factors affecting consolidation of soil
Soil is subjected to downward seepage pressure previously but when it stops later, effective stress reduces. H It is an instantaneous process of reducing the volume of voids due to the expulsion of air voids when the degree of saturation is S <1. The permeability of the specimen at any stage of loading can be measured only in the fixed ring type. The results are presented in a semi log graph paper with applied pressure on log scale at abscissa and corresponding void ratio as ordinate on linear scale. Create a free account and view content that fits your specific interests in geotechnical engineering. Some publications also use "consolidation" in the broad sense, to refer to any process by which soil changes volume due to a change in applied pressure. 11.5: Factors Affecting Soil Development. Soil creep is typically caused by viscous behavior of the clay-water system and compression of organic matter. Land subsidence is an important environmental problem in the North China Plain (NCP). {g}{GE-MrT~ar3=].C?]@ When effective stress over-saturated soil mass increases, then the pore water pressure increases. Soil deformation may occur by change in stress, water content, soil mass, or temperature. Privacy Policy 8. For sands, the index ranges between 0.01 to 0.06, although this is not a particularly meaningful parameter for a sand. These are the soils that are loaded for the first time to the present applied effective stress. 95 Example applications are building and bridge foundations, retaining walls, dams, and buried pipeline systems. H The negative sign indicates that e decreases as increases. C OCR = Pre-Consolidation Pressure/ Present overburden pressure. = Soil compaction can lead to: poor root growthwhich reduces crop yield through poor water and nutrient uptake. 1 = After the consolidation under the last stress increment is over, the specimen is unloaded in two or three stages and the soil is allowed to swell. Before tunnelling, foundation protection measures in the form of grouting of the ground are carried which minimizes the inward movement of soil during tunnelling and reduces surface settlement. . The coefficient of consolidation is an important parameter for calculating and predicting the consolidation settlement of soft soil. During expansion, the specimen never returns to its original volume due to some permanent compression. The 24-hour reading gives the final compression under each stress increment. It is mainly due to immediate compression of the soil layer under untrained condition. The effects of consolidation are most conspicuous where a building sits over a layer of soil with low stiffness and low permeability, such as marine clay, leading to large settlement over many years. a Stamped Concrete - Advantages, Disadvantages & Application, What Is Gabion? = This normally involves loading the soil sample in the laboratory to a series of loads and measuring the corresponding settlements. At this stage, only the water resists the applied load. Initial consolidation: A quick volume loss of the soil mass associated with the application of external stress that compresses the air inside the soils voids. Development of Marshy Areas in Colombo, Sri Lanka, Proc. ( The value of induced vertical stress below the centre line of a loaded area is always greater than its value at the same depth below the edge of the loaded area. z The ratio of diameter to height of the specimen is between 2.5 to 5. This process is an essential part of the construction of any structure, as it strengthens the soil. Since the test is intended to measure only the deformation of the soil, the other movements (machine deflections) must be measured and later subtracted from the total deformation. The test is carried out in a device called Oedometer or Consolidometer. Soil structure and fabric. Earth pressure, Slope Stability and Soil Last modified: Monday, 23 September 2013, 11:23 AM, The total settlement of the soil is the summation of three settlements (i) immediate settlement (ii) primary consolidation settlement and (iii) secondary consolidation settlement or settlement due to creep. If the soil is in a completely saturated state, volume reduction takes place due to the expulsion of pore water from voids. The compression of the specimen is measured by means of dial gauge fitted at the loading cap. Thus, consolidation is a major issue in case of clay due to its low permeability. + Hdr is the average longest drain path during consolidation. When the test is completed, the final height of the sample and its water content are measured. This process of creep is sometimes known as "secondary consolidation" or "secondary compression" because it also involves gradual change of soil volume in response to an application of load; the designation "secondary" distinguishes it from "primary consolidation", which refers to volume change due to dissipation of excess pore water pressure. H For a given soil at a given void ratio, cv increases with increasing magnitude of the consolidation pressure. Settlement may occur almost twice the depth of excavation around open excavations. The commonly used stresses are 25, 50,100,200,400 and 800 kN/. Conf. If you like this article then please share it with your friends & also like our Facebook Page and join our Telegram Channel. t Compressibility and consolidation of soil are crucial . The test is continued by increasing the pressure further, the resulting curve is more or less the extension of the initial portion PQ. 4. Ranjan, G. and Rao, A.S.R. window.__mirage2 = {petok:"DCbVok5mxOz0frRCF59wJWjSIs10t_R9WHMbdP5e33k-3600-0"}; Under typical engineering loads, the compression of soil solids and pour water in negligible. Causes of differential settlements. The term was introduced by Karl von Terzaghi also known as the "father of soil mechanics and geotechnical engineering". TOS 7. which are affecting permeability property of soils and these factors are briefly discussed in this article. r Secondary compression (creep) H = Hi + U Hc + Hs. Dial gauge readings are noted at 30 sec, 1, 2, 4, 8, 15, 30 mins, 1 hr, 2, 4, 8 and 24 hrs. Figure 6.1 (a) and (b) show fixed ring type and floating ring type consolidometer set up. U(H>=o#rbH B_=V R:GM"&8#Btjq("UV/w k+W!D^8&?b>E( Coarse-grained soils do not undergo consolidation settlement due to relativity high hydraulic conductivity compared to clays. In this study, horizontal and vertical permeability . 0 Determination of Void Ratio by Dry Weight Method: This method is applicable to both saturated and partly saturated specimens. Many factors influence the degree with which the soil is compacted. Such a change in volume may be due to: (a) a compression of the solid soil particles, (b) a compression of water and . PPT of Professor N. Sivakugan, JCU, Australia (www.geoengineer.org/files/consol-Sivakugan.pps). For compaction specified compaction techniques are used, whereas consolidation occurs due to application load on the soil. The primary consolidation depends on the permeability and compressibility of the soil. Yan and Chu (2003) stated that the cost of soil improvement by vacuum preloading is approximately 30% less than that by conventional surcharge alone. The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. In the following decades Biot fully developed the three-dimensional soil consolidation theory, extending the one-dimensional model previously proposed by Terzaghi to more general hypotheses and introducing the set of basic equations of poroelasticity. t is the length of time after consolidation considered Compaction of the soil is the process where the dry density of soil is increased by reducing air content or air voids present in the soil. Figure 6.8 shows a pressure bulb of perfectly flexible, loaded area of width B. S c = C c H c /(1+e 0) log[(' 0 +' av)/' 0]. Overview. when calculated in base-10 logarithm.[3][4]. i.e., due to drying of soil, effective stress reduces and the soil becomes overconsolidated. It does not require the expulsion of pore water. x]I\W-) L rrJq*rrsE#iF{_ \E[y;>\N7L6S|y-7n[MO]WKf_LoxzSeZoF0 Rmm#qS>Nv52mw^1[.wf$WR>xbZmcS6nFmL6Mg\oOYsf?&][}uvbFqcfM?9S2WvdT\b+ Ljx:==VF%QSiQ-mO+_m4*N($XVO]h'0$+/F|2Hjixzi7;t|74{M4 R_t>*^e? Piping leaks, sewer drainage etc. The rate of volume change depends on the permeability of soil. The consolidation procedure is commonly separated into 3 stages: The simplest case of consolidation examined is the one-dimensional consolidation. The only possibility is the change of volume i.e., compression of soil. The drainage path represents the maximum distance which the water particles have to travel for reaching the free drainage layer. Water moves more quickly through the large pores in sandy soil than it does through the small pores in clayey soil, especially if the clay is compacted and has little Taken together, these reports will inform industry par-ticipants, researchers, and policymakers about the forces affecting competition and change in the produce . when calculated in natural logarithm and V Some empirical expressions that relate the Compression Index, CC, with the Liquid limit (LL) and Plasticity Index (PI) of the soil, are the following: Table 1: Typical values of the Cv coefficient. Soft clay consolidation is an important aspect to be considered for large construction projects undertaken in or near coastal areas. 100% consolidation) 1. ( ) Eng., Paris, Vol. The settlement during post primary consolidation period is known as secondary consolidation settlement or creep. Primary Consolidation. Besides these, from this test permeability and swelling behaviour of soil can also be determined. Given the initial height of the specimen (Hi) and the compression of the soil sample at 50% consolidation (), the drainage path (for double drainage), Hdr, is computed as: Taylor Square Root of Time Fitting Method (Taylor, 1948): In this method, the dial readings are plotted against the square root of time. When the maximum load is reached, and possibly in a load increment in between, an unloading stage is introduced that may be conducted in one or multiple steps; typically, the load is reduced by a factor of 4 at each step. Primary Consolidation ; Secondary Consolidation; Primary Consolidation. In general, consolidation in sandy soils is a quick process (occurring possibly immediately during construction) whereas the process may last for many years or even decades in clay soils. India's best GATE Courses with a wide coverage of all topics!Visit now and crack any technical exams https://www.gateacademy.shopDownload our Live Classroom . There is little or no reduction in the water content. K The compressibility of soil is defined as the capability of soil to decrease its volume under mechanical loads, whereas the consolidation is the compression of saturated soil under steady pressure and it is occurred as a result of water expulsion from the soil voids. Friction is a resisting force between two surfaces. Immediate (or elastic) settlement occurs almost immediately after the loading is applied due to the distortion of the soil without any volume change due to removal of water. The specimen is allowed to consolidate under a number of increments of vertical pressure such as 0.1, 0.2, 0.5, 1, 2, 4, 8 and 10 kg/cm2. The process of consolidation is often explained with an idealized system composed of a spring, a container with a hole in its cover, and water. The only way to guarantee a pile will carry the load is with a load test. When stress is removed from a consolidated soil, the soil will rebound, regaining some of the volume it had lost in the consolidation process. In this system, the spring represents the compressibility or the structure of the soil itself, and the water which fills the container represents the pore water in the soil. In coarse-grained soil like gravels and sands, secondary consolidation is negligible. a Five soil-forming factors . Weathering can be a physical, chemical or biological process: physical weatheringbreakdown of rocks from the result of a mechanical action. It is a time-dependent phenomenon. There are two, most commonly used, methodologies: Casagrande Logarithm of Time Fitting Method (Casagrande and Fadum, 1940): The coefficient of consolidation, CV, is determined by estimating the time at 50% consolidation (t50), as shown in the short animation/presentation below. That is, after the application of each load, the deformation is measured at 6, 15, 30 seconds, then at 1, 2, 4, 8, 16, 30 min and at 1, 2, 4, 8 and 24 hours, respectively. This report addresses the second objective. The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. For normally consolidated clays the index commonly ranges between 0.20 to 0.50 and for silts between 0.16-0.24. Wallace, G.B and Otto, W.C. (1964). Ranjan, G. and Rao, A.S.R. This excess pore water pressure is dissipated as water drains away from the soils voids and the pressure is transferred to the soil skeleton which is gradually compressed, resulting in settlements. Shear strength of soil influenced by the following factors: a) Cohesion i.e. A Study of the One-Dimensional Consolidation Test, Proc. It is denoted as cv = K/mvw. 1, 469-472. 50 Compaction of soil is mainly used for sandy soil. Due to creep the soil moves downhill, producing a material that is inferior to the parent soil. = Active factors: Which represent agents that supply energy that act upon the mass for process of soil formation - They are climate and biotic organisms. Cv is defined as the coefficient of consolidation found using the log method with, C When stress is applied to a soil sample its volume decreases. This process is started when the soil is fully saturated. The volume of expelled water is equal to the change in volume of soil. To obtain the void ratio vs. pressure relationship, the equilibrium void ratio is computed with the help of 24-hour reading. }6Z+|V.ex"Y}w Pbn6P>~gGUi!%;VWp6*t H If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. Table 6.4 Mass of disturbed soil sample required for various tests from BS 5930: 1981 Soil type Testing Clay, silt or sand (kg) Fine and medium gravel (kg) Coarse gravel (kg) Moisture content, Atterberg limits, sieve analysis, chemical tests 1 5 30 Grain size. (Fully saturated soil), A load is applied onto the cover, while the hole is still unopened. Overburden pressure or surcharge was placed in the past which is removed later. f until recently, protection measures were based on vibration induced peak particle velocity and its decay with distance from the source. This mechanism can move large quantities of water and can be able to produce ground surface heaves of 12 inches or more. Secondary consolidation is more seen in plastic soil and in highly plastic clays. (Development of excess pore water pressure), As soon as the hole is opened, water starts to drain out through the hole and the spring shortens. The Compression CC and Recompression Cr indices are also presented. Soil erosion is a gradual process that occurs when the impact of water or wind detaches and removes soil particles, causing the soil to deteriorate. H Particle shape. e This increase in vertical strain causes the ground to move downward. The third objective will be addressed in a forthcoming ERS report. The consolidation procedure lasts until the excess pore water pressure is dissipated. When a load is applied in a low permeability soil, it is initially carried by the water that exists in the porous of a saturated soil resulting in a rapid increase of pore water pressure. when calculated in natural logarithm and If the coefficient of permeability of the soil is more, water will come out of the soil pores more easily and hence the consolidation will be more. The diameter of the specimen used should be from 65 to110 mm and thickness of the specimen should be 15 to 30 mm is used. In case of consolidation, the soil mass is applied with a steady load for long period of time. C v Melting of the glacier which was covered by the soil mass in the past. Soil management and health. From the phase diagram (as shown in Figure 21.1), the vertical strain can be written as: \[\varepsilon={{\Delta e} \over {1 + {e_0}}}\] (21.2). To determine the consolidation properties, laboratory consolidation tests are carried out on a suitable undisturbed soil layer. Consolidation of soil (normally consolidated) can be evaluated from the following equation as discussed in this article. + c Over consolidated soils are those which have been subjected to effective stress in the past greater than the present applied effective stress. Sivakugan, N., (1990). t95 is the length of time for achieving 95% consolidation. It is due to particle reorientation, creep and decomposition of organic materials. At each loading stage, readings of deformation are taken systematically to develop a time-settlement curve. This can be expressed in the following equation, which is used to estimate the volume change of a soil layer: Before going to know about these factors, take a look at the general expression for . The increment of applied stress that causes consolidation may be due to either natural loads (e.g. It is the portion of the settlement which occurs immediately after application of load. = z Factors affecting soil formation. Compaction is the process in which the soil particles are packed more closely together by mechanical means i.e., dynamic loading such as rolling, tamping and vibration etc. The loading beam should be almost horizontal. Since many factors affect c v, the experimental behavior of soil in the one-dimensional consolidation test does not completely match with the theoretical relationship of consolidation as obtained by Terzaghi's equation, which is made use of in the curve tting procedures. 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Of soils and these factors are briefly discussed in this article then please share it with your friends & like. Loading cap to 0.06, although this is not a particularly meaningful parameter for and! Telegram Channel von Terzaghi also known as the highest stress experienced divided factors affecting consolidation of soil the following factors: )! Applied effective stress particles have factors affecting consolidation of soil travel for reaching the free drainage.! Coarse-Grained soil like gravels and sands, secondary consolidation settlement or creep of! Is subjected to effective stress deformation may occur by change in stress, water content are.... Sample in the laboratory to a series of loads and measuring the corresponding settlements following:. The result of a mechanical action clay-water system and compression of the initial portion PQ lasts until the excess water! To move downward the excess pore water pressure is dissipated of volume change on. Load is with a steady load for long period of time considered for large projects! Loaded area of width b fits your specific interests in geotechnical engineering pressure further the. Time-Settlement curve and its water content are measured set up void ratio, cv with... Stress over-saturated soil mass, or temperature water and nutrient uptake previously but when stops! Then please share it with your friends & also like our Facebook Page and join our Channel. For sandy soil soil influenced by the following equation as discussed in this article then share. Shear strength of soil ( normally consolidated ) can be able to produce ground surface heaves of inches. 4 ] to travel for reaching the free drainage layer Otto, W.C. 1964... Jcu, Australia ( www.geoengineer.org/files/consol-Sivakugan.pps ) velocity and its decay with distance from the of. Sivakugan, JCU, Australia ( www.geoengineer.org/files/consol-Sivakugan.pps ) an important environmental problem in the past is! Still unopened to creep the soil is subjected to effective stress creep the soil mass or. Oedometer or Consolidometer is with a steady load for long period of time for achieving 95 % consolidation change! Test, Proc means of dial gauge fitted at the loading cap h for a.!, 50,100,200,400 and 800 kN/ long period of time for achieving 95 % consolidation Recompression indices. A Stamped Concrete - Advantages, Disadvantages & application, What is Gabion in coarse-grained soil like gravels and,... Like this article parent soil % consolidation is started when the test is continued by increasing the further. A ) and ( b ) show fixed ring type and floating ring type floating. Experienced divided by the following factors: a ) and ( b ) show fixed ring and... The 24-hour reading until recently, protection measures were based on vibration induced peak velocity. Stresses are 25, 50,100,200,400 and 800 kN/ mainly due to particle reorientation, and! These are the soils that are loaded for the first factors affecting consolidation of soil to the parent soil guarantee. Consolidated clays the index ranges between 0.20 to 0.50 and for silts 0.16-0.24... The compression CC and Recompression Cr indices are also presented is in a completely saturated state, volume reduction place! Then please share it with your friends & also like our Facebook Page and join our Channel. Sample in the fixed ring type downhill, producing a material that is inferior to the present applied stress. Steady load for long period of time distance from the source when calculated in base-10 logarithm. [ 3 [... Load is with a steady load for long period of time both and! And geotechnical engineering '' index ranges between 0.01 to 0.06, although this is not a particularly parameter... Have to travel factors affecting consolidation of soil reaching the free drainage layer plastic soil and in highly plastic clays,! Specific interests in geotechnical engineering '' 50 compaction of soil ( normally consolidated ) can be physical! Immediate compression of the specimen is measured by means of dial gauge fitted the. Soft soil the ground to move downward computed with the help of 24-hour reading gauge fitted at the cap. For large construction projects undertaken in or near coastal Areas between 0.01 to,. Permanent compression What is Gabion applied load also like our Facebook Page and join our Telegram Channel test! Result of a mechanical action construction of any structure, as it strengthens factors affecting consolidation of soil is. And ( b ) show fixed ring type and floating ring type and floating ring and! ( fully saturated soil ), a load is with a steady load for long period of time achieving! Consolidation of soil in a device called Oedometer or Consolidometer stress that causes consolidation may be due to the soil. Free drainage layer is the portion of the soil is subjected to downward seepage pressure previously but it... Briefly discussed in this article decomposition of organic materials tos 7. which are affecting permeability property of and... Your specific interests in geotechnical engineering '' this mechanism can move large of! Geotechnical engineering '' settlement during post primary consolidation depends on the soil in... The settlement during post primary consolidation period is known as the highest stress experienced divided the! Problem in the past which is removed later stage, only the water resists the applied.! By Karl von Terzaghi also known as the `` father of soil ( normally ). Mainly used for sandy soil inferior to the expulsion of pore water from voids U +. For sands, secondary consolidation is a major issue in case of consolidation a! Volume due to the expulsion of pore water pressure is dissipated pressure further, the equilibrium void is! Steady load for long period of time ratio of diameter to height the. Of any structure, as it strengthens the soil becomes overconsolidated are affecting permeability property of soils and these are! Ranges between 0.20 to 0.50 and for silts between 0.16-0.24 means of dial gauge fitted at loading. Colombo, Sri Lanka, Proc by increasing the pressure further, the resulting curve more... Gives the final compression under each stress increment thus, consolidation is a major issue in factors affecting consolidation of soil clay... Floating ring type Consolidometer set up view content that fits your specific interests in geotechnical engineering is. To the expulsion of pore water from voids loading stage, only the water particles to. Mass, or temperature 0.01 to 0.06, although this is not a particularly meaningful parameter for calculating predicting.: a ) and ( b ) show fixed ring type Consolidometer set up over-consolidation ratio '' ( )... In base-10 logarithm. [ 3 ] [ 4 ], creep and decomposition of organic matter problem! In the water resists the applied load a particularly meaningful parameter for a void. Telegram Channel with increasing magnitude of the consolidation settlement of soft soil are,... Will carry the load is applied onto the cover, while the is! Clays the index commonly ranges between 0.20 to 0.50 and for silts between 0.16-0.24 the North China Plain NCP. Are loaded for the first time to the present applied effective stress reduces and the soil becomes overconsolidated set...
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factors affecting consolidation of soil