New light-weight device for measuring degree of compaction and dynamic load bearing capacity

Transcription

1 New light-weight device for measuring degree of compaction and dynamic load bearing capacity Zoltán TOMPAI assistant lecturer Department of Highway and Railway Engineering Budapest University of Technology and Economics Budapest Hungary Light-Weight Deflectometers Experience and Best Practise - Loughborough, 18 April, 2007.

2 Introduction In-situ assessment of earthworks and subgrade materials in Hungary 1.) Degree of compaction T rρ = ρ d,max ρ ρ d d,max [%] modified Proctor-test In-situ testing nuclear density test Generally prescribed values: 85 %, 90 %, 95 %, sometimes 97 % (!) 2.) Bearing capacity (still exclusively) static plate load test (E 2 ) Generally prescribed values: N/mm 2 on subsoil N/mm 2 under pavement structure Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 2

3 Introduction Pavement design Catalogue design based on - Type of subgrade material - Thickness of base course layer - Traffic data (numberofpassingaxleload) Assuming that the required bearing capacity of subgrade is reached! Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 3

4 Development of a new light-weight device B&C ( Bearing capacity and Compaction ) Developed by: ANDREAS Ltd. (Hungary) Mr. ISTVÁN SUBERT andreas@andreas.hu Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 4

5 Development of a new light-weight device B&C Basic similarities Same applied dynamic load (7.07 kn) Same load pulse time (18±2 ms) Calculation of classical dynamic stiffness modulus (from the 4th, 5th and 6th drops) LFWD Basic differences Plate diameter: D = 163 mm Selectable Boussinesq plate coefficient (p/2 rigid; 2 flexible) Selectable Poisson s ratio (0.3 granular solis; 0.4 fine grained soils, silty fine sands; 0.5 clayey, cohesive soils) Calculation of terminal dynamic stiffness modulus" (characteristic to the compacted state of the layer) (from the last 3 drops of total 18 drops) Calculation of relative and final degree of compaction ZORN Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 5

6 Basic theoretical background 1. LFWD Boussinesq plate coefficient set to 2 (flexible) Poisson s ratio set to 0.40 ( average ) - Allows free selection of these parameters 2. Dynamic load of 7.07 kn + Load pulse time of 18±2 ms + Plate diameter of D = 163 mm - Contact stress of MPa - Calculation of dynamic stiffness modulus (E d ) close to the magnitude of the static moduli 3. Calculation of Relative degree of compaction - 18 drops applied calculation of compaction curves - Applying same compaction work on site as the modified Proctor-test (at a given moisture content) RELATIVE DEGREE OF COMPACTION (T re %) (i.e. generating a single point of the Proctor-curve on site) Showing the actual compaction at the given field moisture content (95 % relative degree of compaction means that more rolling should be applied to reach 100 % compaction at the current moisture content) Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 6

7 Basic theoretical background 4. - w opt optimum moisture content 100 % degree of compaction - adjust the relative degree of compaction to the optimum moisture content - MOISTURE CORRECTION COEFFICIENT (T rw ) (one point of the normalized Proctor-curve) T rw, i ρ = ρ d,i d,max ( 1,00) Moisture Correction Coefficient Curve M cc Earthwork fine sand M7 y = -0,0016x 2 + 0,0292x + 0,8666 R 2 = 0,9586 Trw <=1,000 1,00 0,95 0,90 0,85 - more Proctor points (min. 7 or 8) - curve fitting for applicable equation 0, w% Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 7

8 Basic theoretical background 5. Measurement of the moisture content of the layer on site (with conventional drying method or by a calibrated electronic device) - Calculation of the moisture correction coefficient 6. Calculation of the DYNAMIC DEGREE OF COMPACTION (T rd ) Trd % = Trw Tre% ( = T %) Identical to the Degree of Compaction measured by conventional methods! rρ (Mathematically proven + strong correlation found based on field measurements) Basis Proctor-method volume of wet soil is constant (moisture content is changed) B&C method dry weight of soil is constant (moisture content is changed) w opt height of the compacted soil cylinder is the lowest, thus the degree of compaction is the highest difference in cylinder heights = diference is settlements on site (if the applied work is the same) Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 8

9 T re %

10 Interpretation and applicability of results BENEFITS: Calculation of the terminal stiffness modulus (E d,v ), which charaterizes the layer after compaction (calculation of stiffness before and after compaction correlation to static modulus E 2?) Inmediate information on the effectiveness of the compaction (Can the layer be compacted more at the given moisture content?) Moisture content of the layer + Proctor-curve of the material Can the prescribed degree of compaction be achieved at all? (need of dehydration or watering?) Accuracy: ±2-3 % (nuclear method: ±5-6 %) Two-in-one (measurement of bearing capacity and degree of compaction) No nuclear izotopes, environmental friendly Cheap and fast Easy to use Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 10

11 Interpretation and applicability of results Correlation to static stiffness modulus - M7 Highway medium sand, sandy gravel for dynamic stiffness modulus:e 2 = 8.91 E 0.52 d (r = 0.87) for terminal dynamic stiffness modulus: E 2 = 6.47 E 0.56 d,v (r = 0.84) or E E d,v (significant scatter) - M6 Highway furnace slag (recycled material, few measurements) E 2 = 1.44 E d (r = 0.97) - Road nr. 4 near Albertirsa silty sand, chrushed stone stabilization E 2 = 1.12 E d (r = 0.65) Hungarian experiences with LFWD: E E dm (r = ) Austrian experiences with LFWD: E E dm (r = ) Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 11

12 Future prospects Possible application and introduction of the theory in Continous Compaction Control Introduction of new parameters in quality control of earthworks New classification for unbound granular materials in Hungary Review of the required degree of compaction values (85 %, 90 %, 95 %, 97 %) in Hungary Zoltán TOMPAI, Department of Highway and Railway Engineering, Budapest University of Technology, Hungary 12

13 THANK YOU FOR YOUR ATTENTION! ZOLTÁN TOMPAI assistant lecturer Budapest University of Technology and Economics Department of Highway and Railway Engineering Hungary Tel: Fax: Mobile: Light-Weight Deflectometers Experience and Best Practise - Loughborough, 18 April, 2007.