特殊截面抗滑桩受力特征与土拱效应分析

对于传统矩形截面抗滑桩的受力而言,由于混凝土抗压不抗拉的力学性质,使截面受拉区的混凝土没有发挥出最大效用。通过对矩形截面形状的改变,即把受拉区面积减小和受压区面积增大,进一步利用了混凝土在截面中的抗压性能,使得抗滑桩截面的抗弯承载力和抗弯刚度都得到了提升,并通过计算,验证了此说法。截面形状的改变,也使得桩间土拱受力发生了改变,即从以前的一个土拱,变为了由一个主要拱和一个次要拱来共同承担,对桩间土拱效应有一定增强。通过对矩形截面和特殊截面抗滑桩的数值模拟对比分析,论证了桩间土拱效应在截面改变后得到增强的观点,也表明特殊截面抗滑桩降低了土体从桩间滑出的可能性,可为抗滑桩的传统设计提供理论参考。     

Mechanical properties of lime-treated clay reinforced with different types of randomly distributed fibers

In this paper, a comparative experimental study was carried out to evaluate the effect of inclusion of different fiber types on strength of lime-stabilized clay. In this scope, a series of unconfined compressive strength tests were carried out on specimens including basalt and polypropylene fiber compacted under Standard Proctor effort (i.e., 35% by weight of soil). The effects of curing period (1, 7, 28, and 90 days), fiber type (basalt and polypropylene), fiber content (0, 0.25, 0.5, 0.75, 1%), fiber length (6, 12, and 19 mm), and lime content (0 and 9%) on strength properties were investigated. The results revealed that both basalt and polypropylene fibers increased the strength without inclusion of lime. For specimens including lime, strength of polypropylene fiber-reinforced specimens was remarkably higher than that reinforced with basalt fiber for lime-stabilized clay. However, greatest strength improvement was obtained by use of 0.75% basalt fiber of 19 mm length with 9% lime content after 90-day curing. Additionally, results of strength tests on specimens including 3 and 6% lime and 12-mm basalt fiber after 1, 7, 28, and 90-day curing were presented. It is evident that the use of 6-mm basalt fiber and 12-mm polypropylene fiber were the best options; however, efficiency of fiber inclusion is subject to change by varying lime contents. It was also observed that the secant modulus was increased by use of lime; however, strength of the correlations among secant modulus and unconfined compressive strength values was decreased by increasing amount of lime for specimens including both basalt and polypropylene fibers.     

Influence of Random Inclusion of Synthetic Wicks Fibers of Hair on the Behavior of Clayey Soils

Several soil improvement methods are used to enhance the engineering properties of soil, among which, reinforcement by fibers is considered as an effective ground improvement method because of its cost effectiveness, and easy adaptability. The present investigation chooses synthetic wick and vinifera raphia fibers as reinforcement. The synthetic wick fiber was randomly included into the soil at four different percentages i.e. 0, 2, 4, 6% by volume of raw soil. Vinifera raphia fiber was used at one percentage (4%) as control. The main objective of this research is to focus on the strength behavior of clayey soil reinforced with randomly included synthetic wick fiber. The physical and mineralogical characterization was carried out on ten soil samples. The compression, flexion, abrasion, water absorption and capillarity tests were performed on synthetic wick reinforced specimens with various fiber contents. The results of these tests have clearly shown an improvement in the compression strength values from 1.65 to 2.84 MPa for the wicks fibers, and the flexural strength values which varied between 1.08 and 1.96 MPa. Hence, the waste of synthetic wick fibers is therefore an efficient reinforcement for compressed earth blocks, which are very significant for construction of durable and economic infrastructures.     

Interpretation of Soil–Cement Properties and Application in Numerical Studies of Ground Settlement Due to Tunneling Under Existing Metro Line

Uncertainty of properties of improved soft ground with chemical grouting often results in discrepancy between simulated results and observed data and makes prediction for ground subsidence difficult. It also made practice usually adopts unconfined compressive strength of soil–cement mixtures as design control criterion. This paper presents a methodology to interpret the strength and deformation parameters from unconfined compressive strength of soil–cement mixtures for advanced numerical analysis which is widely used in reinforcing the soft ground and pre-supporting excavation. Observed data are used to compare with the simulated results and validate the interpretations. Numerical experiments with two-dimensional finite element model for covered undercutting of large cross-sectional twin tunnel under an existing subway station are presented. Issues with respect to design and construction of excavation that potentially affect the ground surface subsidence are explored. It was found that the ground subsidence caused by tunneling in soil–cement medium under existing subway station is similar to that in a greenfield site but with flatter settlement trough. Unconfined compressive strength of soil–cement mixtures ranging from 1.5 to 2.0 MPa can significantly reduce the settlement to an acceptable control criterion. Settlement magnitude is influenced by pillar width but not obviously by the location of umbrella arch installed in twin tunnels.     

Effect of Random Inclusion of Wheat Straw Fibers on Shear Strength Characteristics of Shanghai Cohesive Soil

The effect of random inclusion of wheat straw (fibers) on shear strength characteristics of Shanghai cohesive soil is presented in this paper. 1 year old natural wheat straw (fibers) with four section lengths of 5, 10, 15, 20 mm (aspect ratio: l/d = 1.67, 3.33, 5, 6.67) are used as reinforcement and specific Shanghai cohesive soil is used as medium. Locally available cohesive soil is compacted with standard Proctor’s maximum density with low percentage of reinforcement (0.1–0.4 % of wheat straw sections by weight of oven-dried soil). A series of direct shear tests were conducted on unreinforced as well as reinforced soil to investigate the shear strength characteristics of wheat straw-reinforced soil. The test results show that the inclusion of randomly distributed wheat straw sections (fibers) in soil increases the shear strength to one degree or another. It is noticed that the optimum wheat straw (fiber) content for achieving maximum shear strength is 0.3 % of the weight of oven-dried soil for wheat straw fiber length 15–20 mm (aspect ratio: 5–6.67).     

纤维混凝土的低温性能和冻融损伤机理研究

研究了低温环境下(气温变化为-15~5℃),聚丙烯腈(PAN)纤维对混凝土力学性能增长趋势的影响,探讨了快速冻融试验条件下(-17.5~7.5℃)PAN纤维混凝土的抗冻融耐久性,通过扫描电子显微镜(SEM)观察了PAN纤维在混凝土中的分散性以及纤维和混凝土界面结合状况.结果表明:掺入PAN纤维增加了混凝土的含气量、改善了混凝土的微观结构,提高了混凝土抗裂阻力,因而有利于混凝土低温环境下的强度增长和提高了混凝土的抗冻融耐久性.混凝土经受冻融循环破坏实质上是疲劳损伤累积的过程.通过实验研究和理论分析,探讨了聚丙烯腈纤维混凝土冻融疲劳损伤的机理,研究了纤维对混凝土抵抗冻融破坏的影响,建立了聚丙烯腈纤维混凝土冻融损伤的演变方程.     

Construction of Large-Span Twin Tunnels Below a High-Rise Transmission Tower: A Case Study

The structure on the ground bears impact from the tunneling-induced settlement, especially when the tunnel is shallow and its span is large. This paper presents the construction of Lijiachong twin tunnels below a high-rise transmission tower and the prevention techniques to avoid the failure of the tower. The span of each tunnel is about 18 m, and the tunnel embedded depth below the tower foundations is only 15.5 m. There was a high risk of influencing the performance of the tower during the tunneling. To reduce the risk of collapse of the transmission tower, the available methods in field to reinforce the tower foundations were proposed. For engineering cost and construction convenience, the separated pile foundations were connected with framed girders, resulting in that the separated foundations worked as a whole. The effectiveness of the reinforcement was evaluated by monitoring deformation and stress in the tower, indicating that the measured values were lower than their respective allowable ones. With reinforcing the tower foundations using the framed girders, the Lijiachong twin tunnels safely passed beneath the transmission tower, and the continuous performance of the transmission tower was ensured.     

Experimental study of the influence of loading rate on tensile mechanical behavior of sandstone damaged by blasting

The drill and blast method (D&B) is perhaps the most common excavation method for rock mass, and intense blasting vibrations would induce an excavation damage zone (EDZ) around the excavated space. The tensile failure of rock mass in EDZ at diverse rupture velocities results in various geological disasters in engineering practices. The objective of this paper is to investigate the effect of blasting on the tensile strength of sandstone rock and the influence of loading rate on the disk specimens affected by blasting. We firstly performed a D&B exercise on a sandstone block with a size of 600 mm × 600 mm × 120 mm. Then, a total number of 49 standard disk specimens were prepared from large fragments of this blasting sandstone block and an undamaged block. A series of Brazilian split tests was carried out using these specimens to determine their indirect tensile strength, and to assess the effects of the distance from the blasting source and loading rate (varying from 1.67 × 10^?5 to 8.33 × 10^?2 mm s^?1). The results show that the tensile strength of specimens exhibits an upward trend with increasing distance from the blasting source, to approach that of undamaged rock, following a power function with a positive exponent (0~1). The loading rate affects the tensile mechanical behaviors of disks, in terms of the convergence of microscopic defects, the main load-bearing area, and the absorbed energy at the fracture moment of specimens. Both the tensile strength and absorbed energy have positive linear correlations with the natural logarithm of the loading rate. In addition, the fragmentation degree of disk specimens also increases due to an increasing brittleness of sandstone with the loading rate.     

Utilization of waste marble to enhance volume change and strength characteristics of sand-stabilized expansive soil

In this paper, marble waste is evaluated as a secondary material to be utilized as potential stabilizer to improve the volume change and strength characteristics of sand-amended expansive soil, proposed as a possible landfill, pavement or sub-base material in a semi-arid climate. An experimental program was conducted on sand-expansive soil enhanced with marble waste, abundantly found as a by-product of construction industry, obtained from two different sources with different gradations, denoted as marble powder (MP) and marble dust (MD). One-dimensional swell, volumetric shrinkage, consolidation, unconfined compressive and flexural strength tests were conducted on expansive soil–sand mixtures with 5, 10 and 20% waste marble inclusions over curing periods of 7, 28 and 90 days. Test results showed that 10% marble powder and 5% marble dust by dry mass were the optimum amounts for mitigating the swell–shrink potential and compression index as well as yielding the highest unconfined compressive and flexural strength values. Moreover, the rate of reduction in swell potential versus the flexural strength over the curing periods studied is highest in 10% MP- and 5% MD-included specimens, the latter being more insensitive to this change. The soil mixtures displayed brittle behavior after marble addition, hence its utilization as a secondary additive to sand-amended expansive soil is recommended for soils exposed to lower flexural loads such as light traffic.     

Prediction of Unconfined Compressive Strength for Jointed Rocks Using Point Load Index Based on Joint Asperity Angle

This research paper is aimed to briefly highlight the correlation between unconfined compressive strength and point load index for jointed rocks based on joint asperity & orientation. In this observe, specimens were tested to obtain their unconfined compression strength and point load index for a different joint condition. The different joint conditions considered for this study were clean joint and joint filled condition. For both clean joint and joint filled specimens were prepared by various asperity angles of 30°, 45°, 60° and 90° with different orientation angles such as 0°, 30°, 45°, 60°, 90°. Plaster of Paris was used as model material to simulate weak rock mass in the field. By testing intact model specimens for unconfined compressive strength leads to revealing of optimum moisture content for further testing. The curing period for the model specimens is 3 days at room temperature. To simulate jointed rocks, various moulds of different orientation of joint with respect to major principal stress are prepared separately. The inner diameter of the mould is 50 mm and height is 100 mm. After casting, a rough joint was created by cutting the prepared sample using the cutter. The specimens are tested for both clean joint and joint filled condition to determine the favorable joint orientation and asperity angle. After curing, the specimens are tested for unconfined compressive strength and Point load index. The new multi-linear correlation for determining unconfined compressive strength with the help of point load index is developed and cross checked with equations formed for actual rock. On comparing both results it is found that the new equation can suitable for assessing the unconfined compressive strength of limestone and serpentinite rocks through point load index value.     

Water Saturation Effects on the Brazilian Tensile Strength of Gypsum and Assessment of Cracking Processes Using High-Speed Video

This study investigates the water weakening effect on the tensile strength, as well as the fracturing behavior, of an artificially molded Hydrocal B-11 gypsum rock. Brazilian disc tests, with the aid of a high-speed video system to monitor and record the cracking processes, are conducted on dry and wet specimens to determine their tensile strengths. The dry specimens are oven-dried, while the wet specimens are prepared by soaking in water for 1, 3, and 10 weeks to achieve different levels of water content. The test results show that the tensile strength drops to nearly half of its dry value after being soaked in water for only 1 week. The tensile strength reduces only slightly further after the specimens have been immersed in water for 3 and 10 weeks. An analysis of the recorded high-speed footage shows that the primary crack initiates at the center as observed from the surface for the majority of the tested specimens. Most importantly, the cracking processes of dry and wet specimens are distinctly different with regard to the speed of crack propagation and the number of cracks developed.     

Co-management of landfill leachate concentrate with brick waste by solidification/stabilization treatment

The treatment of landfill leachate by reverse osmosis (RO) generates huge volumes of heavily polluted concentrate that has to be properly treated before its discharge into the environment. The aim of this work was to assess the solidification/stabilization (S/S) treatment of the leachate concentrate (LC) for chemical/physical immobilization of contaminants and for obtaining durable monolithic matrix suitable for storage, landfilling, or use. In addition, the possible use of brick waste as a partial replacement of natural aggregates used for S/S process was investigated. Concrete mixtures were prepared using local PC, sand, gravel, and tap water/LC. The substitution of coarse aggregate material by brick waste was examined for the replacement ratios 25, 50, and 75%. Hardened concrete specimens were subject to compressive test as well as flexural strength test at 7 and 28 days. Besides, a leaching test was performed, and the collected eluates were analyzed for pH, total dissolved solids, chemical oxygen demand, chlorides, sulfates, phosphorus, and heavy metals. The aggregate replacement with brick waste showed various trends according to the substituted fraction size and ratio. A 28-day compressive strength of more than 25 MPa was obtained even at 50% simultaneous substitution of PC, gravel, and sand. Leaching test analysis confirmed that S/S could be a successful treatment for RO LC decreasing most of the pollutants to comply with landfilling criteria, except for chromium known to be mobile at high pH. Furthermore, the substitution of natural aggregates with brick waste revealed the possibility to cast valuable masonry units. However, a long-term assessment is still needed to ensure the mechanical and chemical stability/durability of concrete.     

Experimental Studies on Permeability of Intact and Singly Jointed Meta-Sedimentary Rocks Under Confining Pressure

Three different types of permeability tests were conducted on 23 intact and singly jointed rock specimens, which were cored from rock blocks collected from a rock cavern under construction in Singapore. The studied rock types belong to inter-bedded meta-sandstone and meta-siltstone with very low porosity and high uniaxial compressive strength. The transient pulse water flow method was employed to measure the permeability of intact meta-sandstone under a confining pressure up to 30 MPa. It showed that the magnitude order of meta-sandstone’s intrinsic permeability is about 10^?18 m². The steady-state gas flow method was used to measure the permeability of both intact meta-siltstone and meta-sandstone in a triaxial cell under different confining pressures spanning from 2.5 to 10 MPa. The measured permeability of both rock types ranged from 10^?21 to 10^?20 m². The influence of a single natural joint on the permeability of both rock types was studied by using the steady-state water flow method under different confining pressures spanning from 1.25 to 5.0 MPa, including loading and unloading phases. The measured permeability of both jointed rocks ranged from 10^?13 to 10^?11 m², where the permeability of jointed meta-siltstone was usually slightly lower than that of jointed meta-sandstone. The permeability of jointed rocks decreases with increasing confining pressure, which can be well fitted by an empirical power law relationship between the permeability and confining pressure or effective pressure. The permeability of partly open cracked specimens is lower than that of open cracked specimens, but it is higher than that of the specimen with a dominant vein for the meta-sandstone under the same confining pressure. The permeability of open cracked rock specimens will partially recover during the unloading confining pressure process. The equivalent crack (joint) aperture is as narrow as a magnitude order of 10^?6 m (1 μm) in the rock specimens under confining pressures spanning from 1.25 to 5.0 MPa, which represent the typical ground stress conditions in the cavern. The in situ hydraulic conductivity measurements conducted in six boreholes by the injection test showed that the in situ permeability of rock mass varies between 10^?18 and 10^?11 m². The lower bound of the in situ permeability is larger than that of the present laboratory-tested intact rock specimens, while the upper bound of the in situ permeability is less than that of the present laboratory-tested jointed rock specimens. The in situ permeability test results were thus compatible with our present laboratory permeability results of both intact and jointed rock specimens.     

Study on frost resistance of rapid-hardening magnesium phosphate-ferro-aluminate composite cement北大核心CSCD

随着冬季抢修抢建混凝土工程的增多,研发适用于严寒地区具有良好抗冻性的快硬水泥意义重大。磷酸镁水泥具有早期强度高、初凝时间短、与混凝土相容性好等特点,被视为混凝土工程的良好快修快建材料。然而,磷酸镁水泥制备的水泥砂浆或混凝土在北方地区的冬季往往会受到冻融循环作用,导致其耐久性和强度出现不同程度的退化。为增强磷酸镁水泥的抗冻性,在磷酸镁水泥制备中用铁铝酸盐水泥代替一定数量的过烧氧化镁,制备出快硬磷酸镁-铁铝酸盐复合水泥。通过冻融循环前后磷酸镁-铁铝酸盐复合水泥砂浆试件的质量损失测试、强度试验、孔隙率测试及SEM-EDS测试,得出：铁铝酸盐水泥代替氧化镁的数量在30%~40%时,制备的磷酸镁-铁铝酸盐复合水泥砂浆试件冻融循环后的质量损失率最小,抗压强度和抗折强度达到峰值,抗压强度和抗折强度剩余率最高,孔隙率最小,因而该配合比的磷酸镁-铁铝酸盐复合水泥具有最好的抗冻性。由SEM-EDS测试可知磷酸镁水泥砂浆试件冻融循环后,基体中的胶凝材料K-鸟粪石部分溶解,试件整体结构疏松,晶体间存在大量间隙;磷酸镁水泥制备中掺入铁铝酸盐水泥后,制得的磷酸镁-铁铝酸盐复合水泥水化生成大量晶体填充于砂浆试件基体内部,无定形水化产物对砂浆试件的强度有一定补偿作用,使得磷酸镁-铁铝酸盐复合水泥砂浆试件在冻融循环后孔隙率大幅减小,密实度得到提高,使得磷酸镁-铁铝酸盐复合水泥的抗冻性能得到了显著增强。磷酸镁-铁铝酸盐复合水泥为北方严寒地区冬季混凝土抢修抢建工程提供了一种新材料。     

Shrinkage Properties of Soft Clay Treated with Cement and Geofibers

In this study, effects of two types of geofibers, namely polypropylene and recycled carpet, on three dimensional shrinkage properties of cement treated kaolinite and bentonite clays are investigated. Cement treated clay specimens were prepared with cement contents of 5, 10, and 15 % by weight of dry soil for kaolinite samples, and 30, 40 and 50 % for bentonite samples. To investigate and understand the influence of different fiber types and contents, three different percentages of fiber content (i.e. 0.1, 0.2 and 0.5 % polypropylene fibers; and 0.5, 0.75 and 1 % carpet fibers) were adopted. The results of shrinkage tests on 126 cylindrical samples of cement treated clay with various cement and fiber contents were analysed to understand the relationships between these parameters and the shrinkage percentage of treated soil. Results of this study indicate that combination of cement and fiber is effective in reducing the volume change of clayey soils undergoing drying process. In the applied ranges of cement and fiber contents, the influence of cement addition on the shrinkage reduction is more significant than the addition of fibers for the treated kaolinite. However, addition of fibers in curtailing the shrinkage of bentonite clay is more significant than the cement addition.     

The presentation of an agro-environmental nanocomposite: the study of its acoustic,physical and mechanical properties

Nanocomposites can be used as an acoustic panel to adsorb noise. The aim of this study was to evaluate: (1) acoustic, (2) physical, and (3) mechanical properties of agro-environmental nanocomposites. To prepare the nanocomposites, wood flour, PVA glue, and aluminum nanoparticles (between 1 and 4 %) were hardly mixed and heated at near 220 °C for 120 min. In the next step, sound absorption coefficient, transmission loss, water absorption percentage, thickness swelling percentage, density, flexural strength, flexural modulus, tensile strength, and tensile modulus of nanocomposites were measured. This study showed that the increase in nanoparticle percentage led to the increase in flexural strength, flexural modulus, water absorption percentage, thickness swelling percentage, density, and sound absorption coefficient. But, the increase in nanoparticle percentage led to the decrease in tensile strength, tensile modulus, and transmission loss. The authors think that the nanocomposites are suitable as an agro-industrial nanocomposite to reduce noise.     

Effect of strain rate on strength properties of low-calcium fly-ash-based geopolymer mortar under dry condition

This paper presents the mechanical and elastic properties of inorganic polymer mortar under varying strain rates. The study includes a determination of the compressive strength, modulus of elasticity and Poisson’s ratio at 0.001, 0.005, 0.01 and 0.05 mm/s strain rate. A total of 21 cylindrical specimens having 100 mm length and 50 mm diameter were investigated, and all tests were carried out pursuant to the relevant Australian Standards. Although some variability between the mixes was observed, the results show that, in most cases, the engineering properties of geopolymer mortar compare favourably to those predicted by the relevant Australian Standards for concrete mixtures. It was found that the change in the strain rate causes different behaviour related to the percentage of the ultimate load. The ultimate strength, Young’s modulus and Poisson’s ratio of the geopolymer mortar depend on the strain rate. It was also found that as the strain rate increases, mechanical and elastic properties of geopolymer mortar substantially increase in logarithmic manner.     

Time-dependent changes in the strength of repair mortar used in the loss compensation of stone

Repair mortar and mixture of repair mortar with porous limestone sand aggregate were tested under laboratory conditions. Water absorption properties and micro-fabric analyses with a combination of strength tests were applied to assess the durability and compatibility of repair mortar with porous limestone. Uniaxial compressive strength and flexural strength were measured after 3, 7, 14, 28 and 90 days of casting. Durability was tested by comparing strength test results of samples kept air dry, water saturated, dried in drying chamber, freeze–thaw and non-standardized freeze–thaw cycles. The results indicate that with time various trends in strength were observed. In general, limestone aggregate content decreases more the compressive strength more than the flexural strength of the mortar. Standardized freeze–thaw tests of saturated samples caused a rapid material loss after 25 cycles, while freeze–thaw tests of undersaturated samples demonstrated that even after 100 cycles the test specimens still have a significant strength. Water-saturated samples that contain 50% of limestone aggregate have a 50% loss of strength in comparison with saturated repair mortar, while air-dry and water-saturated repair mortar has a minor strength difference after 90 days. The use of smaller amounts of porous limestone aggregate in repair mortar allow the preparation of repairs that are compatible with the monuments of Central Europe that were constructed from porous limestone.     

Water leakage from the power tunnel of Gezende Dam,southern Turkey: a case study

This study covers the investigations of the reasons of deformations and leakages in the energy tunnels of Gezende Dam constructed in 1990 for hydroelectric energy and the recommendations for treatments of the problems. Gezende Dam is located 30 km southwest of Mut county/Mersin in southern Turkey. The dam is concrete arch type with a height of 72 m. The energy tunnel with an approximate length of 9 km passes through six different geological units in age of Mesozoic to Cenozoic. After a short period of time of the operation of the tunnel, leakage has started from the section of gypsum, which is intercalated with dolomitic limestone between chainage from 5,970 to 6,840 m. The deformations have occurred in the concrete tunnel and springs have been detected at different places and times through the Ermenek Canyon since 1996. The preventive precautions of the water effect caused by groundwater effect on gypsum are as follows: (1) contact and consolidation grouting in the tunnel between chainage from 5,910 to 6,840 m, (2) removal of damage on the tunnel line, (3) reinforcement of the tunnel again, and (4) application of new concrete lining. Besides, a drainage gallery of 320 m was excavated in the 23 m lower and 15 m left part of tunnel base elevation in order to diminish the effect of groundwater in the section where the deformation occurred.     

An Experimental Study of the Fracture Coalescence Behaviour of Brittle Sandstone Specimens Containing Three Fissures

To analyse the fracture coalescence behaviour of rock, rectangular prismatic sandstone specimens (80?×?160?×?30?mm in size) containing three fissures were tested under uniaxial compression. The strength and deformation behaviours of the specimens are first analysed by investigating the effects of the ligament angle β₂ on the peak strength, peak strain and crack initiation stress of the specimens. To confirm the sequence of crack coalescence, a photographic monitoring technique is used throughout the entire period of deformation. Based on the results, the relationship between the real-time crack coalescence process and the axial stress–strain curve of brittle sandstone specimens is also developed, and this relationship can be used to evaluate the macroscopic deformation characteristics of pre-cracked rock. The equivalent strain evolution fields of the specimen, with α?=?β₁?=?45° and β₂?=?90°, are obtained using the digital image correlation technique and show good agreement with the experimental results of pre-cracked brittle sandstone. These experimental results are expected to improve the understanding of fracture mechanisms and be used in rock engineering with intermittent structures, such as deep underground excavated tunnels.