To address the intense stress evolution and severe floor heave in roadways of extra-thick coal seams, this study investigates the catastrophic evolution laws and mechanisms of medium-hard floor strata using the 122,110 working face of Caojiatan Coal Mine as the engineering background. By integrating field monitoring, theoretical analysis, and numerical simulation, the research challenges the traditional perception of damage caused by a single load and reveals that the “low-level stepped rock beam + high-level articulated rock block” composite load-bearing system, formed after mining, is the root cause of the extreme stress imbalance between the coal pillar side and the solid coal side. The study identifies the non-symmetric evolution characteristics of the roadway driven by a “non-symmetric stress gradient”: the stress on the coal pillar side (26.62 MPa) significantly exceeds that on the solid coal side (22.07 MPa) by approximately 20.6%. This imbalance results in an average maximum floor heave of 473 mm, with the peak heave position shifting markedly toward the solid coal side. A mechanical model and criteria for the non-symmetric stress gradient under the influence of lateral overburden structures were constructed. The dynamic process of “high-pressure extrusion” and its coupling with non-symmetric shear paths in the floor rock mass—driven by the intense “stress potential difference” between the central destressed zone and the high-stress zones on both ribs—was elucidated. Consequently, a synergistic control theory featuring “pressure relief at the structural source, blockage of the stress transmission path, and non-symmetric reinforced support” is proposed. These findings provide a novel theoretical perspective and technical support for managing floor heave in high-stress roadways of extra-thick coal seams.

Mudstone's mechanical properties are extremely susceptible to engineering disturbances, and studying the effects of dynamic pile driving (DPD) is crucial for geotechnical stability and pile foundation design. This study conducts a multi-scale experimental investigation, including uniaxial and triaxial tests, and scanning electron microscope (SEM) analyses, to examine the mechanical and structural degradation of pile-surrounding mudstone induced by DPD using an 8.3 t hammer at 1 Hz. Results show that uniaxial compressive strength (UCS), elasticity modulus (E), internal cohesion (c), and internal friction angle (phi) decreased by an average of 28.66 %, 41.24 %, 13.12 %, and 56.18 %, respectively. The disturbed mudstone exhibited significant plastic characteristics, with both strain hardening and softening. Multi-scale analyses reveal that cracks and pores increased markedly in number and connectivity, evolving from scattered distributions to dense networks, which closely correlate with the observed mechanical deterioration. Strength reduction varied around the pile, with the least strength loss occurring in the compaction zone below the pile end due to densification from pile penetration. These findings are supported by standard penetration test (SPT) results before and after pile driving, indicating that pre-driving geological surveys overestimate mudstone strength and may pose potential engineering risks.

For large-diameter bored piles in coastal and nearshore infrastructure, pile-head settlement and bearing capacity do not fully capture the effects of shaft post-grouting and pile geometry. In layered soil–rock strata, their influence extends to how axial load is mobilized and redistributed with depth. This study presents full-scale compression tests on six instrumented piles, comprising post-grouted and ungrouted piles, diameters (D) of 0.8 and 1.0 m, and rock-socket depths (h). Axial force, pile–ground relative displacement, shaft resistance, near-toe load and stratum-based load sharing were examined. Load transfer varied with stratigraphy and loading stage. Post-grouted piles mobilized higher shaft resistance at smaller displacement, with persistent differences in the upper sand, differences emerging mainly at higher loads in the middle transition zone, and limited differences in weathered rock. The contribution of the overlying soil strata increased from 41.1% to 62.1%, while the deep weathered-rock contribution decreased from 58.9% to 37.9%. The 1.0 m group showed greater weathered-rock participation than the 0.8 m group, while larger h/D was associated with farther load-transfer development toward the lower socket and near-toe region. These results show that post-grouting and pile geometry affect interconnected parts of the depth-wise load-transfer process under the tested conditions.

Whether the inhomogeneity of mudstone foundation leads to abnormal bearing capacity of the driven pile remains controversial. This study introduces the standard penetration test hammering number and needle penetration strength for quantitative analysis by macroscopic observation of the engineering field on the mudstone stratum self-structure and microscopic observation by simple and feasible electronic magnification. The analysis of typical engineering examples demonstrated that the abnormal bearing capacity of piles in the mudstone stratum was related to mudstone inhomogeneity. This study also proposes a method of evaluating mudstone uniformity using the heterogeneous index η, in which η > 2 suggests the need for engineering measures. These findings assist in determining a reasonable solution to the problem of abnormal bearing capacity at driven piles in mudstone foundations.

In order to study the variation of soil pressure in the process of jacked pile penetration. A model test of jacked pile driving in saturated clay was carried out. The double-wall model pipe pile was used to separate the internal and external friction resistance, and a micro-soil pressure sensor was installed on the pile to monitor the soil pressure at the pile-soil interface. The variation law of pile pressure and pile tip resistance in pile driving process was analyzed. The distribution characteristics of soil pressure at the pile-soil interface in the process of pile sinking under static pressure were discussed. It was clear that the soil pressure at the pile-soil interface had obvious degradation effect in the process of pile driving. The change mechanism of soil pressure at the pile-soil interface during the process of pile sinking in saturated clay was revealed. The test results showed that the pile compression force increased linearly with the penetration depth, and the pile compression force of the closed pile was obviously larger than that of the open pile in the later period of penetration. The pile tip resistance increased linearly, accounting for 62.3% of the pile pressure in the process of piling. The soil pressure at the pile-soil interface increased at a low rate at the initial stage of the static pile penetration, but increased linearly and at a high rate with the gradual penetration of the static pile. At the same depth, with the gradual penetration of the static pile into the pile-soil interface, there was an obvious phenomenon of earth pressure degradation. The research results could provide reference for the study of soil pressure at the interface between piles and soil under static pressure. At the depth of 20, 30, 40, 50, 60 and 70 cm, the earth pressure degraded by 14.6%, 13.8%, 13.2%, 9.2%, 7.2% and 6.1% on average.

To study the vertical compressive bearing characteristics of large-diameter rock-socketed cast-in-place piles, eight manually-excavated rock-socketed cast-in-place piles were subjected to vertical compressive on-site load and pile stress tests. The test results showed that the load–displacement ( Q-s ) curves of the eight test piles were all slow-varying, and the settlement of the piles was less than 11 mm, which met the minimum engineering requirements. The unloading rebound rate was between 55 and 75%, and the elastic working properties of the piles were apparent. The pile axial force gradually decreased with depth, and the slope of the axial force distribution curve reached a minimum in the moderately weathered muddy siltstone layer while the pile side friction resistance reached its maximum value. Pile end friction increases with the increase of load. But the pile end resistance was inversely proportional to the single pile length-to-diameter (L/D) ratio and the depth of rock embedment for the pile. The percentage of pile side friction resistance under maximum load was 86%, indicating that these were characteristic friction piles. Based on the test results and the current Chinese code, the friction coefficient of the pile side soil layer η and the total resistance coefficient of the rock-socketed section ζ were introduced. A revision to the calculation equation for the vertical bearing capacity of the rock-socketed cast-in-place pile in the code was proposed, together with an optimization design method for large-diameter rock-socketed cast-in-place piles.

To investigate the bearing mechanism of super-long piles in reclamation, this study performed a series of field tests on super-long cast-in-place piles. The load distribution and bearing characteristics of the piles were analyzed, and the bearing capacity calculation method was evaluated. The findings revealed that dynamic compaction (8000 kN & sdot;m) improved the compactness and bearing capacity of the filled soil, and was capable of avoiding negative friction around the pile. The pile bearing characteristics were friction type, and bearing capacity was mainly borne by axial friction resistance. The pile end resistance accounted for 15.7 %-35.1 % of the bearing capacity, and the peak friction resistance was distributed in the upper soil at a depth range of 0.13-0.31 times pile length. The measured value of friction resistance was 9.8 %-90.2 % higher in the upper soil layer and 46.7 %-60.8 % lower in the rock layer than the value recommended by the current Chinese code. The hyperbolic model overestimated the bearing capacity by 26.8 %-50.4 % and the exponential model error was -4.5 % - +18.9 %. The hyperbolic model was corrected, and the correction factor was determined as 0.73. This study provides guidance for the structural design and theoretical calculation of super-long piles in reclamation areas.

Abstract This paper researched the vertical load-bearing capacity of rock-socketed cast-in-place piles using static load tests, and high- and low-strain dynamic tests, based on a construction project in Indonesia. On this basis, an exponential curve model was used to predict the ultimate load capacity of each test pile. The test piles were divided into 800 mm and 600 mm diameter groups. Under the maximum test load conditions, the end resistance of the 800 mm diameter piles accounted for more than 50% of the load, showing good friction end-bearing pile characteristics. In contrast, the maximum end resistance of the 600 mm diameter piles accounted for less than 35% of the load, showing end-bearing frictional pile characteristics where the vertical bearing capacity of a single pile is predominantly borne by the pile side friction resistance. The piles' load-settlement (Q‑s) curves varied slowly, with a maximum settlement of less than 30 mm. The rebound settlement rate at the top of the pile was significant, while the residual settlement was small. Under the maximum load, the pile side friction resistance reached a maximum in the rock-embedded section at the location of the flattest slope of the axial force curve.

Compared to traditional steel reinforcement, GFRP anchors demonstrate outstanding mechanical performance and corrosion resistance, and so they are an ideal substitute for steel reinforcement in anti-floating projects. Based on finite element software, a 3D axisymmetric calculation model of GFRP anti-floating anchors in medium-weathered granite was established in this paper. Combined with the in-situ ultimate pull-out tests, the bonding anchoring performance and bearing characteristics between the anchor body, anchoring mortar, and rock–soil mass were analyzed. The research findings indicated that the cohesive bonding elements exhibited a high degree of conformity in defining the interface contact relationship of the GFRP anti-floating anchor anchoring system. The axial force of the GFRP anti-floating anchor body is “attenuated” along the depth direction, and there was a critical value of anchoring length; under the same conditions, the reasonable anchoring length should be 3.5~5.0 m. All the anchors in the in-situ tests exhibited interfacial shear slip failure between the anchor body and the anchor mortar, with an average maximum load of 450 kN, which is consistent with the maximum failure load of the simulated anchors. Compared to a load of 50 kN, the maximum stress of the anchor mortar increased by 50% under a load of 450 kN. The displacement variation of the surrounding rock–soil mass showed a decreasing trend from the inside to the outside and from the top to the bottom. The research results provided valuable references for the optimization design of GFRP anti-floating anchors.

The degradation of lateral friction resistance significantly affect the bearing capacity traits of pile foundations. The paper summarizes the existence of degradation effects on the lateral frictional resistance of piles. The causes of the degradation of pile lateral friction resistance during pile sinking and the shear fatigue degradation effect at the pile-soil interface under cyclic loading are analyzed. The method of calculating the bearing capacity of piles in the case of degradation effect of pile lateral frictional resistance is summarized and analyzed.

The bearing capacity of the driven pile in the mudstone bearing layer is consistently lower than the design value. In this paper, the uniaxial compression test, pile driving model test, and needle penetration test were carried out on the mudstone samples before and after driving, and the influence of driving on the mudstone around the pile was studied. Based on the test results, the pile-bearing capacity evaluation method was proposed, and a numerical simulation was carried out. The findings revealed that the mudstone around the field piles was damaged by hammer pile driving, and the strength and elastic modulus reduced by 28.2% and 41.40%, respectively. The damage range of mudstone caused by dynamic pile driving was noted as 2d (pile diameter). For area within 0∼2d, 4 damage zones were defined every 0.5d. The strength of mudstone in four zones decreased by 66%, 40.5%, 17%, and 7%, and the elastic modulus decreased by 80.5%, 54.5%, 26.5%, and 11%, respectively. Besides, the reduction factors of damaged zones were determined, and the evaluation method of bearing capacity of mudstone considering damaged zones was proposed. The bearing capacity evaluated by this method was found to be consistent with the measured value with a 10.5% difference in measured mean value, and the conventional method overestimated the pile's bearing capacity by 57.9%. In addition to providing a specific method for the pile design and bearing capacity evaluation, this study clarified the dynamic damage characteristics of mudstone after the pile driving process has been completed.

In response to the difficulties in driving piles into mudstone foundation, insufficient bearing capacity, and the difficulty in preparing a model foundation due to the disturbance of soft rock, a simulation pile driving and static load test device based on undisturbed soft rock was preliminarily developed. The device mainly includes undisturbed soft rock constraint model box unit, hammer-driven unit, guide rail support unit and static load unit. Calibration tests and application tests were carried out to verify the feasibility and stability of the device. The penetration and bearing characteristics of driven pile were analyzed, the mechanical characteristics of mudstone around pile caused by pile driving damage were defined, and further research prospect and engineering application suggestions were put forward. The study shows that: 1) The results of tests are consistent with that of field test, and the penetration characteristics and bearing characteristics are both the same as those of field test, which verifies the feasibility of the test device. 2) The stability of the load transfer factor a further proves that the load transfer of the test device is stable and reliable. 3) As mudstone has intensive soft and hard interbedding, as a result, there is a significant difference in penetration resistance represented by the number of blows per 10 mm of penetration, and the static load failure of low strength soft interlayers presents a precipitously increasing settlement. 4) The mudstone within 2d (d is the pile diameter) around the pile is damaged by pile driving; for every 0.5d interval, the strength loss is 66.0%, 40.5%, 17.0%, 7.0% and the elastic modulus loss is 80.5%, 54.5%, 26.5%, 11.0%, respectively. 5) The reduced values of the undisturbed mechanical parameters should be selected according to the damage characteristics induced by pile driving in the design and bearing capacity evaluation of mudstone. The test device has the advantages of stability, reliability and controllability, which can provide support for related research on pile driving in mudstone.

随着城市规模的不断扩大,高层、超高层建筑物及大型桥梁的建设需求,桩基础逐渐向大直径、深埋深的方向发展.嵌岩桩是目前城市建设中经常遇到的桩型,有效确定嵌岩桩的竖向承载力并厘清其竖向荷载传递机制,是实现嵌岩桩安全、可靠使用的前提和保障.充分掌握嵌岩桩承载性能的前提是明确基桩的竖向承载力特征值,从宏观上得到基桩的荷载传递性状、桩-土-岩相互作用规律及桩受荷后的破坏模式.掌握嵌岩桩的破坏模式和荷载传递规律对深入认识嵌岩桩承载性能具有重要的意义.为此,从嵌岩桩的荷载传递规律、破坏模式、承载特性和影响承载特性的主要因素等4 个方面对嵌岩桩承载性能的研究现状进行梳理,归纳和评述了嵌岩桩荷载传递特性及破坏特征的最新研究进展,总结了嵌岩桩承载性能现场试验和室内试验的研究进程,详细分析了影响嵌岩桩竖向承载性能的主要因素,讨论了现阶段嵌岩桩承载性能研究工作的不足之处,并针对研究的不完备提出相应的建议和研究方向.

We conducted anchoring performance, stress distribution, and full-scale indoor pulling tests on glass-fiber-reinforced polymer (GFRP) bolts. The tests were conducted using finite element software while considering the multi-interface contact and BK criterion by using the cohesive element to simulate the contact relations between the anchor rod body and concrete and building an axial symmetry calculation model of the GRFP bolt and concrete. The results indicated that the finite element model based on cohesive element accurately represents the load–displacement relationship of the GFRP bolt and the distribution law of axial stress along the anchoring length. In addition, the simulation outcomes of the load–displacement relationship were in good agreement with the measured test values. Under the same load, the axial-force-transferred depth of the bolt body was identical regardless of the anchorage length. As anchoring length increases, the pull load on the bolt and the decay rate of axial stress along the anchoring length rises gradually. There is a critical value for the anchorage length of the bolt.

Glass fiber reinforced polymer (GFRP) bolt, which has excellent mechanical properties and corrosion resistance, is gradually replacing metal bolt in rock and soil anchoring, compared with traditional reinforced bolts and other composite materials with high cost. In the current study, the influence of anchorage length and anchorage mode on the bonding property of bolt and concrete was investigated, and the stress mechanism of glass fiber bolt was analyzed based on the tensile test of a full-size laboratory sample. The results show that the failure modes of GFRP anti-floating anchor were pull-out failure and fracture failure, the ultimate bearing capacity of mechanical anchorage was noted as 1.08-1.24 times that of linear anchorage. Under the same anchorage method, with the increase of anchorage length, the relative displacement and the proportion of load bearing in the easing section of the bolt load-displacement curve decreased; thus, the load-displacement curve of the anchor in the form of mechanical anchorage was smoother. With the increase of load, the main load bearing mode of the bolt-concrete interface changed from the interface friction force and chemical adhesive force to the mechanical bite force, and then the interface concrete was broken, and the concrete no-acting zone was transformed into the acting zone until the bolt was damaged. Anchor had a maximum anchorage length beyond which the bearing capacity of the anchors increased minimally. Comparing the calculation formulas of anchor length under different national standards, it was suggested to use Chinese or European standards to calculate anchor length.

以青岛市黄岛区的软弱地基为背景,通过现场试验和ABAQUS数值模拟相结合的方法,探讨重型吊装场地换填垫层后持力层变形计算问题.采用内插法对沉降计算经验系数进行修正以及反演瞬时沉降的地基弹性模量,并将修正的沉降结果和反演值与数值模拟结果进行比对,研究内插法优化程度及反演弹性模量的实用性.结果表明:内插法修正分层总和法中的沉降计算经验系数能使计算的沉降结果更加接近数值模拟结果,将反演的弹性模量在数值模拟中进行赋值,使模拟结果与静载试验结果相吻合,二者均能达到优化变形计算的目的.在重型吊装场地换填垫层的持力层变形计算中采用以上两种方法具有较强的实用性.研究结果可为类似地层的地基处理和吊装工程提供参考.

玻璃纤维增强聚合物(Glass fiber reinforced polymer,GFRP)锚杆因具有耐腐蚀性能强、抗拉强度高、导电性差、造价相对低等诸多优势成为钢筋锚杆的潜在替代品应用于地下结构抗浮工程中.采用倒置基础底板对GFRP筋和钢筋两种材质的抗浮锚杆开展现场极限抗拔试验,明确GFRP抗浮锚杆与地基底板之间的黏结锚固特性,揭示锚筋材质、竖向锚固长度、弯曲半径、弯折锚固长度及黏结长度等因素对抗浮锚杆与基础底板黏结强度的影响机制.结果表明:(1)GFRP抗浮锚杆及直锚的钢筋抗浮锚杆易发生剪切滑移破坏,弯锚的钢筋锚杆发生锚筋断裂破坏;(2)本试验条件下,直径28 mm的抗浮锚杆与基础底板的黏结强度介于1.23～7.79 MPa;(3)弯折锚固长度是影响抗浮锚杆与基础底板黏结强度的主要因素,且对GFRP抗浮锚杆的影响最显著,GFRP锚筋不宜在基础底板内进行弯折;(4)对这两种材质抗浮锚杆的黏结-滑移曲线进行对比,直锚钢筋锚杆的黏结-滑移曲线存在明显拐点,而直锚GFRP锚杆则几乎为线性上升状态.

The mudstone around the pile is damaged during pile driving, altering the mechanical properties of the mudstone. This study conducts standard penetration, uniaxial compression, and triaxial shear tests before and after pile driving. It develops a constitutive damage model of mudstone affected by pile driving based on the statistical damage theory and triaxial test data. The findings in this study show that: (1) The standard penetration number (N) of the clay around the pile remains unchanged after driving because of the thixotropic recovery effect. However, the N of mudstone surrounding the pile decreases by 35.1% on average, (2) The average uni-axial compressive strength is 1.56 MPa before pile driving and 1.12 MPa after pile driving, which decreases by 28.2%. After pile driving, c (cohesion) = 217.2 kPa, phi (internal frictional angle) = 21.6 degrees, (3) The calculated value agrees well with the measured one, verifying the rationality of the model, and (4) The mechanical properties of mudstone change considerably after pile driving, and it is unrealistic to use the mechanical parameters of un-disturbed mudstone to design the pile. This research provides theoretical support and parameter preparation for calculating pile driven mudstone foundations.

从全长黏结非金属抗浮锚杆的作用机理和破坏模式出发,对非金属抗浮锚杆的选型、内锚固段设计、外锚固段设计以及稳定性验算进行论述.研究结果表明:在锚杆选型中,应充分利用直径小、强度高的GFRP抗浮锚杆替代大直径钢筋锚杆;在外锚固设计中,明确了内锚固段极限黏结长度的计算方法,提出了机械锚固、金属?GFRP混合连接以及不同直径锚筋连接的设计方法,为抗浮工程设计提供了新思路;在内锚固设计中,建议在保证锚杆抗拔承载力的前提下,适当缩短锚固段长度;在抗浮稳定性设计中,应采用综合安全系数法和分项系数表达方式进行抗浮体系验算.