针对深部岩石工程中传统力学试验存在的取芯困难、数据离散性大等问题,提出一种基于循环加卸载压入试验测定岩石弹性模量的方法。通过在单个压点开展循环压入,获取多组载荷-位移曲线,采用Oliver-Pharr理论与Hertz接触模型耦合的方法计算弹性模量,并系统探究最大载荷、加载速率和保载时间对致密砂岩弹性模量测量结果的影响。试验结果表明:较大的压入载荷会导致计算结果偏大;加载速率对结果影响较小,低加载速率有助于降低测试误差;较长的保载时间可使计算结果更平稳。综合分析得出,采用最大载荷50 N、加载速率0.03 mm/min、保载时间10 s的试验条件时,压入弹性模量与单轴压缩基准值误差最小,数据稳定性最佳。与传统压痕试验相比,该方法试验流程简便高效,数据获取丰富,曲线平滑稳定,准确率更高,无需完整岩芯,可利用钻井岩屑快速测试,为深部岩石工程设计和施工提供准确的岩石力学参数,具有较高的工程应用价值。

[Objective] To address the challenges of difficult coring, high cost, and high data dispersion in traditional mechanical testing for deep rock engineering, as well as the conflict between testing efficiency and accuracy in existing indentation techniques that rely on multi-point array statistics, this study aims to propose a new, efficient, and accurate method for determining the elastic modulus of rocks. This method enables the rapid acquisition of mechanical parameters without the need for intact cores. [Methods] An innovative macroscopic indentation testing scheme was adopted, featuring continuous cyclic loading and unloading at a single indentation point. Tight sandstone from the Tarim Basin at burial depths of 6 500-8 038 m was used as the research object. Standard cylindrical specimens (for uniaxial compression benchmark tests), rectangular specimens, and solidified drilling cutting specimens (simulating field application scenarios) were prepared simultaneously. The experiments combined the Oliver-Pharr theory with the Hertz contact model. Through a three-factor, three-level orthogonal experimental design (maximum load: 50, 100, 200 N; loading rate: 0.03,0.06,0.09 mm/min; load holding time: 0, 10, 30 s), the influence of key experimental parameters on the elastic modulus measurement results were systematically investigated. Thirty cycles of loading and unloading were performed at each indentation point to collect a greater amount of load-displacement data. Initial indentation deviations and dispersion were corrected through linear fitting. After removing outliers, statistical characteristic values were calculated and compared with the results from uniaxial compression tests for validation. The experiments were conducted using a modified WANCE 503A electronic universal testing machine to ensure high-precision acquisition of load and displacement data. [Results] The maximum load had a significant impact on measurement accuracy. The indentation elastic modulus under a 50 N load showed the best agreement with the uniaxial compression reference value, with an error of only 9.70%. In contrast, the errors increased to 12.18% and 24.74% under loads of 100 N and 200 N, respectively. The loading rate had a secondary influence, with the lowest rate of 0.03 mm/min providing the best data stability (coefficient of variation <7.5%), effectively reducing dynamic effect interference. A load holding time of 10 s achieved a balance between contact stability and deformation instantaneity, resulting in a low error of 4.73%. No holding time (coefficient of variation 9.2%) or excessively long holding time (30 s) both led to increased data dispersion. The elastic modulus exhibited a gradual increasing trend within 30 cycles and tended to stabilize after 20 cycles, with an increment ≤20%, which was consistent with the patterns of rock cyclic hardening and micro-damage accumulation. The error of the elastic modulus measured by this method was <10%, significantly better than the 13.5%-15% error level of traditional indentation tests. Drilling cuttings, after simple solidification treatment, could meet the testing requirements without the need for intact cores, greatly improving testing efficiency compared to traditional multi-point array indentation. Under uniaxial compression, tight sandstone exhibited typical splitting failure, with the main fracture plane parallel to the axial direction. During the cyclic loading and unloading process, the proportion of plastic deformation gradually decreased with increasing cycle number and eventually approached a purely elastic response, verifying the rationality of the physical mechanisms of the method. [Conclusion] The core innovation of this study lies in proposing a “single indentation point with continuous cyclic loading and unloading” testing mode. This approach overcomes the limitations of traditional indentation techniques that rely on multi-point array statistics and simultaneously improves data density and accuracy through multiple tests at a single point, thereby resolving the conflict between efficiency and accuracy. The determined optimal experimental parameters (maximum load of 50 N, loading rate of 0.03 mm/min, load holding time of 10 s) can ensure the accuracy and stability of measurement results. The method features a simple experimental procedure, portable equipment, and eliminates the need for deep coring. It enables the rapid acquisition of elastic modulus directly from drilling cuttings, with errors controlled within an engineering-acceptable range. This provides an efficient and reliable technical pathway for on-site mechanical parameter testing in deep rock engineering. Its applicability covers brittle rocks such as sandstone, limestone, and granite. Future integration with digital image correlation techniques can further reveal the dynamic relationship between rock microstructure and elastic modulus under cyclic loading.