Ground Improvement-Applications and Quality Control

Transcription

1 Indian Geotechnical Conference 2010, GEOtrendz December 16 18, 2010 IGS Mumbai Chapter & IIT Bombay Ground Improvement-Applications and Quality Control Raju,V. R. Managing Director Keller Far East, Singapore ABSTRACT This paper presents an overview of various ground improvement techniques available and discusses factors influencing the choice of technique. It then briefly describes relevant quality control procedures for common techniques. This is followed by some applications of these techniques to different types of structure as well as different soil conditions. Structures and facilities that have utilized ground improvement include roads and highways, railways, ports and airports, land reclamations, storage tanks, chemical plants, tunnels and residential buildings. The basis for choosing the particular technique for the project is explored, be it time, cost, technical performance or environmental considerations. In addition, the quality control procedures adopted for various techniques are explored. The paper will show that ground improvement is often the ideal foundation solution for such structures. 1. INTRODUCTION Infrastructure projects such as highways, railways, airports and harbours, cover large areas of land, sometimes over tens of kilometers. This often leads to highly variable soil conditions for the same project. Almost invariably, projects such as railways or highways encounter problematic soils. In addition, a large portion of infrastructure and building work is in coastal regions, where soils typically have low strengths and are highly compressible. Construction in increasingly urban environments means that sites with poor soil conditions and even landfills are being utilized for various structures and facilities. This construction activity on poor soils often leads to the necessity for ground improvement prior to start of construction. The type of ground improvement required depends very much on the type of structure to be built (and its sensitivity to ground movement), the type of soil being treated (and its short and long term behaviour) and the types of tools and materials available. However, it is not sufficient to merely select the appropriate ground improvement method. One must also ensure that the work is done to an acceptable standard of quality. This paper presents an overview of the more common ground improvement methods in use and quality control procedures that need to be adopted. Specific projects are described to illustrate the various techniques and quality control procedures. 2. TYPES OF GROUND IMPROVEMENT Ground Improvement refers to any technique or process that improves the engineering properties of the treated soil mass. Usually, the properties modified are shear strength, stiffness and permeability. Ground improvement is usually done based on the following principles: Consolidation (e.g. prefabricated vertical drains & surcharge, vacuum consolidation, stone columns) Chemical Modification (e.g. deep soil mixing, jet grouting, injection grouting) Densification (e. g. vibro compaction, dynamic compaction, compaction grouting) Reinforcement (e.g. stone columns, geosynthetic reinforcement) Some techniques improve the ground by a combination of mechanisms. For example, compaction grouting not only densifies the in-situ soils, but also forms high-strength, high stiffness grout bulbs that reinforce the ground. Stone columns installed in silty sands reinforce the ground, densify the in-situ soils and function as large drainage elements. Consolidation Methods In consolidation methods, the essential elements are (a) the introduction of very permeable elements to shorten drainage paths and (b) a means of increasing the stress that the soil matrix experiences. In the PVD + Surcharge method, the drainage elements are thin plastic drains, about 100 mm x 5 mm in cross section. These prefabricated vertical drains are installed at fairly close spacings- from about 1 m to 2 m apart, on a triangular or square grid. A soil pre-load is placed to increase the total stress on the soil, leading to a temporary

2 122 V. R. Raju increase in excess pore pressures. As the excess pore pressures dissipate, consolidation occurs. The principle is that by preloading the soil, much or all of the settlement that would occur under the final structural load can be forced to occur prior to construction. Therefore, little or no settlements will occur during the service life of the structure. Often, a load higher than the final structural load is placed as a pre-load, to reduce the consolidation time. With the PVDs installed, the total compression of the ground under the pre-load is not altered, but the consolidation process is accelerated. In vacuum consolidation, the load is applied by suction, rather than by a physical pre-load. This has the advantage of maintaining better internal stability of the soil mass (no sudden increase in excess pore pressures). Although pressures measured at the pumps can be -80 to -90 kpa, losses in the system and differences in the groundwater level and pump inlet, means that the practical negative pressure that can be maintained in the soil is usually between -50 to - 70 kpa. For this reason, vacuum pressure is often combined with a physical preload. Stone columns, typically 1.0m in diameter, function as large drainage elements. However as the columns act primarily to reinforce (i.e. strengthen and stiffen) the ground, a pre-load higher than the final load is seldom necessary. Chemical Modification Chemical modification relies on the introduction of a chemical binder to alter the physical properties of the soil mass. Typical chemical binders include lime, cement and fly ash. Often, the objective is to improve the strength and stiffness of the soil. In some cases, the objective is to reduce permeability. Ground improvement by chemical modification is usually classified according to the means by which the binder is introduced into the soil matrix. Broadly, these categories are: Grouting- The voids in the soil matrix are filled with a chemical such as sodium silicate or Portland cement. The voids can simply be the pore spaces between sand grains, or fissures within a limestone formation. Often, the objective of grouting is to reduce the overall permeability of the soil/ rock mass. Fracture Grouting- In this group of techniques, the binder is injected under pressure resulting in controlled fracturing of the soil rather than permeation of the soil matrix. This technique is used mainly to lift structures (on the surface or even buried) or to compensate for settlement or volume losses. Hence it is also referred to as Compensation Grouting. There is some overall strength gain and reduction in permeability, but this is not usually the primary purpose. In-situ Soil Mixing- The soil grains are mixed with a binder, such as cement or lime using a mechanical tool. The binder can be introduced as a slurry or dry powder. The binder cures over time and the strength and stiffness increases. When applied to sands, permeability is reduced. Jet Grouting- The soil grains are eroded by a high pressure fluid jet, and mixed with a fluid binder (typically cement grout). Typically columns are formed, with significantly increased strength and stiffness. In the case of sands, the permeability is significantly reduced. Because of the jet s ability to form a good connection with the neighbouring column, jet grouting is often used to form base slabs for groundwater control. Densification While we apply the term consolidation to fine grained soils such as clays, densification methods are used to reduce the pore spaces between the particles of coarse grained soils such as sands or gravels. To some extent, silts can also be densified. The primary means of densifying sands and gravels is to use a shear wave of energy to induce rearrangement of the soil grains. The energy can be applied at the ground surface (e.g. dynamic compaction, rapid impact compaction) or at depth (e.g. blast densification, vibro compaction, Mueller resonance compaction). Intermediate soils such as silts do not respond as well to wave energy. Densification of soils such as silty sands usually involve the displacement and hence compaction of soil mass. For example, stone columns installed by a depth vibrator displace the silty sands laterally. Together with the intense vibrations produced by the tool, the soil surrounding the column is densified. Compaction grouting involves the introduction of a very stiff grout bulb, injected slowly and at a carefully chosen pumping pressure. The slow, radial displacement of the soil results in increased density of the surrounding soil mass. Densification results in an increase of the internal angle of friction and stiffness. The improved soil has a higher bearing capacity, shows reduced settlements and improved resistance to liquefaction. Reinforcement Reinforcement methods introduce a material foreign to the in-situ soil matrix to help carry the loads. The reinforcement can be in the vertical direction (e.g. stone columns) or horizontal (e.g. geotextiles, geogrids). The relative stiffness between the reinforcing element and the in-situ soil will determine the extent to which the loads are shared. Stone columns act together with the in-situ soils and in the process share the load because of their ability to bulge (Greenwood, 1991). Very stiff elements relative to the in-situ soil tend to carry most of the loads and behave

3 Ground Improvement- Applications and Quality Control 123 in a more rigid or pile-like fashion (e.g. vibro concrete columns, deep soil mixing columns, rigid inclusions), (Sondermann & Wehr, 2004). An interesting type of reinforcing element is the mixed-modulus column (sometimes referred to as CMM). The lower portion of the column is a concrete rigid inclusion, while the uppermost section (usually 1.5 m to 2.5 m) is a conventional stone column. The stone column head eliminates the risk of punching failure of overlying floor slab, and allows it to be designed as a regular non-suspended slab. For a more detailed description and comparison of the various techniques, the reader is referred to Holtz et al (2001), Kirsch & Sondermann (2003) and Moseley & Kirsch (2004). Some of the more common ground improvement methods are described in Table CHOICE OF TECHNIQUE As can be seen from Section 3 above, several techniques are available for ground improvement and the choice of the appropriate one is important. The following section gives a few factors to consider. Suitability of the Method Some methods lend themselves naturally to certain soils. Vibro compaction of reclaimed sand fills is a good example. In reclamation fills, the sands are relatively clean, and therefore the method is very fast and economical, even to large depths. Some methods and soils do not go well together. Deep soil mixing of peaty soils is one such example. A large quantity of cement or other binder may be required to achieve the desired strength, if at all possible. Technical Compliance This is usually verified by design calculations to check for sufficient bearing capacity, factor of safety against slope failure or that the magnitude of settlements (total and differential) etc. are within limits. Some structures such as earth embankments and storage tanks are able to tolerate settlements in the order of decimetres during the construction stage. Therefore soft techniques relying on consolidation are often suitable. Other structures such as industrial plants require solutions which do not allow settlements more than a few centimetres. In such cases hard/rigid solutions such as DSM in clays, densification of sands or some form of preload (to preclude long term settlements) are required. Availability of QA/QC Methods The availability of methods to ensure that quality is ensured during and after construction is important. Pre and postimprovement testing by penetration methods (e.g. CPT), sampling etc. are essential. In addition, real-time monitoring during the improvement process using automated data loggers to inform the operator of what is happening below ground are very helpful to ensure quality. In addition, the data loggers can be used to provide a printout of the construction process, a so called birth certificate of the improvement point for daily review by the Engineer. (More details are given in the next section). Availability of Material Ground improvement uses a range of materials, some natural (e.g. stone) and some manufactured (e.g. cement, geotextiles). The availability of these materials will influence the choice of technique. Malaysia for example has several soft soil deposits in the coastal regions with nearby hilly terrain. The hilly terrain makes stone easily available and has led to extensive use of stone columns to treat the soft coastal soils. Time Methods which require long consolidation periods will obviously not be suitable for fast track projects. Installation/ construction time is also important. Nowadays however, modern high-production machinery allows a significant reduction in construction time. For example, the use of the twin configurations in Vibro or DSM equipment or the use of computerised cranes to drop the pounder in dynamic compaction have very significantly increased production rates. Cost Assuming that the solution satisfies technical requirements, cost often becomes the deciding factor. Methods which use less or cheaper added material are of course cheaper. However if the cost of time or the risk of non-performance are added, then other apparently expensive solutions become economical. Convenience Solutions which do not require other additional measures such as the placement of a large preload, or excavations (as in excavate and replace methods) are more convenient and practical. Protection of the Environment Methods which produce spoil are of course not desirable. In-situ treatment methods which do not remove the soil or discharge excess cement/binder are preferred. For example, stone columns installed by the dry method only displace the in-situ soil. In contrast, the wet method of column installation flushes out some of the soil. For this reason, the dry method is often preferable. Similarly in-situ soil mixing would be preferable to jet grouting where possible. Another criterion would be the influence of the method on sensitive structures nearby. 4. QUALITY CONTROL PROCEDURES Quality control procedures are important firstly to assure

4 124 V. R. Raju Technique Table 1: Some Features of Various Ground Improvement Techniques Soil Type Geotechnical Problems Basic Principle(s) Comments PVD + Surcharge Vacuum Consolidation Soft clays, silts Large long term consolidation settlements, Low bearing capacity Drainage/ Consolidation Typical grid spacing = 1m to 2m Typical grid spacing = 1m to 2m The surcharge load is applied by a combination of physical surcharge and negative pressure. Vibro Compaction (or Vibroflotation) Dynamic Compaction Loose sands, gravels settlement, Creep, Liquefaction Densification Energy input is at depth. Typical grid spacing = 2.5m to 5m Maximum depth = 65m Energy input is at the ground surface. Typical grid spacing = 4m to 6m Practical (& Economical) = 10m Vibro Stone Columns Sand Compaction Piles Loose sands, silts, clays settlement, Low bearing capacity, Liquefaction. Reinforcement, Drainage/ Consolidation, Densification Typical area replacement ratios = 15% 30% Maximum depth = 45m (Typical depth = 5m to 20m) Typical area replacement ratios = 40% 70% Mixed- Modulus Columns Loose sands, silts, clays settlement, Low bearing capacity Reinforcement Similar settlement characteristics to Rigid Inclusions, but with no punching effect at the floor slab. Have been installed to depths of 30m. Dynamic Replacement Silts, Clays settlement, Low bearing capacity. Reinforcement, Densification Typical column diameter = 2.5m Typical column spacing = 5m Typical depth = Approx. 5 6m Deep Soil Mixing Sands, silts, clays settlement, Low bearing capacity Chemical modification Typical column diameter = 0.8m 2.5m Maximum depth = 40m Some techniques (e.g. JACSMAN) combine mechanical mixing and jetting to form columns Jet Grouting Sands, silts, clays settlement, low bearing capacity, high permeability (in sands) Chemical modification Typical column diameter = 1.5m to 4m, depending on jetting system and soil. Typical depth = 10m to 30m Injection Grouting Sands, silts High permeability Chemical modification In soils, the binder is often injected via a tubea-manchette giving rise to the name TAM grouting. Binder choice is determined by soil type. Compaction Grouting Sands, silty sands settlement, Liquefaction potential Densification, reinforcement Typical spacing between points = 1 4m Grout bulb diameter = 0.5 1m Has also been used to lift structures.

5 Ground Improvement- Applications and Quality Control 125 the client that the product he receives is of a high standard, secondly to prevent costly re-work for the contractor and most importantly to ensure public safety. Generally, quality control is applied pre-construction, during construction and post-construction. Various standards can be used to aid in the fomulation of good contract specifications and quality control procedures. Some typical quality control procedures for common ground improvement techniques are described below. Vibro Stone Columns For Vibro Stone Columns, it is essential to ensure that columns are built to the right depth, to the right diameter and are properly compacted. Computerized monitoring of the penetration depth of the vibrator easily ensures that the design depth is reached. Sensors within the depth vibrator can readily measure the amperage drawn by the motor, giving an indication of the compaction effort of the depth vibrator. IS (Part 1): 2003 gives guidelines on the estimation of the column diameter based on fill consumption. In the case of dry bottom-feed stone columns (See Raju & Sondermann, 2005), even the location of each charge of stone along the depth of the column may be determined from the record of depth vs. amperage. Postconstruction, load tests are routinely performed as a quality control measure. As we will see from a later example, there are situations where load tests are not practical, and we have to rely on the other quality control methods. Another useful general standard for stone column construction and testing is EN 14731:2005. Vibro Compaction (Vibro-flotation) Once the suitability of the soil for Vibro Compaction is determined by detailed soil investigation, the actual compaction should be carefully monitored. Sometimes, a field trial is required to confirm the compaction parameters, particularly the grid-spacing to be used. With the compaction parameters fixed, it then falls on the site team to ensure that the sand is densified in a systematic, disciplined manner. Computerized recording of the time and date of compaction, point number, depth of compaction and amperage drawn by the depth vibrator greatly assists the crane operators and engineers in eliminating human errors. However, even with well-chosen compaction parameters and meticulous execution, re-compaction is sometimes necessary given the natural variability of the ground. Post-compaction electric cone penetration testing (CPT) is perhaps the most practical tool in determining if the target degree of compaction has been met. Should the CPT result be unsatisfactory, re-compaction of the particular zone can be performed. Using Standard Penetration Tests (SPT) as a quality control test for Vibro Compaction is undesireable as in a granular soil, borehole disturbance and operator errors tend to give erratic results. Also, compared to CPTs, drilling boreholes to perform SPTs are slow and laborious. Chemical/ Cement-Based Techniques For cement based techniques (grouting, deep soil mixing and jet grouting), quality control is focussed on the careful control of the materials that are used, as well as the mixing or pumping process. The grout mix is tested for its density (often using a hydrometer) and viscosity (often using a Marsh cone). In the case of silica gels for permeation grouting, setting times are crucial for the success of the grouting program, and are carefully tested also. The installation process is also carefully monitored. Key parameters such as flow-rate, pressure and total volume injected are carefully monitored, almost always automatically. In the case of deep soil mixing on jet grouting, parameters such as rotation speed and withdrawal rate are also important. Post-construction testing is of some value, especially in instances where re-injection is possible. For permeation grouting, post-construction testing can take the form of pumping tests. In the case of deep soil mixing or jet grouting, coring and UCS testing is often performed. However, for deep soil mixing or jet grouting, it is far more desirable to get it right the first time as re-work is very difficult and sometimes impossible. For further details on grouting works, the reader is referred to Raju & Yee (2006) and Semprich & Stadler (2003). EN 14679: 2005 gives guidance on the construction and quality control of deep soil mixing. Other Techniques Some common techniques such as prefabricated vertical drains (PVD) have standards that govern construction and testing (e.g. IS (Part 2): 2004; EN 15237: 2007). Other techniques like Dynamic Compaction or Rigid Inclusions rely on generally accepted industrial practises, which are then written into detailed contract specifications. Because ground improvement techniques work on different principles and are constructed in a variety of ways, the key features to be checked vary from technique to technique. Therefore it is vital that contract specifications for ground improvement be drafted specifically for the technique. For example, one cannot simply apply piling specifications to Vibro stone columns or DSM columns simply because they are vertical element within the ground. 5. APPLICATIONS Highways & Roads Roads on Hydraulic Sand Fill (Jurong Island, Singapore) Jurong Island is a petrochemical centre, housing petroleum storage tanks, petrochemical plants and other related

6 126 V. R. Raju facilities. It was formed by joining together 7 small islands by reclamation. Reclamation was done using sandfill. This means that certain facilities may be built on the original islands, while others are built on the in-filled channels between islands. The Banyan Region of Jurong Island however is fully reclaimed. It is home to a VLCC jetty, several large storage facilities including Universal Terminal and Helios Terminal, in addition to other chemical plants. To serve these facilities, a network of roads has been constructed by JTC Corporation. In general, the ground consists of 20 to 30 m of sandfill, sometimes followed by a thin layer of marine clay. Underlying the sandfill and marine clay (if any) are stiff Jurong Formation residual soils. Typically sandstone or mudstone is encountered at 30 to 40 m depth. In order to ensure minimal settlement in the reclaimed land, JTC Corporation has specified that if any significant layer of marine clay is present, it is to be treated with PVDs and surcharge. The sandfill is to be densified using Vibro compaction. The design traffic load is 30 kn/m 2. The sequence of improvement is typically as follows: Install PVDs into marine clay layer Complete Vibro compaction of sand layer Place soil surcharge and maintain it for required consolidation time Remove soil surcharge and continue with road construction. The specifications are as follows: For Clay Layers: No more than 100 mm future settlements and a minimum of 90 % consolidation For reclaimed sandfill: Depth (m) Cone Resistance (MPa)* Relative Density (%)* > *Whichever is lower Because the soft clay layers are not common in the Banyan Region, PVD s and surcharge have seldom been necessary. The design concept is shown in Fig. 1. In the Banyan Region, over 500,000 m 2 of road and drainage reserve have been improved in this way. Where PVDs have been unnecessary (absence of significant layer of marine clay), this scheme has proved to be very quick. For example, a single Vibro compaction rig is able to densify m 2 per day, for compaction depths of m. It is common for areas of 3,000 m 2 to be completed in 3-4 days and handed over within a 7-10 days of completion, including testing by CPT. Typically, 1 post-compaction CPT is performed every 1,500 m 2. In Fig. 2, sample pre-compaction CPT result is compared with the post-compaction test in the same area. Usually, Vibro compaction work proceeds for merely 2-4 weeks before the rest of the road works commence. Fig. 1: Ground Improvement Concept for Roads Fig. 2: Sample Pre and Post Compaction CPTs on Banyan Road, Jurong Island Railways Railway Embankment Built on Soft Silts and Clays (Double Tracking Project, Malaysia) The Malaysian government has been upgrading the railway network in the country. Certain sections of the existing network are to be expanded to a double track, for high speed electric trains. As the new line had more stringent restrictions on gradients, in general, embankment heights were raised. The railway line passes through areas that have seen extensive tin mining activity in the past. Soils encountered were highly variable, with a mixture of loose sands, very soft silts and very soft clays as deep as 24 m. Cone tip resistance (q c ) values in the very soft silts and clays were often between 150 and 250 kpa. The performance criteria laid down by the railway authorities are as follows:

7 Ground Improvement- Applications and Quality Control 127 Differential settlement of not more than 10 mm in 10m Total settlement of not more than 25 mm in the first 6 months of operation Factor of safety against slip failure of the embankment greater than 1.5 Various foundation and ground improvement methods were implemented for the track which travelled over a wide variety of ground conditions. Where the soil was stiff, no improvement was done except for surface preparation prior to embankment construction Where the soft soils were 2 m to 3 m thick, they were simply excavated out and replaced with fill and compacted Where deeper soft soils were encountered, Prefabricated Vertical Drains (PVD) + Surcharge were normally used. Vibro stone columns were specified under the following circumstances; (i) Where embankment heights (and therefore loadings) were anticipated to result in higher than acceptable settlements (ii) Where site constraints did not permit excavation & replacement (e.g. close proximity to existing live track or high water table) (iii) Where shorter construction time was required, and therefore a long pre-loading period with PVDs was not acceptable More details of the Vibro stone column works are given below. Where necessary, piles were driven and the railway embankment was constructed on a deck. For an 800 m stretch of embankment near the town of Serendeh, Dry Deep Soil Mixing was also employed. Columns were installed to a depth of 14 m. Geotextile reinforcement was placed over the relatively rigid DSM columns prior to embankment construction to better assist in the transfer of the embankment load to the column. Vibro stone columns were installed to depths of 8 m to 18 m to support embankments with heights from 2 m to 11 m. The design concept is shown in Fig. 3. Work was often carried out very close (2 m) to the existing track, with no disruption to train operations. In addition to the upgrading of the existing track, Vibro stone columns works were carried out to support embankments and reinforced-earth walls for Road-Over-Rail Bridges. The RE walls were up to 12 m high. For this project, over 1,000,000 m 2 of ground were improved using Vibro stone columns. The Ipoh Rawang section has been completed and presently, the Ipoh-Padang Besar and the Seremban to Gemas sections of the double-tracking project are ongoing, with extensive use of Vibro stone columns, PVDs and surcharge as well as Remove-and-Replace techniques. Stone columns Soft Clay Fig. 3: Vibro Stone Column Design Concept & Installation for Railway Embankments A typical single-column load-test result is shown in Fig. 4 below. Ports Fig. 4: Sample Single-column Load Test Access Roads and Hardstanding Pavements on Soft Clay (Pipavav, India) Pipavav Shipyard Limited (PSL) is currently developing an integrated shipbuilding facility in Pipavav. The area being developed is 85 hectares in total. The construction of the shipyard includes the construction of a block making facility for hull blocks, the installation of a ship lift facility and the conversion of an existing wet basin into a 651 m x 65 m dry dock. Geotechnical and foundation activities include Vibro stone column works, bored cast in-situ piles and diaphragm walls. The ground generally consists of murram fill followed by soft marine clay and then weathered rock.

8 128 V. R. Raju As part of the facility, a 2.5 km x 14 m approach road needed to be built between the block making facility and the hardstanding pavement (900 m x 25 m) next to the dry dock. At both these areas, Vibro stone columns were installed to an average depth of 12 m, on a 2.5 m triangular grid spacing. A total of 144, 000 linear meters of stone columns were installed. Fig. 5 shows installation in progress. Fig. 7: Load- Settlement Graph for Single Column Load Test Fig. 5: Installation of Vibro Stone Columns at Pipavav Shipyard Quality control procedures were adopted from precostruction to post-construction. During construction, computerised monitoring of installation parameters was performed. Parameters were displayed to the operator in his cabin. In addition, printouts were generated in the operators cabin in real-time, ensuring rapid review of the construction process for each column. A sample printout from the project is shown in Fig. 6 below. Vibro stone column work is also ongoing for the Offshore Yard area. A load-settlement curve from a singlecolumn load test is shown in Fig. 7 below. At the design load, the measured settlement was 5.38 mm, below the allowable settlement of 12 mm. Fig. 6: Sample Printout from Pipavav Vibro Stone Column Installation Storage Tanks & Industrial Plants Concrete LNG Tanks on Silty Sand (Hazira, India) In 2002, ground improvement works were carried out for Shell India, for 2 nos. LNG tanks in Hazira, India. The tanks were 84 m in diameter, with a filling level of 35 m. The soils consisted of 16 m of silty sand and fill, overlying alternating layers of dense sand and stiff clay. Fig. 8: Hazira LNG Tanks in Operation The ground improvement design required the maximum permissible settlement along a radial line from the periphery to the center of the tank to be limited to 1:300, based on BS 7777 (Part 3, 1993). In addition, the ground improvement was to be designed against a Safe Shutdown Earthquake (SSE) level of a = 0.25 g and an Operating Base Earthquake (OBE) level of a = 0.10 g. Vibro stone columns were chosen as an alternative to the conventional piling method because of significant savings offered in cost and time. A significant technical advantage of the ground improvement solution was its ability to resist lateral loads generated by earthquakes and also to mitigate liquefaction. The lateral resistance is mobilized by base friction between tank foundation and improved ground. (It is to be noted that concrete piles are rather inefficient in resisting lateral loads.) Because of liquefaction considerations, the zone of improvement was 105 m in diameter for each tank, versus a tank diameter of 84 m. Stone column installation works were completed in

9 Ground Improvement- Applications and Quality Control months using 2 Vibro Replacement rigs. Fig. 8 shows a picture of the tanks in operation. Sewage Treatment Plant on Marine Clay and Old Landfill The Jelutong Sewage Treatment Plant in Penang, Malaysia was built in 2008, to cater to a population of 1.2 million. The main structures in the plant are 12 sequential batch reactors of size 80 m x 60 m x 7 m tall. These are large concrete tanks on a raft, imposing a spread load on the ground. Other auxiliary structures are gas storage tanks, sludge holding tanks and compound walls. All these structures impose spread loads on the ground and lend themselves to foundation systems using ground improvement. Soils at this location are soft marine clays to a depth of 10m followed by stiff sandy slits and sandy clays to depths of about 50m followed by very dense to hard silty sands. In addition, the central portion of the plant was a former landfill with household waste to a depth ranging between 2 m and 5 m. Plant specifications required that the total settlements be less than 75mm and differential settlements be less than 1:360. A driven pile solution was considered, but this would have meant driving piles to about 50 m depth. Ground improvement to treat the upper rubbish fill and the soft clay to 10 m depth proved to be an exceptionally economical and quick solution. As part of the quality control program, detailed preconstruction soil investigation was performed. Quality control for the DSM columns, VCC and Vibro stone columns were by means of materials testing prior to construction, automatic monitoring and recording of construction parameters as well as post-construction load tests. Under operating load conditions, settlements measured over a period of 10 months ranged between 5mm and 20 mm for both Cement columns and VCC. A more comprehensive description of the ground improvement works carried out on this project and measured settlement data can be found in the Yee et al (2009). Olefins Plant on Hydraulic Sandfill (Jurong Island, Singapore) Process plants have frequently been founded on improved ground. The Singapore Olefins Plant in Jurong Island was constructed in Vibro Compaction was carried out for the foundation for the process plant (reactors, piping, etc.) where the underlying soils were reclaimed sands. Varying intensities of treatment were adopted to meet the different requirements in specifications. In general however, settlements of the steel structures under working loads had to be restricted to mm. Factors of safety against bearing capacity was to be higher than 2.0. Fig. 10 shows a picture of the Singapore Olefins Plant in operation. Fig. 9: Plan View of the Jelutong Sewage Treatment Plant Showing Various Structures and Treatment Schemes It was important to penetrate and displace the unpredictable and highly organic rubbish fill and also to not rely on any long term support from the rubbish (for obvious reasons of long term decay, etc.). This was achieved by using Vibro concrete columns (VCC) to about 10 m depth (see Fig. 9). The other sequential batch reactors, not affected by the rubbish fill, were founded on Cement columns (or Deep Soil Mixing columns). The sludge holding tanks were built on Vibro stone columns and the substation was built on cement mixed piles. The Vibro concrete columns and Cement columns offer rigid performance with settlements in the treated layers of less than 25 mm. The Vibro stone columns, although flexible, nonetheless provided foundations with expected settlements of less than 75 mm. Fig. 10: SOP1 in Operation As part of the ExxonMobil s Singapore Parallel Train project, Vibro Compaction was also carried out for the new Olefins plant, called SOP 2, adjacent to the existing plant. Vibro Compaction works were completed at the end of 2008 and construction of the plant is ongoing. Fig. 11 shows the compaction work in progress. Quality control was by means of detailed pre-compaction site investigation (using CPTs), automatic recording of compaction parameters and postcompaction CPTs. During the ground improvement works for SOP 2, a certain portion of the reclamation fill was found to contain a large amount of decomposed wood. (This was not detectable by CPTs.) This would pose an unpredictable and hence unacceptable long-term settlement risk. For this reason, that portion of the new plant utilized driven spun-piles as the foundation system for the heavy structures.

10 130 V. R. Raju Fig. 11: Vibro Compaction in Progress for SOP 2 (Nov 2008). The Operational SOP 1 can also be seen Other plants that have used ground improvement include the Shell Malampaya Onshore Gas Plant and the CAPCO- PTA project (See Raju & Sondermann, 2005). In the Middle East, the Jebel Ali Power Plant, Sharjah Power & Desalination Plant, Dubai Aluminum Plant and Al- Khobar Power & Desalination Plant have all been built using Vibro compaction, Vibro stone columns or a combination of the two. Underground Construction Ground Anchors for New Delhi Metro Project The Delhi Metro Rail Corporation project (DMRC) connects the Indira Gandhi International Airport and New Delhi Railway Station with an exclusive Airport Metro Express Line. As a part of this project, an underground metro station and multi-level car parking facility was planned near the New Delhi Railway station. The site in general consisted of silty clay, with the Quartzite bedrock varying from 5 m to 20 m deep. Fig. 12: Typical Ground Anchor The site had to be excavated to a maximum depth of 19 m to facilitate the construction activities for the station building and underground parking facility. The excavation was supported by a Soldier pile Anchor & Strut system. The soldier pile walls were embedded 0.5 m into the Quartzite bedrock. At most locations, two levels of anchors were designed, at 2.5 m and 8 m below ground level. To facilitate the removal of anchor strands after construction of the intended wall, U-Turn retrievable ground anchors were installed. For such anchors, the steel strands are covered with a PVC jacket, turned over a U-loop (U-turn saddle) at the bottom and connected to a reinforcement rod. Fig. 12 shows a typical Ground Anchor. A hydraulic rotary drill rig (Casagrande C6) was used for inclined drilling (30 deg to the horizontal, to a maximum length of 22 m) and simultaneous installation of the casing. The anchors consisted of 7-ply 12.7 mm diameter strands conforming to IS 14268: 2005, with an ultimate tensile strength of about 187 kn. Primary and secondary grouting were performed after washing the borehole. As a part of quality control procedures, operating parameters such as flow rate, grout pressure, total grout volume, etc. were recorded at site for each anchor. Fig. 13 shows a drilling in progress for the second level of anchors. The anchors were designed to withstand a working load of 60 T and were tested at 1.1 times the working load (66 T). Fig. 13: Drilling using a Casagrande C6 for the Second Level of Anchors 6. CONCLUSIONS Ground improvement has developed into a sophisticated tool to support foundations for a wide variety of structures. Properly applied, i.e. after giving due to consideration to the nature of the ground being improved and the type and sensitivity of the structures being built, ground improvement often reduces directs costs and saves time. In Asia, it has been extensively used for the construction of a wide range of infrastructure and building facilities. However, careful attention must be paid to quality control procedures. The focus should not only be on testing after construction (load testing, etc.), but also on careful supervision while the work is in progress. Full advantage should be taken of modern automatic monitoring and recording of key installation parameters. ACKNOWLEDGEMENTS The author would like to thank Jonathan Daramalinggam and G.T. Senthilnath for their contributions to this paper. REFERENCES BS : 1993, Flat-bottomed, vertical, cylindrical storage tanks for low temperature service, Part 3, British Standards Institution, London, England.

11 Ground Improvement- Applications and Quality Control 131 EN 14731: 2005, Execution of Special Geotechnical Work- Ground treatment by deep vibration, European Committee for Standardization, Brussels, Belgium EN 14679: 2005, Execution of Special Geotechnical Works- Deep mixing, European Committee for Standardization, Brussels, Belgium EN 15237: 2007, Execution of Special Geotechnical Work- Vertical drainage, European Committee for Standardization, Brussels, Belgium Greenwood, D.A., Load Tests on Stone Columns. Deep Foundation Improvements: Design Construction and Testing, ASTM STP 1089, Esrig, M.I. & Bachus, R.C. (eds.), Holtz, R.D., Shang, J.Q. & Bergado, D.T., Soil Improvement, Geotechnical and Geoenvironmental Engineering Handbook, Rowe, R.K (ed.), IS 14268: 1995, Specification for uncoated stress relieved low relaxation seven ply strand for prestressed concrete, Bureau of Indian Standards, New Delhi IS (Part 1): 2003, Design and Construction of Ground Improvement- Guidelines, Part 1 Stone Columns, Bureau of Indian Standards, New Delhi IS (Part 2): 2004, Design and Construction of Ground Improvement- Guidelines, Part 1 Preconsolidation using vertical drains, Bureau of Indian Standards, New Delhi Kirsch, K. & Sondermann, W., 2003, Ground Improvement, Geotechnical Engineering Handbook, Volume 2: Procedures, Smoltczyk, U. (ed.), Moseley, M. P. & Kirsch. K. (eds.), 2004, Ground Improvement, 2nd Edition. Raju, V.R. & Sondermann, W., Ground Improvement using Deep Vibro Techniques. Ground Improvement Case Histories, Indraratna, B & Chu., J. (eds.), Raju, V.R. & Yee, Y.W., 2006, Grouting in Limestone for SMART Tunnel Project in Kuala Lumpur, Malaysia, International Conference and Exhibition on Tunneling and Trenchless Technology, March 2006, Kuala Lumpur, Malaysia Semprich, S., Stadler, G. 2003, Grouting in Geotechnical Engineering, Geotechnical Engineering Handbook, Volume 2: Procedures, Smoltczyk, U. (ed.), Sondermann, W & Wehr, W., Deep Vibro Techniques. Ground Improvement, 2nd Edition, Moseley, M.P. & Kirsch, K. (eds.), Yee, Y.W., Chua, C.G., Yandamuri, H.K., 2009, Foundation works for a Sewerage Treatment Plant using Ground Improvement Methods in Malaysia, Ground Improvement Technologies and Case Histories, C.F., Chu, J., Shen, R.F. (eds),