Gravel Soil Research Articles

Shaking table test and numerical research on seismic response of a CFST arch bridge for different soil grounds

Severe damages or failures of arch bridges on different soil grounds have been reported during previous strong earthquakes. The influence of different soil grounds on the seismic response of arch bridges is unclear. In this study, three large-scale shaking table tests were conducted to investigate the seismic response of a model bridge abutment of a concrete-filled steel tubular (CFST) arch bridge, which was set inside a model soil box at a reduced scale of 1/90. Grounds with three types of soil were simulated: silty clay, clay-gravel layered, and bare gravel soil. The accelerations and displacements of the model soils and the sliding displacement and settlement of the model bridge abutment were evaluated through the tests. The test results showed that the soil types significantly affected the seismic response of the soil and bridge abutment system, and the spectral characteristics of input waves significantly affected the acceleration amplitude ratio (AAR) of the bridge abutment; however, the changing trend of the AAR was usually related to the corresponding soil types. The soil grounds exhibited a remarkable filtering effect along the soil heights under seismic excitations, and the filtrations of the frequency components of the input waves for different soil grounds shows significant difference. Furthermore, the dynamic shear stress–strain curves showed that the silty clay soil remained in the nonlinear behavior development stage under strong seismic excitations, while the bare gravel soil remained in the linear behavior development stage. The energy dissipation capacity of the bare gravel soil ground could not be utilized. The test results in this study can be used for seismic risk assessment of different soil grounds, to guide the optimal seismic design of arch bridges for different soil grounds.

Failure mechanism and treatment measures of supporting structures at the portal for a shallow buried and asymmetrically loaded tunnel with small clear-distance

The construction of a tunnel portal faces the challenges of complex geological conditions, such as shallow burial and asymmetrical loading. In addition, the adverse effects of factors such as the layout form of the tunnel must also be considered. Thus, the construction of portals has always been the focus of tunnel engineering. Under the coupling of multiple adverse factors, such as complex geological conditions and special layout form, the tunnel portal is prone to excessive deformation, supporting structural cracking, and even collapse during excavation. In this study, a shallow buried and asymmetrically loaded tunnel with a small clear-distance in northwest China was considered as an engineering case. To address the distresses of slope instability, peeling off and block falling of primary support concrete, and cracking of secondary lining concrete in the tunnel portal construction, combined with field investigations, statistical analysis, numerical simulation, and deformation monitoring, the failure mechanism of supporting structures was deeply studied and corresponding treatment measures were proposed. The research results indicated that loose and broken gravel soil in the shallow buried section, asymmetrical loading, surface water infiltration, and short construction spacing between the two tunnels were the main triggers of supporting structures failure. Affected by topographic bias, the loose load generated by the surrounding rock on the deeply buried side squeezed the entire tunnel to the shallow buried side after portal excavation. This deformation trend became more significant after the gravel soil deteriorated by water immersion. The retaining wall produced a clockwise rotation deformation around the wall corner in the process of limiting the tunnel deviation, and the local wall body cracked owing to excessive tensile stress. The primary support concrete and secondary lining concrete produced excessive asymmetrical deformation because of significant asymmetrical loading. Concrete with excessive deformation was cracked by obvious tensile or shear stresses. The subsequent tunnel excavation had a significant negative impact on the stability of the prior tunnel. Combining the failure mechanism of the supporting structures and the characteristics of the continuous development of cracks, the treatment measures of ‘stabilize the stratum first and then treat the cracks’ were proposed, including the backfilling and tamping the shallow buried side at tunnel portal, reinforcing the interlaid rock by ground surface grouting, setting intercepting ditch at the slope top, and staggering a certain safe excavation distance between the following tunnel and the prior tunnel. Field monitoring and patrol inspection results indicated that the proposed treatment measures achieved the expected results. The research results can provide corresponding construction experience and suggestions for similar projects in future.

Testing the Functional and Phylogenetic Assembly of Plant Communities in Gobi Deserts of Northern Qinghai-Tibet Plateau.

The mechanism governing plant community assembly across large-scale Gobi deserts remains unclear. Here, we inferred the roles of different assembly processes in structuring plant communities in the Gobi deserts of the Qinghai–Tibet Plateau by using a phylogenetic tree, and leaf and root traits. The functional and phylogenetic structures of 183 plant communities were assessed, and their distributions were linked with environmental gradients. Our results demonstrated that functional convergence was prevalent in most functional traits (75% of the traits) and accentuated when all traits were combined. The phylogenetic structure exhibited significant divergence. We observed the contrasting response of functional and phylogenetic assembly structures to environmental gradients. More importantly, we found that the shifts in the functional assembly along environmental gradients were trait-specific, with dominant roles of local factors, such as gravel coverage and soil attributes, in determining the distribution patterns of most traits. However, the distribution patterns of leaf P concentration (LPC), root N concentration (RNC), and root P concentration (RPC) were mainly driven by climatic factors. These results reveal that niche-based processes, such as abiotic filtering and weaker competitive exclusion, are the major drivers of species co-occurrence, which results in the widespread coexistence of phylogenetically distinct but functionally similar species within the Gobi plant community. Our findings could improve the understanding of plant community assembly processes and biodiversity maintenance in extremely harsh drylands.

Natural variation in root suberization is associated with local environment in Arabidopsis thaliana.

Genetic signature of climate adaptation has been widely recognized across the genome of many organisms; however, the eco-physiological basis for linking genomic polymorphisms with local adaptations remains largely unexplored. Using a panel of 218 world-wide Arabidopsis accessions, we characterized the natural variation in root suberization by quantifying 16 suberin monomers. We explored the associations between suberization traits and 126 climate variables. We conducted genome-wide association analysis and integrated previous genotype-environment association (GEA) to identify the genetic bases underlying suberization variation and their involvements in climate adaptation. Root suberin content displays extensive variation across Arabidopsis populations and significantly correlates with local moisture gradients and soil characteristics. Specifically, enhanced suberization is associated with drier environments, higher soil cation-exchange capacity, and lower soil pH; higher proportional levels of very-long-chain suberin is negatively correlated with moisture availability, lower soil gravel content, and higher soil silt fraction. We identified 94 putative causal loci and experimentally proved that GPAT6 is involved in C16 suberin biosynthesis. Highly significant associations between the putative genes and environmental variables were observed. Roots appear highly responsive to environmental heterogeneity via regulation of suberization, especially the suberin composition. The patterns of suberization-environment correlation and the suberin-related GEA fit the expectations of local adaptation for the polygenic suberization trait.

Study on the Tensile Properties and Application of Gravelly Soil Reinforced by Polypropylene Fiber

Incorporating fibers into gravelly soil is an effective method to prevent the core wall of high earth core rockfill dams (ECRDS) from cracking. In this study, a new type of soil tensile device was used to carry out tensile tests on gravelly soil with different gravel contents and fiber contents. The test results show that as the gravel content increases from 0% to 50%, the improvement in tensile strength decreases from 48.9% to 6.4%, which means the increase in gravel content reduces the improvement in tensile strength significantly. The ultimate tensile strain, tensile strength, and post-peak tensile strength of fiber-reinforced gravelly soil are positively correlated with the fiber content. Combined with the Scanning electron microscopy (SEM) results, the reinforcement effect of the three types of fiber interfaces on the gravel soil is qualitatively analyzed, and the microscopic mechanism of the improvement of the tensile strength of fiber-reinforced gravelly soil is revealed. The energy absorption capacity (EAC) results showed that the lower the gravel content in the soil, the higher the degree of improvement in the EAC value. In practical application, it is recommended to use gravel soil with low gravel content and high fiber content. Finally, a regression model considering the gravel content and fiber content was proposed for fast predicting the tensile strength of the soil. The related results can provide references for the anti-cracking design of the core wall of high ECRDS.

Liquefaction assessment of gravelly soils: the role of in situ and laboratory geotechnical tests through the case study of the Sulmona basin (Central Italy)

Even though liquefaction in gravelly soil is well documented in many earthquakes since 1891, most of the “simplified procedures” and national buildings codes still consider only sandy soil liquefaction in seismic hazard assessment. In this study, 109 sites of gravel liquefaction related to 27 historical earthquakes from 1891 to 2020 are reported, with a wide range of moment magnitudes, Mw , (5.3 to 9.2) and focal depths (5.4 to 33 km), highlighting the potential for liquefaction of gravelly soils even during moderate earthquakes. Although gravels are often thought to have hydraulic conductivities high enough to preclude liquefaction, gravels that have liquefied are generally well-graded sandy gravels. The sand content is typically 30% or more so that the hydraulic conductivity is governed by the sand size making them clearly liquefiable. Even for gravels with lower sand contents, a low permeability surface layer has often been observed that could restrict drainage and produce excess pore pressure during strong shaking.The epicentral distance calculated for gravel liquefaction sites plotted vs the magnitude of the earthquake event shows a pattern which closely follows similar curves provided in the literature for sandy soils. However, field observations of liquefaction in gravelly soils are less frequent in the historical record.In addition to examining gravel liquefaction sites in general, this paper provides a case history illustrating the difficulties of liquefaction assessment in gravels at a site in Santa Rufina (Sulmona basin, Central Italy). This site, characterised by high vertical and lateral stratigraphic variability, was selected for gravel liquefaction assessment using a combination of in-situ tests, laboratory geotechnical analysis, and geological studies. We found that, even if SPT- and DPT- based in-situ methods provide conflicting results, the availability of a borehole log, along with standard laboratory test results, proved to be fundamental to achieving a reliable assessment of the liquefaction hazard.

Hydrological simulation and assessment of the optimal parameters of the water replenishment of the floodplain lake and old riverbed on the Uzh river

One of the tasks in modern approach of the water resources management is improving environment health by the way of the river restoration. On the urban area it is impossible to provide full river restoration, but at the same time it is possible to create the environment close to natural. In our work on the example of the river Uzh located inside the city provides the assessment of the restoring possibility of the part of the floodplain by water replenishment of the old riverbed during the vegetation season. Flood control dyke construction interrupted the connection between old riverbed and river and as a result floodplain lake became muddy, silted up and lost its attractive form. To assess the possibility of the floodplain lake replenishment, the simulation of some scenarios were carried out: natural condition, water replenishment during flood, pumping water, raising water level in the river Uzh near the lake. The connection of the lake and the old riverbed with the river will improve slightly the storage capacity of the lake and allows to provide the depth of up to 1.0 m in the lake during flood, but the water will be absent in the old riverbed during the dry season. Hydraulic calculation showed that replenishment during spring floods and pumping water were not possible due to high hydraulic conductivity of the gravel and pebble soils. The old riverbed replenishment is possible by raising water level in the river Uzh, which will ensure the free water flow into the lake and into the old riverbed during the dry season.

Gravel liquefaction assessment using dynamic cone penetration and shear wave velocity tests based on field performance from the 1964 Alaska earthquake

Evaluating the liquefaction potential of gravelly soils using in-situ testing remains a challenge in geotechnical engineering practice. The Chinese Dynamic Cone Penetration (DPT) test provides an alternative for in-situ testing in gravelly soils to Becker Penetration Test (BPT) and the Standard Penetration test (SPT). The Chinese DPT was recently correlated with liquefaction resistance based on field performance data from the Mw 7.9 Wenchuan earthquake. In this study, liquefaction resistance was evaluated using the DPT and shear wave velocity measurements at eight sites in Seward and Old Valdez, Alaska, where gravel liquefaction took place and two sites in Valdez, where no liquefaction occurred in the 1964 Alaska earthquake. The DPT-based liquefaction triggering curve predicted liquefaction potential at all test sites with moderate accuracy. N′120 blow counts from SPT hammers were generally consistent with those from the DPT hammer after energy correction. Back-calculated energy correction factors were typically within 10% of the theoretical energy correction factor. These results suggest that the DPT can provide liquefaction hazard evaluations accurately and economically for many gravelly soils. Liquefaction evaluations using currently available Vs-based triggering curves developed for sands often indicated no liquefaction at sites where liquefaction occurred at the Alaska sites. In contrast, a Vs-based triggering curve developed from a data set of gravelly soil sites correctly predicted liquefaction at all sites.

Effect of hydraulic conductivity and impeded drainage on the liquefaction potential of gravelly soils

Investigating the role of sand and fines content and in situ drainage conditions in governing the hydraulic conductivity of gravelly deposits is highly important to characterize the liquefaction potential of gravelly soil. In this study, a variation of hydraulic conductivity with sand content has been empirically obtained based on the existing gravel liquefaction case histories. It is found that the hydraulic conductivity of a soil matrix having more than about 20%–30% sand content by mass is low enough to cause liquefaction without the presence of any impervious confining layer. In addition, a numerical study has been performed using the commercial software FEQDrain to study pore pressure generation in gravelly soil at a variety of relative densities and hydraulic conductivities with and without an impermeable cap layer when subjected to a variety of earthquake loadings. For both unconfined and confined condition, excess pore pressure ratios consistently increase with a decrease in hydraulic conductivity ( k) and relative density ( Dr). Excess pore pressure ratio is correlated with hydraulic conductivity, soil compressibility, and cyclic stress ratio (CSR). For the confined condition, pore pressure in the gravel layer is primarily governed by the overlying cap layer and even a sandy cap layer instead of highly impervious clay layer can cause liquefaction.

Geotechnical and Mechanical Characterization of Lateritic Soil Improved with Crushed Granite

Since many years, road infrastructures in West Africa are most often subject to premature degradations despite the large number of studies. This problem is often due to the poor control of the behaviour of materials used for the pavement, but also to the scarcity of good quality materials. Nowadays, with economic development, there is a necessity for road infrastructures of good quality. In this framework, the main objective was to study the vertical geotechnical variability of the gravelly lateritic soil from the Saaba site in Burkina Faso and to improve their performances by adding crushed granite. The results show that the physical properties of the soils are almost identical depending on the depth. However, a small difference in the mechanical properties was observed. Due to their poor characteristics, these materials cannot be used for the sub-base layer according to the pavement design guide for tropical countries, CEBTP [1]. In order to improve their geotechnical and mechanical characteristics, crushed granite of class 0/31.5 mm was added at different percentages: 20, 25, 30, and 35%. It appears that the plasticity index, the methylene blue value, as well as the optimal water content of the material decreased. The soaked CBR recorded a maximum relative increase of 164% (from 14 to 37%) with the addition of 20 to 30% of crushed granite. With the addition of 20 to 30% of crushed granite, Young's modulus and unconfined compressive strength also showed a clear increase of 309% (from 80 to 327 MPa) and 140% (from 0.72 to 1.73 MPa). By comparing the results with the CEBTP specifications, the addition of 30% of granites at 95% compactness allows the materials to have a CBR that exceeds the value of 30% and can be used in the sub-base layer of road pavement. The addition of 30% granite allows the materials to record an unconfined compressive strength higher than 0.5-1.5 MPa, which corresponds to lateritic soil suitable for sub-base layer according to Messou [2]. After the addition of 30% granite, the materials record a Young's modulus greater than 300 MPa and can be used as a base layer. The assessment of the improvement of mechanical performance simultaneously based on the CBR, the Young's modulus, and the compressive strength showed the contradictory evolution of the results from these different parameters. A discussion was made on the relationship between these parameters. Doi: 10.28991/CEJ-2022-08-05-01 Full Text: PDF

Stabilization of the Gravels Material for Road Sub-Base: Flexible Pavement

Abstract: In many parts of India, high-quality aggregates that match the standards are becoming increasingly scarce and expensive. High-quality aggregates are required in both the base and sub-base course according to traditional flexible pavement requirements. In many circumstances, locally available aggregates do not fit the standards, and the aggregates that do must be transported over vast distances. This act greatly raises the cost of their construction, as well as their ongoing maintenance and restoration. Thus, in a big country like India, using locally available marginal materials in flexible pavement building is one of the viable solutions to high pavement construction costs and a lack of quality aggregates sources. A broad definition of a marginal aggregate is "any aggregate that does not fully conform to the specifications used in a country for normal road aggregates but can be successfully used in special conditions, made possible by climatic characteristics or recent advances in road techniques, or after being subjected to special treatment." So, if the usage of local resources can be permitted through appropriate material or structural design modifications, construction can be hastened and significant monetary savings can be realised. The study's major goal is to add cement and bitumen emulsion to locally accessible gravel soil/marginal aggregate (Moorum) to improve its qualities. An attempt has been made to use cement for increasing the strength of the gravel and emulsion for increasing the water resisting capacity. The whole work involves increasing strength of gravel soil (Moorum) and expressed in terms of CBR and UCS value.

A Synthetic Chart for Internal Stability Assessment of Soils Based on Soil PSD Curves

Awareness of granulated soils’ internal instability is an important parameter when designing granulated filters, and the ability of a granulated soil’s internal stability can be verified using the soil PSD (Particle Size Distribution) curves’ secant slopes. The current work presents a new method to calculate the soil PSD curves’ secant slopes automatically, and a synthetic diagram is presented for the potential examination of the granulated soils’ internal stability. To verify the feasibility and accuracy of this synthetic diagram, 80 specimens of soil were investigated in this work and categorized into two groups: 50 sand–gravel soils and 30 (clay)–silt–sand–gravel soils. The obtained conclusions indicate that the internal stability and instability potentials of sand–gravel soils can be distinguished successfully with a synthetic chart and the Kenney and Lau criterion but cannot be assessed with the Kezdi and Sherard criteria. None of the criteria studied here can be used for the internal stability assessment of silt–sand–gravel and clay–silt–sand–gravel soils.

Experimental study on mechanical properties of core wall gravel soil of 300-m super high rockfill dam

Experimental study on mechanical properties of core wall gravel soil of 300-m super high rockfill dam

Valuable phosphorus retained by ironstone gravels can be measured as bicarbonate extractable P

The > 2 mm fraction of soils is often excluded from laboratory analysis and glasshouse experiments, but is known to influence whole soil physical, chemical and biological properties. The historical focus on the < 2 mm fraction has led to a knowledge gap in analytical procedures and flow-on effect for agronomic response and advice when the > 2 mm fraction is present, especially when it is porous and chemically reactive.An ironstone gravel soil (Endopetric Pisoplinthic Plinthosol (Arenic)) from south west Western Australia was separated into < 2, 2–4, 4–6, 6–8 and 8–10 mm fractions. Physical analysis included specific surface area (SSA), optical mineralogy, XRD and SEM. Chemical analysis included phosphorus (P) sorption, P retention index (PRI), P buffering index (PBI) and sodium bicarbonate extractable P (Cowell P) on intact and ground samples, and intact mixtures of the < 2 mm and > 2 mm fractions. Δ NaF pH was used as a surrogate P retention measure on intact mixtures of the < 2 mm and > 2 mm fractions.P adsorbed onto the > 2 mm fraction can be measured as Colwell P, suggesting this fraction can provide P to plants. Colwell P determined on ground samples was correlated 1:1 with Colwell P on intact counterparts. Grinding of samples resulted in large increases in PRI and PBI, and is not a supported sample preparation, neither is the use of end over end shakers due to surface abrasion of the > 2 mm fraction increasing P sorption, however the use of Δ NaF pH as a surrogate measure of P sorption offers some potential.Phosphorus adsorption decreased with increasing particle size but adsorption by the > 2 mm fraction is likely significant in the context of an entire unsieved soil and was influenced by SSA. The > 2 mm fraction had higher SSA than their physical size would imply, possibly influenced by the thickness and mineralogy of the exterior coating (rind). Our results show that the > 2 mm fraction contains reactive surfaces that can contribute to the nutrient holding capacity and plant available P of soils.

Evaluating the applicability of conventional CPT-based liquefaction assessment procedures to reclaimed gravelly soils

Gravelly soils are not well represented in current semi-empirical liquefaction procedures, which raises the question of whether state-of-the-practice liquefaction evaluation methods based on sands are applicable to gravelly soils. This paper investigates the applicability of Cone Penetration Test liquefaction triggering and settlement evaluation procedures to case histories of well-graded reclaimed gravelly soil at CentrePort, New Zealand. Sensitivity studies of the liquefaction triggering analysis show the uncertainty in the cyclic demand is larger than the uncertainty in the cyclic resistance within a critical layer. However, the modelling uncertainty over the entire depth of the fill is larger for the cyclic resistance, which can vary by over 50% due to a single material-characterization parameter, i.e., the fines content or soil behavior type index. Sand-based procedures for evaluation of liquefaction-induced settlement are found to be generally applicable to well-graded gravels that have a dominant silty sand fraction in the soil matrix, though they can overestimate the relative density and therefore underestimate post-liquefaction settlement of gravelly soils. The paper emphasizes the importance of soil composition, dominant soil fraction of the soil matrix, and its effects on the soil packing, penetration resistance, and liquefaction resistance in the context of current semi-empirical liquefaction evaluation procedures. • CPT-based liquefaction procedures are applicable to some gravel-sand-silt mixtures • Soil composition and dominating soil fractions are key to liquefaction assessment • FS L is more sensitive to uncertainties in PGA than FC or I c • Use of a constant FC throughout seemingly uniform fill could be problematic • Sand-based methods overestimate D R and underestimate settlement of gravelly soils

An evaluation method for internal erosion potential of gravelly soil based on particle size distribution

An evaluation method for internal erosion potential of gravelly soil based on particle size distribution

Analysis of Area Potential Landslides on Elak Roads Using Geoelectrical Methods

A landslide is a geological event that occurs when rock masses move together. The combination of high rainfall and steep topography and weathered rock creates a landslide-prone environment The many deformations and cracks along Jalan Lintas Elak indicate that the area is prone to landslides. This condition is unquestionably linked to the lithological conditions beneath the surface: Resistivity data measurements were carried out using the electrical resistivity method of the Wenner-Schlumberger array on two-line with a length of each line of 220 m to determine these conditions. The presence of a weak zone with shallow resistivity values (1 - 4 m) located at a depth of 5 - 16 m caused the liquefaction that occurred on the ELAK1 at a distance of 84 – 148 m, according to the results of the cross-sectional resistivity model processed using the Res2DInv software. At a distance of 85–156 meters on the ELAK2, a barrier of sand, gravel, boulders, and clay causes soil subsidence and deformation. This occurs because there is a weak clay rock layer with a resistivity value of ( 5 m) at a depth of 9 m and the tunnel's location

Model test on the development of thermal regime and frost heave of a gravelly soil under seepage during artificial freezing

In order to investigate the development of thermal regime and frost heave of a gravelly soil under seepage during artificial freezing, a large-scale model test system was designed. The typical gravelly soil in Beijing obtained from a construction site was taken as the study object. Artificial freezing tests were carried out on the soil layer under different seepage velocities. The test results indicated that the greater was the seepage velocity, the longer the closure time of frozen wall was needed, while the frozen wall would not intersect when the seepage velocity was too large. Lagged frost heave was observed after the thermal balance was reached. The frost heave of soil layer increased with the increase in the distance from the freezing pipes. Within the frozen range, frost heave increased with the increase in seepage velocity. Under seepage, the soil layer would turn into a soil of weak frost heave according to the Chinese code, while it was classified as non-frost heave under the hydrostatic condition. The model test showed that when the artificial ground freezing is used in the gravelly soil layer under seepage, the influence of seepage on thermal regime should be sufficiently considered, and considerable frost heave of soil layer might be expected.

Geotechnical soil mapping from electrical and mechanical properties: Case study of the Bafoussam urban area, west Cameroon

Preliminary work in civil engineering works often involves the investigation of soil support in order to secure or predict project safety. The objective of this work is to purpose an urban geotechnical soil map combining physical and mechanical behaviour of the soil and its electrical properties. Field work with auger corer allowed collection of samples for analysis. The results of the Atterberg limits and particle size analysis enabled classification of those soils according to HRB as silty or clayey gravels and sands (class A-2-7) and clayey soils (A-7-5). The Casagrande Plasticity Diagram classifies them as At and Lt (very plastic clays and silts) and the GTR classifies them as sandy and gravelly soils with fines (B6) and fine clay soils (A2 and A3). These classifications show that the study area is mainly covered by sandy-clay, lateritic clay and lateritic gravelly soils. The iso-resistivity maps and resistivity sections made from the results of vertical electrical soundings, allow the identification of three ranges of resistivity: a low resistivity less than 300 Ώ.m, a medium resistivity range between 300 and 500 Ώ.m and a high resistivity greater than 500 Ώ.m. These ranges of resistivity correspond to the different formation disparities that make up the subsurface. Associated penetrograms show these soils are very resistive in the cuirass subsurface zones with very compact formations with permissible stress values between 2.5 and 5.2 bars. At greater depths, these values are moderate in the clayey sands with stresses between 0.8 and 3 bars and low in the clays and lateritic soils (˂1 bar). The application of determination coefficient (R2) and Spearman correlation (rs) between permissible stress and true resistivity gives values of 0.79 and 0.74 respectively. There is a good qualitative and quantitative correlation between these two parameters in the study area. The superimposition and comparison of the different results with the geological formations enables development of a geotechnical soil map. This map enables us to understand the lithological and mechanical heterogeneity of the soils during the construction of structures in the urban perimeter of Bafoussam.

Seismic Wave Propagation Characteristics and Their Effects on the Dynamic Response of Layered Rock Sites

To investigate the seismic response of layered rock sites, a multidomain analysis method was proposed. Three finite element models with infinite element boundaries for layered sites were analysed. The results of this multidomain analysis show that stratum properties and elevation have an impact on wave propagation characteristics and the dynamic response of layered sites. Compared with the rock mass, the overlying gravel soil has a greater dynamic amplification effect at the sites. A time domain analysis parameter PGA(IMF) was proposed to analyse the effects of different strata on the seismic magnification effect of layered sites, and its application was also discussed in comparison with PGA. According to the frequency domain analysis, the interface of the rock mass strata has a low impact on the Fourier spectrum characteristics of the sites, but gravel soil has a great magnification effect on the spectrum amplitude in the high-frequency band (≥30 Hz) of waves. Moreover, the stratum properties have a great influence on the shape and peak value of the Hilbert energy and marginal spectrum at layered sites. When waves propagate from hard rock to soft rock, the peak value of the Hilbert energy spectrum changes from single to multiple peaks; then, in gravelly soil, the Hilbert energy spectral peak, its nearby amplitude and the amplitude in the high-frequency band (28–36 Hz) are obviously amplified. The frequency components and amplitude of the marginal spectrum become more abundant and larger from rock to gravelly soil in the high-frequency band (28–35 Hz).