利用合成岩體模擬橫向等向性岩體之基礎承載力

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Title:	利用合成岩體模擬橫向等向性岩體之基礎承載力
Authors:	黃致維;Huang, Chih-Wei
Contributors:	土木工程學系
Keywords:	合成岩體;PFC3D;橫向等向性;正定性;基礎承載力;synthetic rock mass;PFC3D;transversely isotropic;constitutive law;bearing capacity
Date:	2020-11-09
Issue Date:	2021-03-18 16:29:11 (UTC+8)
Publisher:	國立中央大學
Abstract:	岩體因微觀組構優選方位或不連續面在力學、水力傳導等性質受方向所控制，我們稱之為岩體之異向性。而基礎工程配置的方位與異向性岩體之關係亦將顯著影響基礎之承載行為，因此如何評估不連續面在何種方位條件下係屬有利或不利的等級，為基礎工程成敗與否的關鍵因素。本研究利用PFC3D模擬橫向等向性岩體之力學行為及基礎承載行為。首先進行單壓試驗之模擬，以檢核顆粒微觀參數所體現之巨觀岩石力學行為，再求取一系列彈性常數建立橫向等向性岩體之組成律，並與過往理論進行驗證。接著針對不同裂隙位態（走向、傾角）及裂隙條件（裂隙程度、費雪常數），進行一系列極限承載力之模擬試驗，以探討不連續面幾何特徵對承載力、沉陷量及裂縫發展之影響。數值分析結果顯示：（1）含單一裂隙方向之岩體，其力學行為可視為巨觀橫向等向性，組成律柔度矩陣符合正定性，且變形性符合異向性彈性力學之預測。（2）針對Asan片麻岩室內實驗之結果進行力學行為之擬合，說明了合成岩體可以模擬出真實岩體之力學行為。（3）完整岩體之極限承載力與Bell solution (1915)計算得到之理論強度極為接近，且裂縫發展過程與Goodman (1989)描述之破壞過程相符合。（4）橫向等向性岩體之極限承載力與傾角呈異向性關係，而極限狀態下的裂縫數及沉陷量與傾角之關係亦然。（5）觀察不同傾角之岩體於承載試驗下之裂縫發展，發現裂縫會沿著原生裂隙方向生成，且與Bray solution (1977)計算得到之等值應力方向一致。（6）隨著裂隙條件(P32、κ)的增加，承載力的異向性亦隨之增加，且裂縫發展的方向性更為明顯。（7）傾角α (°)對於承載力的影響大於裂隙走向與基礎長軸之夾角γ (°)，且同傾角下之γ (°)於較大的角度時，承載力普遍大於較小的γ (°)。（8）基礎配置方向對承載力亦有相當之影響，其配置方向與裂隙走向垂直較與走向平行為佳，故本文提出傾角與基礎配置方向優劣分級。 ;The properties of rock mass such as mechanical behavior and hydraulic conductivity are controlled by the direction because of the orientation of discontinuities. The relationship between the orientation of the foundation configuration and the anisotropic rock mass will also significantly affect the bearing behavior. Therefore, how to evaluate the orientation of discontinuity is favorable or unfavorable playing an important role in rock engineering. PFC3D is adopted in this study to simulate uniaxial compressive tests, triaxial compressive tests and bearing capacity tests on transversely isotropic rock mass. The simulation of the rock test is used to check the macroscopic rock mechanical behavior by the microscopic parameters of the particles. Through the simulations, we obtain a series of elastic constants to establish the constitutive law of transversely isotropic synthetic rock mass, and verify with the previous theories. In addition, this study carries out a series of simulation tests on the ultimate bearing capacity. By adjusting different fracture orientation (dip angles and strike) and fracture condition (fracture intensity and Fisher constant) respectively, we can discuss the influences of the discontinuity on the bearing capacity, settlement, and crack development. Based on the numerical simulation results：(1) The mechanical behavior of rock mass which involves the single direction of DFN is regarded as transversely isotropy, and the deformability conforms to the prediction of anisotropic elastic mechanics. (2) The experimental results of Asan gneiss can be fitting by using SRM, it illustrates that SRM can simulate the mechanical behavior of real rock mass. (3) The bearing capacity of the intact rock is close to the theoretical strength calculated by Bell solution (1915), and the development of cracks can be compared with the footing test results observed by Goodman (1989). (4) In a transversely isotropic rock, the relationship between ultimate bearing capacity and joint dip angles shows U-type. In addition, the crack number and settlement with different joint dip angles reveal the analogous shape of ultimate bearing capacity. (5) Observing the development of cracks in rock masses with different joint dip angles from bearing capacity tests. It shows that the cracks will be generated along the direction of the inherent fractures, which is consistent with the equivalent stress direction calculated by Bray solution (1977). (6) With the fracture condition (P32、κ) increases, the anisotropy of bearing capacity will be increased, and the direction of crack development will become more obvious. (7) The influence of the α (dip angle) on the bearing capacity is greater than the γ (the angle between the strike and the long axis of the foundation). When γ at the larger angle, the bearing capacity is generally higher than the γ at the smaller angle. (8) The configuration direction of the foundation also has the significant influence on the bearing capacity. When the foundation vertical to the strike, the bearing capacity will be better than it parallel to the strike.
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