Journal of Engineering Geology

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Saline sea water, groundwater into salt domes or municipal waste leachate can affect hydro-mechanical properties of bentonite as a sealing material in nuclear waste repositories or landfills. This paper investigated the effect of sodium chloride solution on Atterberg’s limit, swelling, consolidation and permeability of bentonite. Swelling and consolidation test had been done at 0.05, 0.1, 0.5 and 2 molar solution and pure water by oedometer apparatus in Iran University of Science and Technology. Considering the results, it can be seen that a little increase in concentration of the solution reduces swelling of bentonite. So that the swelling potential of bentonite reduced from about 82% to about 1.5% by increasing in concentration of the solution from pure water to 2 molar solution. Liquid limit and plastic index of bentonite were reduced by increasing concentration of the solution but plastic limit was not changed significantly. Meanwhile increased concentration of the solution will facilitate reaching equilibrium for swelling and consolidation of the samples which occur due to their enhanced permeability. Permeability of bentonite increased about 7 times by increasing in concentration of solution from pure water to 2 molar solutions. Also, the Compressibility of bentonite was reduced by increasing in concentration of sodium chloride in the solution.

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The Schmidt hammer provides a quick and inexpensive measure of surface hardness that is widely used for estimating the mechanical properties of rock material such as uniaxial compressive strength and Young’s modulus. On the other hand, Schmidt rebound hardness can be used for a variety of specific applications. In the mining industries, it is used to determine the quality of rock, which is common practice when constructing rock structures such as those found in long wall mining, room and pillar mining, open-pit mining, gate roadways, tunnels, dams, etc. However, a number of issues such as specimen dimensions, water content, hammer type, surface roughness, weathering, testing, data reduction and analysis procedures continue to influence the consistency and reliability of the Schmidt hammer test results. This paper presents: a) a critical review of these basic issues and b) avaluate the effect of temperature, moisture and uniaxial compressive stress on Schmidt hammer hardness. It was found that water content has a significant effect on the Schmidt rebound hardness (SRH) of rocks. So that increase of water content substantially reduced the SRH of samples. Temperature also had a considerable influence on the SRH. However, relationship between SRH decreases with increasing temperature for tested samples were linear. Also tests results showed that uniaxial loading of samples increases the SRH values.

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./files/site1/files/3.pdfExtended Abstract
(Paper pages 201-224)
Introduction
Soil nails are traditionally designed with uniform length and equal spacing to stabilize slopes which do not meet safety requirements. However, nails with uniform layout in a slope may not be the optimal design if the construction cost is taken into account. The optimal layouts lead to a minimum usage of nails and satisfies the allowable factor of safety and wall deformation.
In this study a decreasing trend of nails length along the wall height was considered to investigate the stability and the performance of the wall in different nail patterns. Then nail density was introduced as an important factor on the overall stability and deformation of the wall. It can be beneficial in the preliminary estimation of the required nail length at the beginning of a project.
Findings of this study are helpful for effective design of soil–nailed slopes.
Materials and Methods
The finite element analyses were conducted to investigate the effects of nails pattern on the overall stability and deformation of soil–nailed walls. Slope/W software was used to obtain the Factor of safety and Plaxis 2D was used to calculate the deformation of the soil nail walls. Soil hardening model was used to simulate the behavior of soil. In this study, various walls with different specifications were modeled and analyzed. As an example, a 10 m deep soil nail wall with C=10 kN/m², ?=25 deg, E_oed=20000 kN/m² is discussed here to monitor the trends (C represents cohesion, ? is the angle of friction and E_oed is the modulus of elasticity of the soil).
As it is shown in Figure 1, by considering the decreasing trend of nail length along the wall height, an ordered arrangement (pattern) is introduced by presenting “L” as the base nail length and “” as the inclination of stabilized zone border then, the effect of nail arrangement on the safety factor and deformation of nailed wall is investigated. The nails were installed with an angle of 15 degrees relative to the horizon. According to FHWA a minimum value of 1.35 is considered for the factor of safety. Circular failure surfaces are assumed and the tensile and pullout resistance of the nails crossing the failure surfaces are considered as the governing stabilizing forces.
Results and discussion
In this study, soil nails pattern effects on the performance and the stability of the soil nail wall are investigated. In Figure 2 variation of safety factors caused by different soil nails arrangements is illustrated. Generally three separated trends are observed in each curve. It demonstrates that at lower values of  with small bond length, the factor of safety is constant. As  increases the bond length behind the slip surface becomes longer and the safety factor is increases gradually. Eventually it reaches a point that the nails are long enough that increasing the nails length is not influential in the stability of the wall. Hence, nails at different elevations of a slope have different contribution to the overall stability of soil–nailed slopes.
Wall deformations need to be controlled by the allowable deformation level in designing the soil nailed wall especially when buildings or other underground facilities exist near the excavation. One of the most important parameters on soil nailed wall deformations is the arrangement of nail lengths.
Figure 3 shows the effect of nail arrangements on the wall horizontal deflection. In general, as and L increase, horizontal deflection of the wall decreases. The rate of this reduction is higher in lower base length. As it is
 


illustrated in Figure 3, by increasing the length of the nails, the deflection is decreased till no significant reduction is observed.
As it is shown the arrangement and the layout of the nails are influential on the stability and deformation of the soil nailed walls. However, it is important to identify an optimal layout in a way that with optimum nail length, allowable stability is reached and the wall deformation stay in an allowable range.
Nail density is defined as the ratio of the required nail length per the unit area of the wall surface and defined as below:

where L_i is nail length of each row and A is the stabilization area. Hence, estimating the nail density can be beneficial for the engineers to have a preliminary estimation of the costs of the project at beginning of the project.
Figure 4 indicates that the nail density governs the wall deformation. As it is seen, for different layouts with the same nail density, the resulted deflections are so close. Hence, it can be concluded that nail density is a key factor in determination of the wall deflection. It is also illustrated that, as the nail density increases, the reduction rate of the deflection is decreased. Effective nail density is defined as a threshold point that increasing the nail density is no longer effective on deformations.


As it is demonstrated in Figure 5, different layouts with a similar nail density have close values of safety factors. In walls with higher nail density increasing the nail length is fruitless and at lower nail density nails are not effective. So Optimum designation should be somewhere at the middle part with an allowable factor of safety. In the middle part the variation of factors of safety is more tangible.
Horizontal deflection profile
During the construction process the wall tends to move outward. Figure 6 illustrates the effect of soil nails arrangements on the deformation of a 10 m deep wall for a constant base length. As it is shown, by increasing  the horizontal deflection at the top of the wall decreases in a way that at higher  values, the wall deformation mode changes from overturning mode to bulging mode.
Conclusion
In this paper the effects of soil nail arrangement on the stability and performance of the wall was investigated. An ordered arrangement of the nails was introduced and the effect of various nail lengths at different elevations of the wall was discussed. Major findings concluded from this research are summarized as follows:


Nail density was defined as a key parameter and the findings demonstrate that nail density plays an important role in controlling the stability and the performance of the soil nail walls, in a way that patterns with the same nail densities but different arrangements, result in the almost similar factors of safety and deformations. Therefore based on the allowable factor of safety and deformation, nail density can be concluded and the nail arrangement which meets the standards, is selected.
Threshold nail density is defined as a value of nail density which no significant reduction of deflection happens afterward.
Uniform distribution of the nails and lower values of  generates the maximum deflection at the top of the wall. As  increases, the bond length in the upper parts of the wall controls the deformation. In that case, the deflection value is bounded and the maximum deflection occurs at the middle depth of the wall. Therefore the mode of deformation changes from overturning mode to bulging mode. As a result, in the projects which their adjacent structures are of high importance, it is recommended to use more 
 

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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
Jet-grouting is a soil improvement technique which was originated in Japan. Jet-grouting method consist of disaggregation of soil or weak rock and its mixing with, and partial replacement by, a cement agent; the disaggregation is achieved by means of a high energy jet of a fluid which can be the cement agent itself. Jet-grouting techniques can be grouped into three main systems, which are named single, double and triple fluid, depending on the number of fluids injected into the subsoil, namely, grout (usually water–cement mixture), air and grout, and water plus air and grout. In the beginning, jet grouting was mostly viewed as a means of improving the subsoil properties for the foundations of large structures. Nowadays, its application are diversified for use in foundations, excavations, tunneling, water barriers and underpinning. This paper studies foundation improvement by jet-grouting in one of Iran northern cities and seeks the optimum design parameters for jet-grout columns in saturated and unsaturated sand. Results of cement grouting as one-fluid jet-grouting method together with site geotechnical characteristics are presented. Diameters of jet-grouted columns, uni-axial strength of soil-cement cores and core recovery index are surveyed as the most important parameters for performance assessment of improved foundation and the primary design is modified and the project completed based on the results.
Material and methods
Design parameter of jet-grout columns were assumed according to guidelines and previous expertise as followsed: single-fluid jet-grout method with 450 bar injection pressure and rod withdrawal speed of 0.5 cm/sec with a grout density of 1600 gr/cm³. Monitor rotation speed was set to 30 rpm. Soil strata consists of a 5 meter sand with some gravels followed by a 7 meter clayey silt with the average SPT numbers of 30 and 7, respectively. To investigate the effectiveness of design parameters, jet-grout columns head were uncovered by excavating its nearby soil and columns diameter were measured. Several core samples were prepared from columns with a L/D ratio of 2 and an average diameter of 74 mm by means of a triple tube core barrel after 28 days of columns installation. The volume of core samples were calculated by multiplying its length to its average cross section (calculated from the average diameter of cores) and their unit weight were obtained by dividing its weight to its volume. Uniaxial compression test conducted in the deformation-control mode with the strain rate of 1 percent on all samples. Core samples were tested in different ages from 34 to 85 days and uniaxial compression strength (UCS) of samples were corrected by age correction factor according to soil type suggested by Sližytė et al.
Results and discussion
It is observed that the average diameter of columns that are constructed in unsaturated sand with design parameters mentioned in material and methods section, is one meter and the average diameter of columns that are constructed in saturated sand with the same density as unsaturated sand is 0.8 meter. This could be due to the dissipation of fluid jet energy under the water.
The modified obtained values from uniaxial compression test show that the strength of samples varies from 28 to 90 kg/cm². By omitting the lower, an upper 5 precent of the data as irrelevant data, the average UCS of the remaining part is equal to 57 kg/cm². By applying a geotechnical safety factor of 2.5 to the modified a filtered UCS values, a UCS of 40 kg/cm² is obtained as the structural strength of get-grout column.
Conclusion
-It is observed that utilizing one-fluid jet-grout method with 450 bar injection pressure in saturated silty sand with mean SPT number 30, rod withdrawal speed of 0.5 cm/sec and grout density of 1600 gr/cm³ will result in 80 cm diameter jet-grout columns, while the same parameters will result in a 100 cm column in unsaturated sand which can be due to fluid jet energy dissipation under water.
-Considering the common design parameter for jet-grout columns in Iran, which are the same as the design parameters discussed in this paper, the UCS of get-grout columns in near shore silty sand with a safety factor of 2.5 is about 40 kg/cm². 
./files/site1/files/123/6Extended_Abstract.pdf

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The present work is conducted to investigate the effect of texture and carbonate content on internal friction angle of carbonate soils. Carbonate soils are majorly found in the bed of shallow waters and also offshores in tropical regions. Recently there is a huge construction projects including oil and gas extraction platform and facilities, harbors, refineries, huge bridges and other big construction projects in many offshore and onshore areas around the world. One of these area is located on southern part of Iran. We collected soil samples from different parts of northern coasts of Persian Gulf, then the following experiments were performed, carbonate content, three-dimensional grain size, angularity, relative density & direct shear. The results showed that the average of internal friction angle of carbonate soil is higher respect to known silicate sands. This angle is affected by effective grain size, grain angularity, and calcium carbonate content. Based on the experimental results of this study, one of the results was that the internal friction angle of carbonate soils decreases as their effective size of soil aggregates increases.
 

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In coastal industrial areas, in addition to the presence of loose soil, sulfate attack on soil improvement elements, such as soil-cement, is a double problem. Generally, the use of type V cement is recommended as one of the methods to reduce the detrimental effects. Considering the limited resources of this type of cement, firstly to determin the relationship between the cement content and the strength obtained in sulfated environments is one of the important engineering question in this field and secondly, as an alternative option, the use of type II cement which is more available, is suggested to use in combination with suitable additives. The present study pursues the above two goals by making cylindrical soil-cement specimens with sand, water and Portland sulfate resistant cements. Sodium sulfate is used as the sulfate in soil and water. In the research, first of all, the relation between type V cement content and unconfined compressive strength of soil-cement is obtained at 0% to 5% sulfate concentration, which results in a cement content of 400 kg/m³ completely limited the sulfate attack effects in a sulfate concentration of 2%. Secondly, the combination of type II cement with barium chloride and hydroxide was tested. The related results show that the combination of type II cement with barium chloride and hydroxide had higher strengths, about 2.7 to 3.3 times, respectively (in 362 days), than the soil-cement containing type V cement../files/site1/files/152/%D8%A2%D8%AA%D8%B4_%D8%A8%D9%86%D8%AF.pdf