Stress history. This process causes a decrease in the volume of voids. This process is called the consolidation of soil. It occurs because of gravity induced down slope shear stresses, frost action, expansion and contraction of clays. This report addresses the second objective. In general for granular soil, St = Si. PRESENTED BY: SHUBHAM KUMAR GUIDED BY: Prof S.P.MUKHERJEE CONTENT INTRODUCTION PROCESS OF CONSOLIDATION TYPES OF CONSOLIDATION DEPENDING UPON STRESS HISTORY 1-D CONSOLIDATION THEORY OF TERZAGHI SAND DRAINS APPLICATION OF CONSOLIDATION CONCLUSION REFRENCES INTRODUCTION When a soil mass is subjected to a compressive force its volume decreases this property of soil is . The 24-hour reading gives the final compression under each stress increment. A clay is said to be pre-consolidated if it has always been subjected to a pressure greater than the present overburden pressure. The commonly used stresses are 25, 50,100,200,400 and 800 kN/. t The highest stress that it has been subjected to is termed the "preconsolidation stress". 1 = Creep extends to depths of 0.3 to 3 m, with the maximum displacements occurring at the ground surface. The vertical settlement of the soil due to consolidation can be written as: \[\Delta H={H_0}{{\Delta e} \over {1 + {e_0}}}\] (21.3), Fig. (Drainage of excess pore water pressure), After some time, the drainage of water no longer occurs. 3. In areas where soil is subjected to freezing, there is upward movement in the ground due to formation of underground ice and this phenomenon is called frost heave. Disclaimer 9. This increase in effective pressure causes settlement in loose sand. e0 is the initial void ratio until recently, protection measures were based on vibration induced peak particle velocity and its decay with distance from the source. Creep typically takes place over a longer time-scale than (primary) consolidation, such that even after the restoration of hydrostatic pressure some compression of soil takes place at slow rate. Soil compaction also compromises soil strength. 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. Terzaghi had an engineering approach to the problem of soil consolidation and provided simplified models that are still widely used in engineering practice today, whereas, on the other hand, Fillunger had a rigorous approach to the above problems and provided rigorous mathematical models that paid particular attention to the methods of local averaging of the involved variables. d More generally, consolidation refers to the process by which soils change volume in response to a change in pressure, encompassing both compaction and swelling. 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. The downward movement of the surface of consolidating layer is called consolidation settlement. Privacy Policy 8. Consolidation is the reduction of water voids, whereas compaction is the reduction of air voids. When the final effective stress is greater than the preconsolidation stress, the two equations must be used in combination to model both the recompression portion and the virgin compression portion of the consolidation processes, as follows, 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. Immediate . e Murthy V.N.S (1996) A Text Book of Soil Mechanics and Foundation Engineering, UBS Publishers Distributors Ltd. New Delhi, India. = 0 Investigations of the factors affecting adoption and use of soil conservation practices began, for the most part, in the 1950s. The soil mass is considered semi-infinite. 8. 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. This can be expressed in the following equation, which is used to estimate the volume change of a soil layer: To obtain the void ratio vs. pressure relationship, the equilibrium void ratio is computed with the help of 24-hour reading. Temperature changes, abrasion (when rocks collide with each other) or frost . London, 100(1-4), 119-135. ( ;V>kM;iPo{a9j6EVhL@-5?qFQP_5>\0pE]*9KzxvB%G!l6;*J[}kq5{@~s R J p+h^G(-$5+4/`J From the equation of consolidation i.e., Tv = Cvt/d2 clear that the coefficient of consolidation (Cv) is directly proportional to the time factor (TV). + lxY*9~ {,LSh|zc 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 Clay samples were collected from 14 boreholes at different depths, and the compression and consolidation behavior of the soil was analyzed by . H c - Height of the clay layer. In this study, horizontal and vertical permeability . (2000). 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. Yan and Chu (2003) stated that the cost of soil improvement by vacuum preloading is approximately 30% less than that by conventional surcharge alone. ( e Compaction and consolidation. Answer (1 of 5): The following factors that affect the movement of water in soil: Soil texture - The size, shape, and distribution of soil particles affects the ability of water to move through the soil. 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. + The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. The test apparatus is called consolidometer. Content Guidelines 2. Terzaghi, K. and Peck, R.B., (1967). Coefficient of volume compressibility The permeability of the specimen at any stage of loading can be measured only in the fixed ring type. d If volume of voids in the soil increases the flow path becomes wider and voids interconnectivity . As the water content increases, water films are formed around the soil grains and water around the soil grains act as lubricant. 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 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. Pw?W1eSim+@v/^g,ywE;SooR[;wx~;LeJ7.(,K
a(f 1d theory of consolidation time-dependent analysis undrained loading: pore pressure generation no change in effective stresses no settlement initial stress final stress primary consolidation log total stress void ratio 1d theory of consolidation time-dependent analysis drained loading: pore pressure dissipation increase in . Soil Mechanics - Third Year Civil Eng.Soil Mechanics (PBW N302) Consolidation Test Objectives: Volume change-effective pressure relationship Stress history of soil Volume change - time - pore water dissipation relationship Soil Mechanics - Third Year Civil Eng.Soil Mechanics (PBW N302) Consolidation Test Loading frame Dial gauge The choice of vertical pressure depends mainly on the expected site pressure, including overburden pressure. The proximity of trees with large roots. O11 !RP4_{EA[ Q2@K[t96Jh KBC tC4M5!`iCeDJ~{n9NfN+Up@ e So the change in volume is equal to the change in depth. (iii) Expulsion of water and air from the void of the soil mass. This allows the consolidation characteristics of the soil to be quantified in terms of the coefficient of consolidation ( 6. Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. If the shear stress in clay exceeds about 70% of the shear strength, slow shear movement or creep begins to occur. The early theoretical modern models were proposed one century ago, according to two different approaches, by Karl Terzaghi and Paul Fillunger. The volume of solid is considered as 1. When effective stress over-saturated soil mass increases, then the pore water pressure increases. The relevant factors affecting the vertical response of a rock-socketed pile group are further discussed. The configuration allows for a constant load to be maintained indefinitely. Friction is a resisting force between two surfaces. These are more compressible soils. What is Consolidation. If you like this article then please share it with your friends & also like our Facebook Page and join our Telegram Channel. The factors which affect the consolidation are: (e) Magnitude of the consolidating pressure and the manner of its distribution across the thickness of the layer. It is also the slope of effective stress v/s void ratio curve. (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. Coefficient of consolidation is the indicative of the combined effect of compressibility and permeability of soil on the rate of volume change. (e) Magnitude of the consolidating pressure and its distribution: Consolidation of the soil is greatly affected by the consolidating pressure and Its distribution. Soil compaction can lead to: poor root growthwhich reduces crop yield through poor water and nutrient uptake. Immediate settlement is very small as compared to primary settlement. Soft clay consolidation is an important aspect to be considered for large construction projects undertaken in or near coastal areas. T Eng., Paris, Vol. Before going to know about these factors, take a look at the general expression for . z + If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. }6Z+|V.ex"Y}w
Pbn6P>~gGUi!%;VWp6*t An undisturbed soil specimen representing an in-situ soil layer is first carefully trimmed and placed in a metallic confining ring. The procedures of fixed ring tests are explained below: 1. For sands, the index ranges between 0.01 to 0.06, although this is not a particularly meaningful parameter for a sand. Secondary consolidation. This stress, in turn, increases the vertical strain in the soil. 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. Shear strength of soil influenced by the following factors: a) Cohesion i.e. In the floating ring test, compression occurs from the top and bottom portions. Geoengineer.org uses third party cookies to improve our website and your experience when using it. Consolidation is a time-dependent phenomenon of soil. a decline in soil structural stability. 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. Soil mechanics is used to analyze the deformations of and flow of fluids within natural and man-made structures that are supported on or made of soil, or structures that are buried in soils. 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. a The soil which is not fully consolidated by the present overburden pressure is called under consolidated soil. Blase (1960) found that the following factors were statistically significant in explaining reductions in soil loss: (1) off-farm income (interpreted as a means to overcome . 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. Figure 1: Typical Oedometer test set-up (photo from the National Technical University of Athens). Sivakugan, N., (1990). Note that there is also a constant rate of strain (CRS) test, that nowadays is becoming more popular. t95 is the length of time for achieving 95% consolidation. 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. Compaction of soil is mainly used for sandy soil. Consolidation is a natural process where soil below the building and other structure compacted by the transferred . v The loading frame configuration is composed of a loading beam and dead weights. 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. In an oedometer test, a series of known pressures are applied to a thin disc of soil sample, and the change of sample thickness with time is recorded. 2 Melting of the glacier which was covered by the soil mass in the past. C The dial gauge readings are taken at the different elapsed times after a load is placed. With vacuum pressure, the inevitable unsaturated condition at the soil-drain interface may be improved, resulting in an increased rate of consolidation. 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