In order to explore the mechanical properties and energy evolution law of unloading coal under cyclic loading，the MTS816 rock mechanics test system was used to carry out triaxial cyclic loading tests with variable lower limit and constant lower limit of coal samples. The relationship between mechanical parameters of coal samples was analyzed by obtaining the whole process stress-strain curve，and the energy evolution law of coal samples during cycle loading process was studied based on the energy principle. The results show that：(1) Compared with the CG group，the peak stress increment extreme value of the coal samples under cyclic loading is 3.540 MPa，and the overall change is not large. The axial strain and lateral strain of the XH1 and XH2 groups are positively correlated and negatively correlated with the confining pressure，respectively. The volumetric strain of the XH1 group increases first and then stabilized and then increased，while that of the XH2 group increased first and then decreased and then increased. (2) The loading modulus of coal samples under cyclic loading is positively correlated with the number of cycles and negatively correlated with the stress level. Both the strain hardening modulus and the drop modulus are negatively correlated with the confining pressure. The high confining pressure condition weakens the ability to resist the inelastic model，and this weakening trend is independent of the stress path. The cyclic stress path has a significant effect on the deformation characteristics of coal samples. (3) The energy density of coal samples is higher under the action of constant lower limit path or high confining pressure. The dissipation energy density of coal samples in each cycle level is basically consistent with the input energy density，showing a trend of decreasing first and then stabilizing，and the elastic energy density is generally stable. (4) Under cyclic loading，the elastic energy density of coal samples accounts for more than 89.11% of the total input energy density，and the mean value of the two is linear. The total energy is mainly stored in the form of elastic energy，and this storage capacity is independent of confining pressure. The average value of dissipated energy density and elastic energy density changes in a power function type，and the energy competition ability of dissipated energy gradually increases with the increase of cyclic stress level.

Taking the excavation and unloading of rock mass under seepage pressure environment as the research object，triaxial cyclic loading failure tests were conducted on unloading rock samples under cyclic pore water pressure to explore the influence of pore pressure level and unloading level on the deformation and energy evolution characteristics of rock samples under dynamic cyclic loading. The results show that：(1) The shape of the stress-strain curve of unloaded rock samples under cyclic loading and unloading is greatly influenced by the pore pressure and the unloading magnitude；(2) During the cyclic loading and unloading process，the difference between the peak circumferential strain and the volumetric strain of unloaded rock samples due to the unloading magnitude shows a trend of first increasing and then decreasing with increasing the initial pore pressure level；(3) The characteristic energy of unloaded rock samples shows a non-linear growth trend with increasing the number of cycles，and the total input energy of unloaded rock samples under the cyclic pore pressure environment is generally than that under the constant pore pressure.

In order to investigate the deformation characteristics of hard rock during the whole creep process，this study carried out indoor creep tests on hard tuff with constant peripheral pressure and graded ascending axial pressure. Through the characterization of hard rock creep under different stress paths，combined with scanning electron microscope(SEM) tests，the relationship between the fine-scale damage evolution mechanism and macroscopic damage characteristics was explored. Based on the introduction of damage variables into the deterioration effect of rock mechanical properties over time during the creep process，an intrinsic model of damage creep was constructed that can describe the whole process of hard rock creep. At the same time，by optimising the BP neural network model，the identification and prediction of the model parameters were improved. The results show that，with increasing the bias stress level，the hard tuff shows more obvious brittle-ductile deformation transformation characteristics，and the rock creep phenomenon is more obvious. Under the continuous action of a higher bias stress，the accumulation of rock damage and the deterioration of mechanical properties are more adequate，which leads to the accelerated creep characteristics of the hard tuff during the damage stage with increasing the peripheral pressure，and the damage of the hard rock becomes more intense. Compared with Burgers，the improved damage constitutive model can better describe the whole process of hard rock creep，which verifies the reasonableness of the model. Based on the optimised BP neural network model，the accelerated creep curve of hard rock under high stress level can be accurately predicted，which improves the applicability of the model. The results of this study not only enrich the theoretical study of hard rock creep constitutive model，but also provide theoretical guidance for the design of long-term stability of engineering rock bodies in hard rock formations.

In order to validate the calculation model and safety factor calculation method for the combined spray-anchor support in the total safety factor method，this paper developed a large-scale tunnel structure model test system from the perspective of structural test，and carried out the loading test of the spray-anchor combined support structure under the unsupported tunnels and the different anchor spacing. The triaxial test of surrounding rock and fine sand material，and the tensile and pull-out test of anchor material were used to clarify the physical and mechanical parameters of each material in the model test，simulate the whole process of loading and damage of the spray-anchor combination support under different anchor spacing and unsupported tunnels，and monitor the stress and strain of the surrounding rock，anchor strain，inner and outer strain of the spray layer，and the displacement of the spray layer with the external load. Based on this，the design bearing capacity，ultimate bearing capacity，and deformation force characteristics of the unsupported tunnels and the combined spray-anchor support with different anchor spacing were analyzed and compared with the theoretical calculation results of the total safety factor method. The results show that：sprayed concrete and anchor can effectively carry the surrounding rock，improve the lateral limiting force of the surrounding rock，play the supporting role of the anchor rock bearing arch，and improve the deformation and bearing capacity of the surrounding rock；the bearing capacity and damage characteristics of the spray-anchor combination support obtained from the test are more in line with the results of theoretical calculations，which shows that the total safety factor method of spray-anchor combination support calculation method is reasonable and the method is on the safe side.

A two-dimensional swelling system was developed in this study to investigate the effect of the lateral stress on the heave behavior of a natural red mudstone embankment under deep excavation. The heaving under a combination of stress path of vertical loading-unloading with the application of the lateral stress was examined in detail. Then，a comprehensive numerical simulation was conducted to characterize the heave of the deep-excavated embankment. Results indicates that the lateral stress is the main consequence of heaving，which accounts for 65.8% to 67.8% of the total heaving. The application of the lateral stress would result in around 1.6 to 1.9 times of the heave to the laterally unconfined case. On the other hand，the hydration-induced heaving becomes around 0.5 times to that caused by the lateral stress. Therefore，the factors affecting the heave emerge in the sequence of the lateral unloading，the magnitude of the lateral stress and the swelling induced by water immersion. The evident heaving of the embankment is seen when the lateral stress ratio is larger than 0.6. In addition，The results show that lateral in-situ stress is one of the important reasons for the heave of the red bed soft rock subgrade. The research results can provide theoretical support or reference for the treatment of the heave.

To improve the accuracy of geostress levels assessment，this study collected 115 engineering cases. Through analyzing engineering data and geological factors，three indexes(measurement depth，main lithology and GSI) were selected to improve the strength-stress ratio criterion proposed by the technical code for underground project geological investigation of hydropower and water resources(GB 50287—2016). Then，a multi-index fusion database was established. The intrinsic connection between the Hoek-Brown strength criterion and the strength-stress ratio criterion is elucidated through derivation，leading to the formulation of a modified strength-stress ratio criterion. Subsequently，the parameters of this modified criterion are determined using Bayesian optimization methods. The research results indicate that the accuracy of the improved strength-stress ratio criterion increases by 26.7% compared to the criterion recommended by the standard. This research provides an effective basis for geostress classification，thereby improving the safety and stability of engineering.

A damage zone that has a certain depth and is circularly distributed along the cavern boundary usually forms within the surrounding rocks of caverns in the excavation blasting and later utilization(for instance，compressed air energy storage) processes. Therefore，exploring a method for determining mechanical parametric values of rock masses inside the damage zone of the cavern surrounding rock is of significance to stability analysis and support design of surrounding rock in underground caverns. Considering the seismic wave velocity and acoustic velocity of rock masses，a formula for calculating the geological strength index GSI and rock mass disturbance factor D of rock mass in the damage zone of surrounding rocks of underground caverns was established. Changes in the disturbance factor D with the depth of damage zone in the surrounding rocks of underground caverns were quantitatively determined. Additionally，the Hoek-Brown strength criterion was introduced to study the determination method of mechanical parameter values of rock mass in the damage zone. The results show that the proposed calculation methods of GSI and D well reflect the change with the depth in the mechanical parameters of rock mass in the damage zone of caverns in the excavation blasting and later utilization (compressed air energy storage for instance) processes. The uniaxial compressive strength of rock mass in the damage zone is most seriously weakened while the internal friction angle is least weakened. The wave velocities of surrounding rock mass of the cavern can be classified into three types：(1) concave-shaped slow increase area and stably fluctuating area；(2) convex-shaped slow increase area and stably fluctuating area；(3) linearly slow increase area and stably fluctuating area. When numerical simulation methods and constitutive relationship are allowed，the depth interval of the damage zone should be selected for modeling according to the degree of importance for engineering projects in the evaluation of the stability of surrounding rock in the damage zone of underground caverns. The rock mass disturbance factor D should be determined based on the tested average wave velocities of rock mass in sub-zones. The results provide reference for evaluating the stability of the surrounding rock mass in the damage zone in similar underground caverns and for determining mechanical parameter values of rock mass in support design.

To investigate the influence of the main roof's periodic weighting path on the dynamic characteristics of impact pillars，dynamic compression experiments were conducted on the impact sandstones which were preprocessed with different cyclic loading and unloading，by using the split Hopkinson pressure bar. The effects of the cyclic loading and unloading paths and the impact pressure on the fracture strength，energy dissipation and fragmentation distribution of rock samples were discussed. The results show that the dynamic stress-strain curve can be divided into the elastic deformation stage，the unstable fracture development stage and the post-fracture stage. In the unstable fracture development stage，the strain hardening phenomenon and the leaping characteristic are obvious. In the post-fracture stage，the damage degree of rock samples is positively correlated with the impact pressure. The reflected energy density，the transmitted energy density and the dissipated energy density increase linearly with the incident energy. The average reflected energy density and average dissipated energy density decrease first and then increase with the upper cyclic stress，showing a "U"-shaped varying characteristic. The higher the rock sample density is，the smaller the reflected energy density and the dissipated energy density are. By contrast，the transmitted energy is larger. Under the impact loading，the rock samples mainly show the crushing failure，the rock fragmentation，the rock side spalling and the rock splitting. The severer the impact disturbance is，the smaller the average particle size. By contrast，the average fractal dimension of the rock samples is larger. The rock samples are destroyed more thorough. The rock debris are distributed more uniformly.

The load-bearing capacity of squeezed branch piles(SBPs) can significantly increase under small incremental settlement deformations. By simultaneously controlling the pile top load and settlement to meet control requirements，the full potential of the SBP?s bearing capacity can be realized. This study introduced a load transfer equation for SBPs without critical displacement，incorporating the displacement parameter corresponding to 0.5 times the ultimate bearing capacity. A failure model for the soil around the bulb was established based on Meyerhof?s bearing capacity theory，determining the effective length of the shaft resistance in the straight section. A pile-soil failure model for SBPs with different bulb spacing was developed，identifying the optimal bulb spacing. An improved load transfer analysis method，considering both pile top design boundary conditions and pile tip control boundary conditions，enables synergistic control of both bearing capacity and settlement，achieving dual control targets. Field static load tests combined with numerical simulations verified the pile-soil failure model of SBPs and determined parameters for the load transfer equation. The theoretical framework optimized the pile length and layout of bulbs or branches under field conditions. Case verification showed that，while meeting design requirements，the optimized scheme reduces pile length by 14.3 meters，with a reduction of 3 branches and 1 bulb. The error between the theoretical ultimate bearing capacity and the numerical model calculation is 2.9%.

The microbially induced calcite precipitation(MICP) is a reinforcement technique aiming at reducing carbon emissions and pollution，and it can effectively enhance the dynamic properties of sandy soils. The MICP is applied to strengthen calcareous sand samples in the South China Sea region. A series of resonant column tests and scanning electron microscope tests are conducted to thoroughly investigate the impact of particle size(d50)，uniformity coefficient(Cu)，and curvature coefficient(Cc) on the maximum dynamic shear modulus(Gmax) of MICP-treated sandy soils. The experiment results indicate that the Gmax of untreated sand increases with increasing d50，decreases with increasing Cu，and initially decreases and then increases with increasing Cc. Meanwhile，the Gmax of the MICP-treated sand maintains the same relationship with Cu and Cc of the untreated sand，but it increases initially and then decreases with increasing d50. Furthermore，the MICP cementing effect correlates with the calcium carbonate content，with differences in calcium carbonate content attributed to variations in particle size and uniformity of particle gradation，which mainly influence bacterial retention through differences in pore number and volume. Separate Gmax prediction models considering particle size and gradation characteristics are proposed，with a large amount of literature data used to verify the validity and applicability of the proposed models，depending on whether the initial pore ratio corrected for calcium carbonate content is taken into account. The experimental study provides a theoretical basis for the practical engineering application of MICP to improve the dynamic properties in calcareous sands.

Pillar support is an important form of support for coal mine roadways. As China?s coal mines move towards high productivity and efficiency and extend to deep and complex conditions，pillar support is expected to become a new way to solve the problem of surrounding rock control in roadways. This article elaborates on the development history of pillars in domestic and foreign coal mines，discusses the development and changes in pillar materials，equipment，processes，and concepts，and achieves a leapfrog development in support resistance from low resistance of 120 kN to high resistance of 14 000 kN，highlighting the importance and advantages of new pump-filled pillars. The design principle of new pump-filled pillars is theoretically explained，and two types of pillars with temporary cutting and permanent high resistance characteristics are developed. Laboratory tests on 1∶1 scale pillars have been conducted to obtain the bearing law of new pump-filled pillars. A collaborative control mechanism for surrounding rock based on new pump-filled pillars has been constructed，and supporting equipment for efficient mixing and continuous pumping has been developed. A pump-filled hanging process that is “stable，reliable，and practical” has been developed，forming a highly reliable and active support technology for pump-filled support. It is listed that new pump-filled pillars have been applied in various scenarios such as gob-side entry retaining，empty roadways，small coal pillars dynamic pressure roadways，and deep soft rock roadways，successfully solving problems such as coal pillar recovery，rapid withdrawal，dynamic pressure management，and soft rock deformation. It is pointed out that the next research direction is new pump-filled materials and intelligent mining construction equipment，and it should be promoted to rock burst and deep soft rock roadways.

In order to explore the formation mechanism of long-distance and high-speed movement of low potential energy landslides，a large-scale construction solid waste landslide，that occurred at a landfill at Guangming New District of Shenzhen，Guangdong，China，was selected as the research object. Based on the hypothesis of soil arching，the axis equation of soil arching and strain energy equation accumulated in soil arching are deduced. By catastrophe theory，the transformation and dissipation of the strain energy are analyzed. The starting kinetic energy of the landslide is determined，and according to the kinetic energy theorem，the starting speed of landslide is calculated. In this paper，the energy source of long-distance and high-speed movement of the low potential energy landslide is studied from a new perspective，Research suggests that：(1) Excess pore water pressure provides power for landslide initiation. (2) The special spoon-shape terrain provides topographic condition for the formation of soil arching，The special binary structure slope with dense leading edge and loose posterior edge provided material condition for the formation of soil arching. (3) The deformation of the slope is blocked by the soil arching，forming a stress concentration area，and a huge strain energy is accumulated in the soil arching. (4) The soil arching destroys suddenly，and part of the strain energy is converted into kinetic energy，The landslide starts up with a high speed，that is，the energy of high-speed movement mainly comes from strain energy rather than high potential energy.

In order to study the toppling deformation and failure mechanism of an anti-dip rock slope in the Three Parallel Rivers area under the combined action of complex internal and external forces. The physical model test of similar materials is carried out，and the evolution process of block-flexure toppling deformation and instability of the anti-dip rock slope under tectonic stress，rapid river downcutting and rainfall conditions is studied. Combined with the discrete element numerical test，the macroscopic deformation characteristics of the slope rock stratum under various working conditions，the displacement variation law of the key points，the evolution of the maximum flexure surface，and the distribution of the plastic zone of the rock stratum are analysed. The results show that：(1) The test results are in good agreement with the simulation results. The evolution process of toppling deformation is divided into four stages：shear flexure of slope toe→maximum flexure surface→flexure and toppling of rock strata under flexure surface→penetration of main fracture surface. (2) The shallow block toppling first occurs in the slope toe area. With the penetration of the maximum flexure surface，the lower strata of the flexure surface show a deep flexure toppling of the laminated network，and the upper strata are relatively stable，which reflects the self-stability characteristics of the anti-dip rock slope. (3) River undercutting is a prerequisite for the formation of flexure toppling deformation of anti-dip rock slope，and rainfall aggravates the transition of toppling body from creep stage to progressive failure stage，which eventually leads to toppling instability of rock strata.

Layered rock mass has distinct microstructures such as bedding planes and microcracks，and exhibits complex anisotropic strength characteristics after being loaded. The anisotropic characteristic of spatial structure is the internal factor，which can be characterized by joint invariants of microstructure tensor and stress tensor，and additional load inducing the rock mass failure is the external factor. There are potential failure planes inside the rock mass under external loads，and the failure strength is determined by inherent strength of the location of the potential failure planes. The SMP criterion explains the positional relationship between the stress loading direction and the paired potential failure planes in the material. The anisotropic strength criterion(ASMP criterion) for layered rock mass is constructed based on the SMP criterion，considering the variation of inherent strength as well as the location of failure plane. Compared with the SMP criterion，there are only two newly added strength values measured by experiments directly in the ASMP criterion. Comparing the existing experimental data and the calculation results of ASMP criterion，it is found that ASMP criterion can effectively predict the failure strength and plane position in multiple types of layered rock masses under complex stress paths，including conventional triaxial and true triaxial compression.

The displacement of layers and mining activities expedite the formation of fractures and spalling in deep coal seams，potentially resulting in dynamic disasters. The dynamic characteristics of coal seams exhibit discrepancies before and after saturation with water，leading to diverse levels of overall instability and failure. To examine the dynamic failure properties of coal samples in natural and saturation states under impact loading conditions，particularly emphasizing the impact of fissure water and goaf water on coal strength at the 61304 working face of Tangjiahu coal mine，split Hopkinson pressure bar(SHPB) tests were carried out on both unaltered coal samples and water-saturated coal samples. The objective of the study was to investigate the variations in displacement，strain，energy dissipation，and degree of fragmentation that occur during the progressive failure of coal samples under dynamic impact loading conditions. The experimental results suggest that：(1) The cracks observed in the coal samples undergo a progressive evolution characterized by four distinct stages：initiation，development，penetration and ultimate failure. The presence of water has a softening effect，causing a deceleration in the length of crack propagation in water-saturated coal samples. However，it leads to an increase in the density of interlaced cracks and the degree of fragmentation. Furthermore，the dynamic compressive strength of coal samples saturated with water is relatively lower in comparison to that of the original coal samples. (2) The energy transformation process of coal samples can be broadly categorized into three stages：compression absorption，absorption dissipation，and energy dissipation. At various impact pressures(0.3，0.5，and 0.7 MPa)，the dissipated energy of the untreated coal specimens rose from 24.13 J to 39.71 J，marking an increment of about 15.58J. In contrast，the dissipated energy of the coal specimens saturated with water escalated from 7.31 J to 31.61 J，showing an increase of approximately 24.3 J. The fluctuation of transmitted energy in the original coal samples remains relatively stable(5.06–6.31 J). In contrast，there is a more significant increase in transmitted energy in water-saturated coal samples，ranging from 1.32 J at 0.30 MPa to 9.39 J at 0.70 MPa. (3) The level of fragmentation observed in coal samples escalates as the pressure rises，manifesting macroscopic features akin to particle and powder fragmentation. The level of fragmentation of coal samples escalates following saturation with water. At lower pressures of 0.3 and 0.5 MPa，minimal disparity exists in the fractal dimensions of coal specimens，irrespective of their water saturation levels. When the pressure is elevated to 0.7 MPa，the fractal dimension of water-saturated coal samples increases by 14.66% compared to that of the original coal samples. Additionally，the particle size exhibits more pronounced fluctuations after fragmentation in comparison to the original coal samples. (4) The experimental investigation into the progressive failure characteristics of coal samples under varying loading rates offers an empirical foundation for estimating the propagation of coal crack extension. The experimental results provide a summary and generalization of the variances in the characteristics of the four indicators pre- and post-saturation with water. These findings offer insights into the fracturing characteristics of coal when subjected to the combined effects of roof rotation and sandstone fissure water at the 61304 working face of Tangjiahu coal mine.

The establishment of an effective landslide early warning model is of great significance for the prevention of landslide disasters. This study aims to establish the early warning model of deflection angle ratio for accumulation landslides. First，the tests that reproduce the deformation-destabilization process of accumulation landslides are carried out. Based on the test monitoring results，a displacement dynamics parameter，the deflection angle ratio，which has directionality and unity，is proposed. Moreover，the corresponding landslide early warning model of deflection angle ratio is presented. Finally，monitoring data from three real landslides are utilized to validate this warning model. The results show that the deflection angle ratio presents a general pattern of first fluctuation and subsequent smoothness during the evolution process of accumulation landslides. The Frobenius norm of 0.2 can be used as the dividing value between the fluctuating and smooth segments of the deflection angle ratio. The smooth characteristic of the deflection angle ratio can indicate the deformation stage of accumulation landslides. Based on this，the single-point warning criterion and the multi-point warning criterion of the Frobenius norm are proposed. When applying the early warning model of deflection angle ratio to real landslides，it is recommended that this warning model is used in conjunction with the warning model that is based on the magnitude of total unidirectional displacement，in order to arrive at a more comprehensive early warning judgment.

Leakage is a common disease in subway tunnels，and as the operational time increases，the extent of tunnel leakage will gradually escalate. The local leakage coefficient is introduced to describe the process of increased permeability of the lining caused by leakage diseases. The generalized Voigt model is utilized to characterize the rheological properties of soft clay. Based on the Terzaghi-Rendulic theory，an equation is established to describe the consolidation process of saturated soft soil around a tunnel under changing lining permeability. The expression for dissipation of excess pore water pressure is derived using the method of complex variables. The generalized Voigt model is degenerated into existing models for comparison，validating the reliability of the proposed approach. With the Shanghai Metro Line 1 tunnel as the engineering background，the effects of initial permeability of the lining，local leakage coefficient，and parameters of the generalized Voigt model on the dissipation and distribution of excess pore water pressure are analyzed. The results indicate that when the ratio of the initial permeability of the lining to soil permeability exceeds a certain value，there is a tendency for complete dissipation of excess pore water pressure under the effects of exacerbated leakage disease. The larger the local leakage coefficient，the earlier the dissipation of excess pore pressure begins and the faster the dissipation rate. The effects of the number of Kelvin bodies and the viscosity coefficient on excess pore water pressure is concentrated in the middle consolidation stage. More Kelvin bodies and smaller viscosity coefficient result in slower dissipation of excess pore pressure. For the engineering case in this study，when the time is less than 1×105 days，the excess pore pressure above the tunnel decreases gradually with depth，and then the position of maximum excess pore pressure continuously moves towards the ground surface.

When using vacuum preloading for soft soil foundations that contain high permeability sand layers，it is effective to establish a clay sealing wall to maintain the integrity of the vacuum system. The silt mixed with silt forms a flocculent structure at a microscopic level，which significantly affects the soil permeability when subjected to external disturbance. Experiments were conducted to determine the relationship between soil permeability coefficient(kv)，effective stress(?′)，and clay content(Nc). This relationship can be used as a basis for evaluating the construction of sealing walls. Subsequently，field tests were conducted on this type of foundation with different PVD spacing. The test results revealed that the permeability coefficient of silty sand and silt is less than 10－5 cm/s，considering the effect of ?′. The vacuum pressure under the membrane was maintained at around 83 kPa，indicating good sealing performance of the vacuum system and suggesting that a sealing wall is unnecessary for this type of foundation. After reinforcement，the moisture content is reduced by 20% and the void ratio of silt is reduced by 30%. The vane shear strength increased by 22.3–32.23 kPa.

Lightweight geomaterials obtained by mixing expanded polystyrene(EPS) or waste tires(WTS) with soil are widely used in geotechnical engineering，but lightweight materials(such as EPS) can be harmful to the environment. In recent years，the mycelium bio-composites lightweight soil(P. ostreatus MBLS)，which is composed of wheat bran(lightweight material or substrate material)，sand(aggregate)，and Pleurotus ostreatus(cementing material)，has attracted wide attention due to the advantages of its lightweight and non-pollution. In this paper，a series of static drained triaxial compression tests were performed. The impact of substrate material content，effective confining pressures，and hyphae on the mechanical properties of P. ostreatus MBLS was studied. It is found that increasing substrate material content reduces the strength and density of P. ostreatus MBLS. The presence of mycelium changes the structure of P. ostreatus MBLS，improves strength and reduces volumetric contraction，depending on effective confining pressure. The effect of mycelium on the strength and deformation of the specimens is more significant at low confining pressures(about 100 kPa) and at small strain stages. The preparation method of P. ostreatus MBLS is straightforward and poses no environmental pollution risks. It represents a promising alternative to conventional shallow backfill geotechnical materials.