Geotechnical Engineering, Grouting - Research Paper Example

GEOTECHNICAL ENGINEERING due: Table of Contents Table of Contents Question 3 Use of grout curtains in water retaining dams 3 Introduction 3 General information on the dam 4 Geological and geotechnical characteristics of a dam 4 Materials used in making the groutings 4 Sulphate-resistant cement 4 Bentonite 5 Sand 5 Chemical additives 5 Grout curtain geometry 6 Grouting applications 6 How grout curtains are used 6 Concrete gravity dams 6 Arch dams 7 Buttress dams 7 Embankment dams 7 Faced dams 8 Homogenous dams 8 Question 2: 8 A permanent strain of unbound granular materials 8 Abstract 8 Introduction 9 Shakedown concept 10 Cyclic behaviour of unbound granular materials 13 Conclusion 15 Bibliography 16 Question 1 Use of grout curtains in water retaining dams Introduction Grout curtains are barriers to groundwater flow which is created by grouting a volume of soil or rock of large extent which is normal to the flow direction and of limited in the flow of direction. They are normally used alongside or beneath a dam for prevention of drainage of the impounded water. To prevent water inflow, the grout curtains are normally placed around construction sites or shafts. Grouting is a widely used and popular method of controlling leakage of water in the fill dam constructions. The design of the grouting curtain will depend on the geological and geotechnical facets of the rock to be grouted. In their construction, grouts are pressure-injected into the soil at closely spaced intervals. They are referred to as grout curtains, simply because their spacing is such that each ‘pillar’ of grout is intersected with the next, forming a continuous wall or curtain. Grouting is the filling of the fluid material by applying pressure, to the structural and lithogical defects caused by the drilled whole. Materials used for grouting include hydraulic cements, clays, bentonite and silicates. These materials are however prone to cracking may be chemically incompatible or may not be durable. To counter these weaknesses, polymer grouts are used because they are impermeable to gases, liquids; resist radiation, acidic and alkaline environments. The grouts are injected with grouting jets, which usually use a high-pressure fluid stream for erosion of a cavity in the soil. The main reason for grouting is to form a more competent and less permeable parent soil or rock (Johnson 2008: 945-950). To exhaustively discuss the use of grout curtains in water retention dams, Cindere dam in Turkey will be used as the main reference dam, where its construction will be discussed at length more so focusing on the grout curtains (Devrim & Yeşđl 2008: 4039-4047). General information on the dam It is built on the Menderes River located on the northwest of Guney District. The dam is used both for irrigation and generation of energy, where it produces 88GWh/year. Cindere dam is the first one built using RCC (Roller compacted hardfil) (Devrim & Yeşđl 2008: 4039-4047). Geological and geotechnical characteristics of a dam In the construction of any dam, considerations have to be made on the permeability and the mechanical physical properties of the mica schist and the lime schist which are the bedrock, the thickness as well as permeability of the talus and alluvium. Schistosity planes are irregular and are characterised by calcite and quartzite veins. The veins have different thickness values, which may range between 5cm- 2m. Among the schist masses, graphite is the weakest. Filling of the dam reservoir is by the water effect would change for the schists. The schists have the quality of being a medium rock (Devrim & Yeşđl 2008: 4039-4047). Materials used in making the groutings Sulphate-resistant cement For better results, the sulfate-resistant cement should contain tricalcium aluminate not exceeding 3.5%. Normal Portland cement is to be used in all areas apart from the regions where the sulfate-resistant cement would be used. This cement should have a specific surface of 2400 cm2/g, leaving a relic of maximum 1% on the sieve, with a 200 micron aperture size. However, for sections where water leakage could be more, cement with higher values of specific surface and more relic amount should be used (Eriksson, Friedrich, & Vorschulze, 2004: 1111-1119). Moreover, the water used should be clear and clean with desirable characteristics of mixing the concrete. Bentonite The main purpose of using bentonite is to enable sensitivity of the mortar during the mixing, in order to ensure that cement particles and water are suspended and also to minimize the disintegration of water in the cement water composition. The ratio of bentonite used should be in the ratio of 2 to 5% of the cement amount. Bentonite is used to reduce bleed and increase resistance to pressure filtration. It provides lubrication and penetrability benefits. Excessive use may however increase viscosity and cohesion weakening the grout. It should, therefore, be added as a pre-hydrated suspension (Koch 2002: 1-11). Sand Sand should be used in the ratios of 25, 100, and 200% of the cement amount. For the strength of the grout curtains, the preferred sand should have particles which are circular, thin or medium sized, with no organic material, sulfate or even clay in the sand. However, if the harmful materials exceed 5% then the sand should be washed to restore its desirable characteristics (Ozgurel & Vipulanandan: 2005: 1457-1465). Chemical additives They are additives like thinners and hardening accelerators. Other additives like sodium sulphate can be used when the permeability of the mica schist and calc-schist is low and where there is water absorption without slurry absorption. The ratio of sodium sulphate should be between 1 to 2%. Dispersants or water reducers include super plasticizer and fluidifier. They cause particles to repel one another, reducing agglomeration of particles which will reduce the grain size by inhibiting the development of macroflocs. They also reduce viscosity and cohesion. Using large quantities of the dispersants should be avoided since it may accelerate or retard the hydration process. Grout curtain geometry A single line curtain is desired due to its competence which forms a low general permeability of the dam. A primary hole spacing of 12m is desired .The hole alignment provides an optimum intersection with the main geological features (Devrim & Yeşđl 2008: 4039-4047). Grouting applications In the construction of the Cindere dam, design was according to the principles in “drilling and grouting technical specification”. Grout curtain, and grout connections were used to prevent any possible water leakage in the limestone, schist and the mica schists forming the base of the embankment, after the removal of alluvium under the embankment. On the other hand, the contact groutings were used for the sole purpose of filling the space between the coating concrete and the bedrock. For further reinforcement, consolidation groutings were used to strengthen the bedrock (Ivanov & Chu 2008: 139-153). How grout curtains are used Grout curtains are used on different types of dams. Discussion on the use of grout curtains will be done on concrete gravity dams, arch dams, buttress dams, embankment dams, faced dams and homogenous dams (Devrim & Yeşđl 2008: 4039-4047). Concrete gravity dams The grout curtains are normally used where the foundation of a concrete dam would pass too much seepage, or pass a dangerous seepage. The amount of seepage passing through the curtains is picked up in drainage holes which are located downstream the curtain; this is because the grout curtains are not fully water-tight. The water stored in the dam exerts a horizontal pressure on the upstream of the dam. The water pressure will be counteracted by the weight of the dam thus stopping the dam from overturning towards the downstream toe. The grouting under the dam prevents seepage which could pass along any open cracks at the base exerting pressure upwards. This could be catastrophic, and the use of the curtain grouts serves to improve the safety of the dam. This is because the curtain provides interception of the seepage, cutting off most of the uplift pressure and thus improving the stability of the concrete dam (Tekie & Ellingwood 2003: 2221-2240). Arch dams Grout curtains in this type of dam are constructed to limit the quantity of underground seepage and reducing the pressure of the seepage. The curtain cushions any seepage passing through the curtain and scatters the remaining pressure. Pressure from the stored water is transferred by an arch action to the abutments, and the other pressure carried to the base rock by a cantilever action. Buttress dams The grout curtains in this particular dam have the same purpose as that of the arch dams. Drainage holes may however be omitted since seepage can emerge between buttresses without necessarily affecting the stability of the dam. The concrete face of the buttress dams retains the water. Buttresses support this concrete face at intervals. Embankment dams In this type of dams, grout curtains restrict seepage so as to avoid loss of the storage. It also ensures that the foundation is not dislodged downstream and that the dam is not eroded at the base. The seepage passing through the core is picked up by filters in the downstream of the dam thus preventing the seepage from carrying away the core material. On the upstream side of the core are filters which protect the core from sloughing in case the storage is drawn down rapidly. Large shells of rock fill hold the core in position, giving the dam stability. Faced dams In these dams, the grout curtains limit the quantity of the underground seepage. If the material of the dam is pervious enough, drainage provisions are not required. On the upstream location of the dam is a water-retaining membrane made of either bitumen or plastic and supported by the rock fill. Homogenous dams Homogenous dams are built almost entirely with one material and have no zoning. The material used is unable to provide safe dissipation of seepage passing the grout curtain. The foundation surface has a filter on the downstream of the grouting to protect the base of the fill from erosion by seepage. Grout curtains in these particular types of dams limit the amount of seepage passing under the dam. The filter, therefore, provides drainage. Question 2: A permanent strain of unbound granular materials Abstract For an approximation of the loading experienced by the material element in a pavement, an apparatus called Repeat Load Tri-axial (RLT) is used. Stress level is tested by subjecting the unbounded granular materials to at least 50,000 load cycles which give an indication of the resistance of the materials as a result of their resistance to permanent strain. To ascertain the resistance of the materials to this stress, a number of RLT permanent strains were conducted on two Northern Ireland unbound granular materials (UGMs) and four New Zealand materials. Obtained results of the tests were recorded as accumulated permanent strain against load cycles and categorised into three types of ranges (A, B and C). For the range A, the incremental increase of permanent strain of each of the load cycle is decreasing, proving a stable behaviour. Range C and range B is expressed as behaviour amid the two extremes A and C. For the design of pavement, range A is the most preferred. For the application of the Range A behaviour criteria, the finite ABAQUS finite element package was employed. A yield line was dedicated to the granular material representing the boundary between the behaviour of Range A and Range B. In addition, analysis of the granular depths of different asphalt pavements was done. As a result, contours of permanent strain were obtained, showing the regions in the pavement that had yielded. The resulting cumulative yielding was labelled as the total permanent surface deformation. Various observations were made depending on the particular type of material tested. For instance, asphalt cover thickness of around 200mm exhibited minimal amounts of yielding leading to the conclusion that Range A or stable behaviour in the granular material would be predicted. The other results produced showed the shifting of permanent strain of the regions of the pavement relying on the thickness of the asphalt and granular. It was observed that maximum amount of permanent strain would occur ain a thin asphalt cover of less than 25mm, with granular layers exceeding 600mm, at a depth of 150mm and the subgrade would exhibit no permanent strain at all (Arnold, Dawson, Hughes, & Robinson, 2004: 169). Introduction Current assumptions are that most rutting occurs in the subgrade only as shown by pavement thickness design guides (Hall & Beam 2005: 65-73). Determination of the thickness of the unbound granular sub-base layers is done depending on the subgrade condition and design traffic, which includes traffic during construction (Werkmeister, Dawson & Wellner, 2004: 664-674). Unbound granular materials should comply with the material specifications, leading to the assumption that rutting only occur in the sub-grade. The material specifications for the UGMs include the criteria for aggregate strength, grading, durability, cleanliness, and angularity. However, none of these criteria is a measure of resistance to rutting resulted by repeated loading. Tests of the permanent strain based on the Repeated Load Tri-axial (RLT) apparatus show that the granular materials will perform differently even though they all comply with the same specification(Dawson, Mundy & Huhtala, 2000: 91-99). Accelerated tests on pavements show that 30% to 70% of the surface rutting is due to UGM layers. Recycled aggregates, on the other hand, may fail the highway agency material specifications restricting their use. This also applies to unbound sub-base pavement layers. The permanent strain test in the RLT apparatus will be used for assessment of the suitability of the alternative materials such as the recycled aggregates for use in the various depths within the pavement. It is of vital concern that the current pavement design methods and specifications to consider the repeated load-deformation performance of the UGM layers. The design method makes use of the RLT permanent strain tests for modification of the Drucker-Prager yield criteria for reflection of a stress boundary between the different rutting behaviours defined in the shakedown behaviour ranges(Deng & Zheng 2006: 735-739). Shakedown concept This is based on an alternative approach applied to reverse the limitations of the current practice in the ABAQUS finite element package. Due to the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers, it is important to take into account the mechanistic Empirical formulas (Habiballah & Chazallon 2005: 577-596). This is because there is a diversification of permanent strain triggers to stress level and load cycles that a single equation cannot fully describe. Higher levels of additional stress ratio, there is no stabilisation of permanent deformation, and it instead appears to increase linearly. With increased levels of additional stress ratio, there is a rapid increase in permanent deformation resulting in failure of the specimen. The range of behaviours is as illustrated in figure 1 below, and the description can be done using the Shakedown concept Figure 1: Shakedown range behaviours for permanent strain versus cumulative loading. Source: Dawson, A. (Ed.). (2004). Pavements Unbound: Proceedings of the 6th International Symposium on Pavements Unbound (UNBAR 6), 6-8 July 2004, Nottingham, England. CRC Press. Results of RLT permanent strain tests are reported as either shakedown range A, B or C. From this, the determination of the stress conditions causing the various shakedown ranges used in the definition of stress boundaries is done. The shakedown ranges are: Range A, also called the plastic shakedown range. They occur when the response shows high strain rates per load cycle for a given finite number of load applications in the initial compaction period. This range is known as the plastic shakedown range. It occurs at low-stress levels. Range A response to loading is desirable in covers to UGM in pavements. This is because during compaction, the permanent strain rate per load cycle reduces until to the point where the response becomes dormant resulting to no further permanent strain. In this range, complete stabilisation of permanent strains is observed after being subjected to a finite number of load cycles. The behaviour is entirely resilient Range B, also called the intermediate range behaves like range A during the compaction period. After compaction period, permanent strain rate. In this range, the response does not result to resilience state. Increasing the RLT test numbers load cycles to a large number like 2 million will result to either range A or range C. In range B, there is no complete stabilisation Range C, also called the incremental collapse range represents the incremental collapse shakedown range. There may be an initial compaction period after which the permanent strain rate increases as the load cycles increase. The first decrease leads to an increase in the permanent strain rate resulting to a progressive failure. Illustration of the ranges is as per the figure 2 below Figure 2: different types of permanent deformation behaviour, depending on the stress level. Source: Hornych, P., & El Abd, A. (2004). Selection and evaluation of models for prediction of permanent deformations of unbound granular materials in road pavements. Work Package, 5. For a well-designed pavement, it can be seen that Range A should be the most preferable and range C should be avoided by all means. Range B can be adopted on condition that the amount of rutting because of the design traffic can be approximate at a reasonable accuracy. Cyclic behaviour of unbound granular materials Since UGMs are materials with individual grains, having little or no cohesion, their behaviour is dependent on the stress state and the grading of the material and the shape of the grains. To study their mechanical behaviour, cyclic triaxial test is the most widely used test. The test has the advantage of having the possibility to study the behaviour of the material under cyclic loadings, by simulating accurately the in-situ conditions Figure 3: principle of the repeated load triaxial test. Source: Hornych, P., & El Abd, A. (2004). Selection and evaluation of models for prediction of permanent deformations of unbound granular materials in road pavements. Work Package, 5. Figure 4: Example of stress-strain cycles obtained in a repeated load triaxial test on a granular material. Source Hornych, P., & El Abd, A. (2004). Selection and evaluation of models for prediction of permanent deformations of unbound granular materials in road pavements. Work Package, 5. Cyclic triaxial apparatus for UGMs may vary largely in their characteristics in terms of specimen size and loading capabilities. In figure 1 above, the material is subjected to a cyclic vertical stress and a cyclic horizontal varying in phase. This type of loading is known as the variable confining pressure (VCP). It is advantageous in that it simulates more closely in the in situ loading conditions. In figure 2, a granular material is shown how it responds in a cyclic triaxial test. It is evident that there is a rapid accumulation of permanent strains in the first load cycles, which then tend to stabilise making the response of the material elastic. There is also non-linearity observation made on the elastic part of the material. The observed resilient behaviour can be described using non-linear elastic models. Implementation of such models is done on the pavement analysis programs and used for pavement modelling and design. Conclusion To sum it up, there is a general requirement for a high quality quarried crushed rock aggregates to be in compliance with the specifications for unbound granular materials (UGMs). There is a limitation on the use of aggregate materials which do not meet the specifications. Criteria considered for such materials include resistance to permanent deformation and degradation. Governing of the pavement design methods is dependent on the final thickness of the asphalt cover and pavement depth. Pavement design method should include a design criterion on the assessment of the resistance to deformation of a UGM in a pavement structure. Aggregates chosen should have the ability to resist the stresses on the surface in the pavement (Arnold, Hughes, Dawson, & Robinson, 2003: 194-200). Bibliography ARNOLD, G., DAWSON, A., HUGHES, D., & ROBINSON, D. (2004). Deformation behaviour of granular pavements. In International Symposium on Unbound Aggregates in Roads, 6th, Nottingham, United Kingdom. ARNOLD, G., HUGHES, D., DAWSON, A. R., & ROBINSON, D. (2003). Design of granular pavements. Transportation Research Record: Journal of the Transportation Research Board, 1819(1), 194-200. Available online at. http://trb.metapress.com/content/g7h021321w412144/. DOI: 10.3141/1819b-25 DAWSON, A. R., MUNDY, M. J., & HUHTALA, M. (2000). European research into granular material for pavement bases and subbases. Transportation Research Record: Journal of the Transportation Research Board, 1721(1), 91-99. Available online at http://trb.metapress.com/content/t242j07474kup129/. DOI: 10.3141/1721-11 DAWSON, A. (Ed.). (2004). Pavements Unbound: Proceedings of the 6th International Symposium on Pavements Unbound (UNBAR 6), 6-8 July 2004, Nottingham, England. CRC Press. DEVRIM ALKAYA AND BURAK YEŞĐL (8 September, 2011). Grouting applications of grout curtains in Cindere dam and hydroelectric power plant. Scientific Research and Essays Vol. 6(19), pp. 4039-4047, Available online at http://www.academicjournals.org/SRE. DOI: 10.5897/SRE11.103 DENG, C. J., HE, G. J., & ZHENG, Y. R. (2006). Studies on Drucker-Prager yield criterions based on MC yield criterion and application in geotechnical engineering. Yantu Gongcheng Xuebao(Chinese Journal of Geotechnical Engineering), 28(6), 735-739. Available online at http://www.cgejournal.com/EN/abstract/abstract12083.shtml. ERIKSSON, M., FRIEDRICH, M., & VORSCHULZE, C. (2004). Variations in the rheology and penetrability of cement-based grouts—an experimental study. Cement and Concrete Research,34(7),1111-1119.Available online at http://www.sciencedirect.com/science/article/pii/S0008884603004198. DOI: 10.1016/j.cemconres.2003.11.023 HABIBALLAH, T., & CHAZALLON, C. (2005). 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Available online at http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282005%29131:12%281457%29.DOI:10.1061/(ASCE)1090-0241(2005)131:12(1457) TEKIE, P. B., & ELLINGWOOD, B. R. (2003). Seismic fragility assessment of concrete gravity dams. Earthquake engineering & structural dynamics, 32(14), 2221-2240. Available online at http://onlinelibrary.wiley.com/doi/10.1002/eqe.325/abstract. DOI: 10.1002/eqe.325 WERKMEISTER, S., DAWSON, A. R., & WELLNER, F. (2004). Pavement design model for unbound granular materials. Journal of Transportation Engineering, 130(5), 665-674. Available online at http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-947X%282004%29130:5%28665%29. DOI: 10.1061/(ASCE) Read More