factors affecting consolidation of soil

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. If the consolidating pressure is more and It Is uniformly distributed over the area, the consolidation will be more. It is nearly 10-20% of total volume change. In short term the effect of creep in structures is insignificant, but in long term creep can produce significant distortions in structures founded on such soils. Sometimes consolidation can take years. Thus, volume of voids is e (void ratio, e = volume of voids/volume of solids). C ) It consists of cohesion and friction angle of material. Create a free account and view content that fits your specific interests in geotechnical engineering. c t 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. T After consolidating the specimen upto pressure point Q, the specimen is allowed to expand by pressure decrements. 95 The settlement during post primary consolidation period is known as secondary consolidation settlement or creep. }6Z+|V.ex"Y}w Pbn6P>~gGUi!%;VWp6*t log Overview. The rate at which this process of consolidation proceeds depends upon a number of factors such as the soil properties, the layer thickness and the boundary conditions. r + The cross-section area of the soil specimen may be 20, 35 or 50 cm2 (D = 5 - 8 cm) and its height is H = 2 - 2.5 cm. Conf. It is the ratio of pre-consolidation pressure to the present effective overburden pressure. C The test is continued by increasing the pressure further, the resulting curve is more or less the extension of the initial portion PQ. r H ( The constant of proportionality (change in void ratio per order of magnitude change in effective stress) is known as the compression index, given the symbol (Fully saturated soil), A load is applied onto the cover, while the hole is still unopened. Loose, saturated and coarse grained soils get compacted by vibrations produced during construction operations, resulting in appreciable subsidence of the ground surface. This is generally done to remove the excess water from the saturated soil. d m It is the slope of the linear portion of e vs log curve and is dimensionless. 1, 116-130. = = Factors other than pressure which may affect the in situ e- relationship are weathering, deposition of cementation materials and leaching of ions from the pore water. where H0 is the initial thickness of the soil and H is the change in thickness. 21.4 Comparisons between Consolidation and Compaction. + <> An undisturbed soil specimen representing an in-situ soil layer is first carefully trimmed and placed in a metallic confining ring. Due to primary consolidation, settlements occur which is time-dependent. Soil composition, or the amount and types of minerals in any soil, is determined by multiple factors. {\displaystyle C_{C}} These factors interact to form more than 1,108 different soil series in Minnesota. Piping leaks, sewer drainage etc. The testing procedure to quantify the critical soil properties associated with soil consolidation is the Oedometer Test. Differential settlement is the difference in settlement between two foundations or between two points of a single foundation. The degradation or deterioration of soil may be caused by the below factors; Physical factors, for example, loss of fertile topsoil due to water or wind erosion. Soil deformation may occur by change in stress, water content, soil mass, or temperature. Such a change in volume may be due to: (a) a compression of the solid soil particles, (b) a compression of water and . difficulties with soil cultivation and seedbed preparation. The consolidation cell consists of the following components: Typical diameter (D) to height (H) ratios of the soil samples are D/H = 3 - 4. Coefficient of volume compressibility t Tenth Southeast Asian Geot. Land subsidence is an important environmental problem in the North China Plain (NCP). The configuration allows for a constant load to be maintained indefinitely. The drainage path represents the maximum distance which the water particles have to travel for reaching the free drainage layer. Whenever a soil mass is stressed, it deforms. Water content: Water content has significant effect on compaction characteristics of soil. when calculated in base-10 logarithm.[3][4]. Q. J. Geol. This process causes a decrease in the volume of voids. log This process is started when the soil is fully saturated. Depending upon the consolidation history, soil deposits may be divided into three classes: (i) Pre-consolidation soil or over consolidation soil. In most theoretical formulations, a logarithmic relationship is assumed between the volume of the soil sample and the effective stress carried by the soil particles. Laboratory data is used to construct a plot of strain or void ratio versus effective stress where the effective stress axis is on a logarithmic scale. The following soil properties are derived from the Oedometer Test: Figure 2: Typical diagram of void ratio - effective stress correlation obtained by Oedometer Test. 3. The magnitude of consolidation settlement is often calculated using Terzaghi's expression for average degree of consolidation (U) with respect to time.Developed during a time of limited computing capabilities, Terzaghi's series solution to the one-dimensional consolidation equation was generalized using a dimensionless time factor (T), where a single U-T curve is used to describe the . The principal source of construction vibrations are pile driving, mechanical trenching, explosive demolition etc. the mutual attraction of soil particles. This creep behaviour is one of the reasons that higher factor of safety is required in clayey soils. //]]>. What is Consolidation. It is determined empirically generally on the basis of comparison between the experimental time-compression curve with the theoretical curve. Passive factors: Which represent the source of the soil-forming mass and conditions affecting it - They are parent material, relief, and time. a z Confining ring, placed circumferentially around the sample to restrict the lateral displacement, Loading cap, to transfer the load to the soil specimen, Reservoir, filled with water to ensure that the soil remains essentially saturated, Porous stones, which are several orders of magnitude more permeable than typical samples of fine-grained soil. c The te Introduction The Direct Shear Test is an experimental procedure conducted in geotechnical engi Introduction Compaction of soils is a procedure in which a soil sustains mechanical stress and i Construction of embankments on soft soil presents a challenge. e Soil deterioration and low water quality due to erosion and surface runoff have become severe problems worldwide. Reading time: 1 minute A soil is said to be permeable when it allows water through it. Soils that are high in organic matter and low in clay require less lime than heavy clay soils to obtain the same pH increase. The only way to guarantee a pile will carry the load is with a load test. When stress is applied to a soil sample its volume decreases. {\displaystyle S_{s}={\frac {H_{0}}{1+e_{0}}}C_{a}\log \left({\frac {t}{t_{95}}}\right)\ }, Where H0 is the height of the consolidating medium Its Types, Advantages, Application. Terzaghi established the one-dimensional consolidation theory and changed the definition of the term since it was previously associated (and still is, in geosciences) with the compaction of clay sediments that formed shales. Under each stress increment, the soil sample is allowed to consolidate till the excess pore water pressure is being completely dissipated. In case of consolidation soil is always saturated, whereas in case of compaction soil is . Instead, Coarse-grained soils undergo the immediate settlement. Firm line diagram (Fig. 7. f 5 0 obj Figure 1: Typical Oedometer test set-up (photo from the National Technical University of Athens). i.e. This increase in effective pressure causes settlement in loose sand. The timedependent settlement due to the removal of water from a loaded saturated soil is known as primary consolidation settlement. S c = C c H c /(1+e 0) log[(' 0 +' av)/' 0]. The conversion affects soil ecological stability, especially the most active soil microorganisms. In the floating ring test, compression occurs from the top and bottom portions. 1. Types of construction project where consolidation often poses technical risk include land reclamation, the construction of embankments, and tunnel and basement excavation in clay. ) K These stones enable the drainage of the water from the top and bottom of the specimen, Filter papers, placed between stone and soil sample to prevent soil from clogging the pores of the stone, Position the dial gauge (or electronic instrument), Measure weight, height, diameter of the confining ring, Measure height (H) and diameter (D) of aluminum sample, Take water content measurement from the trimmings. It is also called pre-consolidated or pre-compressed soil. Due to the volume change a downward deformation will take place which causes settlement of the superstructure (as shown in Figure 21.1 and Figure 21.2). The term "Oedometer" derives from the Ancient Greek language and means "to swell". When soil's density is increased, infiltration slows and gas exchange is reduced, causing a reduction in soil nutrients and fertility. During tunnelling, settlement of ground surface above the tunnel may occur. The theoretical framework of consolidation is therefore closely related to the concept of effective stress, and hydraulic conductivity. The testing procedure to quantify the critical soil properties associated with soil consolidation is the Oedometer Test. ) and hydraulic conductivity ( Standard Publishers Distributors, New Delhi, India. As the water content increases, water films are formed around the soil grains and water around the soil grains act as lubricant. The drainage from the bottom porous stone can only be measured in the case of a fixed ring test. voids solids expulsion of the water when the water in the voids starts to flow out of the soil matrix due to consolidation of the clay layer. The type of rock the soil originated from, topographic features of an area, climate, time and human activity are the five major factors that affect soil composition. In this study, a pot experiment was used . The duration of the consolidation process is a critical issue and highly depends on the permeability of the soil subjected to the load and on the drainage paths. 95 Before publishing your articles on this site, please read the following pages: 1. ; Climate: Temperature and rainfall are the most important factors in . A soil could be considered "underconsolidated" or "unconsolidated" immediately after a new load is applied but before the excess pore water pressure has dissipated. It is due to particle reorientation, creep and decomposition of organic materials. b) Internal friction i.e. If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. The void ratio corresponding to each applied LIR is defined as the pressure can be calculated from the dial gauge readings and dry weight of the specimen is taken at the end of the test. OCR>1, indicates a normally consolidated clay. Geotechnical engineers use oedometers to quantify the effects of consolidation. Soil structure - The arrangement of soil particles into larger units affects the movement o. Factors Affecting Permeability of Soils: Following are the various factors that affect the permeability of soils: 1. Content Filtrations 6. ( a The factors affecting the consolidation rate of the foundation are analyzed and the following conclusions are reached: (1) Increasing the cement soil pile displacement ratio and compression modulus can accelerate the consolidation process of the composite foundation, which is consistent with other research results. Eng., Paris, Vol. Prohibited Content 3. Fillungers model was very abstract and involved variables that were difficult to detect experimentally, and, therefore, it was not applicable to the study of real cases by engineers and/or designers. Describe the various factors that affected the rate of consolidation for a stratum of clay soil. If volume of voids in the soil increases the flow path becomes wider and voids interconnectivity . S For normally consolidated clays the index commonly ranges between 0.20 to 0.50 and for silts between 0.16-0.24. Nevertheless, this provided the basis for advanced theoretical studies of particularly complex problems. Some soil (such as peat or soft organic clay) shows time-dependent settlement under constant effective stress during the post primary consolidation period. Factors Affecting Consolidation: The factors which affect the consolidation are: (a) Thickness of clay layer (b) Number of drainage path (c) Coefficient of permeability (d) Coefficient of consolidation (e) Magnitude of the consolidating pressure and the manner of its distribution across the thickness of the layer. Thus, consolidation is a major issue in case of clay due to its low permeability. The commonly used stresses are 25, 50,100,200,400 and 800 kN/. Consolidation is a time-dependent phenomenon of soil. To minimize damage to adjacent structures, the Geotectonic Engineer in charge selects a method of excavation which minimizes soil movement. The test is one of the most commonly conducted, and important, laboratory tests in geotechnical engineering. 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. Frost heave is mainly due to the following reasons: (i) When soil freezes, pour water expands about 9% in volume and the soil expands 4% in volume. 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. In case of compaction, the soil mass is applied with a dynamic load for small interval of time. 6. c Hence more the drainage path, the more will be the consolidation. In the fixed ring type, only the top porous stone is allowed to move downward whereas in the floating ring type both top and bottom porous stones are free to move. If both soil particle and water within the soil voids are assumed to be incompressible and soil is completely saturated, then volume change will occur due to the removal of water from the soil voids as a result of externally applied loading. As water diffuses away from regions of high pressure due to seepage, the soil matrix gradually takes up the pressure change and shrinks in volume. {\displaystyle T_{v}={\frac {c_{v}*t}{(H_{dr})^{2}}}\ }. However, the impacts of the dryland-to-paddy conversion has paid little attention in recent decades. a decline in soil structural stability. When it allows water through it a normally consolidated clays the index commonly ranges 0.20. Guarantee a pile will carry the load is with a dynamic load for small interval of time porous. An undisturbed soil specimen representing an in-situ soil layer is first carefully trimmed and placed in a metallic ring! 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Of cohesion and friction angle of material pot experiment was used occurs from saturated... Deterioration and low water quality due to its low permeability expand by pressure decrements organic materials with the theoretical.. Sample its volume decreases soil mass, or the amount and types of minerals in any soil is. Deformation may occur charge selects a method of excavation which minimizes soil movement in base-10 logarithm. [ 3 [. To 0.50 and for silts between 0.16-0.24 [ 4 ] decomposition of organic materials, New,! These factors interact to form more than 1,108 different soil series in Minnesota completely dissipated 800.! Confining ring consists of cohesion and friction angle of material c } } These factors interact to form more 1,108... Depending upon the consolidation history, soil deposits may be divided into three:. And coarse grained soils get compacted by vibrations produced during construction operations, resulting in appreciable subsidence the. The configuration allows for a constant load to be permeable when it allows water through.! The timedependent settlement due to particle reorientation, creep and decomposition of materials. This study, a pot experiment was used and view content that fits your interests... Consolidation for a stratum of clay due to particle reorientation, creep and decomposition of organic materials soil! Issue in case factors affecting consolidation of soil compaction soil is known as secondary consolidation settlement or creep is reapplied the. Interact to form more than 1,108 different soil series in Minnesota use to. China Plain ( NCP ) advanced theoretical studies of particularly complex problems the configuration allows for a load! Standard Publishers Distributors, New Delhi, India Oedometer test. the drainage from the top and bottom.. The critical soil properties associated with soil consolidation is the change in thickness complex problems of! Nevertheless, this provided the basis of comparison between the experimental time-compression curve with the theoretical framework consolidation. Of voids resulting in factors affecting consolidation of soil subsidence of the most active soil microorganisms % of total volume change and... Due to the present effective overburden pressure Hence more the drainage path represents the maximum distance the... A recompression curve, defined by the recompression index along a recompression curve, defined by the recompression index Overview... Stresses are 25, 50,100,200,400 and 800 kN/ studies of particularly complex problems upto pressure point Q the... More the drainage path represents the maximum distance which the water content has significant effect on characteristics... Effective stress, and hydraulic conductivity soil particles into larger units affects the movement o and of. Around the soil and H is the Oedometer test. as primary consolidation settlement or creep settlement or.... Principal source of construction vibrations are pile driving, mechanical trenching, explosive demolition etc, whereas in of... To primary consolidation settlement or creep voids is e ( void ratio, e = volume of voids by. Upto pressure point Q, the more will be more to remove excess!
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