Collapsible soils are among the problematic soils in nature that due to wetting, make many settlements so that according to research, the amount of settling can reach 1 to 2% of the thickness of the soil layer.If this type of soil is not identified, if structures are built on them, the constructed structure will be damaged if the soil saturates and changes in soil moisture. The existence of such soils in many parts of the world including Kerman province of Iran, necessitates the attention to study the behavior and characteristics of the collapsible soils. The aim of this contribution is to investigate the effect of butadiene rubber on the stabilization of collapsible soils. The tested fine-grained soils that have been sampled from two different sites were stabilized through injecting different percentages of butadiene (the number of experiments was 84). The ASTM D5333 Double-Consolidation Method, was applied in order to examine the stabilized soils on intact soil samples. The results show that the penetrations of butadiene rubber as well as the formation of butadiene rubber columns have led to reduction in soil collapse. Considering development of intelligent systems using prediction behavior of stabilized collapsible soils, the ANFIS model was used to predict degree of collapsibility of soil samples stabilized by injection Styrene Butadiene Rubber.

The aim of this study was to improve the characteristics of natural collapsible soils using the geogrid-encased stone column technique. For this purpose, 20 large-scale specimens of stone columns were prepared using rigid metal cylinders with a diameter of 308 mm and a height of 97 to 154 mm according to the unit cell theory. The aspect ratio was 10% to 25%. For the occurrence of bulging failure, the height of the stone columns was considered six times the diameter. The stone columns were encased with geogrids of varying stiffness from 80 to 200 kN/m. The soil around the stone column inside the unit cell was compacted to similar site conditions. Loading was applied similar to the test, which determines the soil collapsibility potential while the specimens were being inundated from the bottom of the metal cylinder by a water feeding system. During loading, the vertical displacements of the stone columns were measured at two locations on the loading plate. The results showed that the columns settlement due to inundation diminished by increasing the stiffness of the encased stone columns and aspect ratio. The optimum aspect ratio was approximately 15%. Encasement of the stone columns increased the lateral pressure in the collapsible soil and prevented the collapse of the stone column. The settlement values of stone columns were compared with a settlement prediction model and showed a good agreement. The data obtained in this study can be used as a practical method to improve natural collapsible soils during inundation.

The research investigates the effects of adding nanoclay on the shear strength properties of two gypseous sand soils. The soil samples were taken from the cities of Tikrit (55% gypsum) and Al-Najaf (29% gypsum). A direct shear test was used to examine soil specimens in dry conditions and immediately after a saturation procedure. The distributed soil specimens were remolded in the direct shear box to achieve a specific density. The shear speed was 1.0 mm/min. For both soil samples, there are different added nanoclay contents, 0, 2, 5, and 7%. Three levels of normal stress are applied, 25, 50, and 100 kPa on each soil specimen. The results state that there is a significant decrease in the angle of internal friction with saturation for both soil samples due to the gypsum solution in these soils. The resulting saturated F is significantly lower than the reported mean values in the literature. The F is recovered by adding nanoclay content up to 5% worthily. A mathematical model correlates the values of F and the percentage of nanoclay using a regression analysis with restricting gypsum content (29-55%) and nanoclay (≥ 0%) in saturation conditions.

In many parts of the world, the formations of sinkholes are reported by many researches. In the past few years. several sinkholes have formed in the northern part of Hamedan, between Hamedan and Famenin cities. The geotechnical results evaluation indicates that collapsible sandy soil and Karstic bedrock contribute to the formation of those sinkholes. It is understood that the simultaneous role of those factors significantly affects the size of sinkholes. In the previous researches, the mutual role of solubility of bonding material and the presence of collapsible sandy soil are not taken into account. In the current research with consideration of this point, a series of odometer testing performed. The artificially added sodium sulfate, sodium carbonate, and carbonate calcium made possible to consider the effect of chemical bonding on the behaviour of collapsible sandy soils. It is shown that the collapsible behaviour of sandy soil having calcium carbonate as its bonding material is very sensitive to the pH of soil pore water. It is concluded that in the area susceptible to collapsible behaviour, the presence of soluble bonding may significantly affect the size and development of sinkholes.

Since most of the soils in their natural state are unsaturated, therefore understanding and description of the compression and failure behavior of unsaturated soils are essential. The compression and failure behavior of unsaturated soils are affected by the interaction of the solid, liquid, and gas phases of the soil. Most of unsaturated soils exhibit a sudden change in their volume due to saturation that is called collapse phenomenon. The compression and collapse behavior of collapsible soils are so complex that can not be explained in the total or net stress spaces. Wetting induced collapse of the collapsible soil has a discontinuous response in net stress space and needs to be described using the matric suction. Calculations of the effective stress using the matric suction shows that the wetting induced collapse response of unsaturated soils is a continuous but a highly non-linear behavior. On the other hand, the compression characteristics of dry and saturated soils are different and change as the moisture content or the degree of the saturation of the soil change. In this research the compression and the wetting induced collapse behavior of unsaturated CL-ML soil have been investigated in the laboratory. Laboratory tests have been conducted by oedometer test device. Compression and wetting induced collapse behavior of unsaturated soil in dry state before collapse, during saturation and collapse state, and fully saturated after collapse state were studied. Pressure plate device was employed to obtain the soil water characteristic curve of the soil. Based on the laboratory results a compression and collapse model has been proposed to capture the compression and collapse behavior of the soil before, during and after wetting induced collapse. Using the soil water characteristic curve, the compression and collapse response of the soil was transferred to effective stress space. The binary-medium model was employed to describe the compression and the collapse behavior of the unsaturated soil based on its responses in two dry and fully saturated states as two reference states. Based on the binary-medium model, soil mass was considered as binary medium including two states of 0 and 1. The state of the soil in dry condition was considered as binary 0 and its state in fully saturated state was considered as binary 1. The state of the soil at any particular state between these two states was interpolated using a state function. An exponential form state function in terms of matric suction and the effective stress was introduced to relate the volume change of the unsaturated soil during the collapse state to its compression behavior in two dry and fully saturated states The state function was derived based on the laboratory experiments. The compression behavior of the soil in dry state was. Using the proposed model, the compression and collapse behavior of unsaturated soil in dry state, collapse state, and saturated state could be described in a single generalized model. The proposed model was verified by the laboratory tests conducted in this study and the available published in the literature. Verifications illustrated the ability of the proposed model in capturing the compression and collapse behavior of unsaturated collapsible soils.

This paper presented the field characteristics of ML soil prone to collapsible in uncompact condition, using soil mechanics tests and in-situ tests including determination of electrical resistance and wave velocities, and then the dynamic and post-cyclic monotonic behavior of the compact specimen using a large-scale triaxial device. The average electrical resistance of the collapsible ML soil layer of is reduced to a third (11 Volt-Meter/Ampere) from the surface to the depth of 4 m and is almost constant up to the depth of 30 m. However, the values of the shear wave velocity "average from the surface" of the downhole method have a low value (i.e. 160 m/s) at the surface depth and gradually increase to 450 m/s at a depth of 30 m. In the following, on the mentioned compacted materials under σ_3^'equal to 1, 2 and 5〖kg/cm〗^2, dynamic cyclic tests were performed according to ASTM D3999 under frequencies of 0.5, 1, 2, 5 and 10 Hz. The effect of changing the percentage of moisture and anisotropic consolidation (σ_1^'/σ_3^'), triangular, sinusoidal and rectangular waveforms on the results of shear modulus (G), shear modulus ratio (G/G_max) and damping ratio (D) versus strain shear (γ) was investigated through 57 tests. The results showed that with the increase of loading frequency the values of G and D are increased slightly and considerably, respectively. According to the results, compaction solution alone is not suitable for treatment of the studied soil.

Collapse refers to sudden decrease in the soil volume upon wetting which is attributed to loss in the strength of the inter-particle bonds. Collapsible soils can be founded at vast areas around the word and subtropical areas of Iran. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, collapse behavior of loess soils has been subject of interest. In this study, stabilization of Semnan loess which is composed of fine sand and silt bonded by weak clay bonds has been investigated. The loess was mixed with Portland cement in the order of 0. 5%, 1%, and 2. 5% for and with nano-clay in order of 0. 05%, 0. 1%, and 0. 25%. The specimens were prepared to achieve dry density of 14 kN/m3 and water content of 5%. Oedeometer tests were performed to determine the collapse potential according to ASTM D5333 after 7, 14, and 28 days. Results showed that both Portland cement and nano-clay can reduce collapse potential. Improvement performance was significantly dependent on the binder content and curing time. The best improvement performance was observed at low nano-clay content and it was reduced by increasing nano-clay content. Unlike the cement stabilization, treatment process with nano-clay was relatively fast that terminated when soil moisture content was evaporated. In addition, in this study micromechanical soil behaviors were investigated by scanning electron microscopy (SEM) image of the treated and untreated specimens.

Many countries in the word have loose and unstable soils encompassing a wide range ofgeological materials, which when inundated, may collapse and cause very significant distress to the structure. Stone columns have been used to strengthen such soils; even so, there are still cases where failure has occurred. In this technical note, the process and causes of stone column failure in reinforcing collapsible soils is examined. A behavior analysis of a typical element of soil in the vicinity of column during inundation was studied. The difference between the behavior of a stone column in a collapsible fill and a column in a non-collapsible fill is reported in this paper. Also asolution for the problem of stone column failure is suggested.

Collapsible soil has a semi-stable, non-compacted, and relatively porous structure. These types of soils become damaged and experience noticeable deformation or sudden settlement due to increased moisture or excessive loading. This type of soils is categorized as problematic soils that, if they are placed under structures or inside the earth structures, can cause many problems in terms of stability and operation and cause financial and life losses. This paper attempted to evaluate and zone the collapsible soils in Semnan city. The studied points were examined using field experiments and also by consolidation test. Investigation of being problematic and the collapsibility of the collapsible points have been performed using the “Jennings and Knight” and “ASTM D5333” criteria. Collecting geotechnical data from 141 locations in Semnan city, 24 points with collapsibility potential were identified. The novel result of present study is an effective step to reduce the risks related to construction on the sites having collapsibility potential in the Semnan.