Journal of Engineering Geology

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Saline soils are of challengeable soils that may cause many problems in civil engineering projects. In this study, volume change behaviour of saline soils and also the effect of improvement and reinforcement on them have been investigated using laboratory tests as well as consolidation test, swelling pressure test and free swelling test. The case study is Amirkabir Highway which connects the cities Qom and Kashan.  Fifty four kilometer of this highway was deformed like waves due to existence of saline soils. The laboratory investigations showed that the studied soil has a considerable swelling potential which appears to be the main cause of damage to the highway pavement, therefore it is decided on improving the subsoil condition. The research program comprises of studying volume change behavior of saline soil, stabilized with lime and epoxy – resin polymer and reinforced with polypropylene fiber. Afterwards, results for two cases of stabilized and non-stabilized samples have been compared. According to the results, the main cause of swelling is soil disturbance and structure destruction of initial soil composition. Considering all of test conditions, it is appeared that, although lime is a traditional stabilization material but is economic for the most geotechnical projects and usage of polymer is suggested only in special applications due to its rapid setting

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The collapsible soils are usually known as soils with open structure and weak bonding between particles. The behavior of such soils is similar to very loose soils. These types of soils, when saturated without any changes in loading or subjecting vibratory loads, experiences huge settlements. The present research deals with investigation on collapsible soils located in the North East of Mashhad. The results of laboratory and in situ tests show that collapsible soil in this region was very sensitive to the increasing of moisture content. This means that an increase in soil moisture content, significant excess settlement occurs during a short time. This indicates that the soil in this region suffers from high potential collapsibility. The huge soil settlement will lead to the stability of existing structures to be at risk. It is, therefore, necessary for the collapsible soil in the region to be improved. For soil improvement, many techniques including moisture mitigation and soil replacement or compaction may be employed. Also stabilization of soil with lime, cement or coarse aggregates are practical methods. Which The results of the present research indicate that stabilization of soil lime is the most appropriate method for increasing bearing capacity of soil and reducing structural settlement.

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The main objective of this research is to investigate the mechanism of cement-clay-heavy metal contaminant interaction from micro-structural point of view. To achieve this objective series of batch equilibrium and XRD experiments were performed. The results indicate that the addition of 10% cement not only stabilizes the soil, but also at 250 cmol/kg-soil of heavy metals causes 130% increase in heavy metal retention. Furthermore, the XRD analysis shows that in solidified samples with less than 10% cement, the main reason for reduction in peak intensity of clay fraction is due to the presence of heavy metals. However, as the percentage of cement increases, the clay solubility is the main reason for reduction in peak intensity of montmorillonite in XRD test

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./files/site1/files/2Extended_Abstract.pdfExtended Abstract
(Paper pages 29-50)
Introduction
In some soils, special phenomena happen with increases in their moisture content that sometimes inflict major damages on development projects. Dispersive soils are one type of such soils. The physico-chemical properties of the particles in dispersive soils cause them to disperse and separate from each other upon contact with water. If dispersive clays are not accurately identified, they will cause damages and failures. In the Simin Dasht region of Semnan Province, some hydraulic structures have incurred serious damages because they are located on dispersive soils.
The present research studied the soils around the canal transferring water from the Simin Dasht to Garmsar. This 37-kilometer long canal is situated in Semnan Province between the Simin Dasht and the Garmsar diversion Dams. Scouring and soil erosion under the concrete lining of the canal has led to the destruction of the structure. After visiting the site and taking soil samples, double hydrometer and pinhole tests were performed. The effects of adding various amounts of cement, lime and aluminum nitrate on amending dispersive clays were studied and compared in the Simin Dasht region of Semnan Province.
Experiments
The effects of the quantities of cement, lime and aluminum amendment materials on stabilization of dispersive soils in the Simin Dasht region of Semnan Province were investigated. Two types of dispersive clayey soils were amended. Table 1 presents the characteristics of the soils. The effects of various amounts of lime, cement, and aluminum nitrate on reduction in the degree of dispersion in the tested soils were studied. The cement, lime, and soil samples were dried at 40˚C for 24 hours. It must be mentioned that the amount of added lime, cement, and aluminum nitrate were zero, 3, 5, and 7 percent.
Table1. Characteristics of dispersive soils used in this reserch

Gs	Optimum Moisture (%)	Plasticity Index, PI (%)	Plastic limit, PL (%)	Liquid limit, LL (%)	Natural water content (%)	Soil
2.72	15	2.54	15.09	17.63	13.84	A
2.66	11	6.33	16.11	22.44	3.02	B

Results
Average changes in discharge passing through the dispersive soil samples A and B, and through samples of these soils amended with lime, cement, and aluminum nitrate in pinhole tests are presented in Figures 1(a-f), respectively. Figure 1a indicates that the behavior of the A soil samples amended with lime did not follow any specific trend, but we can cautiously say that soil A will become non-dispersive when lime is added at 4.5 percent at all moisture contents. Increases in the quantities of the cement added to the dispersive soils A and B to stabilize them independent of the moisture content of the soils were also investigated (Figure 1c, d). Behavior of the A soil samples stabilized with aluminum nitrate followed a specific trend (Figure 1 e, f) contrary to those amended with the other stabilizers.
Conclusions
Results of the tests show that dispersion in soil A was amended (without completely preventing the occurrence of the scouring phenomenon) by the addition of cement or lime at 5 percent or aluminum nitrate at 3 percent. Moreover, dispersion in soil B was amended by the addition of cement at 3 percent, lime at 5 percent, or aluminum nitrate at 3 percent. Aluminum nitrate was a better and more effective amendment material for the dispersive soils compared to lime. Therefore, aluminum ions replaced the other ions in the structure of dispersive clays more suitably compared to calcium ions. Comparison of the results obtained from the pinhole tests performed on soil samples amended with aluminum nitrate, lime, and cement suggests that it took a shorter time for the samples to be stabilized with aluminum nitrate compared to the other two amendment materials.



Figure1 Variation of discharge due to soil stabilization, Lime (a and b), Cement (d and c), Aluminum nitrate (e and f)
 

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Geotechnical engineers, in many cases face with low strength or high swelling potential of clayey soils. Stabilization methods are used to improve the mechanical properties of this type of soils. Lime and cement are the most popular materials used in chemical stabilization of clayey soils. If sulphate exists in the stabilized clayey soil with lime, or if soil is exposed to sulphates, problems such as strength reduction and swelling increase will occur. Reuse of industrial residual such as Rice Husk Ash (RHA) can be beneficial from the economy point of view. RHA includes a proper amount of silica with high specific surface area which is very suitable for activating the reaction between the soil and lime. In this paper, chemical stabilization of gypsum clays using lime and RHA is addressed Sulphates exist in the constitution of the soil. Unconfined compression strength and swelling potentials of the stabilized soil are evaluated. The results of this study indicate that RHA has positive impacts on improving mechanical properties of the gypsum clays stabilized with lime. From the view point of strength and swelling characteristics, and economy, addition of 6–8% lime and 8-10% RHA as an optimum amount is recommended.

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Introduction
One of the most important 1-ring aromatic organic pollutants is phenol and its related compounds. These compounds are classified as hazardous wastes base on U.S.EPA primary contaminates list. The phenolic compounds are very poisonous and these are harmful for human health and also for other biota.
To control the movement of such hazardous organic waste in a contaminated soil, solidification/stabilization (S/S) process can be an effective alternative.  Due to the negative impact of organic compounds on the cement hydration, the cement-based S/S may be not effective for controlling the movement of such pollutants. To avoid these effects, using some additives during solidification period has been recommended. One of the proposed of such compounds is organophilic clay that is the modified montmorillonite by quaternary ammonium salts (QAS). There are several researches to evaluate the organophilic clay effect on adsorption and stabilization of organic compounds during S/S process. The effectivity of S/S process can be examined by several tests such as leaching test, durability, unconfined compressive strength (UCS), etc.
In this study, efficiency of ordinary and organophilic clay was evaluated in the solidification and stabilization process based on unconfined compressive strength of a phenol-contaminated soil.
Material and methods
In this study, an artificially phenol contaminated sand was considered to evaluate the effectivity of the white cement based S/S process by using two different additives of ordinary and organophilic clay.
The contaminated sand contains 2000 ppm of phenol. S/S process was conducted on 14 samples with different amounts of white cement (15 and 30 wt%) as binder and ordinary/organophilic clay (0, 8, 15, and 30 wt % for each of them) as the additives. Two zero percent additive samples are considered as control samples.
All samples were cured for 28 days and then UCS test was conducted for all of them.
Results and discussion
Unconfined compressive strength of all examined samples were ranged from 2226 to 6999 KPa. In the samples with equal amount of cement, th higher UCS values can be observed in blank samples (without any additives and phenol). By adding phenol in the examined sand, UCS of the solidified sample reduces 3 -3.5%.Moreover, results showed that UCS was reduced by increasing the amount of clays. The reduction of the samples containing organophilic clay was higher than samples containing ordinary clay. Unconfined compressive strength values of all samples met the minimum standards indicated by France, Netherlands, Britain and America for disposal in a sanitary landfill. The sample with 30% white cement and 8% bentonite was the maximum amount of UCS (4856 KPa) and the sample with 15% white cement and 30% organophilic clay was the minimum one (2226 KPa). In this study, the average cost of organophilic clay-based solidified samples was 2.3 to 2.8 times more than the average cost of the bentonite-based solidified samples.
Conclusion
In this study, the strength of the cement-based solidified samples contaminated by phenol was investigated. The summary of the findings of the research is as follows:
1. By adding the phenol to pure sand, the UCS of the samples can be reduced 3-3.5 %.
2. Addition of organophilic clay reduces the UCS of the samples more than the ordinary clay (bentonite) in the same amount.
3. All samples met the recommended UCS level for the S/S process. The minimum UCS level is for the sample with 15% of cement and 30% of organophilic clay.
The cost of S/S process is between 23 and 650 $/ton of contaminated soil depending on the amount of used additives and binder. The samples containing organophilic clay has a higher cost than the similar sample containing ordinary clay.
4. To evaluate the S/S process effectivity, a leaching test of phenol (such as TCLP) is recommended  ./files/site1/files/0Extended_Abstract2.pdf

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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.