**7. Application of wave propagation methods in geoengineering quality control process**

182 Wave Processes in Classical and New Solids

Effect of temperature on time-dependent changes in Go was reported in Bosscher and Nelson (1987), Fam et al. (1998). The dependency of Go on temperature suggests that higher temperatures cause the stiffness increase with time. Fam et al. (1998) presented the evolution in velocity with time for coarse-grained granular salt specimen under a constant effective stress and subjected to a temperature step (heating-cooling cycle) as illustrated in Fig. 17. The rate of increase in velocity with time increases at higher temperatures (Fam et al. 1998). Bosscher and Nelson (1987) studied Go of frozen Ottawa 20-30 sand as a function of the confining pressure, the degree of ice saturation, the relative density, and the temperature. They found that Go of frozen sand is higher than that of non-frozen state. At temperatures near the melting point of ice, Go can be significantly influenced by the confining pressure,

the degree of ice saturation, and the relative density (Bosscher and Nelson 1987).

**Figure 17.** Effect of temperature on time-dependent changes in velocity for a coarse-grained granular

**Figure 16.** Effect of cementation on Go (Acar and El-Tahir 1986).

Small-strain shear modulus, Go (MPa)

salt specimen under a constant vertical load (Fam et al. 1998).

**Temperature** 

The quality of the engineered earth fills depends on the suitability and compaction of the materials used. Earthwork compaction acceptance criteria are typically based on adequate dry density of the placed earthen materials achieved through proper moisture content and compaction energy. For instance, compaction specifications often require achievement of an in-situ dry density of 90-95% of the maximum value obtained from laboratory standard or modified Proctor test. According to this approach, by achieving a certain dry density using an acceptable level of compaction energy assures attainment of an optimum available level of structural properties and also minimises the available pore space and thus future moisture changes.

The question of the achieved structural property, which is the ultimate objective quality control, however remains unfulfilled. Dry density is only a quality index used to judge compaction acceptability and is not the design parameter or relevant property for engineering purposes. For compacted highway, railroad, airfield, parking lot, and mat foundation subgrades and support fills, the ultimate engineering parameter of interest is often the shear modulus of geomaterials, which is a direct structural property for determining load support capacity and deformation characteristic in engineering design.

Shear modulus of compacted geomaterials depends on density and moisture but also on fabric and texture of geomaterials, which varies along the roadway route. The conventional approach of moisture-density control, however, does not reflect the variability of the texture and microstructure of geomaterials and thus their shear modulus. Even if the structural layers satisfy a compaction quality control requirement based on density testing, a large variability in shear modulus can still be observed (Sargand et al. 2000; Nazarian and Yuan, 2000). Additionally, the comparison between density and modulus tests suggests that conventional density testing cannot be used to define subtle changes in the stiffness of the compacted earth fills (Fiedler et al. 1998). Shear modulus is a more sensitive measure of the texture and fabric uniformity than density. The stiffness non-uniformity is directly related to progressive failures and life-cycle cost, direct stiffness testing which can be conducted independently and in conjunction with conventional moisture-density testing is anticipated to reduce variability and substantially enhance quality control of the earthwork construction.

Ismail and Rammah (2006) proposed a test setup and procedure by which the small-strain shear modulus can be measured accurately by propagating elastic shear wave through the compacted geomaterial during laboratory compaction test. They designed a test setup in such a way that it can be readily incorporated into the conventional compaction mould as shown in Fig. 18. In addition, their procedures can be adopted in compaction works e.g. road construction, embankments, and earth structures. Consequently, incorporating the shear modulus into laboratory compaction tests, will guarantee fulfilment of the design criteria in term of dry density-moisture-modulus relationship.

Wave Propagation Methods for Determining Stiffness of Geomaterials 185

**Figure 20.** S-wave traces of the silt and lean clay compacted with standard Proctor effort (Sawangsuriya

4000 0 1

2.294 105

105

2 105

Opt+4%

1.5 105

Opt+2%

1 105

Opt

5 104

Opt-2%

Opt-4%

a 1 b <sup>1</sup> <sup>k</sup> c <sup>1</sup> 2 k d <sup>1</sup> 3k e <sup>1</sup> 4 k

5 104 4.382 104

0

CL-Std

106 <sup>2</sup> 106 <sup>3</sup> 106 <sup>4</sup> 106 <sup>5</sup>

<sup>106</sup> 2.5

4.75 106 <sup>0</sup> <sup>a</sup> <sup>0</sup> <sup>b</sup> <sup>0</sup> <sup>c</sup> <sup>0</sup> <sup>d</sup> <sup>0</sup> <sup>e</sup> <sup>0</sup>

0 1000 2000 3000 5000 microsecond

4000

In the past 20 years, the use of wave propagation methods (e.g. seismic. etc.) seismic reflection and refraction, seismic down-hole, up-hole and cross-hole etc. for ground monitoring has been promoted intensively because it is non-destructive and is conducted under in situ condition. The wave propagation methods are commonly used to determine stiffness-depth profile. Typically, the wave propagation methods can be classified into

The subsurface methods including seismic down-hole, seismic up-hole, and seismic crosshole are normally employed to monitor ground stiffness when the depth of interest is greater than 15 meters (Hooker 1998). In these methods, one or more boreholes are usually required in order that the source and/or the receiver can be installed. While the seismic cone penetration test can provide both stiffness and strength properties of the geomaterials during its penetration. The disadvantage of the subsurface method is that the cost of measurement is relatively high due to the cost of borehole casting. An alternative method is the near-surface method which provides simpler and more cost-effective approaches. The near-surface method is performed on the basis of the ability of wave propagation through the ground strata. When waves propagate through soil layers having different properties, they refract and/or reflect at different time. Once the arrival time is known, wave velocities

With the near-surface method, the Spectral Analysis of Surface Waves (SASW) using surface waves is another technique that can monitor both ground stiffness at shallow depth and layer thicknesses of subsurface profiles. The surface wave method utilises the dispersive characteristic of Rayleigh waves, which are elastic waves that propagate along the ground surface. Surface (Rayleigh) wave velocity varied with frequency is measured by utilizing the dispersion characteristics of surface wave and the fact that surface waves propagate to

**8. Application of wave propagation methods for ground monitoring** 

subsurface and near-surface methods as schematised in Fig. 21.

<sup>106</sup> 4.5

4.75 106 <sup>0</sup> <sup>a</sup> <sup>0</sup> <sup>b</sup> <sup>0</sup> <sup>c</sup> <sup>0</sup> <sup>d</sup> <sup>0</sup> <sup>e</sup> <sup>0</sup>

0 1000 2000 3000 5000 microsecond

and stiffness of each layer can be determined.

0 1 106 <sup>2</sup> 106 <sup>3</sup> 106 <sup>4</sup> 106 <sup>5</sup>

4.186 1 05

Opt+4%

Opt+2%

Opt

Opt-2%Opt-4%

ML-Std

a 1 b <sup>1</sup> <sup>k</sup> c <sup>1</sup> 2k d <sup>1</sup> 3k e <sup>1</sup> 4k

et al. 2008a).

**Figure 18.** Seismic compaction mold (Ismail and Rammah 2006).

Sawangsuriya et al. (2008a) presented the experimental investigation of the shear modulusmatric suction-moisture content-dry unit weight relationship using three compacted subgrade soils. Compacted specimens were prepared over a range of molding water contents from dry to wet of optimum using enhanced, standard, and reduced Proctor efforts. A S-wave propagation technique known as bender elements was utilized to assess the shear wave velocity and corresponding Go of the compacted specimens. S-wave traces of the clayey sand compacted with enhanced Proctor, standard Proctor, and reduced Proctor efforts are shown in Fig. 19. S-wave traces of the silt and lean clay compacted with standard Proctor effort are shown in Fig. 20.

**Figure 19.** S-wave traces of the clayey sand compacted with enhanced Proctor (a), standard Proctor (b), and reduced Proctor (c) efforts (Sawangsuriya et al. 2008a).

**Figure 18.** Seismic compaction mold (Ismail and Rammah 2006).

and reduced Proctor (c) efforts (Sawangsuriya et al. 2008a).

4000

Proctor effort are shown in Fig. 20.

0 1 106 <sup>2</sup> 106 <sup>3</sup> 106 <sup>4</sup> 106 <sup>5</sup>

105

2.088 105

2 105

Opt+4%

1.5 105

Opt+2%

1 105

Opt

5 104

Opt-2%

Opt-4%

a 1 b <sup>1</sup> <sup>k</sup> c <sup>1</sup> 2k d <sup>1</sup> 3k e <sup>1</sup> 4k

5 104 5 104

0

SC-Enh

<sup>106</sup> 2.5

4.75 106 <sup>0</sup> <sup>a</sup> <sup>0</sup> <sup>b</sup> <sup>0</sup> <sup>c</sup> <sup>0</sup> <sup>d</sup> <sup>0</sup> <sup>e</sup> <sup>0</sup>

0 1000 2000 3000 5000 microsecond

Sawangsuriya et al. (2008a) presented the experimental investigation of the shear modulusmatric suction-moisture content-dry unit weight relationship using three compacted subgrade soils. Compacted specimens were prepared over a range of molding water contents from dry to wet of optimum using enhanced, standard, and reduced Proctor efforts. A S-wave propagation technique known as bender elements was utilized to assess the shear wave velocity and corresponding Go of the compacted specimens. S-wave traces of the clayey sand compacted with enhanced Proctor, standard Proctor, and reduced Proctor efforts are shown in Fig. 19. S-wave traces of the silt and lean clay compacted with standard

**Figure 19.** S-wave traces of the clayey sand compacted with enhanced Proctor (a), standard Proctor (b),

<sup>106</sup> 2.5

4.75 106 <sup>0</sup> <sup>a</sup> <sup>0</sup> <sup>b</sup> <sup>0</sup> <sup>c</sup> <sup>0</sup> <sup>d</sup> <sup>0</sup> <sup>e</sup> 0

0 1000 2000 3000 5000

microsecond<sup>4000</sup> 0 1

1 06 <sup>2</sup> 106 <sup>3</sup> 106 <sup>4</sup> 106 <sup>5</sup>

1 05

2.5 105

2 1 05

Opt+4%

1.5 1 05

Opt+2%

1 1 05

Opt

5 1 04

Opt-2%

Opt-4%

a 1 b <sup>1</sup> <sup>k</sup> c <sup>1</sup> 2k d <sup>1</sup> 3k e <sup>1</sup> 24 k

5 104 5 104

0

SC-Red

<sup>106</sup> 2.5

4.75 106 <sup>0</sup> <sup>a</sup> <sup>0</sup> <sup>b</sup> <sup>0</sup> <sup>c</sup> <sup>0</sup> <sup>d</sup> <sup>0</sup> <sup>e</sup> <sup>0</sup>

0 1000 2000 3000 5000 microsecond

4000

0 1 106 <sup>2</sup> 106 <sup>3</sup> 106 <sup>4</sup> 106 <sup>5</sup>

105

2.113 105

2 105

Opt+4%

1.5 105

Opt+2%

1 105

Opt

5 104

Opt-2%

Opt-4%

a 1 b <sup>1</sup> <sup>k</sup> c <sup>1</sup> 2k d <sup>1</sup> 3k e <sup>1</sup> 4k

5 104 1.375 104

0

SC-Std

**Figure 20.** S-wave traces of the silt and lean clay compacted with standard Proctor effort (Sawangsuriya et al. 2008a).
