CHAPTER 2LITERATURE REVIEW 2.0 Introduction This chapter explains about matters that are directly involved in the research profile of the road. Various methods are used to obtain information about road profile which are rod and level, dipstick profiler, profilographs, respond type road roughness meters and walking profiler. All of this based on an objective method of getting the road profile to determine the value of IRI. Instrument and test methods are used to produce a sequence of numbers related to the “true profiler” for an imaginary line on the road. The numbers obtained from some profiler are not necessarily equal to true elevation. A profiler does not always measure true profile exactly. It measures the components of true profile that are needed for a specific purpose. However, the relationship between the true profile and the numbers produced by a profiler must meet a specification that will be given shortly. A profiler works by combining three ways: Longitudinal distance There are two techniques that involved to determine the surface wave velocity and road profiling from the seismic surface waves: i. For greater detail any number of lines can be measured.1 Road Profiling A profile is a two-dimensional slice of the road surface. It is possible to measure the profile for a curved line. the requirements for measuring the profile depend on what we want to do with the data. pavement. Continuous Surface Wave (CSW) 2. Spectral Analysis Surface Wave (SASW) ii. there is a “true profile”. A reference elevation ii. For example. it is harder to exactly repeat a profile measure if the line for the profile very thin. or ground can be measured along any continuous imaginary line on the surface. one in each wheeltrack. taken along an imaginary line. Therefore. A profile of a road. we will focus on longitudinal profiles. while measures made with an ultrasonic system may cover a thicker slice of several centimeters. However. The width of the line is not standard. The concept of a profile is easy to visualize. First. In this topic. Longitudinal profiles show the design grade. plus rutting and other distress.i. and texture. If a measurement is repeated. consider two completely different uses of profile. However. For any line on the road. we can take many profiles for road each along the different a line. roughness. measures made with a laser system may cover a slice of the road just a few millimetres thick. profile is measured along two lines per lane. Profiles taken along a lateral line show the superelevation and crown of the road design. For example. The effect of profile width is not yet understood. The width is usually defined by the type of instrument used. suppose a new bridge . A height relative to the reference iii. Normally. It is easy to see that for a line drawn on a physical surface. Frequently. the same profile can only be expected if the same imaginary line is followed. a “true profile” exists. the expectation for a road is that the line is a constant distance from the centreline or some other reference that follows the road geometry. over a distance of 1 meter. information on the variation of material properties with depth can be obtained. The geological basin make use of seismic signals from explosions is use for geophysics application at regional scale. for a second application. The profile would be adequately described with elevation points taken at 3m intervals. In practice. It reacted by the wave that travels through different layered of soil medium. These technique consist of active and passive pressure surface waves techniques.0 mm (0. Other than in-situ methods. The designer might want the profile of the road on either side of the bridge site. consider a computer analysis to characterize texture based on measured profile. The analysis requires profile points spaced 1.is going to be built. Surface wave method are introduced to the world starting with the Spectral Analysis Surface Wave (SASW) method followed by Continuous Surface Wave (CSW) methods. The longer the wavelength penetrate deeper and their velocity is affected by the material properties at greater depth. For active pressure techniques.1 mm (0. modelling technique also can be used in gaining surface wave’s data. Both sets of numbers are part of the “true profile” for a line on the road.2 Surface Wave Method The surface wave method involves the generation and measurement of surface Rayleigh waves. with a resolution of 0. By utilizing the dispersive characteristics of these waves in layered media. for passive pressure technique consist only one which is Continuous Surface Wave (CSW). one is the traditional Two Sensor Spectral Analysis of Surface Wave (SASW) (Zywicki and Rix. 2.2 . Meanwhile.004 in). In determining surface wave data an in-situ test has been made using a few techniques. for several hundred meters. In measuring the phase different of the data a formula is used and it is shown in equation 2.04 in) apart. with the individual measures having a resolution of a few millimetres. this method can be used to non-destructively determine the thickness of layers and elastic properties of pavement and soil sites. 2005). Now. Vr = Where d is the known distance between receiver and f is the frequency in Hertz (Abbis and Viggiani. 1987) developed the experimental and theoretical aspects of the SASW method as applied to geotechnical and pavement engineering fields. (1987) an-alytically studied the most feasible source-receiver configuration. wavelengths greater than three times the distance between the receivers should not be considered. They indicated that a desirable distance between the source and the first receiver is equal to the distance between the adjacent receivers. Satoh et al. Sheu et al. based upon an experimental investigation. Hossain and Drnevich (1998) presented an algorithm for determination of stiffness profile. They also developed a computer algorithm INVERT (Nazarian.. Hiltenun (1988) experimentally confirmed this recommendation. they studied the possibility of developing an impact-type low frequency source. for the set-up suggested by Sanchez-Salinero et al. The major ground work for the SASW method was laid in the last 10 years. (1991) described an approximate method for the collection and reduction of data that has application in uniform and simple soil profiles. 1994) 2. They applied the algorithm to synthetic dispersion curves with success. 1985 successfully utilized a vibrator connected to a random function generator as a source. Barker and Steven (1991) reported some of the precautions that should be considered during the processing of the SASW field data.1 Spectral Analysis Surface Wave The early development of the surface-wave method for use in the civil engineering field are summarized by Nazarian (1984).2. Rix (1988). and optimization techniques were used to automode the inversion algorithm. Gucunski and Woods (1991) conducted an analytical study to quantity some problems associated with the alternative soft and hard layers. 1987 recommended that. 1984) for determining stiffness profile from a dispersion curve. In addition. They developed the suitable method for conducting the test in situ. Nazarian and Stokoe (1986. . concluded that most of the surface-wave energy is typically associated with the fundamental mode of vibration.. Drnevich et al. Sanchez-Salinero et al. This phenomenon is termed dispersion where the frequency is dependent on Rayleigh wave velocity.1. elastic half-space. Particle motion associated with Rayleigh wave are composed of both vertical and horizontal components. The media energy of Rayleigh waves from the source propagate mechanically along the surface of media and their amplitude decrease rapidly with depth. Rayleigh wave velocity does not vary with frequency. The range of wavelength to be used as a guide for the receiver spacing can be estimated from the shear wave velocities of the material anticipated at the site: (1) . Rayleigh wave velocity varies with frequency in layered medium where there is a variation of stiffness with depth.1 Rayleigh Wave The SASW method is based on the particles motion of Rayleigh wave in heterogenous media.2.Figure 2. isotropic. The shorter wavelength of high frequency penetrates the shallower zone of the near surface and the longer wavelength of lower frequency penetrates deeper into the medium.2 Spectral Analysis Surface Wave 2. The ability to detect and evaluate the depth of the medium is influenced by the wavelength and the frequency generated. which when combined. However. formed a retrogressive ellipse close to the surface. In homogenous. The higher and low frequency waves group needed can be generated by various transient sources of different weights and shapes. The time of travel between the receivers for each frequency can be calculated by: ( ) Where f is the frequency. Rayleigh wave velocity.Where f is the frequency and Vs is shear wave velocity. a theoretical dispersion curve is then calculated using an automated forward modelling analysis of the dynamic stiffness matrix method (Kausel & Roesset. LR may be written as: LR(f)= ( ) (4) The actual shear wave velocity of the pavement profile is produced from the inversion of the composite experimental dispersion curve. 1982) with a wavelength greater than ½ and less than 3 receiver spacing. t(f) and (2) is respectively the travel time and the phase difference in degrees at a given frequency. most of researchers apply the filtering criteria (Heisey et al. The distance of the receiver (d) is a known parameter. 2001). a profile of set of a homogeneous layer extending to infinity in the horizontal direction is assumed. Waves of low frequency for subgrade layer could be generated from hammer weights of 3 to 5 kg (Rosyidi et al. The last layer is usually taken as a homogeneous half-space. VR or the phase velocity at a given frequency is simply obtained by: VR = ( ) (3) And the corresponding wavelength of the Rayleigh wave. In addition. The experimental dispersion curve of phase velocity and wavelength may be developed from phase information of the transfer function at the frequency range satisfying the coherence criterion. The theoretical dispersion curve is ultimately matched . Based on the initial profile. 1981). Therefore. In the inversion process. the effectiveness of CSW monitoring has been investigated on a number of ground-improvement sites involving a variety of different soil types and treatment methods.001%. (5) Where G is the dynamic shear modulus. Since late 1997. 2. so stiffness values are not affected by sampling issues. This will be illustrated by four particular case histories following a brief description of the method itself. The surface wave source generated are detected by low natural frequency (2Hz) geophones. Vs the shear wave velocity. making the method relatively low-cost. 1996). (Nazarian & Stokoe. 1975).2 Continuous Surface Wave The Continuous Surface Wave (CSW) method (Mathews et al.to the experimental dispersion curve of the lowest RMS error with an optimization technique called the “Maximum Likelihood Method” (Joh. The Continuous Surface Wave System (CSWS) used in this testing is completely personal computer based and controlled.2. the outputs of which are passed through signal conditioning amplifiers and then to go high speed 16-bit data acquisition unit. including residual soils and glacial tills which may exhibit marked heterogeneity.. The surface wave source used is an electromagnetic vibrator capable based and controlled. Soils of all types can be tested. The shear moduli of the subgrade materials can then be determined from the following equation (Yoder & Witzcak. Furthermore. 1986) explained that the modulus parameter of material is constant and is maximum at a strain below about 0. There is no ground penetration involved and measurements are made in situ. 1996) presents a number of advantages compared with other testing methods. g the gravitational acceleration and γ the total unit weight of the material. . In this strain range. the equipment is portable and the data acquisition rapid. modulus materials is also taken as constant. Vs Eq.λ Eq. The maximum shear modulus or stiffness. can be used to calculate the wavelength. The geophones are positioned at known distances apart. is then determined using elastic theory as outlined in (Matthews et al. f.2 It can be shown from the theory of elasticity (Richart et al. and so the phase difference between the geophones. Vs2 Eq. The vibrator is energised at discrete frequencies between 5 and 600 Hz at operator specified intervals. and Rayleigh wave. Eq. is determined from the wavelength and the frequency.3 The constant. VR.To acquire data the vibrator is placed on a level ground surface and a row of between three and six 2Hz geophones is inserted co-linearly with it.. Gmax.955 for the range of Poisson’s ratio associated with most soils and rocks if anisotropy is ignored. for each discrete Rayleigh wave frequency..e. λ. in an elastic medium is given by: VR = C.1 The phase velocity of the Rayleigh wave. VR. spectral amplitude v. The frequency domain data is used to determine the phase of the generated signal at each geophone location. 1996). The signals received at the geophones are recorded digitally in the time domain and subjected to a Fast Fourier Transform to convert the signals into the frequency domain (i. C is dependent on Poisson’s ratio and varies from 0.4 . Gmax is given by: Gmax = ρ. 1970) that the relationship between the velocity of shear waves.911 to 0. Vs. . VR = f. d. frequency). If ρ is the bulk density of the medium. 1996).. λ to be approximated (Madun. 2. at which the calculated shear wave velocity is considered representative of the propagation properties of the ground. z.. So retest have to be made to gain the desired frequencies to cover up all the missing data. For spectral analysis this method is used to determine the minimum and maximum frequencies. Gazetas (1982) recommended a ratio of 4 at sites where the stiffness increases rapidly with depth and a ratio of 2 where the stiffness remains reasonably constant. In this method the depth. 2.3: dmin > ……… equation 2.2 While conducting the test.The depth assigned to each stiffness measurement is derived using the factored wavelength method described by Gazetas (1982) and (Matthews et al. a minimum of two receiver have to use to obtain the smallest wavelength. is taken to be a fraction of the wavelength.2 and Equation 2. These empirical formulas are used in this study as measurement to identify the reliable frequencies in gaining results. 2012). hence depths are normally assigned using wavelength/3 in the processing of CSW data.3 Near and Far Field Offset Near and far fields offset is a method in identifying the reliable frequency.Equation 2. dmin. The arrangement of the transmitter and receivers arrays is subject to the near and far offset constraint.4 Acknowledging the Reliability of Results By using SASW method it is hard to identify the frequency gained from the test due to it will be some loses of frequency occur due to the effects of hammering. λ/z is a constant. In identifying the reliable result for the .1 For the far-offset of receivers and the seismic sources the equations used are: dmin > 2λmin ……. In other words. He suggested that a ratio of 3 was a reasonable compromise. The formulas are noted in Equation 2. as a function of the surface-wave wavelength. The empirical rule for the near-offset constraint is recommended between the distance of the sources and the first receiver. 2000). 2.6. 2.1 Surface wave Signal reads the value of small stiffness profile for site investigation process for example in detecting the presents of void in soil. 2012) 2. Apart from that the ground water conditions can be also detected (Luna and Jadi.2 Rayleigh wave In vertical plane it moves both vertically and horizontally pointing to wave direction. soil strata can be determined and construction work will be easier. it also provided info to probes the properties of soil.velocity gained resulting from the test it is acknowledged to take counted with range of 10-20% velocity of the material since by these range of correlation are still reliable to be used as data obtained (Madun. sediments and rock outcrops as well as soil elastic and shear modulus. Nowadays.5 Importance of Geophysical Method in Site Investigation Geophysical method has been in soil and foundation application engineers many years ago.6. Only just by creating impulse or wave.6. it is often used due to the factor of cost since this method is much more cost-saving rather than conventional borehole technique. Other than to determine the dynamic properties of soils which particularly the soil compression and shear wave velocities.6 Summaries 2. it is easy to conduct and save lots of time.3 Spectral Analysis Surface Wave . Seismic wave method is one of the geophysical method that is widely used in determining soil profile. 2. Furthermore. 6.4 Continuous Surface Wave The wave frequency can be control by setting the devices according to desired frequency. Data obtained will be much more accurate due to control frequency and possible to cover just some layer at certain depth. 2. Possible to miss some layer of soil at certain depth due to uncertain and fluctuated value of frequency. .The wave frequency cannot be control (unlimited power source due to the hammer blown effects).