A COMPARISON BETWEEN STATIC LOAD TEST AND HIGH STRAIN DYNAMIC TEST ON BORED PILES

Transcription

1 A COMPARISON BETWEEN STATIC LOAD TEST AND HIGH STRAIN DYNAMIC TEST ON BORED PILES MICHAEL ANGELO A/L AROKIASAMY UNIVERSITI TEKNOLOGI MALAYSIA

2 PSZ 19:16 (Pind.1/97) UNIVERSITI TEKNOLOGI MALAYSIA BORANG PENGESAHAN STATUS TESIS JUDUL: A COMPARISON BETWEEN STATIC LOAD TEST AND HIGH STRAIN DYNAMIC TEST ON BORED PILES SESI PENGAJIAN: 2005/06 Saya MICHAEL ANGELO A/L AROKIASAMY (HURUF BESAR) Mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:- 1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( ) SULIT TERHAD (Mengandungi maklumat berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan dimana penyelidikan dijalankan TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: No 35, E2/5A Lorong Ria, Dr. Nurly Gofar Taman Timur, Teluk Intan, Perak. Tarikh : 19 May 2006 Tarikh : 19 May 2006 CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa /organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.

3 A COMPARISON BETWEEN STATIC LOAD TEST AND HIGH STRAIN DYNAMIC TEST ON BORED PILES MICHAEL ANGELO A/L AROKIASAMY A thesis submitted in fulfillment of the Requirements for the award of the degree of Master of Engineering (Civil Geotechnic) Faculty of Civil Engineering University Technology Malaysia MAY 2006

4 ii I declare that this project report is the result of my own research except as cited in references. This report has not been accepted for any degree and is not concurrently submitted in candidature of any degree. Signature : Name of Candidate: MICHAEL ANGELO S/O AROKIASAMY Date : 19 May 2006

5 iii I hereby declare that I have read this report and in my opinion this report is sufficient in terms of scope and quality for the award of Master of Engineering (Civil-Geotechnics). Signature :. Name of Supervisor : Dr. Nurly Gofar Date : 19 May, 2006

6 iv DEDICATION For my dearest mother and dad (Mariamah & Arokiasamy) My success is your gift and prayers To my beloved brother, sister and relations Everyone and friends whom are the best Success of mine is success of all of yours

7 v ACKNOWLEDGEMENT I would like to thank God for giving me enough knowledge and time to conclude this program. All the help rendered by the lecturers and friend are appreciated. They have contributed towards the completion of this study. The time spent in doing this program gives memories that would last for ages. I would like to also express and record my gratitude towards my lecturer cum supervisor Dr. Nurly Gofar, for the time she allocated and all her guidance in preparation of this thesis.

8 vi ABSTRACT Piles are both statically and dynamically tested to obtain the capacity and to verify design. Both the test will provide results that may vary base on the method applied in conducting the test. It is therefore, necessary to compare the results of a static load test with dynamic load test. Many comparison studies are conducted worldwide, but most of it is for displacement pile. Therefore, the results of the test are compared for replacement piles. The piles are tested statically prior to dynamic test. The test results shows that a good agreement have achieved between both the test with plus minus 2mm at working load in terms of settlement. Comparatively the settlement predicted in dynamic load test is smaller compared to static load test. In terms of total capacity, the Davisson s method gives the lowest value compared to other methods. The Davisson s method is used to compare the results because it is more conservative. The comparison shows that the piles are within 20% relative to the capacity obtained through Davisson s method. Since the static test was conducted prior to dynamic test, the capacity obtained from dynamic test is higher due to the pile undergone elastic compression during static load test and also due to soil setup. The shaft distribution show that large shaft distribution obtained on long piles. They are comparable with the dynamic test taking into account the time factor.

9 vii ABSTRAK Cerucuk biasanya diuji secara static dan dinamik untuk menentukan beban tanggungan dan juga untuk mengesahkan rekabentuk. Kedua-dua ujian akan menghasilkan keputusan yang berlainan berdasarkan kaedah yang digunakan untuk melaksanakan ujian. Oleh demikian, ia adalah penting untuk memperoleh suatu hubungan diantara ujian static dan ujian dinamik beban cerucuk. Banyak kajian yang dijalankan di merata dunia, tetapi kajian-kajian ini tertumpu pada driven pile. Oleh yang demikian, kajian ini adalah tertumpu terhadap bored pile. Cerucuk-cerucuk ini diuji secara static terdahulu sebelum menjalankan ujian dinamik. Keputusan adalah memuaskan bagi bebanan kerja dengan ±2mm. Secara ringkas boleh dikatakan bahawa keputusan yang diperolehi pada bebanan ujian adalah lebih rendah bagi ujian dinamik berbanding ujian statik. Dari sudut bebanan muktamad pula, kaedah Davisson memberi nilai yang paling minima berbanding kaedah-kaedah yang lain. Nilai ini adalah pada had yang rendah, oleh itu ia digunakan bagi tujuan kajian. Keputusan menggunakan kaedah ini memberikan keputusan bahawa nilai ujian dinamik adalah dalam 20% nilai yang diperoleh. Ini adalah kerana ujian static dijalankan dahulu sebelum ujian dinamik dan ini mengakibatan cerucuk mengalami terikan mampatan dan jugan masa perantaran mengakibatkan tanah pulih semula keadaan asalnya. Dari segi bebanan sisi cerucuk, didapati bebanan sisi menguasai nisbah yang lebih banyak bagi cerucuk panjang. Keputusannya dapat dipersamakan dengan ujian dinamik jika masa perantaraan diambil kira.

10 viii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF APPENDICES ii iv v vi vii viii xi xii xiv xvi 1 INTRODUCTION Background 1

11 ix 1.2 Problem Statement 1.3 Objectives 1.4 Scope LITERATURE REVIEW Bored Pile Types of Bored Pile Construction Procedures Dry Method Casing Method Wet Method Techniques and Equipment Boring by Mechanical Auger Boring by Percussion or Grab-type Rig Boring by Continuous Flight Auger Drilling Under-reammed Bored Piles 2.2 Load Test Static Load Test (Maintain Load Test) Test Equipment and Instruments Test Procedures High Strain Dynamic Test Correlation Studies METHODOLOGY Introduction 3.2 Data Collection 3.3 Data Analysis and Results 3.4 Summary DATA ANALYSIS AND DISCUSSION Data Description 35

12 x 4.2 Analysis of field data 4.3 Analysis of Static Load Test Data 4.4 Analysis of PDA test data 4.5 Comparison between Static Load Test and Pile Driving Analyzer CONCLUSION AND RECOMMENDATION FOR FUTURE STUDY Conclusion Recommendations for Future Study 54 REFERENCES 55 Appendices A-E 58 97

13 xi LIST OF TABLES TABLE NO. TITLE PAGE 4.1 Relationship between SPT, N value and weathering grade Subsoil classification (Komoo and Morgana, 1988) Pile details Date and time interval between tests Maximum load implied during static load test Pile settlement Pile capacity for static load test using various methods Pile capacity Shaft and end bearing contributions 51

14 xii LIST OF FIGURES FIGURE NO. TITLE PAGE 2.1 Bore hole created by dry method of construction Process of dry method Bore hole created by casing method Process of casing method Bore hole created by wet method Process of wet method Auger a) spiral auger b) bucket auger c) rock auger d) earth auger Percussion drilling equipment Continuous flight auger machinery Belling tool Under reamed bored pile 19

15 xiii 2.12 Static load test in progress Test equipments a) 30 tonne steel ram with hydraulic release b) pile driving analyzer c) accelerometer d) transducer Flow chart of the study Instrumented bore pile schematic diagram Typical comparison of methods for Pile Pile soil model CAPWAP method iteration program 49

16 xiv LIST OF SYMBOLS A - Cross section Area of the pile c - Wavespeed E - Modulus of Elasticity of the pile material or strain gauge reading F m - Force measured F c - Force calculated ј c - Empirical correlation factor (Case method damping factor) L - Distance along the pile between two telltale anchor plates ΔL - Difference in movement between two telltale rods Q - Quake Q ra - Load in the pile midway between two anchor plates or load in the pile at the location of the strain gauge

17 xv R shaft - Shaft Resistance R toe - Toe Resistance R u - Ultimate resistance in the soil springs Δt - Travel time v m - Velocity measured Z - Pile impedance Ρ - Mass density

18 xvi LIST OF APPENDICES APPENDIX TITLE PAGE A Results of Analysis Pile 1 58 B Results of Analysis Pile 2 66 C Results of Analysis Pile 3 74 D Results of Analysis Pile 4 82 E Results of Analysis Pile 5 90

19 CHAPTER 1 INTRODUCTION 1.1 Background Foundation is an essential part of a structure because it transmit load from the structure to the soil below it. The foundation can be classified into shallow foundation and deep foundation. Shallow foundations such as individual footings, combined footings, and raft foundation are used when the supporting soil is found at shallow depth. While, deep foundations such as caissons and piles are required when the depth of supporting soil is significant or building is placed on soft compressible soil. Deep foundation is also required if construction is subjected to horizontal load or moment. Piles are mainly classified into two categories; displacement piles and replacement piles. Displacement piles consist of reinforced piles, pre-stressed piles, steel-h piles, whereas replacement piles consist of bored piles, and cast in-placepiles. All these piles are designated to a particular situation or site based on location and type of structure, ground condition and durability.

20 2 Piles are designed based on the load that is transferred from the structure to the piles; thus the type, size and length of piles are determined accordingly. However, load test should be conducted to verify the design capacity. Piles that are not properly designed, would pose danger to the structure. Inadequate load or large settlement would cause severe damage to the structure and its occupants. There are several alternatives to load test, i.e.: maintained load test (MLT), high strain dynamic test (PDA), statnamic test and Osterberg Cell load testing. All the mentioned tests are rigorously being carried out in Malaysia. These tests would provide the engineer with the load and the corresponding settlement. It actually enables the engineer in decision making as to resume work or to make changes to the selected design criteria. Of the four, the most viable and the most common as being practiced in the industry are the Static Load Test and the High Strain Dynamic Testing. Maintained load test or static load test is commonly known in construction industry. It uses hydraulic jacking system against a kentledge or against a beam restraint by anchor piles. The load is measured by the reading of pressure gauge on the hydraulic jack. At present the load is measured directly by a load cell interposed between the pile head and jack or between the jack and platform to get an accurate and reliable measurement. This test is also known as conventional test. It requires proper setup, manpower, machinery and longer duration to maintain the load. High strain dynamic test or dynamic pile testing is conducted using two to four sets of sensors known as accelerometer and transducer attached to the pile. The basis for this testing is wave mechanics. The test requires sensors, pile driving analyzer and the pile driving system. On every impact of the driving system/ram, the sensors capture the impact force and velocity. The captured signals of strain and acceleration were conditioned and possessed by the pile driving analyzer to produce plots of force and velocity versus time. The ability to accurately predict static capacity for dynamic pile testing has resulted in many studies and has been the focus

21 3 of dynamic pile tests on many project sites. Standard practice requires performing signal matching on the data to more accurately determine capacity from the dynamic tests. CAPWAP (Case Pile Wave Analysis Program) analysis is the most used program to evaluation capacity from high strain dynamic testing data. Previous studies have demonstrated generally good correlation of CAPWAP signal matching results on dynamically re-striked tests with that of static load tests. Since, the usage of static load test and high strain dynamic test is rapid and almost conducted in every site, comparisons between the two tests for bored pile is attempted in this project paper. 1.2 Problem Statement There are many studies conducted on the comparison between high strain dynamic testing and CAPWAP analysis, and static load test in Malaysia, but most of it was made for the displacement piles. I, in this project study however, will focus on replacement piles (bored piles). Comparison is made between the static load test results and the CAPWAP signal matching result on dynamic re-strike test. Furthermore, an attempt is made to compare the results obtained from the maintain load test and the high strain dynamic test and CAPWAP analysis.

22 4 1.3 Objectives The objective of conducting this study is to compare the results obtained in static load tests with that of high strain dynamic tests and CAPWAP analysis in terms of: 1) The load transfer mechanism through pile; 2) The load and the corresponding settlement of the pile; and 3) The total bearing capacity of the pile. 1.4 Scope In this project paper special attention is provided to the bored piles. The bored piles are vertically tested with both static load test and high strain dynamic test. The data for this paper is obtained from real time projects conducted in construction industry. In this case, the piles are fully instrumented for measurements of stress and displacement. Static load test are conducted prior to the dynamic test. The static load test is conducted using kentledge with load cell, whereas; the dynamic test is conducted using a drop hammer. The subject of this study is not the accuracy, but relative comparison between static load test and high strain dynamic test to evaluate the capacity and load transfer mechanisms within the piles.

23 CHAPTER 2 LITERATURE REVIEW 2.1 Bored Pile A bored pile is a deep foundation that is constructed by placing fluid concrete in a drilled hole. The bored piles are designed based on geotechnical engineering properties of subsoil condition obtained from the soil investigation at proposed site for foundation designs. In soil investigation work, in-situ test are conducted and disturbed and undisturbed soil samples are collected for laboratory testing, and also to determine ground water level at the site. In a project site, piles are selected for a foundation based on loads to be imposed, site subsurface materials, lateral capacity and also cost. In many projects, bored pile has proven cost effective, especially in urban areas and large construction.

24 6 Bored piles have many advantages compared to the displacement pile. When the piles are properly analyzed, designed and constructed, the advantages range from reliability, economy and versatile. Reliability in terms of shaft that can be located easily, soil/rock can be inspected during construction and integrity can be assessed. It is understood that bored piles have high resistance to lateral loads. Piles driven into clay soils may produce ground heaving and cause driven piles to move laterally. This does not occur in bored piles. Furthermore, the surface over which the base of the bored pile is constructed can be visually inspected. In terms of economy, a single bored pile can be used instead of a group of piles and the pile cap. The construction of bored piles generally utilizes mobile equipment, which under proper soil conditions, may prove to be more economical than methods of constructing pile foundations. Bored piles are also versatile. Depth and diameter of piles can are easily varied. Constructing bored piles in deposits of dense sand and gravel is easier than driving piles. Furthermore, the base of bored pile can be enlarged to provide greater resistance to the uplifting load. Areas where driving piles can pose danger to the adjacent structures due to vibration can be avoided by using bored pile.

25 Types of Bored Piles Bored piles are classified according to the ways in which they are designed to transfer the structural load to the substratum. The pile can be cased with pipe when required. For such piles, the resistance to the applied load may develop from end bearing and also from side friction at the shaft perimeter and soil interface. A belled bored pile consists of a straight pile with a bell at the base, which rests on good bearing soil. The bell can be constructed in the shape of a dome or it can be angled. For the majority of bored piles, the entire load-carrying capacity is assigned to the end bearing only. However, under certain circumstances, the endbearing capacity and the side friction are taken into account Construction Procedures The most common construction procedure used involves drilling. There are three major types of construction methods; the dry methods, the casing methods and the wet methods Dry Method This method is employed in soils and rocks that are above the water table as shown in Figure 2.1. The soils are normally strong and not easily collapsible when the hole is drilled to its full depth.

26 8 Dry hole no water content Figure 2.1 Bore hole created by dry method of construction Construction in the dry method uses drilling tools to bore the hole. Spoilt of the hole is dumped nearby or are exported to dumping yard. Concrete is then poured into the hole and if there be any requirements for the reinforcement, then a rebar cage is placed in the upper portion of the pile. Concreting is continued till the required level. The process of the dry method is shown in Figure 2.2 shows Casing Method The casing method is employed in soils and rocks, which are easily caving or collapsible soils when the borehole is excavated as shown in Figure 2.3. The

27 9 construction method is almost the same as the dry method but requires an introduction of slurry during drilling when collapsible soils are encountered. Figure 2.2 Process of dry method Casing introduction into the hole Figure 2.3 Bore Hole created by casing method

28 10 The drilling is continued past the collapsible soil layer into a more stable soil layer. Casing is then introduced into the hole and the slurry is pumped out of the hole. A smaller drill that passes through the casing is then used to drill further into the soil. If there be any need for reinforcement, a rebar cage is introduced to the full length of the pile. Concreting work starts and the casing is retrieved from the hole gradually. Concreting is completed when the concrete fill up to the required level. The Figure 2.4 shows the process of the wet method. Figure 2.4 Process of casing method

29 Wet Method This method is employed in a very soft soil condition as in the Figure 2.5. This method is sometimes referred to as slurry displacement method. Slurry is used to keep the borehole open during the entire depth of excavation. Construction of a bored pile using this method starts with excavation by drilling with the slurry in the hole. The entire depth is drilled with slurry. If needed, reinforcement is introduced in the hole. Concreting starts by placing a tremie pipe to the bottom of the borehole. As concreting progresses, the slurry is slowly displaced to the ground surface where it is collected. Concreting completes when the finish level is reached. Figure 2.6 shows the process of the wet method. Introduction of Slurry into the hole Figure 2.5 Bore hole created by wet method

30 12 Figure 2.6 Process of wet method Techniques and Equipment In a construction of a drilled shaft, more than one method can be employed in accordance to the site requirement. No matter which method is employed, the boring equipments are normally the same but require minimal adjustment for the required work. Generally, the boring is carried out by mechanical auger, percussion/grab type rig or continuous flight auger. The under reaming of the shaft if required is done by using belly bucket.

31 Boring by Mechanical Auger The large spiral auger or bucket auger rotary drilling machines are developed for the installation of large diameter bored piles. These machines are capable of drilling in wide range of soil and also weak rocks using different type of auger as in the Figure 2.7. In cases where there is a potential cave in, a length of casing is placed into the drilled hole by means of a crane or by the mast of the machine. The casing would provide a seal against water entry. A smaller size drill plate is then used inside the casing for the lower part of the hole. Boring by mechanical auger under water or bentonite slurry can cause some loosening of the soil at pile base level. If a higher base resistance is required, then the soil needs to be compacted by injection pressure. A flat circular steel plate is suspended from the bottom of the reinforcing cage, and a thin flexible steel sheet is attached to the bottom of the plate. After concreting the pile, grout is injected around the bottom few meters of the shaft to lock the shaft to the surrounding soil. After a hardening period grout is then injected at high pressure to fill the space between the steel plate and the steel sheet. This forces the sheet down and compresses the underlying soil. Resistance to uplift of the pile at this stage is provided by grout injections around the pile shaft.

32 14 (a) (b) (c) (d) Figure 2.7 Auger a) Spiral auger b) bucket auger c) rock auger d) earth auger

33 Boring by Percussion or Grab-type Rig In ground where mechanical auger drilling is impossible (in water-bearing sands or gravels, stony or boulder clays, or very soft clays and silts), a conventional cable percussion boring rigs are used as shown in Figure 2.8. Figure 2.8 Percussion drilling equipment In these type of boring, the casing is given a continuous semi-rotary motion to keep it sinking as the borehole is advanced. The casing may be with welded joints and left in position, or with bolted joints and withdrawn while the shaft is concreted. A problem in drilling of bored piles in granular soils, either by cable percussion rigs in the case of small diameter piles, or grabbing rigs for the larger diameters, is the risk of excessive removal of soil during drilling. This is expected to

34 16 happen when drilling by cable percussion methods since the soil is drawn up into the shell or baler by a sucking action. Water is required to induce the flow of soil into the drilling tool and if natural ground water is not present it must be poured into the pile borehole. Violent raising and lowering of the shell can cause flow of soil from the surrounding ground with the risk of settlement of any adjacent structures. It is possible to minimize the risk of loss of ground by driving the casing ahead of the boring, but this can make it impossible to withdraw the casing after concreting the pile shaft since driving the casing cause the soil to tighten around it. If there are services or buildings around the piling area than it is best to use rotary-auger drilling method under bentonite slurry or a continuous flight auger Boring by Continuous Flight Auger Drilling Continuous Flight Auger drilling machine is made of spiral auger throughout the stem as in Figure 2.9. The auger can be withdrawn after drilling to the required depth in a stable ground and the pile is concreted by feeding a flexible pressure hose to the bottom of the unlined hole and withdrawing it as sand-cement mortar is pumped down. In cases of unstable ground, the flight auger is provided with a hollow central stem closed by a plug at the bottom. During drilling, the walls of the borehole are supported at all times by the soil rising within the flights. When the required depth is reached, concrete is injected down the hollow stem, which pushes out the bottom plug and the pile is concreted by raising the auger with or without rotation.

35 17 Figure 2.9 Continuous flight auger machineries During concreting, the auger is rotated for a number of revolutions before raising it to ensure that the concrete has completely filled the bottom of the hole. After removing the auger, reinforcing cage is pushed down the shaft, while the concrete in the shaft is still in the form of fluid. The use of continuous flight auger rig avoids many of the problems of drilling and concreting piles experienced when using conventional power augers. However, continuous flight auger piles operation must be monitored closely during construction Under-reammed Bored Piles An under-reammed pile (also known as a belled shaft) is one with an enlarged base. The under-reams are made with special equipments and techniques. The equipment used showed in the Figure 2.10 below. The larger the base of underreammed pile, the higher their end bearing capacity.

36 18 Figure 2.10 Belling Tool However, the displacement required to mobilize the full end bearing is typically on the order of 10% of the base diameter, which may be more than the structure can tolerate. Under-reammed piles also have greater uplift capacities due to bearing between the ceiling of the under-ream and the soil above as is in Figure The construction of under-reammed pile can be hazardous to the workmen. The bottom of the under ream must be cleaned of loose soil before placing concrete. This task is typically done by hand. Thus, under-reammed shafts are not as common as they once were.

37 19 Figure 2.11 Under reamed bored pile 2.2 Load Test Pile load test are executed in two alternative ways based on site investigation, laboratory soil testing and desk study: 1) Test pile piles are tested to failure. This test is done during the preliminary design stage. Load test is then carried out to refine and finalize the design of the pile foundation. 2) Test on working pile piles are tested to two times the design load (working load). This test is done in areas where previous experience

38 20 is available. Pile load test are then carried out on randomly selected actual piles to check the pile design capacities. The equipment and the procedures for these two alternatives are essentially similar. Generally there are two types of testing performed in most part of the world: the static load test and the high strain dynamic test Static Load Test (Maintained Load Test) The most accurate way to determine the load capacity is to install a full-size prototype pile at the site of the proposed production piles and load it to failure. However, load tests also are much more expensive, and thus must be used more judiciously. Varieties of equipment and procedures have been used to conduct load tests. The differences in the equipment and procedures can influence the results and become the point of debate among engineers. Therefore, there is no single correct capacity for most piles. Nevertheless, engineers judge the accuracy of all other methods by comparing them to full-scale load tests Test Equipment and Instruments Test equipments and instruments consist of load application arrangements and the instruments to measure the resulting movements or deformations. Stacking

39 21 large weight on top of the pile as imposed load, posed danger because it is difficult to place large weights without creating excessive eccentricities that can cause them to collapse. As an alternative, a hydraulic jack is used to provide the test load. This system is more stable and less prone to collapse. Figure 2.12 shows the actual setup of static load test using hydraulic jack performed on a bored pile. Figure 2.12 Static load test in progress Traditionally, engineers have measured the applied load by calibrating the hydraulic jack and monitoring the pressure of the hydraulic fluid during the test. However, even when done carefully, this method is subject to errors. Therefore, load cells (an instrument that measures force) are developed. The load cell is placed between the jack and the pile and is used to measure the applied load. Displacement is another measurement that is very important in conducting load test besides the capacity. The displacement is measured by utilizing dial gauges mounted on the reference beams. Surveyor s level can also be used as a cross reference to the measured records of displacement.

40 22 Another measurement employed in load test is the incremental strain measurement along the pile length to determine the distribution of load transfer from pile to the soil. These provide information on pile tip movements or deflections along the pile. In order to obtain this measurement, a pile needs to be instrumented prior to installation. Instruments that can be used are the strain rods (or telltales) and the electric strain gauges (or vibrating wire strain gauges). Telltales or strain rods (vibrating wire extensometer) normally consist of polyvinyl chloride (PVC) tubing extended to steel end plates embedded inside a concrete pile or welded on the steel pile or housed in sonic logging pipe at various locations along the pile length. Inside the sonic logging pipe tubing, a stainless steel/graphite/fiberglass rod is installed extending from the end plate to the top of the pile. Both the tubing and the steel rod extend to the top of pile. The steel rod must be allowed to move freely in the tube. The movement of the top of the telltale or strain rod relative to the top of the test pile is measured with a dial gauge or the measurement of the vibrating wire extensometer is logged using a data logger. Normally, telltale readings are referenced to the top of the pile. By noting the location of the specific telltale rod anchor plate and by measuring the relative movement of the individual rod, elastic shortening of pile at that location can be obtained. At present, data recoded by the data logger can give the elastic shortening of the pile without having to measure the top measurements. With this information, the load in the pile at the midpoint between two telltale anchor plates separated by a distance L can be obtained by the following relationship:

41 23 AΔLE Q ra = L where Q ra A ΔL E L = load in the pile midway between two anchor plates = cross section area of the pile = difference in movement between two telltale rods = modulus of elasticity of the pile material = distance along the pile between the two telltale anchor plates Electric strain gauges or vibrating wire strain gauge can be mounted along the pile length at various locations before the pile is installed. In bored piles, these gauges can be tied up with the reinforcing bars and wires can be brought up through a casing just like the vibrating wire extensometer. Since these gauges are temperature sensitive, additional temperature-compensating gauges should be used for each strain gauge. The strain ε can be determined directly by noting the changes in the strain gauge reading from the unstrained to any desired load. At present the measurements are data logged using a data logger. The load at the point will then be calculated by the following relationship: Q ra =AEε where Q ra A E ε = load in the pile at the location of the strain gauge = cross section area of the pile = modulus of elasticity of the pile material = strain gauge reading

42 Test Procedures There are two categories of load tests: controlled stress tests and controlled strain tests. The former uses predetermined loads (the independent variable) and measured movements (the dependent variable), while the latter uses movement as independent variable and load as dependent variable. Controlled stress tests are the slow maintained load test and quick maintained load test. In slow maintained load test, the pile is loaded in eight equal increments (i.e. 25%, 50%, 75%, 100%, 125%, 150% 175% and 200%) to two times of the design load. The load is maintained under each increment until the rate of settlement is acceptably small. At two times the design load, the load is maintained for 24 hours. After the required holding time, the loading is removed in decrement of 25% with 1 hour between decrements. After one cycle of the load, the pile is reloaded to test load in increments of 50% of the design load, allowing 20 minutes between load increments. Then the load is increased in increments of 10% of design load until failure, allowing 20 minutes between load increments. This method is commonly considered as the ASTM Standard test method and is generally used for site investigation prior to installing contract piles and writing specifications. The disadvantage of this test is that it is time consuming. In quick maintained test the procedure is almost the same as slow maintained test except that each load increment is held for a predetermined time interval regardless of the rate of pile movement at the end of that interval. Pile is loaded in 20 increments to three times of the design load (i.e. each increment is 15% of the

43 25 design load). Each load increment is maintained for 5 minutes with readings taken every 2.5 minutes until the test load has been reached. After 5 minutes interval, the full load is removed in four equal decrements with 5 minutes between decrements. The advantage of this test is that it is fast and economical. The method represents a more nearly undrained condition. This method cannot be used for settlement estimation because it is a quick method. Controlled strain test is the constant rate of penetration test, which presses the pile into the ground at a constant rate. As the test progresses, the load and settlements are measured to develop a load-settlement curve. In this test, the pile head is forced to settle at typically 0.01 to 0.05 in/min (0.25 to 1.25 mm/min) for clays and 0.03 to 0.10 in/min (0.75 to 2.5 mm/min) for sands. The force required to achieve the penetration rate is recorded. The test is carried out to a total penetration of 2 to 3 in. (50 to 75 mm). The advantage of this test method is that the test is very fast and economical. This method can be employed for friction piles but less practical for the end bearing piles because of high force requirements to cause penetration through hard bearing stratum High Strain Dynamic Test High strain dynamic test is a powerful tool to access pile driving, which may supplement or replace static testing. This test is conducted in a fraction of time

44 26 unlike the static load test. This test is based on the dynamic method of analysis. Actual field test is performed on pile by measuring strain and acceleration records under impact of a falling mass. Wave equation analysis program (WEAP) is utilized to design the weight, drop height and cushion of the hammer apparatus to assure a successful test. The pile driving analyzer and the CAPWAP methods are used for data acquisition and analysis. Testing results yield information regarding pile static bearing capacity, structural integrity, and pile-soil load transfer and pile load-movement relationship. High strain dynamic test is conducted using; a pair of strain transducers mounted near the top of the pile, a pair of accelerometers mounted also near the top of the pile and the a pile driving analyzer also known as PDA (pile driving analyzer) as shown in Figure The pile driving analyzer monitors the output from the strain transducers and accelerometers as the pile is being driven, and evaluates the data as follows: 1) The strain data combined with the modulus of elasticity and cross section area of the pile, gives the axial force in the pile; 2) The acceleration data integrated with time produces the particle velocity of the waves traveling through the pile; 3) The acceleration data, double integrated with time produces the pile set per blow.

45 27 (a) (b) (c) (d) Figure 2.13 Test Equipments a) 30 tonne steel ram with hydraulic release b) Pile Driving Analyser c) accelerometer d) transducer Using the above data, the PDA computes the Case method capacity and displays the results immediately. Case method analysis is an analytical technique for determining the static pile capacity from wave trace data. The Case method computations include an empirical correlation factor, j c that can be determined from an on-site pile load test. It is also possible to use the Case method without an on-site pile load test by using j c values from other similar soils. This approach is less accurate, but still very

46 28 valuable. The PDA can also store the field data on a floppy disk to provide input for a CAPWAP analysis. The Case method, while useful, is a simplification of the true dynamics of pile driving. The empirically obtained damping factor, j c calibrates the analysis, so the final results are no better than the engineer s ability to select the proper value. In contrast, a wave equation analysis utilizes a much more precise numerical model, but suffers from weak estimates of the actual energy delivered by the hammer. Fortunately, the strengths and the weaknesses of these two methods are complimentary, so we can combine them to form an improved analysis called CAPWAP (Case Pile Wave Analysis Program). It is a rigorous numerical method for a comprehensive analysis of pile and soil behavior under hammer impacts and also under static loading conditions. The analysis is done in an iterative environment using measured force and acceleration in a wave equation type analysis employing signal matching technique that produces values of R u (the ultimate resistance in the soil springs ), q (the quake), and j c (the Case method damping factor). CAPWAP analyses are not a substitute for pile load tests. However, they may reduce the required number of tests Correlation Studies During the past decade, high-strain dynamic testing of bored piles has enjoyed widespread acceptance around the world. Discuss here are some of the case histories of dynamic and static test results.

47 29 Case 1: Jianren and Shihong (1992). A study was conducted on drilled piles for a 257m high tower span crossing the Yangtze River in Tai Sheng Quan Nanking, China where test shaft consisted of two each 800 and 1500mm diameter with corresponding lengths of 30 and 60m. Subsurface conditions at the site consisted of clay, sand and gravel layers over highly weathered sandstone. Project specifications required that comparisons between dynamic and static load test results be made in a Class A prediction manner. The hammer used for the dynamic testing had a weight of 12 tons with drop heights up to 1 and 2.5m for the 800 and 1500mm diameter shafts respectively. Comparison of dynamic and static was performed within the same time frame indicated that the two methods produced capacity values that were within 2.6% relative to each other. Case 2: Seidel and Rausche (1984). A static and dynamic test program was initiated on drilled shafts for the West Gate Freeway in Melbourne, Australia after questions were raised regarding the shafts bearing capacity and serviceability. Twelve shafts ranging in size between 1100 and 1500mm diameter and 35 to 64m in lengths were dynamically tested. Nine shafts were socketed into mudstone and the remaining three into basalt. Six of the shafts socketed into the mudstone were also statically tested. A hammer with a weight of 20 tons and drop heights between 1.6 and 2.5m was used for the dynamic tests. Dynamic and static tests were done totally independently and results were compared in a Class A prediction fashion. Dynamic activation of static pile resistance forces exceeded 3000 tons for some 1500mm diameter shafts. Direct correlation of ultimate pile capacities was not possible since maximum values were not usually reached during the static tests. Skin friction predictions from dynamic tests and values obtained from instrumented shafts under static tests were remarkably similar. Pile head load-movement relationships obtained from both testing methods was comparable. Case 3: Chambers and Morgano (2004). A 457 mm diameter auger-cast pile was drilled to a depth of 19.8 m on a site in Owensboro, Kentucky. The pile was tested dynamically to evaluate the static load capacity with further analysis by signal matching software, CAPWAP. The test was carried out using a 3 tons ram. Four

48 30 days later, the pile was tested statically using four reaction piles. The test results from the static load test compares well with the computed static load deflection determined from CAPWAP analysis. Based on Case 1 and 2, a reduction on time and cost was anticipated in the project with the use of high strain dynamic testing as a complimentary to the existing static load test. Likins and Rausche (1980) concluded that statistical evaluation of previous studies and the current compilation of results showed the CAPWAP analysis of dynamic pile testing data for re-strikes to be very reliable in determination of ultimate capacity of both driven piles and cast-in-situ piles (e.g. drilled shafts and auger-cast-cfa piles). Accuracy is slightly better for driven piles than for cast-insitu piles. Comparison of CAPWAP results with static load tests on the same piles shows excellent agreement.

49 CHAPTER 3 METHODOLOGY 3.1 Introduction The study was conducted on five data from 3 sites. The data was grouped in high strain dynamic testing and CAPWAP analysis, and static results. All the data was analyzed separately. High strain dynamic test and CAPWAP analysis results from the each of the data were reviewed in terms of shaft distribution and pile load-settlement. Similarly the same procedures were employed to instrumented static load test results. The output of the high strain dynamic test and CAPWAP analysis, and the static load test analysis was compared to obtain a relationship. The results were compared based on the pile load settlement, shaft friction and load bearing capacity. A conclusion is made for the results obtained. Suggestion and improvement is outlined based on the comparison as in Figure 3.1.

50 32 Bored Piles Stage 1 Data Collection Data of High Strain Dynamic Test & CAPWAP analysis Data of Static Load Test Pile Load - Settlement Pile Load - Settlement Shaft Distribution Stage 2 Data Analysis & Results Shaft Distribution Load Bearing Capacity Relationship Stage 3 - Summary Conclusion & Suggestion Figure 3.1 Flow Chart of the Study 3.2 Data Collection The first stage of this study included identification of sites that used bored pile as foundation for the structure. The data required was from instrumented bored piles that were statically and dynamically load tested. The results were made sure to be complete for comparison purpose.

51 33 There were many data obtained but data that contains the static load test results alone is rejected during this stage of study. In the same manner, data that contains only the high strain dynamic load test results were rejected. 3.3 Data Analysis and Results The second stage of this study was to analysis the data that was obtained from the three sites. Based on the data, a plot on pile load settlement was tabulated and plotted. The pile load settlement was for both the data obtained from the static load test and the high strain dynamic load test. The results obtained were compared between each other. The data were also analyzed based on shaft distribution. The shaft distribution was obtained from the readings of the strain gauges at different levels for the static test, whereas for the high strain dynamic load test, results from CAPWAP were tabulated. The percentage of shaft distribution through the length of the pile in regards to the total capacity obtained was compared between each other. In static load test, we obtained a certain capacity. We also obtained certain capacity from the high strain dynamic load test. Both the capacities were compared using various methods available and plotted to get a comparison for all the five data that s available.

52 Summary The third and final stage of the study was to draw a conclusion based on the results of the analysis. It is understood that from previous study there has been good correlation between high strain dynamic test and static load test. It was verified in this stage for the piles in Malaysia. The result that was derived from the analysis was carefully studied based on the objectives. The closeness and the deviation between the results obtained were checked. If there seem to be deviation between the results, then the causes were identified. Suggestions were included to improve the quality of the tests and to refine the tests for better comparison in the future.

53 CHAPTER 4 DATA ANALYSIS AND DISCUSSION This chapter presents the data analysis on five instrumented bored piles. The descriptions of the piles are outlined in following section. All these piles were founded in two types of formation. Each formation has its own characteristic and influence on the pile and corresponding results. In Section 4.3, the static test data is analyzed using various methods available and a brief detail on the employment of the methods. CAPWAP (Case Pile Wave Analysis Program) is also discussed to analyze the dynamic test data in Section 4.4. Finally the results are compared between static load test and dynamic load test. 4.1 Data Description In a routine static load test, the measurements of load and settlement are taken at the pile head only. It is impossible to obtain the shaft friction values in different soil/rock layers. It is also difficult to estimate the contribution of shaft friction and end bearing accurately. Therefore, piles are instrumented with strain gauges and extensometer at appropriate depths along the pile. Figure 4.1 shows an example of the instrumented bore pile in a schematic diagram.

54 36 Figure 4.1 Instrumented Bore Pile Schematic Diagram Instrumentation is generally carried out on trial piles where the piles are loaded three times its estimated working load or preferably to failure to obtain maximum information. An instrumented pile will enables the evaluation of shaft resistance, end bearing resistance and the development of these resistances during static load test. The development of shaft and end bearing resistances represent the load transfer behavior of the pile system. The cost may be marginal to install

55 37 additional instruments to a normal static load, but the information obtained is beneficial for design verifications and optimization of pile lengths for a project of a big scale. In a pile dynamic (PDA) test, the pile force and velocity measurements are obtained by a set of strain gauges and accelerometers attached to the pile head. For the evaluation of the static pile capacity, relative soil distribution, and soil quake and damping characteristic, a more rigorous evaluation using the signal matching technique is utilized with computer software, e.g. Case Pile Wave Analysis Program (CAPWAP). 4.2 Analysis of field data The data used for this study are collected from five numbers of instrumented bored piles. Three of these piles were constructed using dry method of construction and the other two using wet method of construction. Each pile was statically and dynamically tested. Typically, the static load test was conducted prior to the PDA test on each pile. The data was obtained from construction site at three different sites. Based on the Geological Map of Selangor (Scale 1:63,360) and the borehole logs, the Site 1 is located in Kenny Hill Formation. A relationship is tabulated in Table 4.1 between the SPT (Standard Penetration Test), N value obtained from bore hole and the weathering grade of the rocks. Site 2 and Site 3 are located in Old Alluvium based on the Geological Map of Johor Bahru (Scale 1:63,360).

56 38 Kenny Hill Formation consists of monotonous sequence of interbedded clastic sedimentary rocks such as sandstones, siltstones, shale/mudstone. Frequently this formation is also referred to as meta-sedimentary with interbedded meta-arenite and meta-argillite, taking into account that the sedimentary rocks have been partly metamorphosed into quartzite and phyllite. Old Alluvium is consider to be of the pliestocene age that comprises of continental deposits of consolidated sand, clay and boulder beds of fluviate and shallow-marine origin. Holocene marine clays are nearly absent. Studies of these types of sediments, mainly from exposures were done by Kumar (1972) in Johor and Tai (1972) in Singapore. Their measurements of paleo-current directions show a south to eastward trending sediment transport. From this it was concluded that Straits of Johor did not exist at the time of deposition of the Older Alluvium (Bosch, 1988). In the drill holes data of the Public Works Department of Singapore, the base of the formation was found between 100m and 145m below sea-level, while the highest deposits were found at 45m above sea level. Table 4.1: Relationship between SPT, N Value and Weathering Grade Weathering Grade Ting (1979) SPT Komoo (1986) - SPT VI < V IV > III *CRR<70% *CRR-Core Recovery Rate Table 4.2 shows the subsoil classification based on the weathering grade. Based on the geological condition, Kenny Hill formation at Site 1 predominantly Grade IV material with SPT N value greater than 50. The subsoil exists at shallow depth, thus the pile length ranges from 7m to 12m. These piles can be categorized as short piles.