One Dimensional Consolidation - Lab Report Example

Engineering and Construction One Dimensional Consolidation One of the remarkable standards for construction material quality control practices for soils is the British Standard BS 1377-5: 1990. This code discusses tests methods for soils used for engineering purposes. Part 5 focuses on compressibility, permeability, and durability tests. This discussion refers to the procedures and laboratory test for determining one-dimensional consolidation properties for clay B. The test data for the laboratory has been calculated and analysed in accordance to the BS 1377-50:1998. 1.0 Introduction Various soil samples are tested in the laboratory to establish settlement characteristics of soil under load. Once the characteristics are established, they are used to estimate the amount of settlement of a structure that would arise from the consolidation of its earth foundation due to structure load. The test also serves to establish the settlements that happen within dams and earth embankments. Consolidation characteristics of soil mass are influenced by several factors such as size and shape of particles, moisture content, permeability, initial density, as well as physical and chemical properties. Consolidation standard test provides the following information; Magnitude of consolidation under various loads Consolidation rate Impact of saturation on consolidation Permeability of the material under load. This paper discusses a consolidation test done by Group 6, the relevant calculations, and analysis of the test results. Limitations and Assumptions Although the discussion is mainly concerned with one-dimensional test data, the probability of shear failure must be observed. This implies that in the design for any foundation, it is important that the bearing capacity of shear failure and settlement be studied. Consolidation test determines the relationship in the following parameters; Excess pore water pressure Depth below the layer on top of clay layer Time from immediate application of total stress increment. However, there are eight assumptions for the test; Soil is homogeneous The material is fully saturated Solid particles and water are incompressible Compression and flow are one-dimensional or vertical The strains are small D’Arcy’s law is applied at all hydraulic gradient Permeability coefficient and volume compressibility coefficient remain constant through the test and The relationship between void ratio and effective stress are independent of time (Gibbs, 1953). Principles According to the BS 1377-50: 1998, one-dimensional consolidation test determines the magnitude and the rate of consolidation for saturated soil specimen. The specimen is subjected under vertical axial pressure and allowed to drain freely. As the test specimen is laterally loaded, increment of stress is applied. Each increment in stress is held constant until the consolidation process is completed. As water drains from the specimen, there is decrease in specimen height that is measured at intervals. The measurements are used to determine the relationship between compression or voids ratio and effective stress. Calculation parameters describe the amount of stress and the rate of the stress. Procedure Load is applied on the specimen in a series of more increments. For this experiment, 12, 25, 100, 200, 400, and 800 kPa were used. Load intensity depends on the weight of the structure and overburden pressures occurring on the material. This should be of similar values of anticipated pressure on the foundation. The test specimen is loaded expeditiously and accurately to secure readings at second timed intervals. Consolidation rate is determined from observing amount of movement at frequent time intervals until consolidation is completed. The time span is generally 5-24 hours. Interpretation for Test (Board of BSI, 1998) (Appendix A). 2.0 Consolidation Test: Calculations and Plotting Data Sheets Date Tested: Tested By: Group 6 Test Method: BS1377-2:1990:8.3/8.4 Related Test: One-Dimensional consolidation Project Name: Sample Number: Visual Classification: Clay B 2.1 Calculate initial moisture content, wₒ(%) from the specimen Moisture Content Container No. 1 2 3 4 Mass of wet soil + container (m2) g 349.9g N/A N/A N/A Mass of dry soil + container (m3) g 331.0g N/A N/A N/A Mass container (m1) g 246.4g N/A N/A N/A Mass of moisture (m2-m3) g 18.9g Mass of dry soil (m3-m1) g 84.6g Moisture content % 22.3 Average moisture content % 22.3 2.2 Calculate initial Bulk Density, ᵨ (Mg/m³) Specimen ref.   Clay B Mean sample length (L) mm 20.0 Mean sample diameter (D) mm 50.0 Mass of sample (m) g 49.4   Bulk Density ρ = 4000 x m / π x D^2 x L Mg/m^3 5.0344 2.3 Calculate initial Dry Density, ᵨd 4.116 2.4 Calculate Particle Density Specimen ref.   Clay B Pyknometer no.   1 Mass of bottle + soil + water (m3) g 73.8 Mass of bottle + soil + (m2) g 25.4 Mass of pyknometer full of water (m4) g 72.2 Mass of pyknometer (m1) g 23.3 Mass of soil (m2 - m1) g 2.1 Mass of water in full pyknometer (m4 - m1) g 48.9 Mass of water used (m3 - m2) g 48.4 Volume of soil particles (m4 - m1) - (m3 - m2) mL 0.5 Particle density     ρs = ( (m2 - m1) / (m4 - m1) - (m3 - m2) ) x ρL Mg/m^3 4.2       N.B. ρL = 1     (just the decimal density of dionised water)     2.5 Calculate Initial Void Ratio (eₒ) 2.6 Calculate Initial Degree of Saturation (Sₒ) NB: 3.0 Compressibility Characteristics This is demonstrated by plotting specimen compression on a linear scale against corresponding pressure applied p (kP/pₐ) on a logarithmic scale. Compression is indicated in terms of voids ratio but actual thickness of specimen or strain is expressed as percentage reduction in thickness (initial thickness) is also used (American Society for Testing and Materials, 1996). 3.1 Height of Solid Particles, Hs Calculate the equivalent height of solid particles, Hs (mm) from the equation; 3.2 Height of Specimen Calculate height of specimen, H (mm) at each loading Specimen Height (12kPa) Clock Time (Min) Gauge Reading Specimen Height at each loading 0 0.03 19.970 51.4 0.062 19.938 102 0.069 19.931 154 0.072 19.928 206 0.328 19.672 257 0.331 19.669 308 0.334 19.666 360 0.335 19.665 411 0.337 19.663 463 0.339 19.661 514 0.339 19.661 565 0.34 19.66 617 0.34 19.66 668 0.342 19.658 719 0.342 19.658 720 0.342 19.658 Specimen Height (25kPa) Clock Time (min) Gauge Reading Specimen Height 0 0.073 19.927 18 0.13 19.870 36 0.142 19.858 54 0.151 19.849 72 0.157 19.843 90 0.161 19.839 108 0.165 19.835 126 0.168 19.832 144 0.17 19.830 162 0.172 19.828 180 0.174 19.826 Specimen Height (100kPa) Time (min) Gauge Reading Specimen Height 0 0.174 19.826 36 0.524 19.476 72 0.557 19.443 108 0.57 19.43 144 0.576 19.424 180 0.581 19.419 216 0.566 19.434 252 0.568 19.432 288 0.57 19.43 324 0.572 19.428 360 0.572 19.428 396 0.573 19.427 432 0.574 19.426 468 0.575 19.425 504 0.576 19.424 540 0.577 19.423 576 0.578 19.422 612 0.578 19.422 648 0.579 19.421 684 0.579 19.421 720 1.344 18.656 Specimen Height (200kPa) Time (min) Gauge Readings (mm) Specimen Height 0 0.581 19.419 55 0.697 19.303 110 0.718 19.282 166 0.727 19.273 221 1.897 18.103 277 1.901 18.099 332 1.904 18.096 387 1.907 18.093 443 1.909 18.091 498 1.911 18.089 554 1.913 18.087 609 1.915 18.085 664 1.916 18.084 720 1.917 18.083 Specimen Height (400kPa) Time (min) Gauge Readings (mm) Specimen Height 0 0.728 19.272 110 1.097 18.903 166 1.112 18.888 221 2.587 17.413 276 2.591 17.409 332 2.595 17.405 393 2.599 17.401 443 2.602 17.398 498 2.605 17.395 553 2.608 17.392 609 2.611 17.389 664 2.613 17.387 720 2.616 17.384 Specimen Height (800kPa) Time (min) Dial Gauge Readings (mm) Specimen Height 0 1.115 18.885 55 1.548 18.452 110 1.578 18.422 166 1.59 18.41 221 3.365 16.635 276 3.37 16.63 332 3.374 16.626 393 3.376 16.624 443 3.379 16.621 498 3.381 16.619 553 3.383 16.617 609 3.385 16.615 664 3.387 16.613 720 3.389 16.611 3.3 Voids Ratio and Coefficient of Compressibility Calculate voids ratio, e, at each loading from Calculate the coefficient volume compressibility, Mv, (m²/MN) for each loading increment from equation; 12kPa Coefficient of Compressibility, Mv Time (min) Settlement Input (mm)  Cumulative Compression mm (∆H) Voids Ratio   Mv 0 0.03 19.97 0.018358 0.0015 83.33333 0.125 51.4 0.062 19.938 0.016726 0.0031 83.33333 0.258333 102.5 0.069 19.931 0.016369 0.00345 83.33333 0.2875 154.25 0.072 19.928 0.016216 0.0036 83.33333 0.3 205.67 0.328 19.672 0.003162 0.0164 83.33333 1.366667 257 0.331 19.669 0.003009 0.01655 83.33333 1.379167 308.5 0.334 19.666 0.002856 0.0167 83.33333 1.391667 360 0.335 19.665 0.002805 0.01675 83.33333 1.395833 411.3 0.337 19.663 0.002703 0.01685 83.33333 1.404167 462.75 0.339 19.661 0.002601 0.01695 83.33333 1.4125 514 0.339 19.661 0.002601 0.01695 83.33333 1.4125 565 0.34 19.66 0.00255 0.017 83.33333 1.416667 617 0.34 19.66 0.00255 0.017 83.33333 1.416667 668 0.342 19.658 0.002448 0.0171 83.33333 1.425 719 0.342 19.658 0.002448 0.0171 83.33333 1.425 720 0.342 19.658 0.002448 0.0171 83.33333 1.425 25 kPa Coefficient of Compressibility Time (min) Settlement Input (mm) Cumulative Compression mm (∆H) Voids Ratio   Mv 0.00.00 0.073 19.927 0.016165 0.00365 76.92308 0.280769 0.18.00 0.13 19.87 0.013259 0.0065 76.92308 0.5 0.36.00 0.142 19.858 0.012647 0.0071 76.92308 0.546154 0.54.00 0.151 19.849 0.012188 0.00755 76.92308 0.580769 1.12.00 0.157 19.843 0.011882 0.00785 76.92308 0.603846 1.30.00 0.161 19.839 0.011678 0.00805 76.92308 0.619231 1.48.00 0.165 19.835 0.011474 0.00825 76.92308 0.634615 2.06.00 0.168 19.832 0.011321 0.0084 76.92308 0.646154 2.24.00 0.17 19.83 0.011219 0.0085 76.92308 0.653846 2.42.00 0.172 19.828 0.011117 0.0086 76.92308 0.661538 3.00.00 0.174 19.826 0.011015 0.0087 76.92308 0.669231 100 Coefficient of Compressibility Time (min) Settlement (mm) Cumulative Compression mm (∆H) Voids Ratio   Mv 0 0.174 19.826 0.011015 0.0087 13.33333 0.116 36 0.524 19.476 -0.00683 0.0262 13.33333 0.349333 72 0.557 19.443 -0.00852 0.02785 13.33333 0.371333 108 0.57 19.43 -0.00918 0.0285 13.33333 0.38 144 0.576 19.424 -0.00948 0.0288 13.33333 0.384 180 0.581 19.419 -0.00974 0.02905 13.33333 0.387333 216 0.566 19.434 -0.00898 0.0283 13.33333 0.377333 252 0.568 19.432 -0.00908 0.0284 13.33333 0.378667 288 0.57 19.43 -0.00918 0.0285 13.33333 0.38 324 0.572 19.428 -0.00928 0.0286 13.33333 0.381333 360 0.572 19.428 -0.00928 0.0286 13.33333 0.381333 396 0.573 19.427 -0.00933 0.02865 13.33333 0.382 432 0.574 19.426 -0.00938 0.0287 13.33333 0.382667 468 0.575 19.425 -0.00943 0.02875 13.33333 0.383333 504 0.576 19.424 -0.00948 0.0288 13.33333 0.384 540 0.577 19.423 -0.00954 0.02885 13.33333 0.384667 576 0.578 19.422 -0.00959 0.0289 13.33333 0.385333 612 0.578 19.422 -0.00959 0.0289 13.33333 0.385333 648 0.579 19.421 -0.00964 0.02895 13.33333 0.386 684 0.579 19.421 -0.00964 0.02895 13.33333 0.386 720 1.344 18.656 -0.04865 0.0672 13.33333 0.896 200 kPa Coefficient of Compressibility Time (min) Settler (mm) Cumulative Compression n mm(∆H) Voids Ratio   Mv 0 0.581 19.419 -0.00974 0.02905 10 0.2905 55 0.697 19.303 -0.01566 0.03485 10 0.3485 110 0.718 19.282 -0.01673 0.0359 10 0.359 166 0.727 19.273 -0.01719 0.03635 10 0.3635 221 1.897 18.103 -0.07685 0.09485 10 0.9485 277 1.901 18.099 -0.07705 0.09505 10 0.9505 332 1.904 18.096 -0.07721 0.0952 10 0.952 387 1.907 18.093 -0.07736 0.09535 10 0.9535 443 1.909 18.091 -0.07746 0.09545 10 0.9545 498 1.911 18.089 -0.07756 0.09555 10 0.9555 554 1.913 18.087 -0.07766 0.09565 10 0.9565 609 1.915 18.085 -0.07777 0.09575 10 0.9575 664 1.916 18.084 -0.07782 0.0958 10 0.958 720 1.917 18.083 -0.07787 0.09585 10 0.9585 400kPa Coefficient of Compressibility Time (min) Settlement (mm) Cumulative Compression in mm (∆H) Voids Ratio     Mv 0 0.728 19.272 -0.01724 0.0364 5 0.182 110 1.097 18.903 -0.03605 0.05485 5 0.27425 166 1.112 18.888 -0.03682 0.0556 5 0.278 221 2.587 17.413 -0.11203 0.12935 5 0.64675 276 2.591 17.409 -0.11224 0.12955 5 0.64775 332 2.595 17.405 -0.11244 0.12975 5 0.64875 393 2.599 17.401 -0.11265 0.12995 5 0.64975 443 2.602 17.398 -0.1128 0.1301 5 0.6505 498 2.605 17.395 -0.11295 0.13025 5 0.65125 553 2.608 17.392 -0.11311 0.1304 5 0.652 609 2.611 17.389 -0.11326 0.13055 5 0.65275 664 2.613 17.387 -0.11336 0.13065 5 0.65325 720 2.616 17.384 -0.11351 0.1308 5 0.654 800kPa Coefficient of Compressibility Time (min) Settlement (mm) Cumulative Compression (mm) ∆H) Voids Ratio Mv   Mv 0 1.115 18.885 -0.03697 0.05575 2.5 0.139375 55 1.548 18.452 -0.05905 0.0774 2.5 0.1935 110 1.578 18.422 -0.06058 0.0789 2.5 0.19725 166 1.59 18.41 -0.06119 0.0795 2.5 0.19875 221 3.365 16.635 -0.15171 0.16825 2.5 0.420625 276 3.37 16.63 -0.15196 0.1685 2.5 0.42125 332 3.374 16.626 -0.15217 0.1687 2.5 0.42175 393 3.376 16.624 -0.15227 0.1688 2.5 0.422 443 3.379 16.621 -0.15242 0.16895 2.5 0.422375 498 3.381 16.619 -0.15252 0.16905 2.5 0.422625 553 3.383 16.617 -0.15263 0.16915 2.5 0.422875 609 3.385 16.615 -0.15273 0.16925 2.5 0.423125 664 3.387 16.613 -0.15283 0.16935 2.5 0.423375 720 3.389 16.611 -0.15293 0.16945 2.5 0.423625 3.4 Coefficient of Consolidation (Cv) (in m²/year) Coefficient of consolidation is determined by two curve methods; logarithm-of-time curve fitting and the square root time curve fitting methods. This discussion uses the Log time curve-fitting method. 12kPa 12kPa Coefficient of Consolidation 0.025 kPa 25kPa Coefficient of Consolidation 100kPa 100kPa Coefficient of Consolidation 200kPa 200kPa Coefficient of Consolidation 400kPa 400kPa Coefficient of Consolidation 800kPa 800kPa Coefficient of Consolidation 5.0 Discussion Pore pressures increase when soil is loaded un-drained. Under site conditions, excess pore pressures dissipate and water leaves the soil resulting to consolidation. The process takes time as the rate of settlement decreases with time. Amount of settlement depends on permeability of the soil, time for drainage path, and compressibility characteristics of the soil. The laboratory methods of stress-strain parameters (Coefficient of Consolidation, and coefficient of compressibility) are reliable and acceptable so long as the sampling was carefully done (Plaxis 2012, pp. 1-5). However, observed settlement rates are normally greater than the values based on oedometer results. Reliability of the results depends on factors such as anisotropy; for example layers of sand and silt, verves, and fissures, vegetative matter, and voids. The test results show that the Cv is not constant and depends on stress levels and degree of consolidation (Appendix D). However, there is secondary compression that is also considered since it factors the primary compression. According to Terzaghi’s assumption, changes in void ratios during as specimen consolidates occur exclusively due to dissipation of excess pore water pressures. This is governed by the rate of permeability of the soil. According to the experimental data, compression continues decreasing gradually as excess water in the pores is dissipated (Appendix B and Appendix C). There are theories that offer an explanation to this. For example laterally confined clays are thought to continue to adjust to stable orientations resulting from disturbances arising from structures that decrease void ratio (Verrujit, 2001). At the same time, thick clay layers subjected to shear inhibit secondary compression that results to lateral displacements. The magnitude of secondary compression is normally higher consolidated clays than in over-consolidated ones. Primary consolidation and secondary consolidation proceed simultaneously during loading time. 6.0 Conclusion The purpose of the test is to establish the design for the foundations of a structure in terms of soil classification, soil strength parameters, and soil stiffness parameters. The sample Clay B falls under soft soil consistency classification. 7.0 Appendix 7.1 Appendix A It is necessary that the environment for the test is free from significant vibrations and mechanical disturbances. Apparatus sued must be far from sources of heat, direct sunlight, draughts, and at room temperature within ±4ºC. Apparatus for use are the oedometer, consolidation ring, dial gauge, suitable consolidation cell, and loading device. 7.2 Appendix B 7.3 Appendix C 7.2 Appendix D: Analysis of Consolidation Test Data ANALYSIS of CONSOLIDATION TEST DATA Pressure (kPa) Time for 50% Consolidation t50(min) Dₒ (from Graph) D100(from graph) D50=(Dₒ+D100)*0.5 Hj=D50*0.0001 ∆H(from graph) ∑∆H* H** Coeff. Cons. (Cv) Hv 0               20 0   12 0.72 0.07 0.34 0.205 2E-05 0.27 0.27 19.73 0.0263 0.12 25 0.157 0.142 0.175 0.1585 2E-05 0.033 0.3 19.43 0.0002 0.087 100 0.579 0.58 1.38 0.98 1E-04 0.58 0.88 18.54 0.0151 -0.493 200 0.727 0.72 1.92 1.32 0.0001 1.2 2.08 16.46 0.0515 -1.693 400 2.587 1.1 2.7 1.9 0.0002 1.6 3.68 12.78 0.0257 -3.293 800 1.59 1.5 3.45 2.475 0.0002 1.95 5.63 7.145 0.0622 -5.243 8.0 Reference List American Society for Testing and Materials (1996). ASTM Designation: D 2435-96 Standard Test Method for One-Dimensional Consolidation Properties of Soils, ASTM, U.S.A. Board of BSI (1998). British Standard: Methods of test for Soils for Civil Engineering Purposes- Part 5: Compressibility, permeability, and durability tests, BSI. Gibbs, H. J. (1953). Estimating Foundation Settlement by One-Dimensional Consolidation Tests, United States Department of the Interior Bureau of Reclamation Engineering Monograph, No. 13, Denver; Colorado. Plaxis (2012). One-Dimensional Consolidation, Validation & Verification, U.K. Verrujit, A. (2001). Soil Mechanics, Delft University of Technology. Read More