Medium Dense Soil Research Articles

Effect of Ground Motion on Fragility and Vulnerability of Reinforced Concrete Bridge in Different Soil Conditions

Bridges are essential components of transportation networks, serving as lifelines for the movement of people and goods. The bridges' resilience to natural disasters, particularly earthquakes, is an issue of paramount significance. Yet, a critical knowledge gap exists when it comes to understanding how bridges perform in the challenging terrain of medium-density sandy and clay soils during seismic events. This study seeks to bridge that gap by developing fragility curves that quantitatively evaluate the likelihood of bridge damage or failure across varying levels of earthquake magnitudes. The CSI Bridge v25.0.0 was used to simulate earthquake ground motions specifically within medium-density sandy and stiff clayey soils. Nonlinear time history analyses of the bridge were performed by using 5 different earthquake events with PGA ranging from 0.25 – 1.5g. Fragility analysis is performed to develop seismic fragility curves for the critical part of the bridge for various peak ground acceleration (PGA) in two types of soil conditions. The findings revealed that the deck component is more susceptible to damage than the pier. The impact of seismic activity on medium-dense soil is more significant than on stiff clayey soils in relation to the critical components of the bridge. This result enhances the ability to design bridges that can withstand and recover from seismic events more effectively.

Studying Effect of Saturation Degree on the Bearing Capacity and Failure Mechanism of Sandy Soils

In this research, an experimental method was employed on samples of sandy soils from the Tartous and Palmyra regions. The objective was to investigate the impact of saturation degree on the bearing capacity of partially saturated sandy soil and the associated failure mechanism. To achieve the aim of the research, a series of tests were conducted to determine the basic physical properties of the soils. Additionally, a series of laboratory loading tests were conducted for a footing model atop sandy soil under various saturation degrees. Matric suction was measured, and soil water characteristic curves were determined using the filter paper technique. The results were subjected to analysis and discussion, and the experimental work demonstrated that saturation degree had a clear effect on the bearing capacity. It was observed that the bearing capacity of partially saturated soil is higher than that of fully saturated soil. The values of the increase were found to range between 2.3 and 9.7 times the bearing capacity in the fully saturated state. An empirical relationship was proposed to simulate the bearing capacity of partially saturated sandy soil based on the experimental results. Furthermore, the results indicated that the saturation degree exerted a discernible influence on the failure mechanism. In particular, a failure mode associated with dense soils was discerned in medium-dense soils at specific degrees of saturation for the tested soils.

Validation, Reliability, and Performance of Shear Strength Models for Unsaturated Soils

Soil shear strength is the most fundamental property when designing structures in the ground and should be carefully assessed and understood. Several empirical models were introduced to predict the shear strength of unsaturated soils. However, there is uncertainty regarding the applicability and sensitivity of these prediction models. This paper presents a comprehensive verification study to assess the reliability and validity of the existing theoretical models. The results obtained from the prediction models are compared to measured data using thirty experimental data sets. A performance classification program is also conducted to assess the suitability of the analytical models for different soil types as well as over a wide range of matric suctions, saturation degrees, soil densities, soil plasticity, and clay activity. The impact of each single parameter is clarified by the microstructure studies, which also provides insight into the mechanics of unsaturated soils. The results indicated that the applicability of models is more appropriate for sandy soils rather than for clayey ones. The performance of shear strength models tends to decrease with an increase in matric suction, initial density, plasticity index, and clay activity. It is, therefore, recommended that the shear strength estimation models should be carefully selected depending on the soil type and properties. Besides, the analysed results pointed out that the choice to assume the factor chi in the equation of Bishop equals the saturation degree is only suitable for medium-dense soils with low matric suction. This assumption is particularly not effective for clayey soils, or dense soils with high matric suction.

Evaluation of Dynamic Interactions Between Sloped Ground and Pile Through Centrifuge Model Tests

ABSTRACT This study used centrifuge model tests to evaluate the dynamic behavior of piles and sloped ground. Two types of test models were created based on the ground’s saturation. The researchers calculated p-y loops to analyze the dynamic interaction between piles and sloped ground, which can lead to liquefaction. In the dry sand model, the passive earth pressure of the slope greatly influenced pile behavior, while in the saturated sand model with liquefaction, the kinematic force of the slope had a significant effect. The study also derived a p-multiplier that can be applied to medium-dense soil based on the experimental results.

The Effect of Geotechnical Factors in Road of Basrah, Southern Iraq

Most Basrah roads are conducted to a major failure in their layers and bases, which appears in the form of cracking, crushing, landing, as well as massive holes. The influence of geotechnical factors on the performance of Basrah roads has been studied. Sixteen sites were selected for sampling, which are Al-Medaina, West Qurna, Al-Hartha, Al-Dir, Shatt Al-Arab, Al-Tuwaisa, Hayy-Al-Hussein, Al-Shuaiba, Al-Maqal, Al-Gazara, Abu-Al-Khaseeb, Al-Ashar, Umm Qasser, Al-Zubair Petrochemical factory, and Al-Faw. The soil properties were studied up to 3 meters of depth at each location to find out the effect of geotechnical properties on roads. Laboratory tests were carried out on the samples, which included grain size analysis, Atterberg limits, gypsum content, total soluble salts, swelling potential, organic content, and standard penetration test. The results presented that the percentage of gypsum exceeded the allowable limit in the standard specifications at the sites (S7, S8, S13, S14, S16). Also, the percentage of total soluble salts exceeded the allowable limit in the standard specifications at the sites (S5, S8, S16). The results showed that the soils in S1, S2, S3, S4, S7, S11 have medium swelling potential, which requires treating before building roads on them. The results also showed that the percentage of organic materials exceeded the permissible limit in the standards specifications at the sites S1, S2, S3, S4, S5, S9, S10, S11, S12, S15. The results also showed that the cohesive soils in the first meter of the sites (S2, S5, S11), the second meter of the sites (S2, S7, S12) and the third meter of the sites (S5, S9, S10, S11, S12) are medium stiff soils, which requires treating before building roads on them. While the non-cohesive soils at the two sites (S8, S13) are medium dense soils, in two sites (S14, S16) are loose sandy soils in the first meter, while the second meter in sites (S8, S13, S14, S16) are medium dense soils, and the third meter at the site (S14) is medium dense soils.

Performance-based analysis of Transit tunnels in the Chilean subduction zone

In this article, we study the seismic response of a shallow metro tunnel in a subduction zone environment and the use of a performance-based approach to develop seismic demand hazard curves (SDHC) of key engineering demand parameters, such as drift ratio, surface settlement, bending moment, and axial loads. The tunnel consists of a 6-m diameter sprayed concrete lining in medium dense soil and is located in Santiago, Chile. To simulate its seismic response, a finite element model of the soil–tunnel system was implemented in OpenSees and validated against centrifuge test results, linear-equivalent solutions for a 1D soil column, and single elements in cyclic simple shear. The tunnel response was computed for 112 ground motions, selected and scaled using the conditional scenario approach. This approach assigns a rate of occurrence to each ground motion and therefore, allows for a direct computation of annual exceedance rates of the tunnel response parameters. For instance, at this specific location, the 2500-yr return period drift ratio in the lining is approximately 0.25% as a result of large deformations imposed by the surrounding soil. Likewise, axial loads between 0.3 and 1.0 MN/m and bending moments of ±0.2 MN∙m/m are apparent from the axial load-moment interaction diagrams; these results are of great value for the design and verification of the tunnel based on the collapse or life-safety limit states. Notably, the current formulation relaxes the assumption of scaling ground motions to a particular intensity measure and can be a computationally efficient alternative to standard incremental dynamic analyses.

Development of Surface Level Seismic Hazard Maps Considering Local Soil Conditions for the State of Haryana, India

Abstract An extensive ground response analysis has been carried out in order to consider the effect of local soil conditions on surface level strong ground motions in the state of Haryana, India. Non-linear approach has been adopted to analyze 81 sites drilled up to refusal covering the entire state. It has been observed that 75 sites fall under site class D (medium dense soils), 4 sites under site class C (very dense soils), whereas only 2 sites fall under site class E (loose soils) as per the provisions of National Earthquake Hazard Reduction Program (NEHRP). For the estimation of low strain shear modulus (Gmax) using SPT N-value for different type of soils, various correlations have been used due to non-availability of in-situ measured values of shear wave velocity (Vs). The standard backbone curves for clays and sands have been used in the study in the absence of site-specific shear modulus degradation and damping ratio curves. The recorded acceleration time histories of the Ms 7.0 1991 Uttarkashi earthquake, having a focal depth of 10 km with PGA (g) ranging from 0.05g to 0.31g, have been used as input motion for the analysis. Amplification factors for peak ground acceleration (PGA) and spectral acceleration (Sa) for site class D have been calculated which are found to be comparable with those reported in NEHRP provisions. However, the site-specific hazard parameters determined for the tectonic setup of the seismic study region are quite different from that suggested by Indian standard code of practice.

HDPE geogrid-residual soil interaction under monotonic and cyclic pullout loading

The understanding of soil-geosynthetic interaction under cyclic loading conditions is essential for the safe design of geosynthetic-reinforced soil structures subjected to repeated loads, such as those induced by road and railway traffic and earthquakes. This paper describes a series of large-scale monotonic and multistage pullout tests carried out to investigate the behaviour of an HDPE uniaxial geogrid embedded in a locally available granite residual soil under monotonic and cyclic pullout loading. The effects of the pullout load level at the start of the cyclic stage, cyclic load frequency and amplitude, number of cycles and soil density on the load-strain-displacement response of the reinforcement are evaluated and discussed. Test results show that the cumulative displacements measured along the length of the geogrid during cyclic loading increased significantly with the pre-cyclic pullout load level and the load amplitude. In contrast, the cumulative cyclic displacements were found to decrease with increasing frequency and soil density. In medium dense soil conditions, the geogrid post-cyclic pullout resistance decreased by up to 20%, with respect to the value obtained in the comparable monotonic test. However, for dense soil, the effect of cyclic loading on the peak pullout forces recorded during the tests was almost negligible.

Behaviour of Granular Anchor Pile (Gap) and Group Piles In Different Type of Soils under Vertical Pullout Loads

In the present study, the load displacement behaviour of Granular Anchor Pile (GAP) and Group piles under vertical pullout loads in two different type of cohesionless soils have been investigated. The main objective of the study is to investigate the effect of embedment length, diameter and spacing varying (L/D and S/D ratio) on Pullout Capacity of Granular Anchor Pile system in different type of soils. GAP pile is innovative and effective in resisting the uplift pressure exerted on the foundation. Based on the laboratory study on single and group of 2 and 4 GAP systems, it is found that the ultimate Pullout Capacity of single GAP system increases with the increase in length (L) to diameter (D) ratio in both type of soils. The rate of increase of ultimate pullout capacity of single GAP systems having 50 mm diameter and 100 mm diameter was significant up to increase in L/D ratio of 39%. Thus, it was inferred that for single GAP system, there is maximum advantage upto L/D ratio 10.50 for 50 mm and 7.00 for 100 mm. In case of medium dense soil with higher relative density, the increase in pullout capacity is more as compared to loose soil with lower relative density. It was further confirmed that ultimate pullout capacity is a function of diameter of GAP and soil characteristics. The ultimate pullout capacity of group of 2 and 4 GAP systems with 100 mm diameter was found to increase with S/D ratio upto 3.00 and 2.75 respectively only in both the soils.

Evaluation of cyclic and monotonic loading behavior of bucket foundations used for offshore wind turbines

Suction caissons are considered as an alternative foundation solution for offshore wind turbines. In the present study, three-dimensional finite element (FE) analyses are performed to assess the behavior of a bucket foundation and soil supporting the bucket under cyclic and monotonic loading conditions. A parametric study is also performed for a wide range of bucket geometries and two different soil densities. The results indicate that bucket geometry and soil properties significantly affect the foundation response due to cyclic loading conditions. The bucket with the smallest geometry installed in medium dense soil exhibits the lowest stiffness in initial loading and then with the progress of cyclic loads experiences lower stiffness compared to the caissons with larger geometries. The sensitivity of the foundation response to the soil density is higher than its geometry. The bucket under the lowest vertical load experiences the lowest stiffness in both virgin loading and during the progress of cyclic loads. The highest soil displacement is observed near the lid at the interior of the bucket. Stresses caused by cyclic loading belong to certain ranges. Additionally, increases in the skirt length result in increases in the stress ranges and shift the range to the right side. With respect to the monotonic loading conditions, normalized diagrams are proposed that can be used for the preliminary design of suction bucket foundations.

Effect of Pile Spacing on Group Efficiency in Gypseous Soil

As a matter of fact, the gypseous soil is usually considered as collapsible soil, such type of soil illustrates high resistance to settlement and high bearing capacity when it is dry, but it loses these characteristics when it is inundated and collapses excessively because of the sudden decrease in the volume of the surrounding soil mass. It is founded in the arid and semi-arid regions of the world in Asia, South Asia (Iraq, Syria, Jordan, Yemen, and Iran), North Africa, North America, moreover, it covers more than (31%) of the surface area in Iraq. Gypseous soil is one of the most difficult problems facing the process of building any project because of the difficulty of preventing leakage of water to the soil in practice. Deep foundation (piles) are one of the most common types used in collapsible soils which penetrating problematic soil layers and reaching more hard ones (end bearing piles) or transfers loads depending on skin friction (floating pile). The current work is directed to study the behavior of single and group driven pile of square pattern (4 piles) in case of floating pile (friction pile) with different spacing (2D, 4D, 6D) and length to diameter (L/D) ratio of (20) in this special medium dense soil (gypsum content 30% and 61%) under axial load condition. The investigation was carried out to measure the soil collapse before and after inundation. The results showed that the group efficiency for spacing 2D is less than one while for spacing 4D and 6D are more than that value. In addition, the spacing 4D was more efficient to carry 4 group pile in both dry and soaked cases, in addition, the result showed a high reduction in the bearing capacity at inundation state of group pile of (82% in gypsum content 30%) and ( 87% in gypsum content 61%) with respect to dry state.

ESTIMATION OF S-WAVE VELOCITY STRUCTURES IN YOGYAKARTA BASIN, INDONESIA

For the theoretical simulation or prediction of strong ground motion, it is prime importance to get information of underground structures, especially for sedimentary layers overlying on bedrock, like in Yogyakarta Basin. The Standard Penetration Test, Spectral Analysis of Surface Wave (SASW) and other geotechnical properties are used to estimate S–wave velocity structures in this basin. SPT tests were conducted at nine sites and SASW measurements were performed at seventeen sites. As a result, the S-wave velocity structures of top 30 m depth had been evaluated in each site. The average shear wave velocity v30 s had been successful estimated and the sites are classified into three types; soft soil, medium dense soil and hard soil. All sites where SPT performed are on soft soil according to their v30 s . However, according to v30 s from SASW measurements, 10 sites are located on medium dense soils type, 5 sites on dense soils and 2 sites on soft soils. The acceptable equivalent S-wave velocitystructure is observed by comparing the results from SASW and geotechnical approach in Imogiri, Bambang Lipuro, Pundong (Watu, Pranti) and Pandak (Wijirejo) areas. 
 
 Keywords: Ground motion, underground structure, sedimentary layer, SPT, SASW, Pundong

Effect of geogrid reinforcement on soft and medium dense soils

The field tests were carried out to examine the reinforcement effect of a geogrid on various conditions of embankment height, the number of passages of vibratory roller, the number of reinforced layer of geogrid, and soil properties. The test results of the dynamic earth pressure indicate that the soil reinforced by geogrid is very effective to increase the stiffness of soil, especially in soft soil. The dynamic earth pressure ratio, which is defined as the ratio of dynamic earth pressure to self weight of soils, exponentially decreases as the embankment height increases. The dynamic earth pressure ratio increases up to 80% for soft soils reinforced by both one layer of geogrid in place of no reinforced soils and two layers in place of a single layer of geogrid.

Dynamic Instability of Pile‐Supported Structures in Liquefiable Soils during Earthquakes

Piles are long slender columns installed deep into the ground to support heavy structures such as oil platforms, bridges, and tall buildings where the ground is not strong enough to support the structure on its own. In seismic prone zones, in the areas of soft soils (loose to medium dense soil which liquefies like a quick sand) piles are routinely used to support structures (buildings/ bridges). The pile and the building vibrate, and often collapse, in liquefiable soils during major earthquakes. In this paper an experimental and analytical approach is taken to characterize this vibration. The emphasis has been given to the dynamic instability of piled foundations in liquefied soil. The first natural frequency of a piled‐structure vibrating in liquefiable soil is obtained from centrifuge tests. The experimental system is modelled using a fixed‐free Euler‐Bernoulli beam resting against an elastic support with axial load and tip mass with rotary inertia. Natural frequencies obtained from the analytical method are compared with experimental results. It was observed that the effective natural frequency of the system can reduce significantly during an earthquake.

Estimation of freeboard requirements against overtopping of surface impoundments under seismic action

The excitation of structural components and liquid contents of surface impoundments by seismic waves can generate turbulence that is large enough to overtop the bounding berms. In cases in which the liquids are wastes from industrial/municipal operations, their release from impoundments can pose significant risks to the environment. In this analysis, the freeboard magnitudes that can accommodate liquid head levels in impoundments are determined through linkage of configuration of waves in the liquid surface to incident seismic wave characteristics, liquid characteristics and impoundment design. For an impoundment site in a region of ground acceleration levels ranging from 0.2 to 1.0 g and impacted by seismic shear wave velocity of 180 m/s, freeboard requirements are in the range of 0.004–2.0 m on soft soil; 0.008–0.7 m on medium-dense soil; and 0.002–0.1 m for dense soil. For the same impoundment design, ground acceleration and incident wave characteristics, freeboard requirements are directly proportional to the depth of the soil mantle over bedrock. The impoundment slope, which is a key parameter with regards to liquid holding volumetric capacity of the impoundment, is a less significant parameter than depth to bedrock with regard to the size of the required freeboard. This implies that siting of an impoundment should be considered to be critical to impoundment performance in seismic zones.

Characteristics of nonlinear response of deep saturated soil deposits

Abstract Recent EPRI seismic design guidelines call for dynamic soil properties (shear modulus ratio and damping) and liquefaction strength curves to be characterized as a function of the effective vertical stress (or depth). A modified version of the DESRA2 constitutive model for saturated soil has been applied to study the nonlinear seismic response including liquefaction of medium dense soil deposits of various thicknesses. The results of the stress-dependent soil properties model show lower deamplification and higher first-mode (resonant) frequency than that of the stress-independent soil properties model. By using the stress-dependent model with impulse base excitation, the nonlinear behavior of various soil deposits has been investigated under a variety of conditions. The results show that (1) the saturated soil deposit has a smaller surface amplitude and significantly lower resonant frequency than the unsaturated soil deposit of the same thickness; (2) for the saturated soil conditions, the larger the base excitation, the lower the surface amplification and the resonant frequency; (3) the deep soil deposits show lower surface amplification and resonant frequency compared to the response of shallow deposits; (4) when shallow and deep deposits are compared, the shallow deposits develop much higher residual pore-water pressure; and (5) the amplification and residual pore-water-pressure response of deposits deeper than 100 m or so are very similar. The application of the method has also been illustrated using a strong synthetic base excitation applied to the base at a site near Reno. The results in general are consistent with those computed using the impulse loading. The study reveals that the response predicted from the conventionally used stress-independent soil properties model is unconservative for deep deposit.

Cohron sheargraph data: interpretation using critical state soil mechanics

Critical state soil mechanis was used to explain the differences in stress paths recorded in sheargraph tests in weak, strong and medium-strong soils. It was projected that the cohesion of both peak and ultimate strength lines would be near zero for weak and medium-strong soils, but the peak cohesion would be high for strong soil. The friction angle of the peak strength line was projected to be lower than that of the ultimate line for strong soils and less than or equal to that of the ultimate line for weak and medium-strong soils. The projections about the type of stress path and the relationship between cohesion and friction for peak and ultimate strength lines were tested by performing field sheargraph tests in a Vertisol. It was found that the fraction angle of the ultimate line was higher than that of the peak line, which suggests that in loose to medium dense soils it may be more appropriate to use the ultimate line for tine design procedures that employ the friction angle in calculations. The different forms of stress path recorded in field sheargraph tests were associated with different regimes of soil behaviour in laboratory shear, in which the height change during shear was measured. Tests with strong soil resulted in sheargraph tests that showed brittle stress paths with well defined shear stress peaks, and in laboratory shear tests that showed shear accompanied by expansion. Tests with weaker soil resulted in sheargraph stress paths without well defined peaks, and in laboratory shear accompanied by compression. Shear accompanied by expansion is desirable in tillage for seedbed preparation and therefore the sheargraph may be useful in identifying the right soil conditions for tillage.

A comparison of foundation compaction techniques

Soil investigation programs established the presence of locally loose to medium dense noncohesive foundation materials at three major industrial project sites. It was neccessary to densify these materials to ensure that unacceptable differential settlements did not occur between separate foundations and to reduce the potential for liquefaction of the looser zones in the event of seismic disturbance. Horizontal ground accelerations of 0.05, 0.1, and 0.3 g were used in the respective seismic analyses for the three sites. Four different techniques for in-place compaction were employed to densify the loose to medium dense soils: vibro and impact compaction, compaction piling, and deep blasting.Site descriptions and soil parameters measured are presented. A short explanation of design considerations and production work procedures is followed by a detailed comparison of the improvements obtained, measured in terms of standard or static cone penetration resistance and true relative density. Problems encountered and phenomena observed during performance of the work are described, such as the time-dependent strength increase in disturbed sands. Key words: compaction piling, deep blasting, impact compaction, vibrocompaction, foundation, penetration tests.