Non-Nuclear Methods for Compaction Control of Unbound Materials (2014) / Chapter Skim
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47 chapter four METHODS FOR MEASURING THE IN SITU STIFFNESS/STRENGTH OF UNBOUND MATERIALS INTRODUCTION Although the density measurement has been long used for compaction control, it does not reflect the engineering properties of unbound materials necessary to ensure their optimal performance. The key functional properties of soil layers are their stiffness and strength, which are considered to be measures of their stability and resistance to deformation under load.
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48 falls within the guide tube. During impact, the accelerometer mounted on the hammer produces an electric pulse, which is converted and displayed on the control unit.
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49 number of blows to produce dry density values ranging from 90% to 100% of the maximum dry density value obtained in standard or modified Proctor tests. The measured CIVs are used to develop a curve of CIV versus relative dry density at the optimum moisture content.
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50 Maine Study In a laboratory study in which the CH and LWD were used to test five types of base and subbase aggregates compacted in a test container, Steinart et al.
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51 New York State Electric & Gas Corporation Study The New York State Electric & Gas Corporation conducted a field study to compare the CH with the dry density measurement obtained using the NDG (Peterson and Wiser 2003)
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52 laboratory and field testing programs to evaluate the CIV– CBR correlation and proposed the correlations shown in Table 11 for different soil types.
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53 SOIL STIFFNESS GAUGE (GEOGAUGE) The soil stiffness gauge, or GeoGauge (Figure 52)
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54 X2 = displacement at flexible plate, V1 = velocity at rigid plate, and V2 = velocity at flexible plate. K X X X n V V K Knsoil flex flex= = −( )
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55 9.5%. Finally, some studies have reported that the GeoGauge results are extremely inconsistent and highly dependent on the seating procedures and the operator (Bloomquist et al.
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56 quality assurance (QC/QA) procedures during and after construction of pavement layers and embankments.
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57 New Jersey Study Maher et al.
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58 FIGURE 55 Schematic drawing of LWD showing various components of the equipment (Kim et al.
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59 where s = the applied stress, R = the loading plate radius, v = Poisson's ratio (usually set in the range of 0.3 to 0.45 depending on test material type) , dc = central peak deflection, and A = plate rigidity factor: default is 2 for a flexible plate, p/2 for a rigid plate.
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60 ground with a geophone, the Zorn uses accelerometers that measure plate deflection, which is expected to measure larger deflections. Some LWD devices (e.g., Zorn)
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61 fore, they recommended that the first value be excluded in calculating the average LWD moduli value. Davich et al.
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62 11 in.) , which was about 1.5 times the diameter of the loading plate.
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63 obtained during field testing and prepared in the laboratory at varying density and moisture contents. Figure 63 presents the results of the LWD and FWD tests conducted in that study.
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65 samples of three types of granular materials, which were compacted inside an open-topped, steel cylinder (half a 55-gallon steel drum) using a procedure similar to that of the standard Proctor test.
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66 field testing programs conducted in previous studies. Table 13 presents the mean and COV of the LWD modulus corresponding to the range of moisture deviation from optimum and percent-relative compaction based on the standard Proctor test.
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67 FIGURE 67 Correlation between CMV and LWD measurements obtained from field projects with granular materials (White et al.
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68 showed a high spatial variability. In addition, no good correlations were found between the LWD moduli and measurement of either the GeoGauge or the DCP.
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69 60° and a diameter of 20 mm, as shown in Figure 70. The DCP test is conducted according to ASTM D6951 or ASTM D7380, which involves dropping the weight from a 575-mm height and recording the number of blows versus depth.
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70 strength and stiffness properties of various types of unbound materials, such as the CBR, shear strength, resilient modulus, and elastic modulus. Despite its advantages, the DCP has limitations that have been reported in past studies.
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71 did not provide assessments of adequate compaction when compared with direct measurements of dry unit weight. Rathje et al.
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72 Colorado Study Mooney et al.
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73 predicted the laboratory-measured Mr from the DCP penetration rate. The results of this analysis yielded the model shown in Eq.
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74 oped, which was used for compaction control of the remaining 11-m-high embankment. Subsequent construction monitoring and postconstruction evaluation of the bottom ash embankment indicated that the developed criterion was very effective.
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75 DPI DPI Log CBR 2.465 – 1.12 log or CBR 292 (55)
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76 SOIL COMPACTION SUPERVISOR The soil compaction supervisor (SCS) , formerly the soil compaction meter, consists of a disposable sensor that is connected by a cable to a battery-powered, handheld control unit, as shown in Figure 77.
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77 tion of each pass of the compaction equipment. Compaction was continued after the SCS red stop signal was displayed, and the density and moisture content were measured when two and four passes were subsequently completed.
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78 FIGURE 78 Relative compaction at SCS stop signal (Cardenas 2000)
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79 The USW method is an offshoot of the spectral analysis of surface waves (SASW) method applied to high-frequency seismic tests.
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80 ture content more than the dry density. The PSPA modulus, in general, increased with increasing dry density of sandy soil.
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81 A load cell is located above the plate to measure the force applied by the person leaning on the BCD. The BCD works by applying a small repeatable load to a thin plate in contact with the compacted material to be tested.
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82 influence depth might affect its efficacy as a tool for compaction control (Weidinger and Ge 2009)
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83 specifications based on both dry density and modulus, which ultimately would result in uniformly dense and strong compacted soil layers. However, the authors noted that because of the limitation of the BCD's influence depth, it would be difficult to effectively assess the soil modulus beyond several inches below the surface.
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84 it is suggested that all measurements at calibration areas and production areas during quality assurance be obtained at a constant amplitude setting to avoid complication in data analysis and interpretation. Influence Depth The influence depth of the IC roller varies with type of ICMV measurement used.
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85 tests. The compaction information collected using IC rollers provides better assessment of the achieved compaction levels because of the significantly larger depth of influence of ICMVs compared with those obtained using in situ tests such as the NDG, LWD, and GeoGauge, as demonstrated in Figure 88.
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86 the average MDP measurements and those of different in situ tests. Figure 89 presents the simple linear correlations obtained in one of the projects.
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87 The authors attributed this to the relative differences in influence depth between CMV measurements and those of the GeoGauge and LWD. However, relatively good correlations were obtained between CMV and DCP measurements for greater depths (200 to 400 mm)
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88 when the amplitude was changed. Therefore, measurements obtained at different amplitudes should be treated separately.
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89 on their measurement accuracy. Therefore, several DOTs have attempted to establish those values based on pilot projects or by constructing control strips along a project.
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