Gravel Soil Research Articles

Shaking-Table Tests for Seismic Response of Arch Foot of a Long-Span Arch Bridge on Sand-Gravel Soil Sites Considering SSI Effect

ABSTRACT The seismic performance of arch bridges is dependent on the strength of bridges and the built-on soil site types. To investigate the influence of soil-structure interaction (SSI) on the seismic response of an arch-foot arch bridge with a sand-gravel soil site, several shaking-table tests for a 1/90 downscaled arch-foot model placed on sand-gravel soil were conducted based on the engineering prototype of the third Pingnan Bridge with a long-span concrete-filled steel-tube (CFST) arch bridge. The test results showed the following: (1) The seismic acceleration response of both the sand-gravel soil site and arch foot were amplified, which is related to both the non-linear dynamic behavior of sand-gravel soil and frequency-spectrum characteristics of the input seismic waves. (2) The sliding displacement of the arch foot under strong ground motions increased accompanied with a settlement of the soil surface. However, the safety risk of the arch foot may be underestimated in seismic design. (3) The dynamic shear stress-strain loops of sand-gravel soil exhibited a high-energy dissipation capacity, and the energy-transfer mechanism at the interface between the model soil and arch foot was integrated. The results obtained are expected to provide insights into the dynamic interaction behavior of the gravel soil and arch bridge systems and the seismic design of arch bridges built on sand-gravel soil sites in practical engineering.

Monotonic and cyclic triaxial testing of untreated and polyurethane-treated soil and soil–rubber mixtures

The present research focuses on developing alternate sustainable base materials for a high-speed slab track. In this study, a series of monotonic triaxial, cyclic triaxial and permeability tests were conducted on four types of materials, viz. mix-A (gravel soil), mix-B (soil mixed with rubber), mix-C (polyurethane foam adhesive (PFA)-treated soil), and mix-D (PFA-treated soil–rubber mixture). The influence of cyclic loading frequency, effective confining pressure, drainage condition and relative density on the deformation, excess pore water pressure, resilient modulus and damping ratio of these different mixes is evaluated. The monotonic triaxial test results indicate that the PFA treatment of mix-A and mix-B increased their shear strength and critical state strength. In contrast, incorporating rubber into mix-A and mix-C helped enhance their ductility. The cyclic triaxial test results show that the PFA treatment of mix-A and mix-B significantly reduced the magnitude of deformation and generation of excess pore water pressure, which caused these untreated mixes to fail prematurely under lower confinement to which a typical base layer is subjected. The influence of cyclic loading frequency and effective confining pressure on the material's response differed for untreated and treated soil. The permeability test results indicate good drainage for mix-D comparable to mix-A.

Pedogenesis of soils formed on jurassic calcareous sedimentary rock formations: A transect study in northern semi-arid highlands of Ethiopia

With the objective of examining soil characteristics, pedogenic processes and classification in association to local environmental and landscape attributes, a transect study was carried out in Hnitalo Wajerat district of Northern Ethiopia. Six pedons beded on shale and dolerite parent rocks were investigated. The soils were sandy loam to clay in texture, moderately porous, neutral to strongly alkaline, nonsaline, base-rich and calcareous. The dominant pedogenic processes prominent in soils of the area were calcification, vertization, argilluviation, melanization and colloidal eluviations. Mollic and ochric horizons were noticed on surface horizons, while cambic, calcic and vertic horizons were found to be the dominant subsurface horizons. Steep upslope areas were characterized by shallow gravelly soils with continuous hard rock. Shrink-swell cracks, colluvic materials and deep soils were prominent on flat areas. The soils of the area were classified as Leptosols/Entisols, Cambisols/Inceptisols, Calcisols/Aridisols and Vertisols. The study evidenced that the pedogenic processes and soil development were largely patterned by terrain positions, lithology and land use type.

Evaluating screw-shaft pile composite foundations in round Gravelly soil: A study using model tests and numerical simulations

Screw-shaft piles have seen extensive adoption in construction and railroad engineering, due to their superior enhanced bearing capacity and cost-effectiveness. While monopiles have been thoroughly examined, composite foundations that include screw-shaft piles have not been studied as extensively. Proper determination of geometric parameters for both the piles and the cushion is a critical aspect of successful design. This paper introduces a comprehensive examination that merges indoor experiments with numerical simulations, aiming to evaluate the bearing capacity, settlement characteristics, and force characteristics of screw-shaft piles under a variety of conditions. This study scrutinizes key components, such as root diameter, pitch, cushion modulus, and the threaded portion's proportion. The research outcomes offer crucial insights for optimizing the design parameters of screw-shaft pile composite foundations. The results indicate that the side resistance of screw-shaft piles initially increases with the threaded section's length, stabilizing at an optimal length of approximately 0.44–0.55 times the pile length (L). Furthermore, although decreasing the pitch improves bearing capacity, it also introduces variations in pile material usage, with optimal bearing performance noted at a pitch approximately equal to the diameter (D). Moreover, screw-shaft piles with thread widths ranging between 0.58D and 0.67D show a significant decrease in stress concentrations, approximately 22 % less than those with a width of 0.5D. By setting the cushion modulus within the 40 MPa–60 MPa range, reduced settlement and optimal pile-soil stress ratios were achieved. These research outcomes provide critical insights into optimizing screw-shaft pile composite foundation design parameters, serving as valuable guidance for designers and engineers in diverse civil engineering projects.

Research on Rainfall Intensity Threshold of Occasional Debris Flow Based on Infiltration

The rainfall warning method for debris flows usually uses rainfall intensity and duration to establish an I-D relationship internationally and determine the rainfall warning threshold for debris flows. This method requires extensive rainfall data from debris flow events in the study area to establish the I-D relationship. However, some areas with occasional debris flows lack sufficient debris flow events to establish I-D relationships to determine rainfall warning thresholds. Therefore, this study uses the infiltration effect of water flow on gravel soil and establishes a rainfall intensity threshold judgment formula for debris flow initiation based on the limit equilibrium method. Taking the Taiqing debris flow that occurred in Laoshan, China, on June 13, 2018, as an example, the rainfall intensity and characteristics of the debris flow are analyzed. The maximum rainfall intensity during this rainfall process far exceeds the rainfall intensity threshold determined by the judgment formula. Using the judgment formula, it can be determined that the rainfall process will cause debris flow. The judgment result is consistent with the actual situation (where a debris flow occurred during the rainfall process). To further verify the accuracy of the judgment formula, the rainfall process of Typhoon Lichma on August 11, 2019, in the study area was analyzed. The rainfall process has a long history. Still, the rainfall intensity is much lower than the threshold of rainfall intensity for the initiation of debris flow, so this rainfall will not cause the occurrence of debris flow. The judgment result is consistent with the actual situation (no debris flow occurred during rains). Doi: 10.28991/CEJ-2023-09-09-02 Full Text: PDF

Correlation between Shear-Wave Velocity and Dynamic Cone Resistance for Gravelly Soil

Correlation between Shear-Wave Velocity and Dynamic Cone Resistance for Gravelly Soil

A Laboratory Simulation Experiment to Assess Permeability and Shear Strength of a Gravel Soil Colluvium

Landslides are caused by rainfall as one of the main factors. In order to study the effect of rainfall on the physical and mechanical parameters of landslides, a physical model of the colluvium landslide is created in laboratory conditions with silty clay, river sand, and gravel, taking Shuping landslide in the Three Gorges Reservoir area as the prototype. The artificial rainfall is applied to the accumulation model, which is steady for 60 h, and then the gravel soil is taken out along the different elevations of the colluvium for the permeability test and direct shear test, and the evolution law of changes in porosity, the permeability coefficient, and the shear strength parameters along the elevation are studied. Combined with XRF and NMR tests, the spatial variation of the permeability coefficient and shear strength parameters is discussed from the perspective of chemical elements, minerals content, and porosity, and the stability analysis of a colluvium landslide is carried out considering the influence of parameters along the elevation. The results show that under the action of rainfall seepage, the fine particles of clay are transported from upslope to downslope, resulting in more and more fine particles of clay at the toe slope. The original pores are gradually filled, the cementation between particles is stronger, the corresponding cohesion is increased, and the permeability coefficient is reduced. Due to the loss of fine particles at the upslope, the relative content of coarse particles increases, leading to an increase in the internal friction angle. The variability of the slope’s physical and mechanical parameters is a result of the spatial transport of clay particles in the colluvium caused by the rainfall seepage above. Specifically, the permeability coefficient and internal friction angle from upslope to downslope decrease linearly under the action of rainfall, but the law of the cohesion increases linearly. The upslope’s permeability coefficient and internal friction angle decrease by 11% and 8% compared to those of the downslope, while the cohesion increases by 168%. The results of FLAC3D numerical calculation of Shuping landslide show that the maximum deformation in the X direction of 145 m and 175 m water level increases by 12% and 42%, and the safety factor decreases by 0.63% and 5% under the combined action of rainfall and the reservoir water level, that is, when considering the variation of parameters along the elevation of the landslide. The research findings provide a better understanding of the spatial parameters in similar colluvium bodies under rainfall action.

Cyclic Behaviors of Anisotropically Consolidated Gravelly Soils under Triaxial Condition: Effects of Sand Gradation Part of the Soil

Abstract Previous studies have extensively examined the effects of silt contents and gradations on the cyclic behavior of sand and silt mixtures. However, comparable data on the mixture of sand and gravel are limited because of the experimental challenges of getting reliable testing results from gravel-size particles. Furthermore, in several case histories in which liquefaction occurred, the liquefied soils had experienced initial static shear stress because of the sloping ground conditions or the presence of structures and buildings on the site. The effects of initial static shear stress on the cyclic behavior of clean sands have been widely studied, and some recommendations have been suggested for practical engineers. This research aimed to evaluate the effects of the sand gradation part on the cyclic behavior of two gravelly soils, both with 60 % gravel and 40 % sand but different gradations (well-graded vs. uniformly graded). A total of 26 cyclic triaxial tests were carried out on moist-tamped reconstituted specimens of the tested gravelly soils. The specimens were anisotropically consolidated to assess the effects of initial static shear stress combined with sand gradation on cyclic behaviors of the tested gravelly soils. Results of the tests indicated that the gravelly soil with uniform sands had a greater resistance against liquefaction than the one with well-graded sands. The lower cyclic resistance of the gravelly soil with well-graded sands can be attributed to its lower permeability associated with wider gradation and finer particles of the sand part, leading to higher excess pore pressure buildup during cyclic loading. Moreover, a similar increase in the level of initial static shear stress resulted in an increase in the liquefaction resistance of the gravelly soils, whereas the soil with uniform sands experienced a higher increase than the soil with well-graded sands.

The performance comparison of the decision tree models on the prediction of seismic gravelly soil liquefaction potential based on dynamic penetration test

Seismic liquefaction has been reported in sandy soils as well as gravelly soils. Despite sandy soils, a comprehensive case history record is still lacking for developing empirical, semi-empirical, and soft computing models to predict this phenomenon in gravelly soils. This work compiles documentation from 234 case histories of gravelly soil liquefaction from across the world to generate a database, which will then be used to develop seismic gravelly soil liquefaction potential models. The performance measures, namely, accuracy, precision, recall, F-score, and area under the receiver operating characteristic curve, were used to evaluate the training and testing tree-based models’ performance and highlight the capability of the logistic model tree over reduced error pruning tree, random tree and random forest models. The findings of this research can provide theoretical support for researchers in selecting appropriate tree-based models and improving the predictive performance of seismic gravelly soil liquefaction potential.

Application of an improved distributed hydrological model based on the soil–gravel structure in the Niyang River basin, Qinghai–Tibet Plateau

Abstract. Runoff formation and hydrologic regulation mechanisms in mountainous cold regions are the basis for investigating the response patterns of hydrological processes under climate change. Because of plate movements and climatic effects, the surface soils of bare lands and grasslands on the Qinghai–Tibet Plateau (QTP) are thin, and the soil below the surface contains abundant gravel. This characteristic geological structure, combined with snow and frozen soil, affects the water cycle in this region. To investigate the influence of the underlying surface structure on water–heat transport and water circulation processes on the QTP, a comprehensive study was performed combining water–heat transfer field experiments, and a water and energy transfer process model for the QTP (WEP-QTP) was developed based on the original water and energy transfer process model in cold regions (WEP-COR). The Niyang River basin, located on the QTP, was selected as the study area to evaluate the consistency between theoretical hypotheses, observations, and modeling results. The model divided the uniform soil profile into a dualistic soil–gravel structure. When no phase change was present in the ground, two infiltration models based on the dualistic soil–gravel structure were developed; these used the Richards equation to model a non-heavy rain scenario and the multilayer Green–Ampt model for a heavy rain scenario. During the freeze–thaw period, a water–heat coupling model based on the snow–soil–gravel layer structure was constructed. By considering gravel, the improved model corrected the overestimation of the moisture content below the surface soil predicted by the original model and reduced the moisture content relative error (RE) from 33.74 % to −12.11 %. The addition of the snow layer not only reduced the temperature fluctuation of the surface soil, but also revised the overestimation of the freeze–thaw speed predicted by the original model with the help of the gravel. The temperature root-mean-square error was reduced from 1.16 to 0.86 ∘C. In the fully thawed period, the dualistic soil–gravel structure improved the regulation effect of groundwater on flow, thus stabilizing the flow process. The maximum RE at the flow peak and trough decreased by 88.2 % and 21.3 %, respectively. In the freeze–thaw period, by considering the effect of the snow–soil–gravel layer structure, the freezing and thawing processes of WEP-QTP lagged behind those of WEP-COR by approximately 1 month. The groundwater simulated by WEP-QTP had more time to recharge the river, which better represented the observed “tailing” process from September onwards. The flow simulated by the WEP-QTP model was more accurate and closer to the actual measurements, with Nash–Sutcliffe efficiency > 0.75 and |RE| < 10 %. The improved model reflects the effects of the typical QTP environment on water–heat transport and water cycling and can thus be used for hydrological simulation on the QTP.

Impact of Rock Fragment Shapes and Soil Cohesion on Runoff Generation and Sediment Yield of Steep Cut Slopes under Heavy Rainfall Conditions

The erodibility and erosion resistance of Quaternary sediments play a pivotal role in both the hydrologic and erosion processes of soil cut slopes. To investigate the runoff and sediment yield of soil cut slopes along the Pai-Mo road, we performed indoor simulated rainfall experiments under a 50° steep slope and high rainfall intensity (120 mm/h), based on the area’s climatic characteristics and Quaternary sediment properties. The experiments included various rock fragment contents (30%, 40%, and 50%), different levels of rock fragment roundness (i.e., rounded gravel, angular gravel), and varying soil cohesion. The results indicated that the average infiltration rate of the uncemented rounded gravel soil slope (URGSS) was higher than that of the uncemented angular gravel soil slope (UAGSS), resulting in less runoff and a delayed initial runoff time. The runoff shear stress, runoff power, drag coefficient, and Reynolds number of the URGSS were smaller than those of the UAGSS. In contrast, the Froude number and flow velocity of the URGSS were larger, resulting in a stronger runoff erosion capacity. The sediment yield of the URGSS was approximately two times that of the UAGSS, and the cumulative sediment yield was about 20% higher. The cemented angular gravel soil slope (CAGSS) had a larger runoff rate, runoff shear stress, runoff power, and flow velocity than those of the UAGSS, leading to less sediment yield. Overall, a more rounded shape and a larger radius of curvature of the spherical particles resulted in stronger erosion, due to local turbulence. Therefore, the rill density and cumulative sediment yield of the steep alluvial cut slope were greater than that of the steep colluvial cut slope under heavy rainfall. Moreover, due to its strong cohesion, only raindrop splash erosion and inter-rill erosion occurred on the steep moraine cut slopes under heavy rainfall.

Experimental study on long-term dynamic strength of gravel soil under traffic loading

In order to maintain the long-term dynamic stability of gravel soil subgrade under traffic loading and prevent fatigue damage, it is necessary to determine the long-term dynamic strength of gravel soil under different working conditions. The dynamic triaxial test was carried out on the 40 groups of remolded gravel soil samples under chosen 8 working conditions. Based on the results of the dynamic triaxial test, the curves and curves were drawn. Further, the curves of gravel soil were drawn, and finally, the long-term dynamic strength computation model of gravel soil was established. The effects of confining pressure, water content, degree of compaction, loading frequency, and initial static deviatory stress on the long-term dynamic strength of gravel soil were also analyzed. It is concluded that With the increase of confining pressure and compaction degree, the long-term dynamic strength of increases. With the increase of the number of loading cycles and initial static deviatory stress, the long-term dynamic strength decreases. At the optimal water content, the long-term dynamic strength is the highest. And the impact of loading frequency on the long-term dynamic strength is relatively small. The relationship between the long-term dynamic strength under 1 × 106, 5 × 106 and 1 × 107 loading cycles of gravel soil and the resilient modulus was established, and the value of the relationship curve coefficient ranges from 0.885 to 1.945.

Evaluation of the stability of terraced slopes in clayey gravel soil using a novel numerical technique

Evaluation of the stability of terraced slopes in clayey gravel soil using a novel numerical technique

The structure of forest vegetation on industrial landfills of different ages

AbstractThe purpose of the research is to describe plant community formation on the quarry surfaces to determine a path for optimal revegetation. To achieve the goal, the studies determined soil pH, the content of skeletal fraction, basal respiration, and performed the acidimetric assessment of CO2. The research program aimed to investigate the peculiarities of plant communities' formation in areas with different degrees of revitalization and investigate the influence of soil cover on plant associations. Results showed that the average basal soil respiration rate on the quarry was extremely low (about 0.3 mg CO2/g of soil/h). The CO2 content in the carbonate ranged from 0.07% to 0.7%, with the higher figures observed in older Kuzbass rather than Mosbass and Sokolovsky quarries. An analysis of soil samples from three quarries revealed four plant groups at sites associated with the prevalence of specific fractions, such as gravel, sand, silt, and stony soil. Given that Kuzbass is the oldest open‐pit mine, forest vegetation species dominate here in the surveyed areas (>40%), and this feature is typical of gravel soils. The dominant species present on the gravel substrate were downy birch (Betula pubescens), common hornbeam (Carpinus betulus), European oak (Quercus robur), Siberian spruce (Picea obovata), common juniper (Juniperus communis), Siberian larch (Larix sibirica), common pine (Pinus), and Siberian fir (Abies sibirica). Mosbass is also characterized by a diversity of similar species, though work on mineral mining there ended in 2009, more recently than in other sites. Stony and sandy soil fractions predominated in the Sokolovsky quarry, although other studied substrates were also present.

Monotonic and Cyclic Simple Shear Response of Well-Graded Sandy Gravel Soils from Wellington, New Zealand

In the 2016 Kaikoura earthquake, liquefaction of gravelly soils from reclaimed fills occurred in CentrePort, Wellington, New Zealand. This study presents constant volume monotonic and cyclic simple shear tests on well-graded gravel with sand collected from CentrePort. A large-scale cyclic simple shear device is utilized to evaluate the monotonic, cyclic, and postcyclic responses of the sandy gravel soils. Specimens prepared at various relative densities were subjected to a vertical effective stress of 100 kPa and then monotonically and cyclically sheared. After the cyclic loading, the postcyclic response was evaluated, including volumetric compression or monotonic shear with or without dissipation of excess pore water pressure. Shear wave velocity was measured before and after the cyclic loading. The results show that the well-graded sandy gravel has a high potential for liquefaction, with higher relative density specimens having higher liquefaction resistance. Postcyclic volumetric strain is primarily correlated with density and maximum shear strain during cyclic loading. Postcyclic reconsolidation causes densification of the liquefied specimens, resulting in higher monotonic shear resistance, while postcyclic monotonic shear without dissipation of excess pore water pressure reveals that substantial shear strain is required to develop the shear resistance. Shear wave velocity was significantly reduced after liquefaction, but recovered to slightly higher than its precyclic shear values after reconsolidation. Compared to other gravelly and sandy soils, the well-graded sandy gravel showed a similar or slightly higher liquefaction resistance than gap-graded and uniform gravels. Moreover, the well-graded sandy gravel had a relatively lower ultimate postcyclic volumetric strain due to a small variation between its maximum and minimum void ratios. The results advance our understanding of the liquefaction resistance and subsequent postcyclic responses of the well-graded sandy gravel soils.

Multi-scale investigation on the stability of soil–gravel mixture slopes using imaging analyses

Gravel soil slopes are not only prevalent in nature but also are widely used in engineering. Understanding the damage characteristics of gravel soil slopes and preventing slope hazards requires a thorough investigation of the stability and deformation of gravel soil slopes. In this study, the stability and macroscopic deformation of slopes with varying gravel content (GC) were examined using laboratory tests and digital image correlation techniques, and the rock-winding motion on the shear zone was investigated in detail by capturing the relative motion of soil particles and gravels from a micro-scale perspective. In addition, the effects of loading location and slope angle were considered. The results indicated that there are two thresholds of 20 and 70% for the effect of GC on slope ultimate bearing capacity. Gravel soil slope shear damage was primarily caused by the gravel rotation at critical locations. There were at least five rock-inclusive movement patterns in the shear zone, and the primary cause of irregular damage on gravelly soil slopes was the difference in the relative movement of soil particles and gravels. High GC slopes were less sensitive to changes in loading location and slope angle than slopes with low GC.

Column-Hemispherical Penetration Grouting Mechanism for Newtonian Fluid Considering the Tortuosity of Porous Media

The intricate morphology of porous media can considerably affect the progression of penetration and the diffusion of grouting slurry. In this study, a Newtonian fluid’s refined seepage motion equation was proposed to incorporate the impact of tortuosity on the grouting process into gravel soil, and the column-hemispherical penetration grouting mechanism was analyzed using the method of theoretical analysis. Utilizing secondary-development programming techniques, a numerical simulation program was developed with COMSOL Multiphysics to model the penetration grouting mechanism of a Newtonian fluid in a column-hemispherical pattern, considering a medium’s tortuosity. The penetration grouting process of Newtonian cement into gravel soils was then simulated. Finally, the theoretical analysis, experimental values, and numerically simulated values were compared.The findings suggested that incorporating the tortuosity of porous media is more efficacious in depicting the penetration and diffusion behavior for Newtonian fluid grouting in porous media, as compared to omitting the tortuosity. The findings of this study contribute to a better understanding of grouting engineering in porous media strata, guiding practical design and construction.

Landscape characteristics shape surface soil microbiomes in the Chihuahuan Desert.

Soil microbial communities, including biological soil crust microbiomes, play key roles in water, carbon and nitrogen cycling, biological weathering, and other nutrient releasing processes of desert ecosystems. However, our knowledge of microbial distribution patterns and ecological drivers is still poor, especially so for the Chihuahuan Desert. This project investigated the effects of trampling disturbance on surface soil microbiomes, explored community composition and structure, and related patterns to abiotic and biotic landscape characteristics within the Chihuahuan Desert biome. Composite soil samples were collected in disturbed and undisturbed areas of 15 long-term ecological research plots in the Jornada Basin, New Mexico. Microbial diversity of cross-domain microbial groups (total Bacteria, Cyanobacteria, Archaea, and Fungi) was obtained via DNA amplicon metabarcode sequencing. Sequence data were related to landscape characteristics including vegetation type, landforms, ecological site and state as well as soil properties including gravel content, soil texture, pH, and electrical conductivity. Filamentous Cyanobacteria dominated the photoautotrophic community while Proteobacteria and Actinobacteria dominated among the heterotrophic bacteria. Thaumarchaeota were the most abundant Archaea and drought adapted taxa in Dothideomycetes and Agaricomycetes were most abundant fungi in the soil surface microbiomes. Apart from richness within Archaea (p = 0.0124), disturbed samples did not differ from undisturbed samples with respect to alpha diversity and community composition (p ≥ 0.05), possibly due to a lack of frequent or impactful disturbance. Vegetation type and landform showed differences in richness of Bacteria, Archaea, and Cyanobacteria but not in Fungi. Richness lacked strong relationships with soil variables. Landscape features including parent material, vegetation type, landform type, and ecological sites and states, exhibited stronger influence on relative abundances and microbial community composition than on alpha diversity, especially for Cyanobacteria and Fungi. Soil texture, moisture, pH, electrical conductivity, lichen cover, and perennial plant biomass correlated strongly with microbial community gradients detected in NMDS ordinations. Our study provides first comprehensive insights into the relationships between landscape characteristics, associated soil properties, and cross-domain soil microbiomes in the Chihuahuan Desert. Our findings will inform land management and restoration efforts and aid in the understanding of processes such as desertification and state transitioning, which represent urgent ecological and economical challenges in drylands around the world.

Liquefaction Behavior of a Well-Graded Gravelly Soil under Initial Static Shear Stress in Cyclic Triaxial and Simple Shear Conditions

Among other reasons, studies of the liquefaction potential of gravelly soils are limited because of the difficulties involved in preparing uniform specimens, without particle segregation, especially for a well-graded gravelly soil in a dry state for simple shear testing. Errors and difficulties are also involved in compensating for membrane penetration to a gravelly soil specimen in triaxial testing to get reliable data. Thus, innovative approaches for preparing triaxial and simple shear specimens for gravelly soils are introduced and implemented in this study to overcome experimental problems in acquiring accurate test results. In addition to the aim of obtaining reliable testing data on the liquefaction of gravelly soils under initial static shear stress for simulating sloping ground conditions, a study of the effect of various stress paths on the liquefaction resistance of gravelly soils was another goal of this research. In this regard, two sets of cyclic tests using medium-size triaxial and simple shear devices are conducted on a unique soil to compare the liquefaction potential of the tested gravelly soil using these two devices. Results of simple shear tests indicate that as the value of initial static shear stress increases, the cyclic resistance of the tested gravelly soil decreases. However, the results of the triaxial tests show that the variation of cyclic resistance for the tested soil depends on the initial static shear stress level and associated stress reversal conditions. Furthermore, the observed value of the pore water pressure ratio at failure using the strain-based liquefaction criteria for the tested gravelly soil was about 0.85, regardless of the type of testing. In addition, the relationship between the liquefaction resistance of gravelly soils using cyclic triaxial and simple shear devices was obtained.

Investigation of Backfill Compaction Effect on Buried Concrete Pipes

The present study deals with the experimental investigation of buried concrete pipes. Concrete pipes are buried in loose and dense conditions of gravelly sand soil and subjected to different surface loadings to study the effects of the backfill compaction on the pipe. The experimental investigation was accomplished using full-scale precast unreinforced concrete pipes with 300 mm internal diameter tested in a laboratory soil box test facility set up for this study. Two loading platforms are used namely, uniform loading platform and patch loading platform. The wheel load was simulated through patch loading platform which have dimensions of 254 mm *508 mm, which is used by AASHTO to model the wheel load of a HS20 truck. The pipe-soil systems were loaded up to pipes collapse. Pipes were instrumented with strain gauges to measure circumferential strains, in addition to dial gauges, for measurements of the pipe vertical deflections and settlement of the loading platforms. The test results indicated that flexure governed the buried pipe behavior. Flexural cracks formed slightly before the ultimate load. A comparison of soil backfill, between a loose and dense compaction, showed that the dense backfill improve largely the pipe installation and the strength ofpipe-soil system