Dynamic Fragmentation Research Articles

A MODEL OF MICROSTRUCTURE EVOLUTIONUNDER HIGH- STRAIN RATE DEFORMATION OF COPPER

A physical model of high-strain rate deformation of metallic materials has been developed to describe the evolution of microstructure during the process. The model is based on representations of the mechanisms of grain boundary sliding, strain-induced grain growth and dynamic fragmentation of coarse grains developed in the framework of the theory of nonequilibrium grain boundaries. These representations are modified for the description of high-speed flow and supplemented by a model of dynamic recrystallization. It is shown that during high-strain rate deformation of metallic materials, grain boundary sliding dominates in the material regions with a fine-grained submicron structure and the material deforms in the superplasticity mode. In regions of material with larger grain size, grain volume deformation dominates, accompanied by fragmentation and formation of fine-grained structure with submicron grain size. The transformation of the structure from fine-grained to coarse-grained occurs due to strain-induced grain growth. Transformation of structure from coarse grain to fine grain occurs due to dynamic fragmentation. The transition from grain boundary sliding to grain volume deformation occurs at grain size corresponding to the optimum value for the course of dynamic recrystallization. The cyclic change of deformation mechanisms (from grain boundary strain-induced to grain volume deformation) is caused by alternation of the processes of deformation-stimulated grain growth and dynamic fragmentation. The alternation of the above cycles of grain boundary and intragranular deformation in different regions of the material makes it possible to maintain a high strain rate and suppress the processes of both local hardening and local softening. The high strain rate is achieved at the expense of a high strain of the regions in which grain sliding dominates. In the regions dominated by intragranular deformation, the structure is “prepared” for superplastic flow.

Comparison of selected blasting constitutive models for reproducing the dynamic fragmentation of rock

Understanding the behavior of rock under blast- and shock-induced loadings requires a high-fidelity constitutive model. The present paper provides a detailed comparison study of three selected material models that are available in the most popular hydrocodes: the Johnson-Holmquist II (JH-2) model, the Johnson-Holmquist Concrete (JHC) model and the Karagozian and Case concrete (KCC) model. Numerical simulations are carried out to evaluate their performance under different stress conditions and to verify their effectiveness in realistically reproducing dolomite behavior. The outcomes are compared qualitatively based on specimen failure and quantitatively based on measured characteristics. The pros and cons of each model are presented and analyzed. Based on the comparison study, the JH-2 model is selected to simulate a representative blast in a mining face. The cracking, fracturing and fragmentation are correctly captured by the JH-2 model, proving its efficiency in the simulation of drilling and blasting in a mining face.

The Flims rock avalanche: structure and consequences

The Flims rock avalanche has a gliding surface that cuts down section in a limestone sequence and does not follow a weak horizon. The gliding surface is parallel to bedding and/or to the penetrative Alpine foliation in the limestone that is characterized by a shape-preferred orientation of calcite grains. Predisposition was governed by structural weaknesses in form of sub-vertical fault zones within solid limestone. Faults controlled the orientation of lateral scarps of the rock avalanche. The main body of the rock avalanche behaved as semi-coherent mass, which preserved the original overall structure. The internal deformation occurred by dynamic fragmentation, which was distributed rather heterogeneously. Fragmentation starts by the formation of veins consisting of comminuted limestone. In a later stage crosscutting veins coalesce to form a texture with entirely comminuted limestone (“rock flour”) containing angular shattered fragments of limestone of variable sizes. The involvment of the post-glacial water-saturated substrate contributed to the long-runout of the Flims rock avalanche. The substrate was plowed bulldozer-wise at the front of the rock avalanche and escaped upward through the moving rock avalanche as clastic dikes and blow-out pipes. Bulldozing raised the valley floor in front of the rock avalanche by more than 100 m and, on the margins, entrained pieces of the valley flank and the neighboring, older Tamins rock avalanche deposit. The liquefied substrate breached the Tamins rock avalanche at Reichenau and entrained fragments thereof down the valley. The fragments now form the famous tumas of Domat/Ems, Felsberg and Chur. Lake Ilanz, dammed the by Flims rock avalanche, experienced a first major outburst shortly after its formation.

A novel numerical approach for rock slide blocking river based on the CEFDEM model: A case study from the Samaoding paleolandslide blocking river event

To better understand the dynamic process of rock avalanches blocking rivers, a novel numerical approach based on the coupled Eulerian-finite-discrete element method (CEFDEM) is proposed. The Samaoding paleolandslide blocking river event, which occurred at the upstream of the Jinsha River was used as a case study to further validate the new numerical approach. Field investigations, thermoluminescence dating, and geomorphological analysis were conducted to determine basic geological conditions and provide data for the numerical simulations. Then a calibrated 3D landslide blocking river simulation based on the CEFDEM was conducted. The landslide blocking river lasted for 70 s and landslide scale from the numerical simulation agrees well with the field investigation. The maximum overall feature speed of the entire sliding mass is 35 m/s, while part of the sliding mass can reach 69 m/s. Dynamic fragmentation of the rock slide is stratified such that the bottom of the sliding body has higher fragmentation degree than the top. The variation of kinetic energy, accumulated friction dissipation, and fracture energy of the sliding mass are also shown. The impulsive water wave is triggered immediately after sliding mass runs into river, and its maximum height is 132 m, while part of the wave can reach a speed of 64 m/s. The river water will be pushed by the subsequent sliding mass movement. A comparison of the CEFDEM model and particle flow code (PFC) model in landslide blocking river was conducted, and the advantages and limitations of CEFDEM model were discussed in detail.

Geology, geomorphology and geochronology of the coseismic? Emad Deh rock avalanche associated with a growing anticline and a rising salt diapir, Zagros Mountains, Iran

This work documents for the first time the prehistoric, but morphologically pristine, Emad Deh rock avalanche of the Zagros Mountains. The ca. 420 Mm3 rock avalanche was initiated as a rockslide on a dip slope affecting a weak unit of marls with interbedded limestones overlain by a thick and competent limestone formation. The slope is located on the northern limb of the growing Gavbast Anticline and at the edge of the inflating Gavbast Dome, related to a buried salt diapir of Hormuz salt. The unconfined rock avalanche deposits, covering 32 km2, were accumulated on coalescing alluvial fans and a floodplain environment. The depositional lobe shows sectors with distinctive morphological features attributable to the variable flow-depositional behavior of the debris stream, controlled by the nature of the substrate: (1) proximal continuous breccia flanked by levees; (2) intermediate depression; and (3) flat-topped polygonal hills and conical hills. A morphometric and spatial distribution analysis has been performed with the 550 conical hills (hummocks) mapped in the distal sector. The rock avalanche, with 914 m of maximal height drop (H) and 9280 m of runout (L), displays an extraordinarily high mobility (H/L index of 0.09), that can be attributed to the combined effect of dynamic rock fragmentation and basal lubrication by the soft substrate in the floodplain. Relief rejuvenation and slope over-steepening related to the growth of the anticline and the inflation of the Gavbast Dome are considered the main long-term preparatory factors that shifted the slope to a state of marginal stability. The slope failure was likely triggered by a large M ≥ 6.5–7 earthquake at ca. 5.4 ka, as indicated by OSL ages obtained from folded alluvium situated just beneath the rock avalanche deposit. The source of the earthquake was probably a blind reverse fault situated beneath the asymmetric Gavbast Anticline, as support the structural and geomorphic features of the fold. The identification and dating of large coseismic landslides in the Zagros Mountains, where large earthquakes are rarely accompanied by primary surface ruptures, could help to improve both landslide and seismic hazard assessments.

On the Dynamic Fragmentation of Rock-Like Spheres: Insights into Fragment Distribution and Energy Partition

Fragmentation of blocks upon impact is commonly observed during rockfall events. Nevertheless, fragmentation is not properly taken into account in the design of protection structures because it is still poorly understood. This paper presents an extensive and rigorous experimental campaign that aims at bringing insights into the understanding of the complex phenomenon of rock fragmentation upon impact. A total of 114 drop tests were conducted with four diameters (50, 75, 100, and 200 mm) of rock-like spheres (made of mortar) of three different strengths (34, 23 and 13 MPa), falling on a horizontal concrete slab, with the objective to gather high-quality fragmentation data. The analysis focuses on the fragment size distribution, the energy dissipation mechanisms at impact and the distribution of energy amongst fragments after impact. The results show that the fragment size distributions obtained in this campaign are not linear on a logarithmic scale. The total normalised amount of energy loss during the impact increases with impact velocity, and consequently the total kinetic energy after impact decreases. It was also found that energy loss to create the fracture surfaces is a constant fraction of the kinetic energy before impact. The trajectories of fragments are related to the impact velocity. At low impact velocity, the fragments tend to bounce but, as the impact velocity increases, they tend to be ejected sideways. Although testing mortar spheres in normal impact is a simplification, the series of tests presented in this work has brought some valuable understanding into the fragmentation phenomenon of rockfalls.

Release of millions of micro(nano)plastic fragments from photooxidation of disposable plastic boxes

The widespread use of disposable plastic boxes is exacerbating the dangers of microplastics (MPs); however, little is known about the fragmentation behavior of MPs during aging. In this study, the dynamic evolution on the release of micro(nano)plastics and photoaging properties of two disposable plastic boxes (polypropylene (PP) and polystyrene (PS)) were investigated under light irradiation and mechanical abrasion. Results showed that the weight of PP and PS was decreased by 53 % and 100 %, respectively after 60 d of ultraviolet irradiation (UV60). Moreover, a large number of fragmented particles were produced from the combined light irradiation and abrasion, with 0.142 ± 0.006 and 0.141 ± 0.013 million micro(nano)plastics/mL particles from PP and PS boxes, respectively, and the nanometer range (<100 nm) accounted for 70.8 % and 46.8 %. The correlation model of the average size or alteration time versus carbonyl index (CI) was developed, which indicated that the fragmentation behavior was mainly related to the photooxidation, though mechanical abrasion also played a certain enhancing role. Additionally, PS was susceptible to the fragmentation and photooxidation compared to PP possibly since the phenyl ring of PS was more vulnerable to UV attack than the methyl of PP. The findings of this study clarify the dynamic fragmentation process of micro(nano)plastics of disposable plastic boxes and provide useful information to access environmental fate of MPs more holistically.

Effect of dynamic fragmentation on microscopic pore structure in coal: New insights into CH4 adsorption characteristics

Tectonic coal is a necessary condition for coal and gas outburst, and its pore structure is dramatically altered. The pore structure of tectonic coal has unique characteristics in terms of mechanics and gas flow, which plays a critical role in eliminating outburst risk. Therefore, it is important to study the effects of dynamic fragmentation on microscopic pore structure and CH4 adsorption characteristics of coal body. In this study, coal samples from Xintian (XT) and Pingdingshan No.6 (P6) coal mines were crushed and sieved into three particle size fractions of 0.5–1 mm, 0.2–0.25 mm, 0.074–0.1 mm, respectively, simulating dynamic fragmentation by reducing the particle size. A novel index that evaluates the average single-particle equivalent pore length was proposed. This index, Lp, provides a more comprehensive quantitative characterization of the effects of dynamic fragmentation on microscopic pore structure by considering the dynamic particle size reduction process. The LP values of large-sized samples are 23.8 to 24.6 times that of medium-sized samples; the LP values of medium-sized samples are 12.8 to 17.1 times that of small-sized samples. The experimental results show that dynamic fragmentation significantly alters microscopic pore structure, as demonstrated by the positive correlation between the Lp and particle size. With the decrease in particle size, the amount of CH4 molecules adsorbed in XT samples increases from 105.870 × 1019 p/g to 106.934 × 1019 p/g, increasing by 1.0 %; that in P6 samples increases from 39.660 × 1019 p/g to 48.037 × 1019 p/g, rising by 21.1 %. Dynamic fragmentation has a relatively insignificant effect on CH4 adsorption capacity. The total adsorption equilibrium time for XT samples decreases from 242 h to 32 h, and that for P6 samples decreases from 1146 h to 100 h as the particle size decreases. Dynamic fragmentation significantly reduces CH4 adsorption equilibrium time. The results of this study contribute to the understanding of microscopic pore structure under the effects of dynamic fragmentation and new insights into CH4 adsorption characteristics, which are of great guiding significance to the occurrence mechanism of outburst prediction and risk.

Energy dissipation and fractal characteristics of basalt fiber reinforced concrete under impact loading

Basalt fiber reinforced concrete (BFRC) has been gradually used in buildings or structures to resist high-speed impact and explosion loading because of its good dynamic performance and energy absorption capacity. The dynamic compression experiments of BFRC with basalt fiber volume content of 0, 0.13 %, 0.26 % and 0.39 % were conducted using the Φ50 mm-diameter split Hopkinson pressure bar experimental system. The effects of different strain rates (80–220 s−1) on the dynamic compression property, dissipated energy (rate), fragmentation morphology and fractal dimension of BFRC were studied. Meanwhile, the SHPB impact numerical simulation of BFRC is carried out by LS-DYNA simulation platform. The results show that the peak stress and dissipated energy (rate) of BFRC increase with the increase of strain rate. However, the increase of the loading strain rate gradually decreases the fragmentation of BFRC, resulting in the continuous increase of the fractal dimension. The existence of basalt fiber as reinforcement in concrete increases the ability of concrete to resist impact cracking. BFRC with 0.26 % basalt fiber volume has higher dynamic compressive property and energy dissipation rate, but the fractal dimension of BFRC is the smallest compared with other contents. The stress–strain curves and damage evolution of BFRC under different loading rates are discussed by numerical simulation, which is further supplement to the experimental results.

Energy Dissipation and Dynamic Fragmentation of Alkali-Activated Rubber Mortar under Multi-Factor Coupling Effect.

Recycled rubber aggregate (RRA) made from ground tire rubber has been promoted for its light weight and shock resistance. The high alkalinity of alkali-activated slag mortar has a modification effect on the surface of RRA. This paper studies the performance of alkali-activated slag mortar using RRA as aggregate (RASM), which has significance for applications in low-carbon building materials. The orthogonal test analysis method was used to analyze the significance and correlation of the main variables of the test. The dynamic energy absorption capacity and crushing state of RASM under the synergistic effect of various factors were studied using the separating Hopkinson pressure bar (SHPB) test system. The energy absorption characteristics and failure modes of RASM were analyzed by SEM and microscopic pore characterization. The results show that the increase of the alkali equivalent of the mix ratio will increase the peak value of the absorption energy of the specimen. When the size of the RRA is between 0.48 mm~0.3 mm, the dynamic energy absorption of the specimen will reach its peak value. Although the increase in the total volume of RRA will reduce the energy absorption capacity of RASM specimens, its crack resistance is enhanced.

Numerical simulations of dynamic fracture and fragmentation problems by a novel diffusive damage model

In this paper, we report numerical simulations for dynamic fracture and fragmentation problems in brittle materials using a recently developed split strain energy diffusive mass-field damage model in terms of standard finite element method (FEM). The enhanced constitutive laws for mass source and mass flux by means of strain energy decomposition are adopted to overcome certain drawbacks of the original non-split model. We present theoretical formulations in a more general way that is suitable and valid for both small and finite deformation regimes. The coupled system of equations is derived in which the momentum is governed to describe the time-dependent deformation of brittle solids whereas the mass-diffusion balance equations are for the evolution of mass density. We also develop simple techniques for determining crack velocity and estimating amount of mass loss. Numerical examples are considered for both small and finite deformations. The accuracy and performance of the developed theory for dynamic brittle fracture are illustrated through comparison and verification, which are to compare the computed results with respect to experimental data and other numerical methods in terms of crack path trajectories, dynamic response, energy dissipation, and other relevant numerical aspects.

Numerical analysis on dynamic behaviour of novel grooved cylindrical casing with different explosive loads

The grooved casing has been widely used to control the size of the fragment. In order to study the dynamic behaviour and fragmentation of the novel grooved structure casing with different explosive loads, we established a numerical model in which two kinds of grooves with different depths are alternated on the casing, and different diameter charges are used to form different explosive loading. Through the orthogonal test, the rules of casing fragmentation influenced by different factors are also obtained. The study shows that the novel grooved casing can be ruptured in two fragmentation characteristics with different fragment sizes under different explosive loads. The cylindrical casing first ruptured at Groove I and then the stress in the casing was unloaded, so that the growth of the crack at Groove II was impeded. And there were two strain bands formed from the root of the grooves, and the direction was 45° with the radius. The primary factor affecting the fragmentation of casing is the depth of Groove II, followed by the depth of Groove I and load strength under the conditions studied in this paper.

Inferring Dynamic Fragmentation Through the Particle Size and Shape Distribution of a Rock Avalanche

AbstractOn 28 August 2017, a large catastrophic rock avalanche occurred in Nayong, Guizhou Province, China. It claimed 35 lives and caused large property losses. The Nayong rock avalanche provides a rare opportunity to infer the dynamic fragmentation of rock masses from deposits. Field surveys combined with an uncrewed aerial vehicle image analysis system were performed to investigate the particle size and shape distribution along the runout path of the Nayong rock avalanche. The Weibull particle size distribution (PSD) model was tested and possesses the highest accuracy and capability over the entire range of the Nayong rock PSD, and it shows that the median size (D50) values of the particles range from 0.16 to 16.31 m along the runout path. Moreover, the evolution of D50 along the runout path confirms that the degree of rock fragmentation varies greatly in different regions. Additionally, the relative breakage (BR) of particles in the deposition area is 0.191. Particle R values increase significantly from 0.55 to 0.78 along the runout path, which indicates that the rock grinding (shape change) process continuously occurs throughout the avalanche path. The image analysis results confirm that the dominance of rock fragmentation and grinding alternates during granular flow transport. Based on these results, the classic fragmentation‐spreading model for long‐runout rock avalanches is optimized by taking into account the method by which grinding rocks increases the speed of avalanches.

Fragmentation analyses of rocks under high-velocity impacts using the combined finite-discrete element simulation

The impact-induced fragmentation of rock blocks is frequently encountered when the natural hazards (e.g., rockfalls, rockslides, and rock avalanches) occur in mountainous areas. To address the progressive damage and cracking characteristics of rock upon impacting, this paper presents a three-dimensional finite-discrete method (3D-FDEM) study on the complex impact-induced fragmentation process of rock. The influences of the impact velocity on the dynamic fragmentation process, damage evolution, fragment characteristics, fragment flying velocity, and angle were systematically investigated. The parameters as input for simulation were first calibrated by the 3D uniaxial compression tests and rock-impact tests. Then, the complex fragmentation process of rock samples subjected to different impact velocities (i.e., 20–80 m/s) was simulated. The numerical results show that the number of cohesive elements following shear-dominated failures gradually increases with increasing the impact velocity. The fractal method can well describe the distribution of the equivalent fragment length, and the variations of the fractal dimension are consistent with that of the damage ratio, increasing with impact velocity. Both the average and maximum flying velocities of the fragments increase linearly with increasing impact velocity. However, the average flying angle of the fragments shows a sharp increase and then slight increase with increasing the impact velocity.

Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain Rate Dependency and Fragmentation

The aim of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static and dynamic tensile tests. Four rocks with different lithological characteristics, namely: basalt, granite, sandstone, and marble were selected for this study. Brazilian disc experiments were performed over a range of strain rates from ~ 10–5 /s to 2.7 × 101 /s using a hydraulic loading frame and a split Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of (Kimberley et al., Acta Mater 61:3509–3521, 2013). Dynamic fragmentation during split tension mode failure has received little attention, and in the present study, we determine the fragment size distribution based on the experimentally fragmented specimens. The fragments fall into two distinct groups based on the nature of failure: coarser primary fragments, and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The average size of the secondary fragments has a strong strain rate dependency over the entire testing range, while the primary fragment size is less sensitive at lower strain rates. Marble and sandstone are found to generate more pulverised secondary debris when compared to basalt and granite. Furthermore, the mean fragment sizes of primary and secondary fragments are well described by a power-law function of strain rate.

Study on size and load rate effect of dynamic fragmentation and mechanical properties of marble sphere

Impact-induced fragmentation of rock blocks is a frequent phenomenon during rockfall, mining, geotechnical engineering. In order to obtain the fragmentation characteristics of rocks under the action of impact, the marble spheres with diameters of 30, 35, 40, 45, and 50 mm were used for paired-impact using the Split Hopkinson Pressure Bar (SHPB) tests, at the impact velocities of 4.5, 7.4 and 11.2 m/s, respectively, and the corresponding load and failure characteristics of each sample were examined. The experimental results revealed that the peak loading capacity and fragmentations of the rock sphere was influenced by the sample size and impact velocity. The finite element method (FEM) simulation by LS-DYNA was carried out to reveal the failure mechanism of marble spheres under paired-impact. Finally, a theoretical model was proposed to evaluating the breakage of rock block under impact. The results can be used to guide rock breakage in mines and rockfall hazard protection.

Insights into the differential fragmentation processes in rock avalanche emplacement from field investigation and experimental study

Fragmentation is a universal phenomenon associated with rock avalanches, resulting in an abundance of complex sedimentological structures. If studied in detail, these structures can provide insights into rock avalanche emplacement processes. Here, six typical avalanche cases are carefully analyzed in conjunction with an analogue experiment. Findings reveal the carapace facies is characterized by clast-supported structures composed of large blocks with sedimentological structures that include retained stratigraphic sequences, imbricate structures, and jigsaw structures. The body facies presents a high degree of fragmentation, with block-rich zones, fine matrix-rich zones, jigsaw structures, and inner shear zones. The basal facies displays the highest degree of fragmentation, however, it is mainly composed of millimeter grains with thin shear strips. Consistent with the field investigations, differential fragmentation is also observed in the analogue tests, with the vertical dimension of the carapace facies mainly fragmented along the lines of pre-existing structures; the body facies fragmented with an abundance of new fractures; and the basal facies fragmented into fine grains. Meanwhile, layer sequences preserved in longitudinal and vertical profiles are also observed in the analogue tests, indicating a low disturbance in the propagation. We, therefore, propose that a process characterized by a sparse state, dominated by collisions, minor disturbance, and pervasive dynamic fragmentation likely occurs in the carapace facies, with fragmentation mainly controlled by the breakage of pre-existing, fully-persistent structures. The body facies is mainly controlled by the fracturing of the weak, less-persistent structures, and the basal facies displays the highest degree of fragmentation with an abundance of new fractures. In the entire propagation, the avalanche mass displays low-disturbance laminar flow.

Quasi-static and dynamic compressive behavior of BN-BAS composite ceramic at room temperature and 1000 °C

Abstract Boron nitride-barium aluminosilicate (BN-BAS) composite ceramic specimens were prepared by using hot-press sintering at 1700 °C and 20 MPa from composite powders prepared by employing the sol–gel method. The dynamic compressive behaviors of these BN-BAS composite ceramic specimens were investigated by using split-Hopkinson-pressure-bar set-ups at room temperature and 1000 °C. The effects of the strain rate on the dynamic compressive strength, fragment size, and microstructure were investigated. The quasi-static mechanical properties of the composite ceramics were also tested. The results indicated that the quasi-static and dynamic mechanical properties of BN-BAS composite ceramics at 1000 °C were lower than those at room temperature, and this was caused by the crack propagation in the ceramic specimens at high temperatures owing to the high thermal expansion coefficient of hexacelsian. The dynamic compressive strength of the composite ceramic increased linearly with an increasing strain rate. Flake-like h-BN particles absorbed a large amount of energy through bridging and pull-out, which prevented macroscopic breakage of specimens at strain rates lower than 850 s −1 at the initial failure stage at room temperature. As the strain rate increased, the cracks changed from long and sparse to small and dense reticularly distributed ones, and the fragment size decreased accordingly.

Influence of mineral mesoscopic structure on rock dynamic fragmentation under compression

Three types of rock were chosen to investigate the effect of mineral mesoscopic structure on rock fragmentation under dynamic compression. The fragments collected from the tested sandstones and granites were studied using an image-processing method, and the relationship between the fractal dimension of rock fragments and the mechanical properties in dynamic compression was established. Four failure patterns (apparently intact, local splitting, fragmentation and pulverisation) were classified according to the stress–strain behaviour and fragment distribution of the rock. Moreover, rock fragments of porous sandstone are blocky in form while they are more elongated in granite, as attributed to the difference in failure mode on the mesoscopic scale. This study is meaningful for the understanding of rock dynamic fragmentation and useful for the optimisation of rock breaking in the development of underground space.

Petrographic and Geotechnical Characterization of the Magmatic Formations from Hadjer El-Hamis and Dandi (Hadjer-Lamis Province, Chad) for Their Use in Civil Engineering

This paper deals with the magmatic rocks from Hadjer El-hamis and Dandi located in the Hadjer-Lamis Province (Chad). Indeed, Chad is actually engaged in several construction project and consequently needs a large quantity of good quality construction materials. The present study is in straight line with this logic and aims to determine the petrographic and geotechnical characteristics of the Hadjer Lamis rocks in order to define their use in civil engineering. In this area, rocks outcrop in the form of mounds displaying hexagonal, pentagonal and tetragonal prisms in Hadjer El-hamis, and as fractured blocks in Dandi. Petrographic analyses show that rocks from Hadjer El-hamis are rhyolite displaying porphyritic to locally glassy microlitic texture with mineralogical quatz, alkaline feldspar, pyroxene, biotite and opaque minerals. Rocks from Dandi granites (microgranite, porphyritic microgranite and granite) with massive structure and fine grained (microgranite), fine grained porphyritic micrograined and gritty texture composed of quartz, orthose, plagioclase, pyroxene, biotite and opaque minerals of variable proportions from one rock to another. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; The geotechnical analyses carried out on the crushed masses of the sites of Hadjer El-hamis and Dandi concerned their physical and mechanical characteristics. Their physical characteristics show that their average specific density values are 2.40g/cm3 and 2.60g/cm3 and bulk density are 1.41g/cm 3 and 1.38 g/cm 3 respectively for Hadjer El-hamis and Dandi samples. The average values of flattening coefficients are respectively 12.19% and 10.6% for&nbsp; Hadjer El-hamis and Dandi areas. The mechanical characteristics of the studied materials on the basis of average values show that building materials from Hadjer El-hamis resist better to wear than those from Dandi, This difference in mechanical properties is certainly due to the petrographic nature characterized respectively by volcanic rocks in Hadjer El-hamis and plutonic in Dandi. Regarding resistance to impact, the geotechnical material from these two areas show very close average values of Los-Angeles coefficient and dynamic fragmentation coefficient recommended for civil engineering works. It appears from this research work that the studied materials are recommended for civil engineering work except for the sample E6 which presents too high Micro-Deval and Los-Angeles coefficients thus requiring a preliminary treatment before use.