Journal of Engineering Geology

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(Paper pages 735-756) Shear behavior of sand-gravel mixtures is an important issue in geotechnical engineering due to extensive use in earth dams, borrow materials and slope stability problems of natural or man made slopes. Experimental study of behavior of this type of material is usually difficult due to problems associated with use of large testing apparatus or large specimens. Several researchers have proposed methods for the test of these materials by removing larger fraction of them and testing finer matrix. In this research, a regular set of large direct shear tests with a 300*300*160 mm shear box performed to determine shear strength and dilation characteristics of sand-gravel mixtures in high gravel contents. Bad graded fine sand was used besides uniform gravel grains with maximum grain size of 12.5 mm as testing materials. The tests conducted on mixtures prepared in four gravel contents of 70, 80, 90 and 100 percents. Samples constructed in three relative densities of 35, 60 and 85% and tested by different surcharge pressures of 100, 200 and 300 kPa. Experiments conducted on completely dry samples in consolidated drained condition. Shear strength behavior of mixtures was investigated and it was concluded that both shear strength and friction angle increases with gravel content, relative density and surcharge pressure. However, dilation increases by increase in gravel content and relative density and reduces with increase in surcharge pressure. Results were compared with previous experiments on mixtures with less gravel contents and it was observed that in little gravel contents the behavior is controlled by the both sandy matrix and gravel grains. However, as gravel content increases from floating limit, the behavior is mainly controlled by gravelly part of mixture and sand fraction has little effects on its behavior.

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The Alborz dam rock foundation is composed of marl and sandstone. With regard to the proposed plan for the grout curtain in marly rocks (relatively soft and plastic( which is significantly different from the hard and brittle rocks, the boreholes spacing (influence radius slurry), injection pressure (resistance rock), and even the composition and concentration of slurry are important. In the present paper, in order to evaluate the grout curtain of Alborz Dam, emphasis has been placed on two important parameters, namely, the coefficient of permeability and cement take. The results of cement take suggest that the distance between the primary boreholes is long and there is no proper connection between the primary and secondary boreholes. Moreover, grouting results of the fifth and sixth series of grout holes imply that the depth of some of the sixth series of grout holes has not been attained at the water tightening surface. A review of the rate of the cement take - time - pressure graphs and cement take - time graphs on the right abutment indicates that the injection pressure has not been applied in accordance to marly rocks leading to unfavorable phenomenon of opening and closing of joints (hydrojacking). Notably, the check holes results on the right abutment indicate that water tightening at this area has been provided a satisfactory and acceptable job.

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In this paper, a constitutive model is proposed for prediction of the shear behavior of a gravely sand cemented with different cement types. The model is based on combining stress-strain behavior of uncemented soil and cemented bonds using deformation consistency and energy equilibrium equations. Cement content and cement type are considered in a model as two main parameters. Based on the proposed method, the behavior of cemented soil with different cement types is predicted for conventional triaxial test condition. Porepressure developed during undrained loading besides volumetric strains in drained condition are also modeled according to this framework. Comparison of model results with experimental data indicates its reasonable accuracy.

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The objective of this paper is to investigate the bearing capacity of strip foundations next to sand slope. A series of laboratory model tests has been carried out and a new correlation coefficient to estimate the bearing capacity of shallow foundations near slopes is presented. The sand layers were prepared in a steel test tank with inside dimensions 500 ´ 200´ 250 mm. After vertical loading, the applied load and displacement of foundation were recorded and stress-settlement curve is drawn. Finally, the load at which the shear failure of the soil occurs is recorded as ultimate bearing capacity of foundation. The test sand used in this study was Babolsar sand with relative density of 50%. The relative performance of different distance of foundation from the edge of slope and inclination angle of slope are compared using same quantity of soil properties in each test. The results indicate that with increasing distance from the edge of the slope, bearing capacity increases linearly. Also with increasing slope angle, the bearing capacity has declined linearly

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Strength and durability of sandstones and their influences from natural conditions, are the most important factors which should be considered as engineering materials. In this study, the effect of freeze-thaw and salt crystallization phenomena on strength and durability of upper red formation sandstones collected from southern part of Qazvin province was investigated. Nine specimens of sandstones (specified by A, B, C, CG, S, S1, Tr, Min and Sh) were collected from different part of studied area, then their physical and mechanical characteristics were determined. In order to assessing the effect of freeze-thaw on physical and mechanical characteristics of sandstones, 60 cycles of freeze-thaw test was performed. Also in order to investigate the effect of salt crystallization on strength of studied sandstone, sodium sulphate crystallization test (100% weight solution of Na2SO4) was carried out in 20 cycles. Physical and mechanical characteristics of sandstones such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss were computed after different cycles. To evaluate the effect of freeze-thaw and salt crystallization phenomena on durability of sandstones, slake durability test was conducted on specimens subjected to mentioned processes and changes occurred in slake durability index in 15 cycles were investigated. Based on results obtained from current study, it could be concluded that in comparison to freeze-thaw, salt crystallization can considerably reduce the strength and durability of sandstones and deteriorate them. Also it was found that index tests such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss can predict the behavior of sandstones in different cycles of freeze-thaw and salt crystallization tests.

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Consolidated-drained triaxial compression tests were conducted to compare the stress-strain and volume change response of sands and clayey sands reinforced with discrete randomly distributed poly-propylene fibers. The influence of various test parameters such as fiber content (0.0%, 0.5% and 1.0% by weight), clay content (0%, 10% and 20% by weight), relative density (50% and 90%) and confining pressure (100 kPa, 200 kPa and 300 kPa) were investigated. It has been observed that addition of clay particles to the sands decreased the shear strength of samples. Also, increase in clay content reduced dilation and increased compressibility of the mixed soil. Addition of the fiber to both sands and clayey sands samples improved the shear strength and increased ductility and axial strain at failure point. 

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 Introduction
Recently, several studies on buried pipelines have been conducted to determine their uplift behavior as a function of burial depth, type of soil, and degree of compaction, using mathematical, numerical and experimental modeling.
One of the geosynthetics applications is the construction of a reinforced soil foundation to increase the bearing capacity of shallow spread footings. Recently, a new reinforcement element to improve the bearing capacity of soils has been introduced and numerically studied by Hatef et al.  The main idea behind the new system is adding anchors to ordinary geogrid. This system has been named as Grid-Anchor (it is not a trade name yet). In this system, a foundation that is supported by the soil reinforced with Grid-Anchor is used; the anchors are made from 10×10×10 mm cubic elements. The obtained results indicate that the Grid-Anchor system of reinforcing can increase the bearing capacity 2.74 times greater than that for ordinary geogrid and 4.43 times greater than for non-reinforced sand...../files/site1/files/0Extended_Abstract6.pdf
 

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Carbonate soils are different from silicate soils respect to their origination and engineering behavior. Particles of these soils are mainly residual or debris of sea animals or plants with large amount of calcium carbonate. They also may be chemical sedimentation of calcium carbonate over other soil particles in specific region of seas and oceans. The most important characteristic of these soils is the crushability of their aggregates under loading which is mainly due their shape and also small voids inside of them.  Crushability and subsequent volume changes in carbonate soils have caused many engineering problems in some geotechnical structures such as ...../files/site1/files/0Extended_Abstract5.pdf

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Introduction
When saturated sandy soils are subjected to seismic loadings, the pore water pressure gradually increases until liquefaction happens and settlement occurs during and after an earthquake. The mentioned problem is attributed to rearrangement of grains and redistribution of voids within the soils. Over the years many methods have been presented to increase liquefaction resistance. However, the main methods utilized in liquefaction mitigation are classified as densification, solidification, drainage and reinforcement techniques. Utilizing scrap tires in soils is a kind of soil reinforcement which has a wide range of application.
Waste material expulsion is one of the environmental problems each country faces. Accumulation of non-degradable polymeric materials in landfills has serious environmental consequences. Efforts to find new ways of soil reinforcement have drawn the attention of researchers towards the use of new recycled materials like scrap tires derivatives. Derivatives of scrap tires have different applications in civil engineering such as reinforcing soft soil, as a drainage layer in landfills and as filler materials.
Material and methods
In this paper a series of 1g shaking table tests were performed to investigate on the effect of tire powders-sand mixture in reducing liquefaction potential, settlements after earthquake and pore water generation. Shaking table is made of Plexiglas with inner dimensions of 200×50×70 cm. At bottom of the container a void chamber is made by using a number 200 sieve so that the saturation process could be done gradually and uniformly. A plastic plate was rigidly fixed at the center of container to separate reinforced and unreinforced samples from each other and waterproofing carefully. Therefore two models (reinforced and unreinforced) can be tested at once with the same input acceleration. An absorbing layer of foam with 2 cm thickness was employed to decrease the effect of boundary conditions in order to avoid a direct confrontation model with a rigid container. Firoozkuh No. 161 sand and tire powders were used for the mixture in reinforced side, and pure sand in unreinforced side. In this study 4 mixture ratio (TC=5%, 10%, 15% and 20%) were done. Both of unreinforced (pure sand) and reinforced (tire powders-sand mixture) models were prepared by wet tamping method, in which soil is mixed with 5% water. Each model was prepared in six layers. The required weight for each layer was considered based on the desired density (relative density is zero) and exact volume of the layer. Each portion was placed into the model container and then tamped to reach desired level. Carbon dioxide (CO₂) was allowed to pass through the specimen at a low pressure in order to replace the air that trapped in the pores of the specimen. Then water was allowed to flow upward through the bottom of the container at low pressures in order to flush out the CO₂ that cause increasing the final degree of saturation. Vibration with approximate uniform amplitude and 2 Hz frequency was applied to the container.
Results and discussion
Results indicate that acceleration within the soil tends to be increased towards the soil surface. On the other hand, after initial liquefaction (that occurred at un-reinforced models), acceleration is decreased due to the increase in excess pore water pressure. Also, it can be seen that the increase in tire powders ratio remarkably reduces the maximum excess pore-water pressure ratio. The settlement of the tire powders-reinforced models is significantly less than the unreinforced models, and with the increase of the tire powder percentage shows a very small increase of volume. The outcomes show that the value of the mean damping ratio versus the shear strain range of 0.01 is increased with the increase in tire powder content. Shear modulus is obtained from the ratio of the difference in maximum and minimum stress and strain developed in desired loop. The maximum of the shear modulus in reinforced models is more than the unreinforced models.
Conclusion
The main aim of the present paper was to investigate the influence of reinforcing a saturated sandy soil with tire powders on the soil dynamic properties and the mitigation of liquefaction potential. The following conclusions were drawn from this research.
- The increase of pore-water pressure leads to a reduction in soil shear stiffness and acceleration amplitude.
- Reinforcing sand with tire powders reduces the excess pore-water pressure ratio because of liquefaction and increases liquefaction resistance. 
- Reinforcing sand with tire powders decreases settlement caused by liquefaction.
- The damping ratio decreases at large shear strain as liquefaction occurs.
- Maximum shear modulus and mean damping ratio of reinforced soil has been increased with increasing tire powder content in the mixture../files/site1/files/123/3BahadoriFarzali.pdf

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Introduction
In many areas of the world, the mechanical properties of soils for utilization of land are not sufficient. For improvement of these lands, soil stabilization such as compacting, installation of nails, elders of piles, mixing soil with lime or cement before or during constructions on the surface or inside of the ground can be useful. Microbially induced carbonate precipitation (MICP), due to its versatility and stable performance, has been recently attracted the attention of many researchers in the field of the geotechnical engineering around the world. MICP is a biological technique that is naturally caused to create a cementation agent, which is known as calcium carbonate or calcite by controlling the metabolism of bacteria. Although there are many biological processes that can be lead to MICP, but the using of urea hydrolysis by bacteria is commonly used more. In this method, aerobic bacteria with the enriched urease enzymes inject into the soil. Hydrolysis of urea occurs when the bacteria speeds up the hydrolysis reaction to produce ammonium and carbonate ions. In the presence of soluble calcium ions, carbonate ions are precipitated and formed the calcium carbonate crystals. When these crystals are formed on a grain of soil or like a bridge between them, they prevent the movement of grains and thus improve the mechanical and geotechnical properties of the soil.
Material and methods
In the present study, the effect of increasing fines on the improvement of Anzali sandy soil, and soil resistance parameters for improving the clean sand and its mixtures with a fine grained cohesive soil and a fine grained cohesionless soil separately in a percentage weight of 30 by MICP and using a small scale of direct shear test (6×6) have been investigated. In the present study the sandy soil was collected from the coast of Bandar Anzali Free Zone and for the preparation of samples of clayey sand and silty sand, Kaolinite clay soils and Firouzkooh broken silt were used, respectively. Anzali sand is poorly graded and had a rounded corner with an average particle size of 0.2 mm, somewhat, sharpening cores are also found in its granulation. In addition, its fine grained content is very small (less than 1%). The Kaolinite clay is also labeled with a liquid limit of 40, a plastic limit of 25, and a plasticity index of 15 as an inorganic clay (CL). The used microorganism in this study is urease positive Sporosarcina pasteurii, which is maintained with the number of PTCC1645 at the Center Collective of Industrial Microorganisms of Iran Scientific and Research Organization. The bacterium was cultured in a culture medium containing 20 g/l yeast extract and 10 g/l ammonium chloride at pH 9 under aerobic conditions in incubator shaker machine at 150 rpm and temperature of 30 °C. The organism was grown to late exponential/early stationary phase and stored at 4 °C before injection in samples. A solution of calcium chloride and urea with a molar ratio of one is also used as a cementation solution. With the direct shear test (6cm×6cm) as a benchmarking of the shear strength in the before and after improvement steps, molds fitted with a shear box made of the galvanized sheet with a thickness of 0.6 mm and it consists of two main parts, the body,  in the middle of which an exhaust pipe was embedded in the injector waste fluid. At the bottom of the samples, a layer of filter paper was placed in order to prevent soil washes, and then all samples with a thickness of 2 cm, with a relative density of 30% at the same weight and height were pressed. In the upper part of the samples, a layer of filter paper is similarly used to prevent the discontinuity of soil particles when injected biological materials are used. Biological solutions are injected from the top to the specimens and allowed to penetrate under the influence of gravitational and capillary forces in the sample and discharge the inhaled fluid from the exhaust pipe. The criterion for determining the volume of the solution to inject into each sample is the pure volume (PV) of soil. The preparation process of the samples was initiated by injection of a PV water unit, followed by a two-layer mixture of bacterial suspensions and cementation solutions, each with a volume of one PV, and then for biological reactions, 24 hours to the sample at laboratory temperature (25 ± 2) is given. After the time of incubation, the solution of cementation is injected into the sample for a period of three days and every 24 hours. The processing time of samples is also considered 28 days. In this study, optical density (OD) was selected as a benchmark for estimating the concentration of bacterial cells in the culture medium, and in all stages of development, and precisely before injection of bacteria suspension into soil samples, it was measured by a spectrophotometer device at 600 nm (OD₆₀₀) wavelength, which was obtained for all bacterial suspensions in the range of 1.7 to 2 before the injection. To determine the activity of urea bacteria, 1 ml of bacterial suspension was added to nine milliliters of 1.11 molar urea solution, and by immersing the electrode of the electrical conductivity in the solution, its conductivity was recorded for 5 minutes at 20 ± 2 ° C. The rate of urea activity in the pre-treatment stage for all specimens was in the range of 0.8 to 1.23 mS min^-1. In order to evaluate the shear strength parameters of soil samples, before and after the improvement operations, a direct shear test was used based on the ASTM D3080 standard. This test was performed for all samples under stresses of 50, 100 and 150 kPa in undrained conditions at a loading speed of 1 mm/min up to a strain of 15%. Also, samples of soil with a moisture content of 7% and a relative density of 30% (as already mentioned) have been restored. SEM analysis was carried out to determine the distribution of sediment between soil particles and EDX analysis in order to identify carbonate calcium sediment formation elements in improved soil samples, by scanning electron microscopy on Anzali sandy soil samples in before and after improvement conditions.
 
 
Conclusions
The effect of the increasing cohesive and cohesionless fines on the bio-treated process of sandy soil is the main subject of this research. For this purpose, three samples of clean sand, sand containing 30% clay and sand mixture with 30% silt in a relative density of 30% were treated with MICP method and their shear strength parameters were evaluated by direct shear test after 28 days of processing. Using the direct shear test and analyses of SEM and EDX data, the results are represented as below:
1.  The microbial sediment of carbonate calcium has greatly improved the resistance properties of all three soil samples.
2. A sample of clayey sand, in spite of a higher improvement compared to the other samples with an average shear strength of 113.7% in comparison to to its untreated state, it has the lowest shear strength among the three improved samples.
3. Increasing the clay content of 30% increases the soil voids. On the other hand, it reduces the friction angle and shear strength of the soil in the pre-treated state and also facilitates easier movement of the bacteria between the pores in the soil. More favorable distribution of sediment calcium carbonate was occurred and, as a result, increased adhesion between soil particles.
4. The increase of cohesionless fine particles creates more bonding points between sand particles and, therefore, calcium carbonate crystals form shorter distances between the soil bridges. As a result, with the end of the improvement process, the shear strength parameters of the sandy soil containing 30% of the silt compared to the clean sand have a higher value.
5. SEM images of the clean sand in both before and after improvement show that the calcium carbonate precipitation occurred with a uniform and thin layer that surrounds sand grains and another part of the sediments formed in the joint of grains.
6. Cube-shaped crystalline sediments confirm that the sediment formed in the soil is a stable type of calcite and that the relative increase in the friction angle of the improvement samples can be attributed to solid particles and multifaceted sediments. Also, the elements of carbon, oxygen, and calcium, which are the main components for the formation of calcium carbonate deposits, have been found in the EDX analysis of improvement sand samples../files/site1/files/124/7sohrabi%DA%86%DA%A9%DB%8C%D8%AF%D9%87.pdf
 

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Materials such as waste tire chips were widely used to improve the strength of soil. The objective of this study is to discuss the residual strength or steady-state behavior of sand-waste tire chip mixtures. A series of undrained monotonic triaxial compression tests were conducted on reconstituted saturated specimens of sand and sand-tire chip mixtures with variation in the tire-chip contents from 0 to 4 percentages by dry weight of soil. The specimens are prepared using dry deposition method of preparation. The influence on residual resistance of varying confining pressure (100, 200, and 300 kPa) and sand mixture relative density (40, 65, and 80%) were evaluated. Tests results showed that by increasing the tire chip contents, the residual strength increased and steady-state lines move to the right of log S_us-e diagram. Also, the residual resistance improvement induced by tire chip inclusions was found to be sensitive to the relative density of samples and applied confining pressure.

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Introduction
In some ports, the dredging and accumulation of a large amount of sedimentary material turned to a serious challenge, because of their sequent environmental and economic effects. These problems clarify the necessity of reusing dredged materials. Often, owing to their poor mechanical properties, they are not applied directly in technically engineering uses, so they require to be improved. Geocell application is one of the methods used for the improvement of soil behavior, which confines the sand mass through itself in the three-dimensional structure. These methods ease the speed of applying emerged it into a perfect option for stabilizing of the granular soil.
 In Shahid Rajaee port, by the dredging process for developing new phases, a large amount of calcareous sand is being accumulated near the Persian Gulf coastline. Therefore, in order to provide a solution to reuse these materials, this study attempts to investigate the beneficial influence of reinforcing sand by geocell on its load-beneficial behavior experimented by the plat loading test. For this purpose, a large scale model including circular foundation on reinforced and unreinforced sand has been employed under cyclic loading process.
Material and Methods
Soils
Two types of soils were used in this study. The first type was the sand derived from the dredging process of Shahid Rajaee port which has been used in different layers of the models. The second type of soil was well-graded gravel which has been used only in the cover layer.
Geocell
The geocell in this study were made of heat-bonded non-woven polypropylene geotextiles. Single cells were 110 mm long, 100 mm wide and 100 mm height.
Plate load test
In order to determine the bearing capacity of backfills, repeating plate load test was used with 150 mm diameter. Loading process included four stress levels (250, 500, 750 and 1000 kPa) consisting of 10 cycles each.
Test backfills
Four backfills was made by manually compacting the dredged sand, with tamper up to 350 mm in reinforced cases and 450 mm in unreinforced cases. Then geocells placed and dredged sand filled with accuracy in cells. Finally, a 50 mm thick sand or gravel cover layer, was placed. All lifts were compacted to 70% of relative density with 4% moisture content.
Results and Discussion
PLT results are summarized in Table 1. According to the results, only geocell reinforcement backfills can carry standard truck wheel load (550 kPa). Geocell can increase the ultimate strength of backfills with a sand cover layer by 70% (from 416 kPa to 725 kPa) while in backfill with a gravel cover layer showed 80% increase (from 520 kPa to 960 kPa) in ultimate strength. The gravel cover layer in unreinforced backfills increases the ultimate strength by 25 percent (from 416 kPa to 520 kPa).
Table 1. Results of PLT and performance ratings

Backfill name	UR-S	GR-S	UR-W	GR-W
Maximum stress (kPa)	416	725	520	960
Settlement at failure (mm)	4.6	9.0	15.5	14.9
Plastic settlement (mm)	3.5	7.0	12.5	12.0
Number of load cycles	10	20	20	30
Bearing capacity ratio (BCR)	1	1.74	1.25	2.32
Performance rating	4	2	3	1

Base on Table 1, bearing capacity ratio (BCR) has been increased up to 2.3 and has best when geocell reinforcement and gravel cover layer were used together. Geocell utilization as reinforcement for sand backfills, improves the stress-settlement behavior. Dredged sand can be used as backfill material for yards and access roads when reinforced with geocell and covered with a layer of well-graded gravel../files/site1/files/132/3Extended_Abstracts.pdf

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Introduction
Stone column installation method is one of the popular methods of ground improvement. One of the common uses of stone columns is to increase slope stability. Several studies have been performed to examine the behavior of stone columns under vertical loads. However, limited research, mostly focused on numerical investigations, has been performed to evaluate the shear strength of soil reinforced with stone column. The study presented herein is an experimental program, aimed to explore the shear strength of loose sand bed reinforced with stone column. Direct shear tests were carried out on specimens of sand bed material, stone column material and sand bed reinforced with stone column, using a direct shear device with in-plane dimensions of 305*305 mm² and height of 152.4 mm. Experiments were performed under normal stresses of 35, 55 and 75 kPa . In this study, 4 different area replacement ratios (8.4, 12, 16.4 and 25%), and 3 different stone column arrangements (single, square and triangular) were considered for investigation. The obtained results from this study showed that stone column arrangement had an impact on improving the shear strength of stone columns. The most increase in shear strength and stiffness values was observed for square arrangement of stone columns and the least increase was for single stone columns. This study also compares the equivalent shear strength values and equivalent shear strength parameters (internal friction angle and cohesion) measured during experiments with those predicted by analytical relationships. Results show that shear strength values and shear strength parameters measured from experiments are higher than those obtained from analytical relationships. Accordingly, a corrective coefficient was calculated for each column arrangement to represent the correlation between experimental and analytical results.
Material Properties of Loose Bed and Stone Column
Fine-grained sand with particle size ranging from 0.425 to 1.18 mm was used to prepare loose sand bed, and crushed gravel with particle size ranging from 2 to 8 mm was used as stone column material. The sand material used as bed material had a unit weight of 16 kN/m³ and a relative density of 32.5%, and the stone material used in stone columns had a unit weight of 16.5 kN/m³ and a relative density of 80%. The required standard tests were performed to obtain the mechanical parameters of bed material and stone column material. As the diameters of model scale stone columns were smaller than the diameters of stone columns installed in the field, the particle dimensions of stone column material were reduced by an appropriate scale factor to allow an accurate simulation of stone columns behavior.
Testing Procedure
In this study, large direct shear device with in-plane dimensions of 305*305 mm² and height of 152.4 mm was used to evaluate the shear strength and equivalent shear strength parameters of loose sand bed reinforced with stone column. Experiments were performed under normal stresses of 35, 55 and 75 kPa.
Two class C load cells with capacity of 2 ton were used to measure and record vertical forces and the developed shear forces during the experiments, and a Linear Variable Differential Transformer (LVDT) was used to measure horizontal displacement. All achieved data from the experiments including data on vertical forces, shear forces and horizontal displacements were collected and recorded using a data logger, and an especial software was used to transfer data between the computer and the direct shear device. All specimens were sheared under a horizontal displacement rate of 1 mm/min.
Testing Program
Experiments were performed on single stone columns and group stone columns arranged in square and triangular patterns. The selected area replacement ratios were 8.4, 12, 16.4, and 25% for single stone columns, and 8.4, 12 and 16.4% for square and triangular stone column arrangements. To eliminate boundary effects, the distance between stone columns and the inner walls of the shear box was kept as high as 42.5 mm. In total, 12 direct shear tests were carried out, including 2 tests on loose sand bed material and stone column material, and 10 tests on stone columns with different arrangements. From the tests performed on group stone columns, 4 tests were performed on single stone columns, 3 tests on stone columns with square arrangement and 3 tests on stone columns with triangular arrangement. Hollow pipes with wall thickness of 2 mm and inner diameters equal to stone column diameters were used to construct stone columns. To prepare the specimens, first, the hollow pipes were installed in the shear box according to the desired arrangement. Then, bed material with unit weight of 16.5 kN/m³ was placed and compacted in the box in 5 layers, each 3 cm thick. Stone material was uniformly compacted to construct stone columns with uniform unit weight. The compaction energy was 67 kJ/m³ in all tests.
Results and discussion
In this paper, the behavior of stone columns under shear loading was experimentally investigated in large direct shear device by performing tests with different area replacement ratios (8.4, 12, 16.4, and 25%), different stone column installation arrangements (single, square and triangular), and different normal stresses (55, 75 and 100 kPa). The key findings of this study are as follows:
1. Shear strength increases with increase of area replacement ratio due to the higher strength of combined soil-stone column system, and due to the increase of stone column area effective in shear plane. The amount of shear strength increase with area replacement ratio is low for ratios lower than 15%. However, this amount is higher for area replacement ratios higher than 15%.
2. For stone columns with equal area replacement ratios, higher shear strength was mobilized in stone columns with square and triangular installation arrangements compared to single stone columns. Among the installation patterns investigated in this study, stone columns with square arrangement experienced the highest increase in shear strength value, while single stone columns experienced the lowest. One of the reasons of shear strength increase in square and triangular patterns is the increase of confining pressure applied by stone columns to the soil between them. Another reason is the increase the total lateral surface by changing the column arrangement from single column to square and triangular patterns. This increased lateral surface increases the lateral force imposed on the stone columns, resulting in higher shear strength mobilization of stone material.
3. The slope increase of shear strength-horizontal displacement curves shows that soil-stone column system has higher stiffness than loose sand bed, and this stiffness varies with area replacement ratio and installation pattern. The maximum stiffness values refer to stone columns installed in square pattern and the minimum values refer to single stone columns. In general, stone column installation pattern has an effective role in increasing stiffness.
4. Results show that shear strength parameters increase in soil reinforced with stone column. The maximum increase in internal friction angle refers to stone columns with square pattern and the minimum increase refers to single stone columns.
5. The equivalent shear strength values measured from experiments are higher than those obtained from analytical relationships. Accordingly, it is conservative to use analytical relationships to calculate shear strength parameters. It is worthy to mention that these relationships assume that the value of stress concentration ratio is equal to 1. Results from this study indicate that the value of stress concentration ratio should be accurately calculated and used in the relationships.
6. As discrepancy was observed between values measured from experiments and those obtained from analytical relationships, corrective coefficients were calculated to modify analytical relationships. These coefficients were computed and presented based on stone column installation pattern, area replacement ratio and the applied normal stress values../files/site1/files/133/2Extended_Abstracts.pdf 

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Introduction
The geotechnical engineering problems involving unsaturated soils are included water flow, shear strength and volume change. Soil-water characteristic curve (SWCC) describes the constitutive relationship between soil suction and soil water content. SWCC may be determined directly or indirectly in the laboratory. Because of the various difficulties involved in the direct measurements, a simple and economical laboratory method namely filter paper method is of considerable value. The filter paper method is a laboratory technique that has recently been accepted as a standard method of measuring soil potential, reaching far higher ranges of water potential in comparison to other techniques, and is based on the principle of moisture absorption by filter paper until there is a balance in potential between filter paper and soil.
This paper presents an experimental investigation performed to evaluate the soil water characteristic curves of dune sand stabilized with SBR polymer and MICP processes (Sporosarcina pasteurii bacteria with CaCl2 and urea) with contact filter paper method in the Jabal Kandi area.
Material and methods
The dune sand used in this study was obtained from the surface (0–10 cm depth) of Jabal kandi area, located on the south-west of Urmia Lake. SBR polymer is prepared from Paya Resin Company in Esfahan. In the MICP processes, S. pasteurii from Persian Type Culture Collection (PTCC 1645) was used as the urease positive bacterium. Cultivation of the microorganism was conducted in a medium containing 20 g l^-1 yeast extract, 10 g l^-1 NH₄Cl at a pH value of 8. Sporsarcina pasteurii was grown to late exponential phase to final concentration of 1.5 g dry weight l^-1 and urease activity of 2.2 mM urea min^-1 under aerobic batch conditions. Broth cultures were incubated in a shaker incubator operated at 120 rpm. Cementation solution of MICP consisted of CaCl2 and urea. All experiments were performed at an ambient temperature of 25^oC ± 2.
For the tests with Whatman No. 42 filter paper, three different soil samples were prepared (dune sand, dune sand stabilized with (5-10-15) % SBR polymer and dune sand stabilized with (5-10-15) % MICP process). Residual water content is 2.5% and the residual dry density is 15 kN/m³. The soil is mixed with the right quantity of water and placed in a sealed plastic bag for 24 hours to allow the hydric equilibrium to establish. The contact filter paper tests were carried out on soil specimens stabilized with SBR polymer and MICP process to the residual water content (2.5%) and nearly residual dry density (15 kN/m³). The soil specimen sizes were 50 mm in diameter and 20 mm height. The test procedure involves placing a piece of initially air dry filter paper against the soil specimen whose matric suction is required and sealing the whole to prevent evaporation. The filter paper was wetted to water content in equilibrium with the magnitude of the soil matric suction, and careful measurement of the water content of the filter paper enables the soil matric suction to be obtained from a previously established correlation. This provides a measure of the matric suction. ASTM D-5298-93 standard is used for the filter paper method.
Results and discussion
The SWCCs for dune sand stabilized with SBR polymer and MICP process under different SBR polymer and MICP process contents are illustrated in this study. Gradual transition from a unimodel SWCC to a bimodal SWCC was observed as SBR polymer and MICP process content increases. The unimodel SWCC is characterized by having two bends defining the air entry value and residual water content. The air entry value is defined as the matric suction above which air commence to enter the soil pores. The residual water content is defined as the water content beyond which no significant decrease in water content occurs. The bimodal SWCC is characterized by having four distinct bindings: two air entry values and two residual water contents. For SBR polymer and MICP process content equal to or less than 5 percent, the SWCC shows a unimodal form of SWCC. With the increase of SBR polymer and MICP process content greater than 5%, the SWCC indicate a bimodal form. It is further observed that the residual water content and the air entry value increases with the increase of SBR polymer and MICP process content. These observations are attributed to the presence of smaller pore size developed as a result of SBR polymer and MICP process particles filling the voids between sand particles. Bimodal SWCC are generally observed for gap-graded soils as well as soils that include two levels of pore sizes defined as macro pores and micro pores. Therefore, it can be inferred that the increase of SBR polymer and MICP process content, resulted in the formation of micro pores within the dune sand stabilized with SBR polymer and MICP process. The portion of the soil water characteristic curves representing macro pore sizes range between matric suction of 0.1 to 100 kPa. Whereas, the portion of the SWCC representing micro pore sizes lies between matric suction of 200 and 1500 kPa.
Summary and Conclusions
In this study, the effect of SBR polymer and MICP process content on the soil water characteristic curves of dune sand was evaluated. SBR polymer and MICP process contents considered include 0%, 5%, 10% and 15%. Results from this study indicated that, as the SBR polymer and MICP process content increased, the shape of the SWCC transforms from a unimodal form to a bimodal form. Furthermore, the air entry value and residual water content were observed to increase with increase in SBR polymer and MICP process content signifying increase in water retention capacity. The bimodal form of the SWCC indicates the presence of two levels of pore sizes; namely macro pores and micro pores. For 10% and 15% SBR polymer and MICP process content, the macro pores are considered the dominant pore size covering a broad range of the SWCC from 0.1 to 100 kPa. Therefore, it is inferred that the SWCC of dune sand stabilized with SBR polymer and MICP process are strongly related to the texture and pore size distribution of the dune sand stabilized with SBR polymer and MICP process which in turn, has a significant impact on its hydraulic characteristics.
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Sandy soils usually contain different amounts of fines like silt and clay, causing some changes to their shear strength and dilation characteristics. Bolton [1] conducted  some experiments on the different sands and suggested a relation between the parameters of the soil shear strength. In this paper, some experiments were performed on fine contained sand and the extended Bolton's relation was has been proposed. In this paper, shear strength and dilation behavior of a pure sand mixed with different amounts of silt or clay fines were studied using direct shear test device (100*100*30 mm), and a total of 96 tests were carried out. The samples were prepared separately using clay and silt contents of 0, 10, 20 and 30% in different relative densities of 70, 80, 90 and 100%. They were tested under three surcharge pressures of 90, 120 and 150 kPa, under particle crushing threshold. Variations in shear strength, maximum friction angle, critical state friction angle and cohesion, as well as dilation angle were investigated by increasing in the mentioned amounts. The results demonstrate that shear strength, dilation angle, maximum friction angle decreased by clay content increase, however, they increase with increase in silt content. In addition, a new form of the Bolton's relation for fine contained sandy soils was presented.

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The increasing rate of construction activities in urban areas is accompanied by excavation in the vicinity of existing structures and urban utilities. This issue has highlighted the importance of constructing protecting structures in order to control displacements and prevent damage to structures and their neighboring area. Among the important widely used wall stabilization techniques, one can name nailing and grouted anchors. However, these methods suffer some drawbacks such as annoying noise and vibration during the drilling, implementation difficulties below the water table, grouting problem, installation of strands and bars in the borehole in porous and collapse soils, and long curing time for the grout of post-tension anchors. Since the helical anchor method lacks many of the mentioned problems, it is now widely used in many applications.
In the present work, a laboratory model of helical anchor stabilized wall is presented and evaluated. For this purpose, four types of anchors at 20° back slope are designed in a sandy soil and the effect of helix configuration (in term of its diameter and number of blades) is investigated. Considering the laboratory scale of the designed model, the results obtained using helical anchor were compared with numerical results of soil nailing wall by applying the particle image velocimetry (PIV) analyses.
Material and methods
The test box designed in this work is made of a metal plate with a thickness, length, width, and depth of 1.5 mm, 100 cm, 60 cm, and 30 cm, respectively, and a Plexiglas in its opposing side with a thickness of 50 mm. The soil used in the experiments was the dry sand of Soufian region in east Azerbaijan province of Iran. The soil is classified as SP according to USCS classification. The helical anchors were fabricated by welding the helical pitches to a metal shaft. The end part of the shafts is screw threaded such that to fasten a bolt to them.
To start the experiment, the empty box was completely cleaned using the detergents to remove any pollution or soil on the Plexiglas and metal surface. Afterward, the sandy soil was poured on the wall floor and the facing was placed inside the box vertically. Again, the sandy soil was poured from both sides of the facing up to the installation height of the helices. Helices were installed in the assigned holes and their angle was adjusted through the pre-fabricated stencils. The soil height was increased up to the next row assigned for helices installation. These steps were repeated until reach the wall crest. After preparation of the physical model, its behavior during the preparation must be modeled. We first filled both sides of the model and then modeled the stability behavior of the helical anchor wall through excavating its facing opposed side. Overall, the wall was built through eight excavation steps.
Results and discussion
The maximum displacement is related to the anchor type 1, which does not have enough bearing capacity under surcharge conditions. By changing the anchor type and increasing the number of helices, shear strains and their expansion in the wall back decline. The decrease in displacement rate by changing the anchor from type 1 to type 2 is 18%, which is due to the low bearing capacity of type 2 anchor compared to the type 1 anchor. Increasing the number of pitches from one to two (changing the type 1 anchor to type 3 anchor) showed a considerable decrease (i.e., 43%) in displacement rate. Increasing the number of pitches from 1 to 3 (changing the anchor from type 1 to type 3) resulted in a 62% decrease in wall crest displacement. This displacement decrease rate seems to decline with an increase in the number of helixes.
The displacement rate for all four anchors is almost similar in two excavation steps, which probably is because of the need for displacement for activation of the anchors. One strategy to deal this issue in the sensitive projects and control the displacement is to apply post-tension helical anchors. Then, in stages 4 to 6, the displacement was almost constant due to four main reasons including wall rigidity, the presence of reinforcements, formation of pre-step displacement-induced tension force, and enough capacity of anchors to face with more displacement. In stages 6 to 8, type 1 and 2 anchors showed growing displacements due to the reduction and ending the wall rigidity and lower bearing capacity. In type 3 and 4 anchors, the maximum displacement was related to 4 initial stages. In type 1 and 2 anchors, which have two helical plates, almost a similar behavior was observed until stage 6 of excavation, but eventually type 3 anchors showed better performance because of higher bearing capacity to overall displacement.
Conclusion
In the present study, a physical model was designed to investigate the effect of helical anchors’ geometry on displacement rate of helical anchor wall and compare it with a nail wall. Overall, comparing the results obtained by conducting these experiments on a helical anchor stabilized wall and a nail wall revealed that:
- Wall crest displacement is affected by the diameter and number of helices and decreases by an increase in bearing capacity.
- The increase in the number of pitches from one to two (single-pitch to double-pitch anchor) has a higher effect on displacement control compared to the case of changing the double-pitch to triple-pitch anchor. So, it can be stated that a further increase in the number of anchor pitches results in a declined performance of the anchors.
- All anchors need a slight displacement for activation. This issue cannot be resolved by changing the type of helical anchors. Hence, when the displacement required for activation of the anchors exceeds the allowable wall crest displacement, use of post-tensioned helical anchors is recommended.
- A comparison between nailing and helical anchor results revealed that the relative density of the wall stabilized with the helical anchor is less than that of the nail wall; and wall crest displacement in the helical anchor wall was very lower than that of nail wall. Thus, the helical anchor wall stabilization is preferred when other economic and technical requirements are met.

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Introduction
Shallow tunnels have a vital role in urban planning, railway and highway transportation lines. The presence of underground cavities can leads to stress concentration and consequently, instability of the spaces against static and especially dynamic loads. Therefore, the aim of this study was to evaluate the effect of elliptical cavity and its inclination on sandstone rock behavior under compressive static and tensile dynamic loads. In order to evaluate the effect of the cavity under static stress conditions, two groups of intact and hole-bearing sandstone cores with 0, 30, 60, and 90 degrees of hole inclination were prepared and tested under uniaxial compressive loading test. During the test, in addition to the stress recording, damage and deformability of the samples were recorded by using the strain gauge, acoustic emission sensor and camera. Split Hopkinson pressure bar (SHPB) test apparatus was used for doing dynamic loading test. Furthermore, the damage process was recorded using a high-speed camera with 10 micro-seconds interval of frame capability. The obtained results showed that presence of the cavity reduced the rock strength in maximum state (θ=0) up to 55% and in minimum state (θ=90) up to 77% of its initial uniaxial compressive strength. Dynamic tensile loading tests illustrate that the elliptical hole near the free end of sample (reflection boundary of compressive wave to tensile wave) is stable due to locating in superposition area, while the other cavity out of the area with each inclination was undergone to spalling failure. Assessment of failure surface using scanning electron microscope and thin section study indicates that the dominant fracture is grain-boundary type and iron oxide cement has a vital role in developing of this type of fracture.
 


 

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The use of piles, helical anchors and, in general, helical foundations has considerably increased in the last 30 years. The adoption of this technology in the international and domestic codes of each country, as well as in research and studies, and, finally, the publication of numerous books and papers in this area, and the existence of manufacturers’ products, committees, and contractors of this technology has contributed to its expansion and development. However, such methods have progressed at a very slow pace in many countries, especially in developing countries. This paper attempts to assess the global advancement of the helical foundations by reviewing 292 papers from 1990 to 2020 and comparing the related research findings. This will help clarify the issue and determine the scope of technological progress. On the other hand, collecting valuable papers in this area will make it easier for researchers to make further research. Subsequently, the characteristics of this technology are highlighted and the reasons for its lack of progress in the developing countries are addressed. For this purpose, a questionnaire is sent to researchers, developers, designers, and contractors of the geotechnical projects. The purpose of this questionnaire is to specify the type of existing projects, the soil type of project site, the degree of familiarity with the helical foundation technology, the reasons for not using this method and the solutions available to expand and develop this method. Finally, there are suggestions to develop this approach and the issues that need further research.

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Introduction
The ring footings are very important and sensitive due to widespread use in various industries such as oil and gas; so finding some ways for improving the behavior of these types of footings can be very valuable. One of these ways, which is very affordable and also can be help in environmental protection, is the use of granulated rubber that made from disposable materials like scrape tires, as the soil reinforcement. In the present study, the behavior of ring footings with outer constant diameter of 300 mm and variable inner diameters (90, 120 and 150 mm with inner to outer diameter ratio of 0.3, 0.4 and 0.5) placed on unreinforced sand bed and also granulated rubber reinforced bed, has been investigated by field test. The effects of important parameters like inner to outer diameter ratio of ring footing and thickness of rubber-soil mixture on the behavior of ring footing in terms of bearing capacity, settlement and inside vertical stresses of footing bed have been studied and the optimum values mentioned parameters have been determined.
Material and methods
In all tests, a sandy soil was used to fill the test trench which was excavated in the natural bed of the earth with a length and width of 2000 mm and a height of 990 mm. It should be noted that the type of this soil is well-graded sand (SW) according to the Unified Classification System (ASTM D 2487-11). This sand had medium grain size, D₅₀, of 2.35 mm, moisture content of 5.4% and friction angle of 41.7^∘. The granulated rubber particles with dimensions between 2-20 mm, a mean particle size, D₅₀, of 14 mm and a specific gravity, Gs, of 1.15, have been used in all tests for using in rubber-soil mixture layer.
The loading system consists of several parts such as loading frame for providing reaction force, hydraulic jack, load cell, load transfer system (including loading shaft which was located below Load cell and footing cap which was located under the loading shaft) and rigid steel loading plates with different inner to outer diameter ratios (d/D=0.3, 0.4 and 0.5 and constant outer diameter of 300 mm). Some devices like load cell, LVDT, pressure cell, data logger and unit control were applied to collect the data and control the system. Both soil and rubber-soil mixture layers were compacted by vibrating plate compactor to gain their maximum densities. After preparing the tests, the static load was applied on the system at a rate of 1 kPa per second until 1000 kPa or until backfill failure.
Results and discussion
The results of tests on both unreinforced and rubber reinforced beds indicated that the ring footing with inner to outer diameter ratio (d/D) of 0.4 had the maximum bearing capacity in all settlement levels. This behavior can be related to the arching phenomenon within the internal spaces of ring footing with optimum inner to outer diameter ratio. In fact, when the ring footing with optimum inner to outer diameter ratio is subjected to a certain level of loading, the soil inside the ring seems to be compacted due to interface effect of the two sides of the ring. However, by increasing the inner to outer diameter ratio more than its optimum value, the ring behaves like two independent strip footings without any interface effect and therefore the bearing capacity decreases.
The results of tests showed that the vertical inside stresses in different depths of footing bed (both unreinforced and rubber reinforced beds) decrease with increasing d/D ratio. This stress reduction process can be due to the transfer of stress concentration from the points close to the center of the ring to the outer point because of turning from the ring mode with interface effect to the two independent strip footings that mentioned earlier.
The results of rubber reinforced cases illustrated that, regardless of the footing settlement level and also irrespective of d/D ratio, the bearing capacity of ring footing increases with increasing the thickness of rubber-soil mixture layer (h_rs) up to the value equals 0.5 times the outer diameter of ring footing and further increase in this thickness more than mentioned optimum value (h_rs/D=0.5) can decrease the bearing capacity. Even in some cases of reinforced base (h_rs/D=1), the bearing capacity can be reduced to the value less than that of unreinforced cases. It can be due to high compressibility of rubber reinforced layers with higher thicknesses than optimum value.
It should be mentioned that the rubber reinforced layer can reduce the vertical inside stresses compared to unreinforced cases. It can be due to this fact that the rubber reinforced layer acts as a wide slab. Such that it can spread the applied loading over a wider area. Also rubber reinforced layer has high capacity of absorbing energy and therefore can decrease the vertical inside stresses.
Conclusion
In the present study the behavior of ring footing placed on rubber reinforced bed have been investigated by field test. The effect of different parameters such as inner to outer diameter ratio of ring footing and the thickness of rubber-soil mixture layer on the bearing capacity, settlement and vertical inside stresses of the footing bed were studied. The result indicates that:
- In both unreinforced and rubber reinforced bed, the ring footing with inner to outer diameter ratio (d/D) of 0.4 had the maximum bearing capacity, regardless of settlement level.
-The vertical inside stresses in different depths of footing bed decrease with increasing d/D ratio.
-The bearing capacity of ring footing increases with increasing the thickness of rubber-soil mixture layer (h_rs) up to the optimum value equals 0.5 times the outer diameter of ring footing.
-The vertical stresses can be reduced by using rubber reinforced layer../files/site1/files/151/5.pdf