular Materials Geotechnical Characterization of a Heterogeneous Unsuitable Material Stockpile Control of soil compaction in pavement layers: A new approach using the dynamic cone penetrometer (DCP) Use of the Light Falling Weight Deflectometer (LFWD) as a site investigation tool for residual soils and weak rock Correlation Between the Results of the PLT & CBR Tests to Determine the Elasticity Modulus Characterization of Railroad Track Substructures Using Dynamic & Static Cone Penetrometer Remedial Measures to Facilitate the Construction of Stable Bridge Approach Fills A Case Study New and Innovative Approach to Ensuring Quality of Quarry Source Materials in Queensland Road Infrastructure Construction Evaluation of Rockfill Embankments by Field Tests in Siraf Refinery Complex Site, Iran

3 This is not a review It is a session report of interesting bits and discussion points What is interesting. What needs clarification.

4 Verification of an impact rolling compaction trial using various in situ testing methods (Scott et al.) Field based study to compare before and after compaction test results when an impact (non-circular) roller is used on trial. Various in situ testing methods, as well as instrumentation is used to measure the ground response and surface settlement measurements. Contributes to our understanding that deep lift compactions are achievable using rolling dynamic compaction (RDC).

5 Depth (m) Impact rolling compaction trial results Which testing criteria for assessment? Depth (m) Vs (m/s) Dry Density (kn/m 3 ) Velocity improvement to 2.0m Density improvement to 1.0m Traditional density testing of deep lifts erodes the benefit gained from 3.5 faster placement Pre compaction Post compaction 4 Pre compaction Post compaction

6 Impact rolling compaction trial Previous Research Previous Research by authors (2015) was to greater depths. Reduced to1.5m depth in this Trial? 120 kpa Is this suggesting a target 200kPa pressure or depth material dependency?

7 Settlement (mm) Impact rolling compaction trial Lift vs No of passes optimisation? Energy Footprint Number of passes Large No, even at 10 km/h Informative for further research to Vibratory provide cost RDC - energy comparison as Roller compared with other methods / rollers. Reduced $ Testing Reliability These equipment have significant petrol consumption Reduced operational Time Less cost/ Passes Greater Thickness Energy footprint? Less Fuel Measured data

8 Suggested QC criteria for deep compaction using the CPT (Robertson) This application is for quality control (QC) in deep compaction. The CPT is popular due to its low cost, yet current methods for deep compaction often apply only to clean silica sands and are not effective in soils with higher fines. Frequently resulted in uncertainty on the effectiveness of the deep compaction. Suggested approach for QC for deep compaction based on the normalized equivalent clean sand cone resistance. An associated webinar with more details freely down loaded at:- IgW/cpt-for-quality-control-ofground-improvement-deepcompaction Highly recommended reading as it answered some of the questions I had when writing this report.

9 QC criteria for deep compaction using the CPT Clean Sands? What is cleans sands? See webinar for more info F r < 0.5% Not / less compactable Fines content > ~40% CPT I c < 2.6 While ~40% is mentioned, this seems as an upper bound. Soils with 35% fines is considered clays in British Standards

10 QC criteria for deep compaction using the CPT Time effects? Time Effect Considerations Again the webinar provides some insights, but no recent data. Assuming there is less time effects with clean sands, then as the percentage fine increases, then some time effect is likely. Observing Pore Water Pressure dissipation is one approach, but further guidance on this aspect of likely increase in his future research would be appreciated.

11 A new indirect tensile testing setup to determine stiffness properties of lightly stabilised granular materials (Gnanendran and Alam) Cementitiously stabilised granular materials are generally characterised by their tensile strength, stiffness modulus and Poisson s ratio. Flexural beam point load testing method often preferred for characterisation due to similarities in stress conditions it produces with that in the stabilised base layer of a pavement structure under wheel loading. A new IDT testing setup was developed in this study to determine deformations along the horizontal and vertical diameters of a cylindrical IDT specimen. However preparation and handling of a flexural beam of cementitiously stabilized pavement material at such low levels of binder content is quite difficult. The experimental program included the determination of IDT strength, stiffness modulus and Poisson s ratio for a lightly stabilized granular base material

12 Indirect tensile testing Results The paper states an inaccurate Poisson s ratio with a difference of 0.1 from the actual value may increase/decrease the stiffness modulus by up to 25% resulting in an uneconomical and conservative pavement design. The Poisson s ratios ranged from 0.18 to 0.26 for binder content variations of 1% to 3% Interesting as Poisson Ratio (in general geotechnical work) is not usually considered a governing parameter as compared to other material variables.

13 Geotechnical characterization of a heterogeneous unsuitable stockpile (Murrugarra et al.) Geotechnical characterization of a heterogeneous stockpile in order verify the physical stability of the deposit and to optimize the closure configuration. Characterization was based on test pits, CPTU, MASW, field and laboratory tests. Based on the analysis of that information, strength parameters were proposed for slope stability analysis. Amount of data provided by the CPTU tests, allowed statistical analysis for precise strength parameters for the different strata.

14 Characterization of a heterogeneous unsuitable stockpile Any large scale lab tests? Given the nature of mine waste stockpiles with a large quantity of coarse materials and with over 20% average material greater than 20mm fines then scale effects may govern. Fine (64% average fine content) and Coarse (35% average fines) derives strength parameters may be different due to this scale effect Reporter s Note: Gradations large sizes are typically under-reported as soil testers do not shovel over-sizes into sample bag. Typically a boulder size greater than 400mm is over 25kg maximum carrying weight

15 Characterization of a heterogeneous unsuitable stockpile Conundrum on derived friction angles? Coarse Fine = 32 to 34 Field results = 34 to 39 Lab Results This is reverse of what one would expect but is a normal conundrum faced when correlations are adopted 35% average fines content 64% average fines content

16 Control of soil compaction in pavement layers: A new approach using the dynamic cone penetrometer (DCP), (Belincanta et al.) Field penetration tests data for compaction control and comparative laboratory testing used for calibration of penetration index (PI), dry unit weight and soil moisture content. Control can be performed in situ by measuring the PI and soil moisture content, as they are directly related to the degree of compaction of the layer. Results indicate that PI value is inversely proportional to the degree of compaction and that it is strongly influenced by the soil moisture content. A site specific relationship was developed for obtaining the degree of compaction at a given moisture content.

17 Control of soil compaction in pavement layers Site Correlation Any unique properties? A site specific relationship was developed for obtaining the degree of compaction at a given moisture content. This is not a universal equation as it is referenced to a poorly graded gravel with a soil of unit weight of 16.3 kn/m 3. Moisture content tested seems high at 20% to 32% for a gravelly material, and with CBR max above 20%, but 10% to 13% at the optimum moisture content

18 Control of soil compaction in pavement layers DCP Variation vs Density variation? Variation is BEFORE you even start to correlate DCP results to any other design parameters via generic relationships This Paper TOTAL DCP Variation = 30 60% AS

19 Use of the Light Falling Weight Deflectometer as a site investigation tool (Lacey et al.) Light Falling Weight Deflectometer (LFWD) is a surface based, dynamic plate load test provides quick + direct measurement of insitu modulus parameter at near-surface. To demonstrate the potential use of the LFWD as an effective site investigation tool, two brands of LFWD used to assess the insitu modulus of a residual soil and weak sedimentary rock profile. Performance of both LFWDs compared to other traditional site characterisation techniques including DCP profiling and laboratory (soaked) CBR testing.

20 LFWD as a SI tool Tradition vs Current Technology Traditional approach Density as the quality control test, yet in analysis and design the strength or modulus is used. Assumes density controls relates to the strength and modulus values used. LFWD provides direct measurement of modulus + better assessment of strength than a density inference can provide. Yet tradition rather than technology seems to govern. Another barrier is that different LFWDs can provide different modulus This is examined for 2 different LFWDs with one equipment giving ~ ½ value of the other Blows / 100mm Insitu Modulus, E LFWD-100kPa (MPa) Prima 100 LFWD ZFG-2000 LFWD Material Unit / Weathering State SOIL (Fill / Residual Soil) Residual Soil to XW/HW Rock XW / HW Rock HW Rock

21 LFWD as a SI tool CBRs do not account for site oversizes CBR test does not apply for oversize a particles which are discarded during the test. The CBR test would incorrectly plateau at CBR 13% due to discarding the rock sizes. With oversize Oversize removed

22 Correlation between the results of the PLT and CBR tests to determine the elasticity modulus (Kasaeian et al.) CBR test is usually used to determine the relative strength of the subgrade soil and compacted layers. The Plate Load Test (PLT) yields more realistic soil elastic parameters, but is costly. A correlation between PLT and CBR test. Numerical modelling in ABAQUS and PLTs were used to develop a relation for determining the elasticity modulus using CBR test results. The relation was then checked through some PLTs in the site and CBR tests on the rebuilt specimens. The PLT to determine deflections due to loading, bearing capacity of foundations, and soil elastic parameters. The modulus of elasticity yields an approximate estimation of the bed reaction coefficient (Ks). Related PLT load-deflection curves were predicted.

23 PLT and CBR tests to determine the elasticity modulus Test Differences? Plate Load Considerations of 1 st and 2 nd cycle of loading 2 nd Cycle of loading more relevant Plate Load Test Comparison CBR CBR M r Modulus Elastic (E) : E v2 ~ 2.3 E v1 Resilient (M r ) E/M r ratios are material dependent 1.4 for granular bases with stabilized layers 0.3 with embankments below a granular base Low Strain High While the procedure is interesting, any resulting relationship should not be applied outside of this case study due to that material dependency. Linear Elastic not usually taken to failure Failure Pseudo Bearing capacity 2,5 / 5.0mm

24 Characterization of Railroad Track Substructures using Dynamic and Static Cone Penetrometer (Hong et al.) Dynamic and static cone penetrometer (DSCP) developed for characterization of rail-road track substructures. DSCP consists of outer rod for dynamic penetration in the ballast and sub-ballast layer and an extendable inner rod for static penetration in the subgrade Dynamic cone penetration (DSCP) index measured in ballast and subballast layer Cone tip and friction resistances are obtained in the subgrade

25 Dynamic and Static Cone Penetrometer Hybrid of cone penetrometer tests for penetrating ballast material. The dynamic component has a DSCP index associated. The standard DCP has an energy of 45J with a drop height of 575mm / 510mm and hammer weight of 8kg / 9kg. The drop height corresponds to the DCP but with no weight equivalent. DCPI index is therefore new, but the index did not adopt the DCP standard. Main aim was for penetrating the ballast. (Parallel to Split Spoon Sampler for sampling first then counting N values in SPTs) The example experimental result has 2 measurements (DCPI and cone tip resistance).

26 Remedial measures to facilitate the construction of stable bridge approach fills-a case study (Diyaljee) Stability issues associated with proposed 20 m high bridge approach fill. In November 1988 deep seated movements were noted at a depth of 22 m below the original ground from monitoring of slope indicators on the north approach. Remedial measures consisting of wick drains, stone columns, flatter approach fill head and side-slopes, and interceptor drains Implementation of remedial measures did not fully arrest the ground movements. As a result fill slope was modified. the proposed 3-span bridge was abandoned and a one-span Bailey bridge was constructed. Case study which is a bit dated except for a recent site observation in August 2013 which showed that the bridge is still serviceable after 23 years. Typically intolerable movements of 100mm and 50mm for vertical and horizontal movements are used for Bridges but these were not for Bailey Bridges. These movements were significantly exceeded during initial monitoring phase. Case study shows flexibility of Bailey Bridges

27 New and Innovative Approach to Ensuring Quality of Quarry Source Materials in Queensland Road Infrastructure Construction (Evans and Dissanayake) Department of Queensland Transport and Main Roads (QTMR) management system to manage quality of road construction quarry products Source Material Quarry Registration System (QRS) was developed between QTMR and Quarry Industry to address concerns that excessive testing was resulting in increased $ which were being passed on to the Department s construction projects. Guidelines allows the quarry management to self-assess their own testing frequencies and allows the Department as well as Quarry Industry to concentrate testing resources to where risks are highest. Testing frequency reductions of 90% have been realized in some cases with well managed quarries. Quality Registration System QRMR + Quarry Industry Specification Quality Assurance Standards Quality Control Required Tests Criteria

28 Ensuring Quality of Quarry Source Materials in Queensland Frequency of Testing Coefficient of Variation (homogeneous vs heterogeneous) Test Ranking (Weighting Factor) Frequency of Testing Quality Assurance requires establishing the material variability (COV). Each test listed different COV (homogeneous vs heterogeneous) Tests with the largest COV would represent the greatest quality risk. Testing frequency is really only a subset of that risk profile.

29 Ensuring Quality of Quarry Source Materials in Queensland Quality Management System Details? Contributes to our understanding of the requirements for this quality management system But little detail in terms of quality control testing requirements, by only listing the type of test rather than acceptable, uncertain and unacceptable test boundaries. A few such indicators during the presentation would enhance our understanding of the QRS Done

30 Evaluation of rockfill embankments by field tests in Siraf Refinery Complex site, Iran (Asghari-Kaljahi et al.) Rock fill was used to fill valleys with up to 35m height required in some places. 5 million m 3 of cut / fill Trial embankments used with lift thickness of 30, 45 and 60 cm and with 3 different compaction efforts. Constructing to standard maximum loose lift thickness of 300mm with heavy plant and 95% Standard compaction may be adequate for small to medium size project, but with large quantities of fill, a trial should be used to evaluate a best for project specification. Methodology and testing associated with development of such a specification is presented. This is a sound approach with some interesting insights. Differences between compaction percentages of 45cm and 60cm lift thickness showed the vibratory 15 ton roller compaction rate would be more effective in 45cm lifts. Various test were to determine the compaction requirements field grading, large density, plate load test and surface seismic tests. Take away Any project over 1 million m 3 should consider trials for a project specific specifications Time + $ benefit

31 Evaluation of rock fill embankments by field tests Maximum Rock sizes Sizes that cannot fit on to spade not usually tested

32 Category Categorisation of Papers Quality Control Dynamic Cone Penetrometer Modulus Shear Wave Velocity CPTs Instrumentation Cohesion Friction Impact Rolling Compaction Trial Using Various In Situ Testing Trial Compaction EPC, Accelerometers QC Criteria for Deep Compaction Using the CPT Approach to Quality of Quarry Source Materials Lab, Quality Management Compaction Evaluation of Rock fill Embankments by Field Tests Trial Compaction Tensile Testing Setup to Determine Stiffness Properties Lab Heterogeneous Unsuitable Material Stockpile Lab Control of soil compaction in pavement layers: using the DCP CBR LFWD investigation for residual soils & weak rock CBR Trending Less Used PLT & CBR Tests to Determine the Elasticity Modulus CBR Characterization Using Dynamic & Static Cone Penetrometer Remedial Measures - Bridge Approach Fills Inclinometers, Settlement Gauges

33 Pavements & Fills Quality Control (compaction) Issues governs Still wrestling with basics Density DCPs CBRs Gradings Oversize affects lab values Trending in earthworks control Light Falling weight Deflectometers Shear wave velocity Modulus Measurements Penetration testing Deeper Lifts Vennapusa, 2008

34 Historical Basics X X X Symposium on Compaction of Earthwork and Granular Bases, Highway Research Record 177 (1967) M Moisture Content T Lift Thickness S Soil Type C Compactive Effort E compaction Equipment

35 Density - a parallel universe Design Elements Construction Elements Strength / Modulus Classifications (Atterberg / Gradings) Permeability Density Currency Compressibility / Volume change CBR

36 Final Word Traditional Technology Repeatability 3Rs of Testing Rationale Reproducibility