Experimental and numerical investigation on alternatives to sandy gravel

The NATO agreement STANAG 4569 defines the protection levels for the occupants of logistic and light armored vehicle.The Allied Engineering Publication,AEP-55,Volume 2 document outlines the test conditions for underbelly improvised explosive device(IEDs),which must be buried in water-saturated sandy gravel.The use of sandy gravel has some drawbacks,for instance reproducibility,time consumption,and cost.This paper focuses on the investigation of four alternatives to sandy gravel,which could produce similar specific and cumulative impulses:a concrete pot filled with water,a concrete pot filled with quartz sand,a steel pot without filling and a concrete pot filled with glass spheres(diameter 200μm—300μm)and different water contents.The impulses are measured with a ring technology developed at the Fraunhofer EMI.A numerical soil model based on the work of Marrs,2014 and Fi serov a,2006 and considering the soil moisture was used to simulate the experiments with glass spheres at different water contents,showing much better agreement with the experiments than the classical Laine&Sandvik model,even for high saturation levels.These results can be used to create new test conditions at original scale that are more cost-effective,more reproducible and simpler to manage in comparison to the current tests carried out with STANAG sandy gravel.

Penetration grouting reinforcement of sandy gravel

To study the relationship between grouting effect and grouting factors, three factors （seven parameters） directionless pressure and small cycle grouting model experiment on sandy gravel was done, which was designed according to uniform design method. And regressing was applied to analysis of the test data. The two models test results indicate that when the diffusing radius of grout changes from 26 to 51 cm, the grouted sandy gravel compressing strength changes from 2.13 to 12.30 MPa; the relationship between diffusing radius（R） and water cement ratio（m）, permeability coefficient（k）, grouting pressure（p）, grouting time（t） is R=19.953m^0.121k^0.429p^0.412t^0.437; the relationship between compressing strength（P） and porosity（n）, water cement ratio, grouting pressure, grouting time is P =0.984n^0.517m6-1.488p^0.118t^0.031. So the porosity of sandy gravel, the permeability coefficient of sandy gravel, grouting pressure, grouting time, water cement ratio are main factors to influence the grouting effect. The grouting pressure is the main factor to influence grouting diffusing radius, and the water cement ratio is the main factor to influence grouted sandy gravel compressing strength.

Investigation of the seismic behavior of grouted sandy gravel foundations using shaking table tests

Sandy gravel foundations exhibit non-linear dynamic behavior when subjected to strong ground motions,which can have amplification effects on superstructures and can reveal insufficient lateral resistance of foundations.Grouting methods can be used to improve the seismic performance of natural sandy gravel foundations.The strength and stiffness of grouted sandy gravel foundations are different from those of natural foundations,which have unknown earthquake resistance.Few studies have investigated the seismic behavior of sandy gravel foundations before and after grouting.In this study,two shaking table tests were performed to evaluate the effect of grouting reinforcement on seismic performance.The natural frequency,acceleration amplification effect,lateral displacement,and vertical settlement of the non-grouted and grouted sandy gravel foundations were measured and compared.Additionally,the dynamic stress-strain relationships of the two foundations were obtained by a linear inversion method to evaluate the seismic energy dissipation.The test results indicated that the acceleration amplification,lateral displacement amplitude,and vertical settlement of the grouted sandy gravel foundation were lower than that of the non-grouted foundation under low-intensity earthquakes.However,a contrasting result was observed under high-intensity earthquakes.This demonstrated that different grouting reinforcement strategies are required for different sandy gravel foundations.In addition,the dynamic stress-strain relationship of the two foundations exhibited two different energy dissipation mechanisms.The results provide insights relating to the development of foundations for relevant engineering sites and to the dynamic behavior of grouted foundations prior to investigating soil-structure interaction problems.