110507- Project Plan Report

Contents

Department of Civil Engineering Research Project Organisation & Design

ContentsAbstract1. Project objectives2. Background and justification3. Literature review3.1. Introduction3.1.1. Lime stabilisation3.1.2. The effect of lime stabilisation3.1.3. The suitable soil type3.2. The behaviour of lime stabilized clay 3.2.1. The strength behaviour3.2.2. The compressibility behaviour 3.3. Construction procedure4. Experimental program4.1. Material selection4.2. Sample preparation4.2.1. Determination of soil physical properties4.2.2. Initial Lime Consumption Test4.2.3. Soil-lime mixture4.3. Test description4.3.1. Unconfined Compressive Strength Test4.3.2. One Dimensional Consolidation Test 4.3.3. Consolidated Undrained Triaxial Compression Test5. Project expected outcomes6. Work done to date7. Work scheduleAcknowledgementReferences listAbstractThe addition of lime into the fine grain cohesive soil in order to modify its physical and engineering properties has been an extremely potential technique when the construction takes place in a soft clay area. The treatment of soil with lime has been applied for varying project types, for instance, the construction of pavement base layers, the slope protection of earth dam and a provision of a strong layer for shallow foundation. Therefore this project aims to study the utilisation of lime for improving soft clay in some criteria with respect to evaluation of the effect of lime on the plasticity and strength of soft clay, and determination of optimum lime content required for stabilising clay. A range of test types will be carried out in order to quantify the criteria above. They are unconfined compressive strength test, one dimensional consolidation test and consolidated undrained triaxial compression test. Before preparing specimens for these tests, initial consumption lime test was carried out to determine the initial required lime content by 2%.This report presents the background and justification, project objectives and a detail experimental program followed by work plan for the whole project work during summer semester.

1. Project objectivesThe main objectives of this project are to determine the suitability of soil for lime stabilisation and investigate the effectiveness of lime stabilization on plasticity, compressibility and strength of soft clay.In order to achieve these objectives, a range of soil-lime mixture specimens will be tested using: Unconfined Compressive Strength Test (UCS) One Dimensional Consolidation Test (1-D) Consolidated Undrained Triaxial Compression Test (CU)2. Background and justificationChemical stabilisation of soil technique has been employed successfully for more than four decades to strengthen the bearing capacity, reduce the settlement and increase the stability of soft soils ( Broms and Boman, 1976). With the addition of lime, the interaction between lime and clay minerals (silica and aluminia) develops cementation bonds which impart a structure onto the treated soil and provide strength increase( Lo et al, 2003). Several methodologies were used in the last five decades in order to study the behaviour of lime stabilisation and determine the appropriate lime content for modification of soil characteristic and obtaining the target strength to use (Hilt and Davidson 1960). Of such methodologies, unconfined compressive strength test is predominantly employed and reported by many authors. A reason for this is explained by Consoli et al (2009) that UCS test is simple and fast, while being reliable and cheap. Therefore, UCS test is employed mainly in this project to evaluate the effectiveness of lime on the strength of soft clay and determine the optimum lime content.In addition, compressibility is an important characteristic of soft clay that needs to be investigated. However, in the earlier studies conducted the compressibility of lime treated clay has a less attention. In this project, therefore, the effect of lime stabilisation on the compressibility of stabilised clay is also investigated by using one dimension test. 3. Literature review3.1. Introduction3.2. 3.3. 3.1.1. Lime stabilisationLime stabilisation is the addition of lime into fined grain cohesive soil (clay and silt) in order to modify its properties and strengthen its bearing capacity. The use of lime stabilised clay in construction has been over than 5000 years old. An illustration of this is The Pyramids of Shersi in Tibet which were built using the compacted mixture of clay and lime (Greaves, 1996). In the new age, lime stabilisation has an ultimate development since the soil mechanics laboratory techniques were applied widely into soil-lime mixtures in 1950s. Up to date, lime stabilisation is the prior choice for improving soft clay soil or remediating the unsuitable site.Lime stabilisation provides structural improvement to many soils and aggregates. The wide application of lime stabilisation is to provide a strong capping layer supporting road pavement thickness reduce as well as improve the workability of soils by reducing the moisture content . It has also been used for slope protection of earth dam, provision of a strong layer for shallow foundation and clean up the contaminated soil. This soil improvement technique is a simple and economical solution for fined grain cohesive soil.

3.1.2. The effects of lime stabilisation Lime products: Lime stabilisation process can be achieved with calcium oxide (quick lime or burnt lime) or calcium hydroxide (slaked or hydrated lime). Quick lime has higher available lime content (the amount of calcium oxide) than that of hydrated lime. It means that using the quick lime is more economical than hydrated lime in comparison of available lime content. However, there are greater risk of skin and eyes burnt as using quick lime. Moreover, storing quick lime is a concerned issue due to its erosion capacity. Lime stabilisation effects: The result of lime stabilisation is dependent on the reaction between lime and clay minerals (Greaves, 1996 and McDowell, 1966). The principle effects of this reaction: Bearing capacity improvement due to the increase of shear strength Increase plasticity limit leading to the improvement in workability and compaction characteristics. Improve stability against swell and shrinkage Process of lime stabilisationWhen lime is mixed with soft clay soil, the physical characteristic is modified immediately due to the cation exchange (short term effect). Then further chemical reaction between clay mineral (aluminia and silica) and lime (water and calcium oxide) to create the cementicious products which bind the soil particles together (long term effect). This process is called stabilisation. Short term effect: Rapid physio-chemical reactions between lime and clay minerals changes soil properties immediately, particular soil plasticity and workability. Some effects of this term are listed below: Increase of optimum moisture content Increase of plasticity limit while plasticity of soil reduced Bearing capacity increase.

Figure 1: The effect of lime on soil plasticity change (Greaves, 1996)

Long term reaction stabilisation: Soil stabilization occurs when sufficient lime added to a reactive soil results in an alkaline environment with the pH value in excess of 12 so that the long-term strength gain through a pozzolanic reaction. This reaction makes the clay soils chemically changed into a natural cement structure and produces stable calcium silicate hydrates and calcium aluminates hydrates as the calcium from the lime reacts with the aluminates and silicates solubilized from the clay that called cementitious material (Figure 2) (James et al, 2007). The full-term pozzolanic reaction can continue for a very long period of time, even decades - as long as enough lime is present and the pH remains high (Greaves, 1996).CaO + Al2O3 + SiO2->Calcium silicate hydrate+calcium aluminates hydrates+ heat

Figure 2: Cementation material form (James et al, 2007)

Some effects of this phase: Increase the strength of lime stabilised clay Improve stability against swell and shrinkage3.1.3. The suitability of soilThe reaction between lime and soil is the interaction between lime and clay minerals (silica and alumina). Therefore the reaction between lime and clay is dependent on the reactive of clay content. Perry et al (1995) pointed out that soil plasticity limit lower than 10% should assure the ability of soil for lime stabilisation to happen. Therefore, a range of soil tests for suitability and acceptability of material for stabilisation should be carried out before treatment.Smith (1996) proposed some specification requirements to check the ultimate suitability of untreated soil such as 100% passing 75mm seize, high plasticity index, no more than 2% organic matter and no more than 1% total sulphate content.In addition, Initial Consumption of Lime (ICL) test must be carried out prior treatment in order to determine the minimum of lime that is required to be added to a material to allow the reaction with the clay to occur completely (BS 1924-2).3.2. The behaviour of lime stabilized clay3.2.1. The strength behaviourA wide range of investigation of strength behaviour has been studied on soft soil lime stabilisation in previous years by several authors. It is that the stabilised clay strength is affected by many factors such as lime content, curing period, moisture, porosity, compaction process and clay content. Of these factors, lime content and curing period has a significant effect. Consoli (2009) stated that unconfined compressive strength of stabilised soil increases approximately linearly with an increase in the lime content (Figure 3).

Figure 3: Variation of unconfined compression strength with lime content (28 days of curing) (Consoli,2009)On the other hand, from the result of series of unconfined compressive strength tests of four soft clay soil types at different lime content that Davidson and Pietsh did in 1962 (figure 4), it showed that the longer curing period is, the higher strength the soil gains. Moreover, the change of strength at varying lime content is fluctuated. As the initial amounts of lime, the strength increases slightly, stays the same or decrease slightly. Then it increase sharply until a breaking point is achieved with the addition of more lime. After this breaking point, the strength decreases , increases slightly or remains the same. The lime content at this point is called optimum lime content.

Figure 4: Unconfined Compressive Strengths at varying lime contents and curing periods (Davidson and Pietsch, 1962)3.2.2. The compressibility behaviourWith the change in structure, the compressibility of the stabilised clay is improved considerably. From the result of triaxial consolidation test of the soft clay soil treated by 5% lime content, Oh et al (2008) represented the relationship between voids ratio and log mean stress in the figure 5. It can be seen that the lime treated samples undergo very little change when the mean stress increases from 10 KN/m2 to 100 kN/m2. This change is completely different from the compressibility characteristic of soft clay since its voids ratio usually change dramatically at the initial loadings applied. Looking at the shape of the curve (e-logp), it is extremely similar to the cure of heavily over-consolidated clay. Therefore, lime stabilisation not only plays an important role in soft soil strength improvement, it also contribute significantly to improve the stability of soft soil by reducing the swell and shrinkage property.

Figure 5: (e-logp) relationship during anisotropic consolidation tests (5% lime content, 1 month curing) ( Oh et al., 2008)

3.3. Construction procedure of lime stabilized clay3.3.1. Construction procedure overviewThe lime treatment in soil is executed by the following basic procedure

Spreading limeScarifying or partially pulverizing soilAdding water and mixingMaturing periodRemixing and Compacting to maximum practical densityCuring prior to placing the next layer or wearing course

There are two principle methods for lime treatment in soils, in-place mixing and off-site mixing. The criteria for choosing the method are the soil type, site characteristic and availability of equipment. In-place mixingThis method involves in-situ mixing of lime, water and soil using a special mixing device followed by trimming and compaction. It can be applied for soil types from granular to heavy clays and carried out faster than off-site mixing in the same treatment area (NLA, 2004). Therefore, it is more widely used in the world.Off-site mixingThis method involves in using the equipment similar to the concrete mixing plant in order to mix lime, soil and water before the stabilized material is transported to site, laid and compacted. If this method is applied, the first steps in the above procedure can be ignored. This method is more suitable for the small area and the clayey granular materials treatment (NLA, 2004).3.3.2. Detail of construction steps for using hydrated lime in stabilisationLime stabilisation application is various from infrastructure construction to residential buildings. However it is applied mainly in infrastructure construction, particularly in sub base (subgrade) of road construction. Therefore the detail of construction steps mentioned here is for sub base improvement.1. Scarification and Initial PulverizationThe sub base is scarified to the specified depth and width before adding lime (Figure 6). During this stage, non-soil material larger than 3 inches such as stumps, roots, turf and aggregates should be removed (NLA, 2004). Scarification and pulverization stage is to provide more soil surface contact area for lime interaction. In order to avoid the case that lime runs off to the sides, a small soil windrow can be constructed along each side.

Figure 6: Scarification before lime application (NLA, 2004)2. Lime spreading Dry hydrated limeFor the project where the dust can be acceptable, the use of dry lime is preferable. Lime should be uniformly spread at a determined quantity via the suitable equipment. The common device for transporting and spreading lime is the self-unloading bulk tanker due to its operation without rehandling (Figure 7). The spreader is designed to spread lime in a constant rate and it checked by spreading over a tray every 500m2 which is weighted and adjusted to the correct rate (Smith, 1996). Dry lime should not be spread under wind condition due to the excessive dusting. In this case the better method is slurry lime application.

Figure 7: Dry hydrated lime with trunk spreader (NLA, 2004) Slurry methodThe slurry can be spread by a distributor truck (Figure 8). In order to prevent run off and non uniform lime distribution, after spreading lime should be mixed with soil immediately. Distributor trucks with recirculating pump are recommended to keep slurry in suspension.

Figure 8: Lime slurry distributor (NLA, 2004)3. Mixing and wateringOnce lime has been spread, mixing operation should be carried out by a powerful rotovator (Figure 9) in order to distribute lime uniform to required width and height of soil. The typical width of the rotor is 2450mm and the mixing depth up to 500mm can be achievable but the thickness of mixing should be limited to between 250mm and 350mm for the effective compaction operation (Smith, 1996). Water should be added during the initial mixing process through the hood of rotovator ( Fig. 9). Once initial mixing and water addition is complete, the mixture can be slightly compacted to increase the lime-soil contact area, minimise the evaporation loss and lime carbonation as well as reduce possible damage from rain.

Figure 9: Rotovator and water trunk supplier to the hood of rotovator4. Maturing periodLime-soil mixture should be matured sufficiently to allow the chemical reaction between lime and soil to modify the soil characteristic. The maturing period is dependent on soil type and typically between 24 and 72 hours (Smith, 1996).5. Remixing and compactingPrior to the compaction stage, remixing and final water adjustment are carried out by a rotovator in order to achieve the required pulverisation and moisture content. After finishing the mixing stage, compaction should be carried out immediately in compliance with the specification to obtain the required density. For the thicker layers, the tamping sheeps foot, roller followed by a smooth wheeled roller should be employed (Figure 10)

Figure 10: Compaction by using a tamping sheeps foot roller (Balang, 2007)6. Curing and protectionCuring and protection is an important stage to enable the lime stabilisation to achieve its ultimate strength and durability. As with other cementious material, an appropriate period of curing is required for the compacted soil lime mixture getting hardened until the dump truck can operate without rutting the surface prior to placing the subsequent layer. According to NLA (2004), there are two principle ways to cure the soil lime mixture, moist curing by light sprinkling and rolling if necessary, and membrane curing by adopting a bitumen seal coat. 3.3.3. Advantage and disadvantage between using dry and slurry lime Choosing dry or slurry lime for soil stabilisation is an important issue for engineer. While dry lime can be applied more rapidly than slurry, its dust trouble is as significant issue when the construction takes place in a residential area. Moreover, slurry lime method combining sprinkling and spreading leads to less additional water required. However the equipment using for this method is quite expensive and it is not applicable for the very wet soil. In conclusion, it is advised to consider carefully the project condition such as site environment, soil type and weather condition prior to making a choice of what method for application.4. Experimental program4.1. Material selection4.1.1. Soil and lime use Soil useBased on the soil investigation report from the study area in Vietnam, the soil samples can be classified as high and very high plasticity clay according to British Soil Classification System. The consolidation test shows that these soils are extremely compressible. Therefore they are not able to provide a stable foundation for the construction without treatment. However, it is impossible to use soil collected from Vietnam (S2) for sample preparation to test in this project. Therefore, the similar soil samples (S1) collected from the Engineering & Science Learning Centre in University of Nottingham can be considered to employ for this project.According to plasticity chart ( Fig.11) and the value of liquid limit and plastic limit of soil collected from Nottingham University (S1) and Vietnam (S2) shown in table 1, soils in group S1 are laid in the boundary between high clay and intermediate clay type while soils in group S2 are classified as high clay. Therefore, two soil groups have quite similar characteristic. However, the shear strength of soil S2 is weaker than S1. This is due to their much difference in natural moisture. While the soil S1 has moisture of around 23% much under its liquid limit, soil S2 at approximately 71% over liquid limit. Therefore this difference can be dealt with by adding water to soil S1 to cause it weaker and into the same properties with the soil S1. With this analysis, the soil collected from Nottingham University can employed for this project.

Table 1 : Soil comparisonSoil groupBore Moisture Liquid limitPlastic LimitPL(%)Plasticity IndexSoil descriptionSoil Classified Shear strength

HoleW(%)LL(%)PI(%)(BSCS)(kPa)

S1BH121522131Brown clayCHN/A

BH225481929Brown clayCI29

BH375101-N/ABlack clayN/A6

S2BH370.5693138Black clayCH11.6

BH170.97703139Black clayCH6.9

Figure 11: Plasticity Chart (BS 5930:1981) Lime use Hydrated lime is chosen to stabilise clay.4.2. Sample preparation4.2.1. Determination of soil physical properties It is applicable to use the soil investigation report for soil collected from Nottingham Unviersity for determination the physical properties of soil sample. However in order to evaluate the effect of lime on the plasticity of soft clay, Atterberg limits test need to be carried to determine the liquid limit and plastic limit before and after treatment. 4.2.2. Initial Lime Consumption Test (ICL) DescriptionInitial Lime Consumption Test developed by Eades and Grim is used for the determination of minimum lime content that is needed to add to a material so as to cause a significant change in its properties.It is required to maintain an environment with pH of 12.4 (the pH value when saturated lime in distilled water) in order to enable the pozzolanic reaction between lime and any clay mineral. Therefore 7 soil specimens are mixed with different lime content (0%, 1%, 2%, 3%,4%,5%,6%) and water to determine the minimum amount of lime required to give a pH of 12.4. Testing and ResultsThe test is carried out in compliance with British Standard BS1924 part 2. The apparatus prepared for this test is shown in the figure 12 and the results are shown in the table 2.Based on the data collected from the test, a plot of lime content (% of oven dry weight) against the pH value corrected at 25oC is represented. From the graph, it can be seen that the lime content interpolated at the pH value of 12.4 is around 2%. With the addition of lime , the pH value is stayed the same . Therefore, the initial required lime content for lime stabilisation can be chosen by 2%.

Figure 12: Apparatus for ICL test: Distill water, lime, plastic bottles, pH meter, thermometer, clock, seize 425 mm, device to break down soilTable 2: Determination of the initial consumption of lime (BS 1924-2:1990 clause 5.4)

LaboratoryL2/132MaterialSoil sample received at Laboratory

OperatorHung NguyenSiteESLC, University of Nottingham

JobMSc StudentDate21/04/2011

Type of lime usedHydrated lime

pH of lime-water mixture12.72

Temperature (oC)21

pH corrected to 25 oC12.6

Lime content (%)0%1%2%3%4%5%6%

pH of soil lime water mixture7.5311.9412.5712.712.7112.7112.71

Temperature (oC)20202020202020

pH corrected to 25 oC7.3811.7912.4212.5512.5612.5612.56

The graph of Lime content(%) against pH(25oC)

4.2.3. Soil-lime mixture procedure (BS 1924-2) Mixture made procedureFirstly, spreading out the test portion into a suitable metal tray and place it in the oven and dry at 105oC until the material is readily broken. Then the dry soil is broken down by hand roller or the gentle use of a normal pestle. Next, the initial amount of water is added to the soil and they are mixed thoroughly to bring them to a uniform consistency. Subsequently, a required mass of lime is added and mixed to a uniform condition by hand for 2 minutes. The remainder water is then added and mixed for further 8 minutes. After mixing allow the material to stand for 24 to 48 hours before proceeding further step.

Moulding and Curing The mixed material is sieved on the 5mm test sieve and only the fraction passing the sieve for preparation of specimens. Next, the material is placed in the mould for compaction and can be kept until it gets harden. Then, the specimen is removed from the mould and coat with wax to keep its moisture content. In this project, the specimens will be cured for 28 days before testing.

4.3. Tests description4.3.1. Unconfined Compressive Strength Test (BS 1377-7:1990, load frame method) PrinciplesThis test is applicable to fine grained soil or cemented soil which can keep their form without confining pressure. This test is used for rapid determination of undrained shear strength of the soil and normally carried out on 38mm diameter specimen of a length equal to about twice the diameter.An axial load is applied to the specimen in a predetermined rate (