高、低壓下砂土剪切帶及砂土—結(jié)構(gòu)界面層力學(xué)行為演化研究
發(fā)布時(shí)間：2018-08-20 11:35
【摘要】：論文以巖土材料內(nèi)部剪切帶及巖土體-結(jié)構(gòu)體接觸界面層問題為背景，針對(duì)應(yīng)變局部化現(xiàn)象尤為突出的砂土材料，通過(guò)室內(nèi)物理試驗(yàn)、模型理論分析構(gòu)建了能夠?qū)⑸巴脸合录裘涇浕⒏邏合录艨s硬化特性進(jìn)行統(tǒng)一的砂土材料模型，并結(jié)合無(wú)網(wǎng)格方法實(shí)現(xiàn)了砂土剪切帶、砂土-結(jié)構(gòu)接觸界面層產(chǎn)生、發(fā)展過(guò)程的模擬計(jì)算，使得對(duì)巖土工程真實(shí)的破壞過(guò)程進(jìn)行描述成為可能。 通過(guò)砂土室內(nèi)試驗(yàn)，對(duì)砂土常壓至高壓范圍內(nèi)的強(qiáng)度、變形特性進(jìn)行了系統(tǒng)研究，獲得結(jié)論有：①因高壓條件下砂土出現(xiàn)一定量的顆粒破碎，破碎顆粒充填砂樣原有結(jié)構(gòu)，使得砂樣孔隙比迅速減小。砂土在0至8MPa范圍內(nèi)等向壓縮曲線呈指數(shù)衰減型，孔隙比-圍壓擬合關(guān)系可表示為e a b exp c ln p。砂土的壓縮特性具有明顯的粒徑效應(yīng)，大尺寸砂土顆粒在高壓力下較小尺寸顆粒更易破碎，會(huì)產(chǎn)生較大的孔隙比變化。②砂土峰值應(yīng)力比受砂土粒徑、圍壓共同影響，峰值強(qiáng)度公式不再符合經(jīng)典的M-C強(qiáng)度準(zhǔn)則，而殘余應(yīng)力比對(duì)應(yīng)的強(qiáng)度公式則基本不受粒徑、圍壓的影響，符合典型的無(wú)粘性摩擦型巖土材料特性。③砂土材料在剪切過(guò)程中存在明顯的臨界狀態(tài)，不同圍壓條件下剪切穩(wěn)定時(shí)的孔隙比e與平均應(yīng)力p間的擬合曲線關(guān)系表達(dá)式為e l m exp n ln p，這一指數(shù)衰減曲線可作為砂土在剪切過(guò)程中最終趨于穩(wěn)定的一個(gè)狀態(tài)線。 基于對(duì)砂土強(qiáng)度、變形特性的分析，構(gòu)建了能夠?qū)⑸巴良裘涇浕凹艨s硬化特性進(jìn)行統(tǒng)一的砂土模型。模型采用應(yīng)力路徑相關(guān)因子對(duì)等向壓縮路徑獲得的屈服面硬化參數(shù)進(jìn)行修正得到與應(yīng)力路徑無(wú)關(guān)的砂土當(dāng)前屈服面硬化參數(shù)，同時(shí)由砂土臨界狀態(tài)參數(shù)推導(dǎo)得出能夠體現(xiàn)砂土臨界特性的潛在屈服面硬化參數(shù)。根據(jù)當(dāng)前、潛在屈服面間的關(guān)系定義了能夠反映砂土當(dāng)前狀態(tài)的動(dòng)態(tài)密實(shí)參數(shù)及潛在強(qiáng)度。模型共有涉及彈性、臨界破壞強(qiáng)度、當(dāng)前屈服面及潛在屈服面的參數(shù)共計(jì)10個(gè)，各參數(shù)物理意義明確，均可通過(guò)室內(nèi)三軸試驗(yàn)獲得。 通過(guò)試驗(yàn)得知砂土-結(jié)構(gòu)面接觸剪切力學(xué)特性受砂土顆粒與結(jié)構(gòu)形貌相對(duì)尺度的影響呈三段式，存在著兩個(gè)明顯的特征點(diǎn)，分別定義為“極限相對(duì)尺度”與“臨界相對(duì)尺度”。在“極限相對(duì)尺度”Rmax前，砂土-結(jié)構(gòu)面接觸力學(xué)特性受形貌尺度的影響較為明顯，接觸剪切作用機(jī)制為接觸剪切力用于克服砂土顆粒跨越結(jié)構(gòu)表面的粗糙形貌的阻力，論文將這一相對(duì)尺度范圍內(nèi)的砂土-結(jié)構(gòu)接觸剪切模式定義為“粗糙摩擦接觸”機(jī)制，相應(yīng)的結(jié)構(gòu)面類型為“粗糙頻”結(jié)構(gòu)面。在“極限相對(duì)尺度”Rmax之后，砂土-結(jié)構(gòu)面接觸力學(xué)特性受形貌尺度的影響基本消失，此時(shí)的接觸剪切作用機(jī)制為砂土顆粒群內(nèi)部發(fā)生翻滾跨越耗能，論文將“極限相對(duì)尺度”Rmax之后的砂土-結(jié)構(gòu)面接觸剪切模式定義為“形貌約束接觸”機(jī)制，相應(yīng)的結(jié)構(gòu)面類型為“形貌頻”結(jié)構(gòu)面。論文針對(duì)不同結(jié)構(gòu)面類型提出了不同的接觸力學(xué)特性參數(shù)獲取方法。針對(duì)“粗糙頻”結(jié)構(gòu)面，采用砂土-結(jié)構(gòu)面接觸剪切試驗(yàn)獲得峰值接觸剪應(yīng)力與殘余接觸剪應(yīng)力，，得到的峰值接觸摩擦角與殘余接觸摩擦角即對(duì)應(yīng)于計(jì)算中的接觸靜止摩擦角與滑動(dòng)摩擦角；“形貌頻”結(jié)構(gòu)面在接觸剪切中對(duì)砂土顆粒提供形貌約束邊界，其結(jié)構(gòu)表面形貌特征需在計(jì)算建模中進(jìn)行真實(shí)描述。 論文分析明確砂土剪切帶及砂土-結(jié)構(gòu)接觸界面層演化模擬計(jì)算中的應(yīng)變軟化計(jì)算不收斂以及大變形網(wǎng)格畸變兩個(gè)關(guān)鍵難點(diǎn)。通過(guò)分析相關(guān)計(jì)算理論并比較現(xiàn)有數(shù)值計(jì)算方法，選用無(wú)網(wǎng)格SPH方法作為論文砂土模型的二次開發(fā)平臺(tái)，將模型子程序與之進(jìn)行對(duì)接編譯生成新的SPH求解器，克服了計(jì)算難點(diǎn)使得對(duì)砂土等應(yīng)變軟化材料的大應(yīng)變問題模擬計(jì)算成為可能。利用新生成的求解器開展砂土自身剪切及砂土-結(jié)構(gòu)接觸界面剪切試驗(yàn)?zāi)M，分析了不同邊界條件下的力學(xué)行為以及應(yīng)力、應(yīng)變場(chǎng)的發(fā)生、發(fā)展過(guò)程，再現(xiàn)了試驗(yàn)中的應(yīng)變局部化剪切帶及界面層現(xiàn)象與特征，獲得結(jié)論：①礫砂在常壓下內(nèi)部產(chǎn)生應(yīng)變局部化剪切帶與其應(yīng)變軟化、剪切體脹特性密切相關(guān)；高壓下試樣呈現(xiàn)應(yīng)變硬化、剪切體縮特性，應(yīng)變局部化剪切帶不再產(chǎn)生。②常壓下砂土雙軸力學(xué)特性受端部邊界影響，端部約束則會(huì)增大峰值應(yīng)力，試樣內(nèi)部應(yīng)變局部化區(qū)域也較為集中，產(chǎn)生明顯的單對(duì)“共軛”對(duì)稱應(yīng)變局部化剪切帶；端部光滑邊界條件下的應(yīng)變局部化發(fā)展相對(duì)分散而呈現(xiàn)多對(duì)“共軛”對(duì)稱應(yīng)變局部化帶狀區(qū)域。③砂土與結(jié)構(gòu)面界面剪切過(guò)程中存在著顯著的應(yīng)變局部化區(qū)域，剪切力學(xué)特性隨結(jié)構(gòu)面相對(duì)形貌尺度的增大而逐漸趨近于砂土自身剪切力學(xué)特性，且隨結(jié)構(gòu)面的下移，剪切特性受結(jié)構(gòu)面影響逐漸消失，最終與砂土自身剪切特性相近。
[Abstract]:Based on the problems of internal shear band of geotechnical materials and interface layer between geotechnical body and structure, aiming at the sandy soil material with prominent strain localization phenomenon, a unified sandy soil material model is constructed through laboratory physical experiments, which can soften the sandy soil under normal pressure and perform the shear-dilatancy-hardening characteristics under high pressure. With the meshless method, the sandy soil shear band, the sandy soil-structure interface layer and the development process are simulated, which makes it possible to describe the real failure process of geotechnical engineering.
The strength and deformation characteristics of sand from normal pressure to high pressure are systematically studied by laboratory tests. The conclusions are as follows: (1) Under high pressure, a certain amount of particle breakage occurs in sand and the original structure of sand sample is filled with broken particles, which makes the porosity ratio of sand sample decrease rapidly. The isotropic compression curve of sand in the range of 0 to 8 MPa is exponential. The relationship between porosity ratio and confining pressure can b e expressed as e a B exp C ln P. The compression characteristics of sand have obvious particle size effect. The large size sand particles are easier to break up under high pressure, and the smaller size sand particles will produce larger pore ratio changes. 2 The peak stress ratio of sand is affected by the particle size of sand, confining pressure and peak strength formula. It is no longer in accordance with the classical M-C strength criterion, but the strength formula of the residual stress ratio is not affected by the particle size and confining pressure, which conforms to the characteristics of the typical non-viscous friction geotechnical materials. The relation expression of fitting curve is e l m exp n n n n n n n p, which can be used as a state line of sand which tends to be stable in the process of shearing.
Based on the analysis of the strength and deformation characteristics of sand, a sand model which can unify the dilatancy softening and shear hardening characteristics of sand is constructed. The potential yield surface hardening parameters are derived from the critical state parameters of sand. According to the relationship between the potential yield surfaces, the dynamic compaction parameters and the potential strength are defined to reflect the current state of sand. The total number is 10, and the physical meaning of each parameter is clear, which can be obtained by indoor three axis test.
The results show that the shear behavior of sand-structure interface is affected by the relative scale of sand particles and structure morphology in three-stage form, and there are two distinct characteristic points, which are defined as "limit relative scale" and "critical relative scale", respectively. The mechanism of contact shear is that contact shear force is used to overcome the resistance of sand particles across the roughness of the structure surface. In this paper, the sand-structure contact shear model is defined as "rough friction contact" mechanism, and the corresponding structure surface type is "rough frequency" structure. Surface. After Rmax, the influence of morphology scale on the contact mechanical properties of sandy soil-structural plane disappears, and the mechanism of contact shear action is the energy dissipation of rollover within sandy soil particles. In this paper, the contact shear mode of sandy soil-structural plane after Rmax is defined as morphology constraint. In this paper, different methods for obtaining contact mechanical parameters are proposed for different types of structural planes. For "rough frequency" structural planes, the peak contact shear stress and residual contact shear stress are obtained by sand-structural plane contact shear test, and the peak joint is obtained. The contact friction angle and the residual contact friction angle correspond to the contact static friction angle and the sliding friction angle in calculation, and the "topography frequency" structure plane provides the topography constraint boundary for sand particles in contact shear, and the topographic characteristics of the structure surface need to be described in the calculation model.
In this paper, two key problems in the simulation of sand shear band and the evolution of sand-structure interface layer, i.e. non-convergence of strain softening calculation and large deformation mesh distortion, are analyzed and clarified. A new SPH solver is generated by connecting and compiling the model subroutine with it, which overcomes the computational difficulties and makes it possible to simulate the large strain problem of strain softening materials such as sand. The new solver is used to simulate the self-shearing of sand and the shearing test of sand-structure interface. The forces under different boundary conditions are analyzed. The phenomena and characteristics of strain localization shear band and interfacial layer are reproduced by the occurrence and development of stress and strain field. The results show that: (1) strain localization shear band is closely related to strain softening and shear dilatancy in gravel sand under normal pressure; the specimen shows strain hardening and shear volume shrinkage under high pressure. The strain localization shear bands do not occur at normal pressure. 2. The biaxial mechanical properties of sandy soils are affected by the end boundary, and the peak stress increases with the end constraint. The strain localization region in the specimen is also concentrated, resulting in a single pair of "conjugate" symmetrical strain localization shear bands. (3) There is a significant strain localization region in the interfacial shear process between sandy soil and structural plane, and the shear mechanical properties of sandy soil gradually approach the shear mechanical properties of sandy soil with the increase of the relative morphological scale of structural plane, and shear with the downward movement of structural plane. The influence of the structural plane gradually disappeared, which was similar to the shear property of the sand itself.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU43
本文編號(hào)：2193453
[Abstract]:Based on the problems of internal shear band of geotechnical materials and interface layer between geotechnical body and structure, aiming at the sandy soil material with prominent strain localization phenomenon, a unified sandy soil material model is constructed through laboratory physical experiments, which can soften the sandy soil under normal pressure and perform the shear-dilatancy-hardening characteristics under high pressure. With the meshless method, the sandy soil shear band, the sandy soil-structure interface layer and the development process are simulated, which makes it possible to describe the real failure process of geotechnical engineering.
The strength and deformation characteristics of sand from normal pressure to high pressure are systematically studied by laboratory tests. The conclusions are as follows: (1) Under high pressure, a certain amount of particle breakage occurs in sand and the original structure of sand sample is filled with broken particles, which makes the porosity ratio of sand sample decrease rapidly. The isotropic compression curve of sand in the range of 0 to 8 MPa is exponential. The relationship between porosity ratio and confining pressure can b e expressed as e a B exp C ln P. The compression characteristics of sand have obvious particle size effect. The large size sand particles are easier to break up under high pressure, and the smaller size sand particles will produce larger pore ratio changes. 2 The peak stress ratio of sand is affected by the particle size of sand, confining pressure and peak strength formula. It is no longer in accordance with the classical M-C strength criterion, but the strength formula of the residual stress ratio is not affected by the particle size and confining pressure, which conforms to the characteristics of the typical non-viscous friction geotechnical materials. The relation expression of fitting curve is e l m exp n n n n n n n p, which can be used as a state line of sand which tends to be stable in the process of shearing.
Based on the analysis of the strength and deformation characteristics of sand, a sand model which can unify the dilatancy softening and shear hardening characteristics of sand is constructed. The potential yield surface hardening parameters are derived from the critical state parameters of sand. According to the relationship between the potential yield surfaces, the dynamic compaction parameters and the potential strength are defined to reflect the current state of sand. The total number is 10, and the physical meaning of each parameter is clear, which can be obtained by indoor three axis test.
The results show that the shear behavior of sand-structure interface is affected by the relative scale of sand particles and structure morphology in three-stage form, and there are two distinct characteristic points, which are defined as "limit relative scale" and "critical relative scale", respectively. The mechanism of contact shear is that contact shear force is used to overcome the resistance of sand particles across the roughness of the structure surface. In this paper, the sand-structure contact shear model is defined as "rough friction contact" mechanism, and the corresponding structure surface type is "rough frequency" structure. Surface. After Rmax, the influence of morphology scale on the contact mechanical properties of sandy soil-structural plane disappears, and the mechanism of contact shear action is the energy dissipation of rollover within sandy soil particles. In this paper, the contact shear mode of sandy soil-structural plane after Rmax is defined as morphology constraint. In this paper, different methods for obtaining contact mechanical parameters are proposed for different types of structural planes. For "rough frequency" structural planes, the peak contact shear stress and residual contact shear stress are obtained by sand-structural plane contact shear test, and the peak joint is obtained. The contact friction angle and the residual contact friction angle correspond to the contact static friction angle and the sliding friction angle in calculation, and the "topography frequency" structure plane provides the topography constraint boundary for sand particles in contact shear, and the topographic characteristics of the structure surface need to be described in the calculation model.
In this paper, two key problems in the simulation of sand shear band and the evolution of sand-structure interface layer, i.e. non-convergence of strain softening calculation and large deformation mesh distortion, are analyzed and clarified. A new SPH solver is generated by connecting and compiling the model subroutine with it, which overcomes the computational difficulties and makes it possible to simulate the large strain problem of strain softening materials such as sand. The new solver is used to simulate the self-shearing of sand and the shearing test of sand-structure interface. The forces under different boundary conditions are analyzed. The phenomena and characteristics of strain localization shear band and interfacial layer are reproduced by the occurrence and development of stress and strain field. The results show that: (1) strain localization shear band is closely related to strain softening and shear dilatancy in gravel sand under normal pressure; the specimen shows strain hardening and shear volume shrinkage under high pressure. The strain localization shear bands do not occur at normal pressure. 2. The biaxial mechanical properties of sandy soils are affected by the end boundary, and the peak stress increases with the end constraint. The strain localization region in the specimen is also concentrated, resulting in a single pair of "conjugate" symmetrical strain localization shear bands. (3) There is a significant strain localization region in the interfacial shear process between sandy soil and structural plane, and the shear mechanical properties of sandy soil gradually approach the shear mechanical properties of sandy soil with the increase of the relative morphological scale of structural plane, and shear with the downward movement of structural plane. The influence of the structural plane gradually disappeared, which was similar to the shear property of the sand itself.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU43
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