Dynamic Detection Research On Cavity Beneath Cement Concrete Pavement Slab And Subgrade Compaction

Cavity beneath slabs is the generally disease of the cement concrete pavement. It is the chief reason of the pavement slabs rupture. In the engineering practice, there isn't effective measure to detect the existence and the destruction degree of the slabs up to the present. After being transient impacted with the hammer, the cement concrete pavement slab will vibrate freely. The natural frequency of vibration relates to the supporting condition, the destruction degree, etc. In order to offering theoretic basis for the detection of cavity beneath slabs in the engineering, using the theory of slab vibration, the vibration characteristic of the slab in different conditions is discussed in this paper, and the relation of the destruction degree with the vibratory frequency is established. By analyzing the results of theoretic calculations and detection in the engineering practice, the standard to detect the cavity beneath the slab in the engineering is provided finally. If the cavity beneath the cement concrete pavement slab is serious, the natural frequency of the slab vibration is relative low-commonly less than fifty Hz. If the subgrade is well and can support the slab very well, the natural frequency of the slab vibration is more than two hundreds Hz generally.The lack of subgrade compaction and asymmetric distortion are the primary reasons of forming cavity beneath slabs. In the construction of roadbed, controlling the compaction strictly is significant means to alleviate destruction of the slabs. At present, in the course of detection the compaction of highway roadbed, the methods of annulus-reamer and filling-sand are still the mainly means. Because of greatness laboring intensity, tardiness and destroying the subgrade, with the development of the highway construction, the conventional detection means can't meet the demand. The means of the Rayleigh wave is a newly nondestructive detection technique. It utilizes two kinds of characteristic of Rayleigh wave to detect subgrade compaction. One is the velocity of the Rayleigh surface wave disperse in the delaminated medium, the second is the velocity of the Rayleigh surface wave is correlative with the medium' density. On the base of the first characteristic, we can carve up the strata and calculate velocity of each stratum. Using the latter, with the correlativity of soil' density and the velocity of the Rayleigh surface wave, we can obtain the compaction of the subgrade. For thesake of establishing the correlativity of the soil' density and the velocity of the Rayleigh surface wave, by indoor experimenting with different soil, this paper analyzes the experimental results using four kinds of curve model. According to the detection of subgrade compaction with the method of the Rayleigh wave technique, how to deal with the dispersion curve and the detection signal is analyzed in this paper. The applied results indicate that the dispersion curve reflects the complexion of subgrade compaction very well.