0 It is a time-dependent phenomenon. 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. Consolidation is the process in which soil particles are packed more closely together over a period of time under the application of continued pressure i.e., static loading. r When the test is completed, the final height of the sample and its water content are measured. On reloading, recompression curve RS is obtained. a If volume of voids in the soil increases the flow path becomes wider and voids interconnectivity . The increment of applied stress that causes consolidation may be due to either natural loads (e.g. The upward movement of soil is called heaving. In the subsequent test, the incremental loading consolidation test is described. Creep extends to depths of 0.3 to 3 m, with the maximum displacements occurring at the ground surface. The commonly used stresses are 25, 50,100,200,400 and 800 kN/. End of consolidation), This page was last edited on 26 January 2023, at 18:20. 0 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 correlation of Index Properties with Some Basic Engineering Properties of Soils. y1{W-b*D=|qGLx N1`f]=a 2ETD"d[1:m0-8,(#x| ]o4q]&pd# nP%HG(6:P!#{fX}E]moiG~:'|P>+g?hG These volume changes may be brought out by two distinct processes. Thus, consolidation is a major issue in case of clay due to its low permeability. This normally involves loading the soil sample in the laboratory to a series of loads and measuring the corresponding settlements. Thus, volume of voids is e (void ratio, e = volume of voids/volume of solids). r Secondary Consolidation. where e0 and e are the void ratios at the beginning and end of the consolidation under the pressure increment . The rate of volume change depends on the permeability of soil. (2003) Soil Mechanics and Foundation Engineering. (ii) If the ground water table is high, capillary action can draw water up-to the frozen zone where it forms ice lines as shown in figure 6.11. The following factors affect the consolidation: Type of soil. Z}l)|X_ATLVUY!}_`[:>5GW When consolidation under the final pressure is complete, the specimen is unloaded and allowed to swell. The vertical deformation measurements of the soil specimen is performed using a dial gauge (most often) or an electronic instrument. [6] The more compressible the clay, the more pronounced the influences of cation type and electrolyte concentration on compressibility. Some soil (such as peat or soft organic clay) shows time-dependent settlement under constant effective stress during the post primary consolidation period. Determination of Coefficient of Consoli MODULE 4. Plagiarism Prevention 4. (i) becomes, Change in thickness, H due to pressure increment is given by. Soil compaction can lead to: poor root growthwhich reduces crop yield through poor water and nutrient uptake. the resistance of soil particles in sliding over each other. Before publishing your articles on this site, please read the following pages: 1. The settlement during post primary consolidation period is known as secondary consolidation settlement or creep. Soil deterioration and low water quality due to erosion and surface runoff have become severe problems worldwide. Conf. Void ratio. C The configuration allows for a constant load to be maintained indefinitely. To obtain the void ratio vs. pressure relationship, the equilibrium void ratio is computed with the help of 24-hour reading. In order to analyze the sensitivity of various pipe-soil interaction influencing factors and highlight the relationship between the factors and the pipe's mechanical characteristics during frost heaving, a pipe-soil interaction model based on a semi . 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. kets: Consumption and Consolidation Grow,published by ERS in August 2000. Soil research has shown that soil profiles are influenced by five separate, yet interacting, factors: parent material, climate, topography, organisms, and time. Conf., Taipei, Vol. It is mainly due to immediate compression of the soil layer under untrained condition. v }6Z+|V.ex"Y}w
Pbn6P>~gGUi!%;VWp6*t where H0 is the initial thickness of the soil and H is the change in thickness. With vacuum pressure, the inevitable unsaturated condition at the soil-drain interface may be improved, resulting in an increased rate of consolidation. Tenth Southeast Asian Geot. Effect of capillary pressure which is later destroyed by the rising of the water table. It is termed as uniform settlement. Then, CV can be estimated as: where Hdr is the average drainage path (typically, half the specimen height). The coefficient of consolidation, CV can readily be estimated from the time-settlement curve using graphical methods. The testing procedure to quantify the critical soil properties associated with soil consolidation is the Oedometer Test. Taken together, these reports will inform industry par-ticipants, researchers, and policymakers about the forces affecting competition and change in the produce . Primary consolidation. 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 The dial gauge readings are taken at the different elapsed times after a load is placed. Cc can be replaced by Cr (the recompression index) for use in overconsolidated soils where the final effective stress is less than the preconsolidation stress. Chemical factors such as the depletion of nutrients or the toxicity due to acidity or alkalinity (salinization) or waterlogging. 3. After consolidating the specimen upto pressure point Q, the specimen is allowed to expand by pressure decrements. Occasionally, soil strata form by natural deposition in rivers and seas may exist in an exceptionally low density that is impossible to achieve in an oedometer; this process is known as "intrinsic consolidation".[5]. Dial gauge readings are noted at 30 sec, 1, 2, 4, 8, 15, 30 mins, 1 hr, 2, 4, 8 and 24 hrs. H Prohibited Content 3. Figure 1: Typical Oedometer test set-up (photo from the National Technical University of Athens). The theoretical formulation above assumes that time-dependent volume change of a soil unit only depends on changes in effective stress due to the gradual restoration of steady-state pore water pressure. The loading beam should be almost horizontal. H 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. Some types of soil, mainly those rich in organic matter, show significant creep, whereby the soil changes volume slowly at constant effective stress over a longer time-scale than consolidation due to the diffusion of water. TOS 7. This process is called the consolidation of soil. Primary consolidation is completed when pore water expulsion stops. on the soil prior to shear, the stress history of the soil, stress path, and any changes in water content and density that may occur over time. This can be expressed in the following equation, which is used to estimate the volume change of a soil layer: When effective stress over-saturated soil mass increases, then the pore water pressure increases. ) To determine the consolidation properties, laboratory consolidation tests are carried out on a suitable undisturbed soil layer. Over consolidated soils are those which have been subjected to effective stress in the past greater than the present applied effective stress. Soil deformation may occur by change in stress, water content, soil mass, or temperature. 0 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. In view of the 0 The timedependent settlement due to the removal of water from a loaded saturated soil is known as primary consolidation settlement. S The settlement during post primary consolidation period is known as secondary consolidation settlement or creep. z Stress history. A typical Oedometer test set-up, shown in Figure 1, is composed of: i) a consolidation cell, ii) a loading frame, and iii) a deformation measurement mechanism. 3 As for the amount, it depends on the current and the target pH of the soil, as well as the texture of the soil. ). When soil saturated with water is subjected to an increase in pressure, the high volumetric stiffness of water compared to the soil matrix means that the water initially absorbs all the change in pressure without changing volume, creating excess pore water pressure. Depending upon the consolidation history, soil deposits may be divided into three classes: (i) Pre-consolidation soil or over consolidation soil. According to terzaghi, every process involving a decrease in the water content of a saturated soil mass due replacement of water by air is called a process of . Soil Mechanics in Engineering Practice, John Wiley & Sons, New York, 729 pp. This increase in vertical strain causes the ground to move downward. Under each stress increment, the soil sample is allowed to consolidate till the excess pore water pressure is being completely dissipated. Explanation: Grain size, properties of pore fluid, structural soil arrangement of soil particles, entrapped air and foreign matter and adsorbed water. e [1] The former was based on diffusion equations in eulerian notation, whereas the latter considered the local Newtons law for both liquid and solid phases, in which main variables, such as partial pressure, porosity, local velocity etc., were involved by means of the mixture theory. Heave problem arises when soil expands due to reduction in confining pressure or increase in water content. Besides these, from this test permeability and swelling behaviour of soil can also be determined. This analysis can be carried out by means of . If the soil mass below a structure compress uniformly throughout, then the settlement of the structure is uniform. This mechanism can move large quantities of water and can be able to produce ground surface heaves of 12 inches or more. (Drainage of excess pore water pressure), After some time, the drainage of water no longer occurs. Foundations of the structures present in the affected zone may move which results in tilting of the structures or formation of cracks in the structures. Types of construction project where consolidation often poses technical risk include land reclamation, the construction of embankments, and tunnel and basement excavation in clay. 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 terms consolidation and compaction are frequently interchanged. = 1, 469-472. Eng., Paris, Vol. New Age International Publisher, New Delhi, India. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. 2 The test apparatus is called consolidometer. [2], Consolidation is the process in which reduction in volume takes place by the gradual expulsion or absorption of water under long-term static loads. Settlement may occur almost twice the depth of excavation around open excavations. The gradient of the swelling and recompression lines on a plot of void ratio against the logarithm of effective stress often idealised to take the same value, known as the "swelling index" (given the symbol V Soil creep is typically caused by viscous behavior of the clay-water system and compression of organic matter. This process is commonly referred to as creep. Secondary consolidation: A subsequent settlement procedure that occurs after primary consolidation and is associated with internal changes in the soils structure while subjected to nearly constant load. Deformation may be either in the form of distortion or a change in volume of the soil mass. If the shear stress in clay exceeds about 70% of the shear strength, slow shear movement or creep begins to occur. Primary Consolidation. T Melting of the glacier which was covered by the soil mass in the past. Ranjan, G. and Rao, A.S.R. Creep is the slow and long term movement of soils in steep slopes. The soil sample is loaded in increments of vertical loads. If the drainage path is more than the distance of travel of water particles are reduced proportionality and in turn water will come out of the soil layer causing consolidation. Cv is defined as the coefficient of consolidation found using the log method with, C 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. In clay soil, the increase in effective pressure will cause large settlement because clay is highly compressible. In this case, the lateral strain of the soil mass is neglected. 2 1 The procedures used in this test are according to IS: 2720(Part XV)-1965. H Consolidation of soil is mainly used for clayey soil. 2. . (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 index Cc, which is defined as the change in void ratio per 10-fold increase in consolidation pressure, is in the range of 0.19 to 0.28 for kaolinite, 0.50 to 1.10 for illite, and 1.0 to 2.6 for montmorillonite, for different ionic forms. Therefore eqn. 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