## 2 Material  
A detailed description of the compositional features of DNA-1A can be found in [PERSON] and [PERSON] [30], who also studied its mechanical behaviour by element testing. At the particle scale, a micromechanical study on this simulant was carried out by [PERSON] et al. [33]. The repose angle of the material, which is about 40\({}^{\circ}\), reflects the grain size, shape, and roughness. The shear strength parameters measured during direct shear tests seem to vary depending on the normal stresses range employed for their determination: at low confining pressure, i.e., less than 10 kPa, [PERSON] and [PERSON] measured on self-weight compacted specimens a friction angle of 56\({}^{\circ}\) and a cohesion of 2-3 kPa, whereas at pressures higher than 10 kPa they found null cohesion and 44-47\({}^{\circ}\) friction angle. It should be underlined, however, that the mechanical properties deduced for simulants  
Figure 2: Characteristic stiffness-strain behaviour of soil with typical strain ranges for laboratory tests and structures (after [25; 26]). (Reprinted with permission from [PERSON] ©2000 ICE Publishing). under terrestrial conditions could differ from those characterizing the material in the lunar environment [34]. For lunar grains, van der Waals forces need to be considered [35]. Experimental data obtained by [PERSON] [36] and [PERSON] [37] under ultrahigh vacuum (10-7 Pa) and high temperature (394 K) showed an increase friction angle of 13\({}^{\circ}\) and an increase cohesion of 1.1 kPa testing simulated lunar soil. Increased cohesion of lunar simulant in high vacuum is also mentioned in [PERSON] et al. [38; 39]. More experimental effort is desirable to detect the effect of temperature and high vacuum on the elastic moduli of lunar soils, that is at present an important source of uncertainty. The dilatancy angles of lunar simulants, when not measured during laboratory tests, can be deduced as a function of the difference between peak and critical state friction angles and based on empirical equations linking Relative Density, \(D_{r}\), and mean stress at failure to dilatancy [40], as made by [PERSON] and [PERSON] [41], who proposed a statistical model for JSC-1A based on triaxial compression tests. [PERSON] and [PERSON] [42], for example, discuss this calculation approach for a simulant at low confining pressure. [PERSON] and [PERSON] [30] measured the Young modulus of DNA-1A at different confining pressures and over different axial strain interval (Table 1). The modulus greatly depends on both factors. Values of stiffness of other lunar simulants reported in the literature may be very different, probably depending on the measurement technique and adopted strain interval. For example, [PERSON] et al. [43] mention Young modulus of about 8 MPa at \(D_{r}=66\%\) for MLS-1 [44] and of 65-110 MPa at \(D_{r}=60\%\) for JSC-1 [45]. Since the elastic moduli of the material play a role in the load propagation through the layer, it is crucial to measure the material stiffness over proper strain interval when modelling impulsive phenomena. Under low kinetic energy impact in the laboratory, realized by free fall of sphere, the lunar simulant DNA-1A has revealed a crater morphology with ray system (Figure 3a,b). This phenomenon has been already studied, for example by [PERSON] et al. [46]. Numerical simulations for granular material performed by [PERSON] et al. [47], who studied the crater-ray formation, showed that clear mesh pattern appeared at lower coefficients of restitution between particles but was less clear at larger one, suggesting that the inelastic collisions between particles cause the clear mesh-pattern formation of impact ejecta.