The problem of roadway support in swelling soft rock was one of the challenging problems during mining. For most geological conditions, combinations of two or more supporting approaches could meet the requirements of most roadways; however, in extremely swelling soft rock, combined approaches even could not control large deformations. The purpose of this work was to probe the roadway deformation mechanisms in extremely swelling soft rock. Based on the main return air-way in a coal mine, deformation monitoring and geomechanical analysis were conducted, as well as plastic zone mechanical model was analysed. Results indicated that this soft rock was potentially very swelling. When the ground stress acted alone, the support strength needed in situ was not too large and combined supporting approaches could meet this requirement; however, when this potential released, the roadway would undergo permanent deformation. When the loose zone reached 3 m within surrounding rock, remote stress p
 ∞ and supporting stress P presented a linear relationship. Namely, the greater the swelling stress, the more difficult it would be in roadway supporting. So in this extremely swelling soft rock, a better way to control roadway deformation was to control the releasing of surrounding rock’s swelling potential.

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Deformation mechanisms in a coal mine roadway in extremely swelling soft rock

There is high demand for roadway support in coal mines for the swelling soft rocks. As high strength steel sets can be taken as an effective alternative to control large deformation in this type of rocks, based on an original set, three new sets, including a floor beam set, a roof and floor beams set, and a roof and floor beams and braces set, are proposed in this research. In order to examine the strengths of new sets, four scaled sets of one original set, and three new sets, have been manufactured and tested in loading experiments. Results indicated that three new sets all exhibited higher strength than the original set. In experiments, the roof beam in set plays a significant effect on top arch strengthening, while the floor beam plays significant effect on bottom arch strengthening. The maximum bearing capacity and stiffness of the top arch with roof beam are increased to 1.63 times and 3.06 times of those in the original set, and the maximum bearing capacity and stiffness of the bottom arch with floor beam are increased to 1.44 times and 3.55 times of those in original set. Based on the roof and floor beams, two more braces in the bottom arch also play a significant effect in bottom corners strengthening, but extra braces play little role in top arch strengthening. These new sets provide more choices for roadway support in swelling soft rocks.

Assessment of Bearing Capacity and Stiffness in New Steel Sets Used for Roadway Support in Coal Mines

In mine roadway support operations, floor bolting not only played a role in floor heave control, but also in reinforcing roof and its two sides. Correspondingly, bolting of roof and two sides also played a part in floor heave control. To quantify the effect of such bolting, based on roadway support in extremely weak rock, three physical models were produced and tested in laboratory. Through comparison of their displacements in three physical simulation experiments, the reinforcing effect of bolting in extremely weak rock roadways was quantified. Reinforcing coefficients was defined as displacement ratio between original support and new support regime. Results indicated that the reinforcing coefficients, for bolting of roof and its two sides, on floor, two sides, and roof reached 2.18, 3.56, and 1.81 respectively. The reinforcing coefficients for floor bolting on floor, two sides, and roof reached 3.06, 2.34, and 1.39 respectively. So in this extremely weak rock, the surrounding rock should be considered as an integral structure in any support operation: this allows for better local strength improvement, and provided future design guidance.

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Effect of bolting on roadway support in extremely weak rock.

Design in swelling mediums is mostly based on uniaxial data since the standards proposed by the International Society for Rock Mechanics Commission on Swelling Rocks for uniaxial tests are in the form of recommendations, triaxial sets are not highly available; and there is no standard developed for triaxial tests. The main purpose of this study is to define the relationship between the uniaxial and the triaxial swelling equations and to predict the triaxial values using the uniaxial data. The other purpose of the study is to contribute to the development of the standards and to expand the data available in the literature about triaxial swelling behavior. Numerous uniaxial and triaxial swelling tests were performed on the samples from seven different locations, in Turkey, in a state of the art swelling laboratory. As a result of the determination of the triaxial swelling behavior of these samples, the relationships between the uniaxial and the triaxial swelling data for the individual samples as well as the whole set of samples are expressed by the equations derived from the statistical analyses.

Determination of the relationship between uniaxial and triaxial swelling equations for clay bearing rocks

The Middle Miocene evaporites of Abu Dabbab Formation, north of Quseir City along the Red Sea coast of Egypt are composed mainly of thinly laminated, bedded and nodular anhydrite and microcrystalline gypsum especially in its lowermost part. Highly cracked inter-bedded clay, dolomite and stromatolite layers were recorded within the evaporite succession. The cracks in the inter-bedded clays are filled with evaporite materials indicating arid climatic conditions during exposure episodes. Swelling mechanisms in clay-evaporites include mechanical swelling due to hydration of clay minerals and transformation of the anhydrite into gypsum. Field observations as well as powder x-ray diffraction investigations have shown that anhydrite/gypsum modal ratio decreases gradually downward indicating that gypsum has transformed to anhydrite by solar heating. The clay minerals of the inter-bedded clay layers are dominated by smectite (46 %), illite–smectite mixed-layer (18 %), chlorite (13 %), palygorskite (9‘%), kaolinite (8 %), and illite (6 %). The liquid limit of the Abu Dabbab Formation (anhydrite and inter-bedded clays) is higher than 65 %, so considered as of very high swelling capabilities. Also, its swelling percentage was found to be (11–14 %), (28–35 %) and (58–65 %) for gypsum, clay and anhydrite, respectively. The swelling pressure was found to be (1.4–1.5 kg/cm2), (2.3–3.1 kg/cm2) and (4.7–5.1 kg/cm2) for gypsum, anhydrite and inter-bedded clay. The swelling pressure of gypsum is moderate and for both anhydrite and clay is high. The highly swelling capability of anhydrite and the inter-bedded clays causes geotechnical problems when got into contact with water. Alternating volume change due to phase transformation and solubility of calcium sulfate adds to the severity of problems associated with the host expansive clay strata.

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Geotechnical Characteristics of Anhydrite/Gypsum Transformation in the Middle Miocene Evaporites, Red Sea Coast, Egypt

Increase in the volume of rocks containing swelling minerals like montmorillonite and anhydrite due to physico-chemical reaction with water is defined as swelling. If increase in the volume is prevented, a swelling problem which harms engineering structures occurs. In the design of these structures the data obtained from swelling tests should be used. Triaxial swelling test is important in terms of the success of the design. In this study swelling problem caused by claystone containing smectite group clay mineral in Tire Lignite Enterprise (Izmir, Turkey) was investigated and triaxial swelling behavior of the claystone was determined.

	 

	Key words: Swelling, triaxial, stress, strain, claystone, smectite.

Swelling problems and triaxial swelling behavior of claystone: A case study in Tire, Turkey

The swelling characteristic in soil and rock mass is recognized due to presence of clay minerals such as montmorillonite and anhydrite. However, this swelling feature does not pose a threat to the engineering structure until physico-chemical reaction with water takes place. In this case, stability of engineering structure is jeopardized due to volume and swelling stress increase. Long routes of tunnels excavated in different geological rock formations increase the probability of failure as tunnels pass through swelling soils or rocks. Tunnels are the most affected engineering structure from swelling problems as a result of their long service life. The Terzili tunnel, which is the subject of this article, is double-tube and 1180 m long and cuts the swelling geological units along its route. It passes through a flysch and clay unit consisting of alternation of conglomerate-sandstone-claystone. Claystone has a swelling property and its maximum swelling stress range between 0.77 and 2.0 MPa; the maximum swelling deformation ranges from 5.97 to 9.75%. After some excavation has been made from the entrance and exit parts of the right and left tubes in the Terzili’s tunnel, the advance in the tunnel has stopped. After 17 months, cracks were observed on the 2-m thickness invert concrete as a result of swelling stress. As a remediation, it was decided to reinforce 40 cm thick steel reinforced concrete slab on the existing filling concrete, depending on the thickness of the superstructure. In the numerical modeling, Phase2 program does not have a module to model the effect of swelling minerals included clay units, directly. Swelling effect in models was created by applying additional distributed load to the tunnel support. In addition, to model umbrella arch effect, the impact zone of the umbrella arch has been created as a new material. For section 1 of the tunnel, in the case where the swelling pressure is 0.5 MPa, the maximum principal stress and displacement around the tunnel are 2.5 and 9 times, respectively, compared to the non-swelling pressure. For section 2 of the tunnel, the calculated values are 1.3 times of the maximum principal stress and 21 times of the displacement if there is 0.5 MPa swelling pressure.

Stability assessment of Terzili tunnel in swelling rock mass

In this study, since the city of Bartin in Northwest Turkey on the Black Sea is in the first-degree seismic zone and its residential area only occupies 7% of the total acreage that is expected to expand with newly flourishing urbanization, soil samples were obtained from a total of five different locations where there are open areas for the construction of dwellings. Engineering properties of the soils were assessed by laboratory experiments and the allowable bearing capacity and elastic settlement (Schmertmann method) values of the soils were calculated. The results showed that calculated settlement values are very high and can damage the foundation systems of any building constructed in future; therefore, allowable settlement value was fixed at 50 mm and allowable bearing capacities of the soils were obtained from back calculations by using the Schmertmann method. The aim of calculating allowable bearing capacity modified by settlement analysis is to propose a procedure about the foundation designs of the building laying on compressible sandy soils.

	 

	Key words: Shallow foundations, allowable bearing capacity, silty sand, Schmertmann method, settlement.

https://www.academicjournals.org/article/article1380633434_Citiroglu et al.pdf

Allowable bearing capacity based on Schmertmann method for sandy soils

Rockfall is one of the serious worldwide natural hazards that endangers the safety of life and property. Roads and railroads passing near slopes, and residential areas built at the bottom of the slopes are under threat of rock falling. Rock block falling from the top of the slope with high velocity under the influence of gravity can result in damages to civil structures, disrupting transportation, injuries, and fatalities. This study investigates rockfalls on a roadway passing near the slope with a residential area. Rockfall analyses have been carried out on the Zonguldak-Kilimli roadway based on the field investigations, laboratory studies, and using the two-dimensional Rocfall v.4.0 software. The rock blocks falling in the study area have been observed for 2 years. As a result, a detailed discontinuity survey together with detached and already falling blocks was carried out. The average block size was 34.7 cm and the number of volumetric joints was calculated as 11.2 joints/m3. Ten-kilogram, 100-kg, 500-kg, and 1500-kg mass blocks were used in the analysis. The mean of the restitution coefficient (Rn and Rt) values which are the input parameters in the rockfall analysis was chosen as Rn 0.28 ± 0.79 and Rt 0.64 ± 0.11. Some of the falling blocks remain in the road ditch. The other blocks move out of the road ditch and move along the road. According to the results of the analysis, the blocks with a mass of 10 kg move 3.8 m towards the roadway. This situation endangers road safety. The kinetic energies of the blocks depend on their mass. The maximum kinetic energy value of the falling movement blocks was calculated as 160 kJ. The highest restitution value of the blocks that hit the ground is 1.85 m. It was calculated that the height of the restitution was 0.7 m at a distance of 1 m from the slope. Since it is not possible to change the slope geometry, concrete barrier along the roadside is recommended as a preventative measure. The concrete barrier is designed to absorb maximum total kinetic energy of 240 kJ with height of 1.3 m and 1 m ahead of the slope.

Investigation of rockfall potential of Zonguldak-Kilimli roadway (Turkey)

Zonguldak city is a mountainous area in Turkey’s Western Black Sea. In such mountainous areas, it is highly recommended to undertake precautions measures due to sudden and uncertain risk arising from rockfall events causing significant damage to infrastructures and structures. Therefore, this phenomenon is investigated as an important and special issue in civil and mining engineering. The main objective of this study is to investigate the possible rockfall events and risk assessment of the potential rockfall that may occur near the Zonguldak-Istanbul roadway slopes. In Zonguldak mountainous area, the rockfall event occurred due to presence of the discontinuities in the rock, tectonism of the rock units and rainfall factors, and a combination of these factors. For this purpose, a detailed field observation on slope and rock characteristics has been carried out. In this present study, rockfall analysis has been performed out on two selected slope profiles taken in one location by using of the Rocfall numerical analysis program based on the lumped mass method. Thus, bounce height, fall-out distance, velocity, and kinetic energy of the blocks along each survey has been analysed. Therewithal, the assessment of rockfall potential hazard has been carried out by applying of the Evolving Rockfall Hazard Assessment (ERHA) method. As a result, the investigated area is defined as a moderate to high risk category and necessary protective measures are recommended.

Mehmet Erdinç Bilir

Papers

Swelling problems and triaxial swelling behavior of claystone: A case study in Tire, Turkey

Stability assessment of Terzili tunnel in swelling rock mass

Allowable bearing capacity based on Schmertmann method for sandy soils

Investigation of rockfall potential of Zonguldak-Kilimli roadway (Turkey)

Rockfall analysis and risk assessment on steep slopes of the roadway (Zonguldak, Turkey)