Energy conversion of rocks in process of unloading confining pressure under different unloading paths

Based on energy theory and tests of rocks with initial confining pressures of 10, 20 and 30 MPa under different unloading paths, the processes of strain energy conversion were investigated. The absorbing strain energy for axial compression, the dissipating strain energy for plastic deformation and cracks propagation, the expending strain energy for circumferential deformation, and the storing and releasing elastic strain energy were considered. Unloading paths included the condition of fixing axial pressure and unloading axial pressure, increasing axial pressure and unloading confining pressure, as well as unloading axial pressure and confining pressure simultaneously. Results show that expending strain energy for circumferential deformation has mainly evolved from absorbing strain energy for axial compression in three unloading paths during unloading processes. Dissipating strain energy is significantly increased only near the peak point. The effect of initial confining pressure on strain energy is significantly higher than that of unloading path. The strain energy is linearly increased with increasing initial confining pressure. The unloading path and initial confining pressure also have great influence on the energy dissipation. The conversion rate of strain energy in three paths is increased with increasing initial confining pressure, and the effect of initial confining pressure on conversion rate of strain energy is related with the unloading paths.

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal-hydrologicalmechanical coupling of coal containing methane,an experimental study was carried out to investigate mechanical property and gas permeability of raw coal,under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions.Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure.The research results show that,compared with the peak intensity of conventional triaxial loading,the ultimate strength of coal samples of triaxial unloading confining pressure was lower,deformation under loading was far less than unloading,dilation caused by unloading was more obvious than loading.The change trend of volumetric strain would embody change of gas permeability of coal,the permeability first reduced along with volumetric strain increase,and then raised with volume strain decrease,furthermore,the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure.When gas pressure was greater,the effective confining pressure was smaller,and the radial deformation produced by unloading was greater.When the unloading failed confining pressure difference was smaller,coal would be easier to get unstable failure.

Effects of combination of irbesartan and perindopril on calcineurin expression and sarcoplasmic reticulum Ca^(2+)-ATPase activity in rat cardiac pressure-overload hypertrophy

Aim： To observe effects of angiotensin （Ang） II receptor antagonist （ATI） irbesartan and angiotensin-converting enzyme （ACE） inhibitor perindopril on rat myocardium calcineurin expression and sarcoplasmic reticulum Ca^2＋-ATPase activity in the model of pressure-overload cardiac hypertrophy. Methods： Forty male adult Sprague Dawley rats were divided into 5 groups One group was treated by sham operation; four groups were myocardium hypertrophy cases caused by banding aortic above renal artery. Drugs were given one week after operation. Group 1： sham group, rats （n=8） were gavaged with normal saline 2 ml/（kg·d） （ig）; Group 2： control group, rats （n=8） were treated with normal saline 2 ml/（kg·d） （ig）; Group 3： rats （n=8） were given perindopril 2 mg/（kg·d） （ig）; Group 4： rats （n=8） were treated with irbesartan 20 mg/（kg·d） （ig）; Group 5： rats （n=8） were given irbesartan 20 mg/（kg·d） plus perindopril 2 mg/（kg·d） （ig）. Morphometric determination, calcineurin expression and sarcoplasmic reticulum Ca^2＋-ATPase activity were done at the end of 6 week of drug intervention. Expression of calcineurin in myocardium was detected by immunohistochemistry. Results： Left ventricular mass index （LVMI）, transverse diameter of myocardial cell （TDM）, calcineurin activity were remarkably decreased after drug intervention and this decrease was most remarkable in the combination drug therapy group. Sarcoplasmic reticulum Ca^2＋-ATPase activity was increased after drug intervention, especially in the combined drug therapy group. Calcineurin expression in myocardium was remarkably decreased after drug intervention. LVMI was positively correlated with TDM and calcineurin, negatively correlated with sarcoplasmic reticulum Ca^2＋-ATPase. Conclusion： These data suggest that irbesartan and perindopril inhibit cardiac hypertrophy through the increased activity of sarcoplasmic reticulum Ca^2＋-ATPase and decreased expression of calcineurin. Their combination had better effects on regressing of ventricular hypertrophy.

Targeting at SUR2B/Kir6.1 subtype of ATP-sensitive potassium channel opener natakalim improves pressure overload-induced heart failure

Objective To explore the new stratigies targeting at SUR2B/Kir6.1 subtype against pressure overload-induced heart failure.Methods Pressure overload-induced heart failure was induced in Wistar rat by abdominal aortic banding(AAB).The effects of natakalim(1,3,9 mg·kg-1·d-1,10 weeks)were assessed on myocardial hypertrophy and heart failure,cardiac histology,vasoactive compounds,and gene expression.Isolated working heart and isolated tail artery helical strips were used to examine the influence of natakalim on heart and resistant vessels.Results Ten weeks after the onset of pressure overload,natakalim therapy potently inhibited cardiac hypertrophy and prevented heart failure.Natakalim inhibited the changes of left ventricular haemodynamic parameters,reversed the increase of heart mass index,left ventricular weight index and lung weight index remarkably.Histological examination demonstrated that there were no significant hypertrophy and fibrosis in hearts of pressure overload rat treated with natakalim.Ultrastructural examination of heart revealed well-organized myofibrils with mitochondria grouped along the periphery of longitudinally oriented fibers in natakalim group rats.The content of serum NO and plasma PGI2 was increased,while that of plasma ET-1 and cardiac tissue hydroxyproline,ANP and BNP mRNA was down-regulated in natakalim-treated rats.Natakalim at concentrations ranging from 0.01-100 μM had no effects on isolated working heart derived from Wistar rats;however,natakalim had endothelium-dependent vasodilation effects on the isolated tail artery helical strips precontracted with NE.Conclusions These results indicate that natakalim improves heart failure due to pressure overload by activating KATP channel SUR2B/Kir6.1 subtype and reversing endothelial dysfunction.

Study of the structure and architecture of aortic smooth muscle cells under pressure overloading in rats

Male Wistar rats were used to study the changes of the structure and architecture of the smooth muscle cells(SMCs) of the aorta under pressure overloading(PO).The aorta was cut open longitudinally and the tunica media was examined with a histological tech

Effects of Ligustrazine on Myocardial Fibrosis in Rats with Pressure Overload

Objective: To investigate the effects of ligustrazine (Li) on myocardial fibrosis in rats with pressure overload. Methods: Pressure overload rat models were established by constricting the abdominal a-orta. Sixty-three SD rats were divided into 3 groups: Sham operated group (SOG, n = 21), operated group (OG, n = 21) and operated combined with ligustrazine group (OG+Li, n = 21). Each group was randomly assigned to seven time points: The 1st, 2nd, 4th, 7th, 14th, 21st and 30th day after operation. Three rats were included in each time point. Serial sections of cardiac tissues were examined and the morphological or morphometric analysis of the SOG, OG and OG+Li done by histopathological and computer image analyzer technique. Results: (1) It showed that there were reactive fibrosis (from the 4th day on after operation) and reparative fibrosis (from the 21st day on after operation) in the OG, while myocardial fibrosis in the OG+Li was alleviated. Though reactive fibrosis (from the 21st day on after operation) was shown, reparative fibrosis wasn't seen. (2) Perivascular collagen area (PVCA) in the OG (2. 09±0. 45) was significantly higher than SOG (0. 83±0.06) from the 1st day on after operation and then steadily increased, while in the OG+Li (1.16±0.06), it was significantly lower than OG at the same time; collagen volume fraction (CVF) in the OG (3.08±0. 56) significantly increased compared with the SOG (2. 78±0. 64) from the 2nd day on after operation and showed a trend of rapid ascending from the 21st day on after operation; and in the OG + Li (4.69±0.85), it was significantly decreased compared with the OG (7.56±0.88) from the 21st day on after operation, with all P<0.05. Conclusion: Ligustrazine could alleviate and postpone the accumulation of myocardial collagen and has protective effects on the heart.

Involvement of mitochondrial TRPV3 in cardiac hypertrophy induced by pressure overload in rats

Mitochondria play an important role in pressure overload-induced cardiac hypertrophy.The present study aimed to investigate the role of mitochondrial transient receptor potential vanilloid 3(TRPV3)in myocardial hypertrophy.A 0.7 mm diameter U-shaped silver clip was used to clamp the abdominal aorta of Sprague Dawley(SD)rats and establish an animal model of abdominal aortic constriction(AAC).Rat H9C2 myocardial cells were treated with angiotensin II(Ang II)to establish a hypertrophic myocardial cell model,and TRPV3 expression was knocked down using TRPV3 small interfering RNA(siRNA).JC-1 probe was used to detect mitochondrial membrane potential(MMP).DHE probe was used to detect ROS generation.Enzyme activities of mitochondrial respiratory chain complex I and III and ATP production were detected by assay kits.Immunofluorescence staining was used to detect TRPV3 expression in H9C2 cells.Western blot was used to detect the protein expression levels ofβ-myosin heavy chain(β-MHC),mitochondrial TRPV3 and mitochondrial NOX4.The results showed that,in the rat AAC model heart tissue and H9C2 cells treated with Ang II,the protein expression levels ofβ-MHC,mitochondrial TRPV3 and mitochondrial NOX4 were up-regulated,MMP was decreased,ROS generation was increased,mitochondrial respiratory chain complex I and III enzyme activities were decreased,and ATP production was reduced.After knocking down mitochondrial TRPV3 in H9C2 cells,the protein expression levels ofβ-MHC and mitochondrial NOX4 were down-regulated,MMP was increased,ROS generation was decreased,mitochondrial respiratory chain complex I and III enzyme activities were increased,and ATP production was increased.These results suggest that mitochondrial TRPV3 in cardiomyocytes exacerbates mitochondrial dysfunction by up-regulating NOX4,thereby participating in the process of pressure overload-induced myocardial hypertrophy.

Coefficients of earth pressure at rest in thick and deep soils

The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.

Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling

This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.

Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance.The Brazilian disc(BD)test is the suggested method by the International Society for Rock Mechanics and Rock Engineering(ISRM)for measuring both the static and dynamic tensile strengths of rock-like materials.However,due to the overload phenomenon and the complex preloading conditions,the dynamic tensile strengths of rocks measured by the BD tests tend to be overestimated.To address this issue,the dynamic BD tensile strength(BTS)of Fangshan marble(FM)under different preloading conditions were measured through a triaxial split Hopkinson pressure bar(SHPB).The fracture onset in BD specimen was captured through a strain gage around the disc center.The discrepancy between the traditional tensile strength(TTS,determined by the peak load P_(f) of the BD specimen)and the nominal tensile strength(NTS,obtained from the load P_(i) when the diametral fracture commences in the tested BD specimen)was applied to quantitatively evaluating the overload phenomenon.The Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress states.The results demonstrate that the overload ratio(s)increases with the loading rate(σ)and decreases with the hydrostatic pressure(σ_(s)).The TTS corrected by the Griffith criterion is independent of theσ_(s)due to the overload phenomenon,while the NTS corrected by the Griffith criterion is sensitive to both the andσ.Therefore,it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.

Comparison between Diastolic Subendocardial Tissue Pressures Measured Directly or Calculated from Pressure-Flow Relations

Changes in intramyocardial tissue pressure modulate the relationship between coronary pressure and flow during the cardiac cycle. The present study compared the relation between measured and calculated diastolic subendocardial tissue pressure and coronary pressure at zero flow in anesthetized dogs after modulation of either coronary sinus (i.e. Fogarty catheter) or left ventricular intracavity (i.e. volume loading) pressure. Experiments were conducted in anesthetized, instrumented dogs;coronary pressure flow relations were constructed during pharmacologic vasodilatation and intramyocardial tissue pressure was measured using micromanometer pressure sensors. Elevated coronary sinus pressures did not affect subendocardial pressure-flow relations signifying that diastolic tissue pressure within this layer is the effective coronary back pressure. Higher left ventricular intracavity pressure did not affect either diastolic subendocardial tissue pressure or pressure flow relations within this layer. Results show a direct linear relation (y = 1.106x - 0.652;r2 = 0.59. P = 0.001) between measured and calculated diastolic subendocardial tissue pressure and coronary pressure at zero-flow over a wide range of pressures after either LV systemic or coronary sinus pressure modulation. Knowledge of back pressure in the subendocardium is useful for the evaluation of efficacy of cardiac interventions on myocardial perfusion particularly at the level of the microcirculation.

Dynamic responses and failure mechanisms of the existing tunnel under transient excavation unloading of an adjacent tunnel

Engineering disasters(e.g.rock slabbing and rockburst)of the tunnel groups induced by the transient excavation of an adjacent tunnel threaten the stability of the existing tunnel,especially for those excavated by using the drill and blast tunneling(D&B).However,the dynamic response and failure mechanism of surrounding rocks of the existing tunnel caused by adjacent transient excavation are not clear due to the difficulty in conducting field tests and laboratory experiments.Therefore,a novel transient unloading experimental system for deep tunnel excavation was proposed in this study.The real stress path and the unloading rate can be reproduced by using this proposed system.The experiments were conducted for observing the dynamic response of the existing tunnel induced by adjacent transient excavation under different lateral pressure coefficients l(?0.4,0.6,0.8,1,1.2,1.4,1.6,1.8)with a polymethyl methacrylate(PMMA)specimen.The propagation of the impact wave and unloading surface wave was detected through the digital image correlation(DIC)analysis.The reflection of the unloading surface wave on the incident side of the existing tunnel(tunnel-E)was observed and analyzed.Moreover,the dynamic characteristics of the stress redistribution,the particle displacement and vibration velocity of surrounding rocks of tunnel-E were analyzed and summarized.In addition,the Mohr-Coulomb(MeC)failure criterion with tension cut-off was adopted to evaluate the stability of the existing tunnel under adjacent transient excavation.The results indicate that the incident side of the existing tunnel under the dynamic disturbance of transient excavation of an adjacent tunnel was more prone to fail,followed by the shadow side and the top/bottom side.

高渗压与循环加卸载环境下开挖卸荷岩体力学特性试验研究

探究高渗压与循环加卸载环境下深部开挖卸荷岩体力学特性的演化规律,有助于揭示复合荷载作用下工程开挖卸荷围岩的变形破坏机理。从区分开挖扰动强度与渗压量级入手,以高渗压环境下遭受开挖扰动的卸荷岩体为对象,开展了考虑特定孔压与循环荷载复合作用条件下的三轴加卸载试验。结果表明:(1)卸荷量级直接影响循环加卸载过程岩样的变形规律及其破坏强度,孔隙水压促进了岩样循环加卸载过程的拉剪破坏;(2)孔压增幅加剧了同量级卸荷岩样循环加卸载过程的延性变形及强度衰减,且卸荷岩样的轴向、环向与体积变形曲线均在2MPa孔压时产生波动;(3)伴随孔压增加,岩样卸荷量级为30%时的环向变形呈先增加后减小的趋势,而岩样卸荷量级为60%时的环向变形呈现先减小后增加的规律;(4)伴随卸荷量级与孔压增加,岩样破坏时端部裂隙的倾角逐渐增大,沿岩样轴向产生的拉剪破裂面愈加凸显。

各向异性层状千枚岩渗透率及有效孔隙率试验研究

采用岩石全自动三轴伺服仪和气体渗透装置,对一种致密的各向异性层状千枚岩开展了气体渗透率及有效孔隙率试验,研究常规三轴压缩和围压循环加卸载2种应力路径下,气体渗透率、有效孔隙率随层理倾角及偏应力的演化规律。结果表明:围压相同时,岩样的初始气体渗透率k0随着层理倾角β的增大呈“W”型变化,在β=45°时取最大值;在围压循环加卸载过程中,气体渗透率先随围压的加载而减小,后随围压的卸载而增大,卸载时的气体渗透率小于加载时的渗透率;层状千枚岩有效孔隙率和气体渗透率呈指数关系;平行于层理方向的气体渗透率远大于垂直于层理方向的气体渗透率;岩样有效孔隙率和气体渗透率随偏应力变化经历初始压密阶段、线弹性阶段和塑性变形阶段,随着偏应力的增大,岩样有效孔隙率和气体渗透率先减小,接着保持稳定,最后快速增大,并在岩样应力-应变曲线斜率接近于0时达到最大值。

三维动静加载下煤的本构模型及卸荷破坏特征

为研究非静水压条件下煤体动力学性能及动力扰动后卸荷破坏特征,在三维动静加载实验的基础上,研究了卸荷方式对动力扰动后卸荷煤样宏观破坏特性的影响。首先,采用Ф50 mm的分离式霍普金森压杆系统,开展三维动静加载下煤样的动力学实验,研究轴压、应变率对煤样动力学响应规律的影响;其次,基于响应曲面理论,借助中心复合试验法,构建考虑因素交互作用的回归模型,并分析单因素及因素交互作用的显著性;然后,结合因素交互作用、Weibull分布、Drucker-Prager准则,修正煤的强度型统计损伤本构模型,对比理论与实验结果,验证模型可靠性;最后,借助加卸荷电液伺服装置,探究轴压、冲击气压、卸荷方式对煤样破坏特征的影响及作用机制。结果表明,构建的强度型统计损伤模型,相关系数R~2≥0.88,可表征煤样动力学响应行为。冲击后同步卸荷的煤样多呈层裂破坏,拉伸界面随轴压增大而后移直至消失,无法形成层裂破坏;非同步卸荷下煤样破坏形式主要包括整体完整、层裂、压剪破坏,而当冲击气压0.4~0.6 MPa,轴压14.5 MPa时,表现为“层裂+压剪”混合破坏。

加卸载花岗岩强度与岩爆倾向性试验研究

为了进一步提高硬性花岗岩岩爆倾向性预测水平,系统开展了花岗岩巴西劈裂、单/三轴和不同卸围压速率应力路径下的岩石力学试验,详细分析了花岗岩强度和岩爆倾向性特征。研究结果表明:花岗岩在主应力σ_(3)–σ_(1)平面内,不同应力路径下的强度受围压和卸围压速率影响显著,呈带状分布;在τ_(oct)–(σ_(1)+σ_(3))/2平面内,不同加卸载应力路径下的强度都呈良好的线性特征。据此建立了花岗岩八面体强度计算通式,可统一表达不同加卸载应力路径;针对花岗岩硬岩的压密和屈服特性不明显,弹性特性显著的特征,提出了简化剩余弹性能指数岩爆分级法;并依据花岗岩试验岩样破坏形态和破坏声学特征,对已有花岗岩岩爆等级进行了细分。揭示了在相同初始围压下,卸围压速率越大,简化剩余弹性能指数越大,岩爆倾向性越强;相同卸围压速率下,初始围压越大,简化剩余弹性能指数也越大,岩爆倾向性也越强。研究成果可为更科学合理的评估花岗岩岩爆倾向性提供理论参考。

基坑开挖卸荷对下卧隧道压力拱的影响研究

城市地下空间的开发与利用日益增多,运营的城市隧道周边不可避免地需要开挖,而隧道上方基坑的开挖卸荷对既有隧道压力拱的形成存在较大影响。针对前人研究,总结了基坑开挖3种卸荷比模型,并依据压力拱内外边界判别方法,通过数值模拟研究了基坑开挖卸荷对下卧隧道压力拱形成的影响作用。结果表明:隧道拱顶岩土体受到上方基坑两侧岩土体侧压力的综合作用,相较于一维卸荷比N 1,二维卸荷比N 2与压力拱边界的相关性更为显著。基于基坑开挖对下卧隧道压力拱形成的影响分析,提出了基坑开挖卸荷的工程影响分区,即一般影响区、次要影响区、显著影响区、强烈影响区;基坑开挖宽度L不大于D且基坑开挖深度h小于0.15H时,视为一般影响区;基坑开挖宽度L不大于D且基坑开挖深度h介于0.15H与0.225H之间时,视为显著影响区;基坑开挖宽度L大于D且其二维卸荷比N 2小于0.33时,视为次要影响区;基坑开挖的二维卸荷比N 2不小于0.33时,视为强烈影响区。

卸围压下弱胶结软岩分数阶蠕变损伤本构模型

为研究地下硐室开挖卸荷诱发的软岩蠕变损伤特征,以西部矿区弱胶结软岩为研究对象,利用GDS HPTAS开展了分级卸围压蠕变试验,研究了不同含水条件下弱胶结软岩卸围压下蠕变特征和蠕变速率特征。基于稳态蠕变速率倒数的方法,确定了弱胶结软岩长期强度和含水率的数学指数函数关系。基于蠕变速率曲线特征提出了一种确定衰减蠕变与等速蠕变分界点t_1和等速蠕变与加速蠕变分界点t_2的新方法。引入Riemann-Liouville分数阶积分算子和负时间指数损伤演化变量,定义了非线性损伤Abel黏壶,建立了一个包括弹性元件、黏弹性损伤元件、黏性元件和非线性黏塑性损伤元件的六元件分数阶蠕变损伤本构模型。基于试验结果,采用Trust-Region算法进行了模型参数识别和敏感性分析。结果表明,所建立的模型具有物理意义明确、与试验值吻合度较高等特点,可较为准确地反映开挖卸荷条件下弱胶结软岩蠕变损伤特性,对保障地下工程长期稳定性具有重要的意义。

分级循环卸-加围压下粉砂岩的力学特征

针对不同的实际工程,开展不同应力路径的试验来研究岩体的力学特性是解决实际问题的关键。为研究粉砂岩在围压循环卸-加载特殊应力路径下的力学特征,采用MTS815岩石力学测试系统开展不同轴力水平下分级循环卸-加载围压试验,研究不同轴力水平下轴、环向塑性应变及弹性模量的演化特征,并结合耗散能量的计算,分析能量演化与试件变形破坏之间的关系。结果表明:随着循环次数的增加,滞回环向应变增大方向移动,卸-加围压下应力-应变曲线逐渐闭合,滞回环间距整体表现为由“疏”到“密”的变化特征;单一变量时,围压卸载等级越低弹性模量越低,轴力水平越低弹性模量越高,弹性模量受轴力水平和围压卸载等级两种参量共同作用;单次循环中环向塑性应变在数值上总是大于对应的轴向塑性应变,循环卸-加围压特殊应力路径下,高轴力水平下岩石抵抗塑性变形的能力要强于低轴力水平;岩石破坏最终所耗散的总能量与轴力水平一定程度上呈线性正相关。

活动门试验中土压力盒标定方法

为确保活动门试验结果的准确性,根据试验填土深度的不同,对一批相同型号的电阻式土压力盒进行了垂直方向上的分级加载和卸载标定,并考虑标定装置内壁摩擦力影响,修正了作用在土压力盒上的有效加载和卸载应力。通过对加卸载过程进行离散元模拟,证明有效加载和卸应力修正方法较为合理。标定试验结果表明,加载过程中微应变量-有效应力曲线呈线性变化,可使用线性函数拟合;卸载过程中微应变量-有效应力曲线存在明显的滞后现象,且滞后程度随有效加载应力的增大而增大,可使用单指数曲线拟合。标定土压力盒后,开展了填土试验,结果表明土压力盒不宜在压力过小或填土深度过小时使用。