广义有效应力及剪切波速度与土的力学特性的研究及其在路基工程中的应用

Study on Generalized Effective Stress and Shear Wave Velocity with Soil Behaviors and Its Application in Subgrade Engineering (An Abstract of the Ph.D. Thesis)

In classical soil mechanics, many of theories are based on non-cohesive soils and normally consolidated saturated cohesive soils. Constitutive relations at present are actually developed on remolded or non-cohesive soils. In fact, soils in geotechnical engineering are often structural undisturbed and unsaturated. These soils have nothing in common with normally consolidated saturated soils, but none of theories is mature for them. Subgrade of existing railway is hard to be reinstated in a short time if its structural strength sustains losses. Thus it is necessary to study on mechanical behaviors and to protect structural strength and to develop test and appraise procedure for these soils. With equivalent suction including all factors which can increase the resistance against sliding between soils particles, the generalized effective stress(G.E.S.), a equivalent effective stress, comes out, and all kinds of soils are united in the G.E.S. theory [1,2] .In this paper for mentioned problems, the following items are researched with G.E.S.. 1 Study on Generalized Effective Stress and Mechanical Behaviors of Expansive Soils For the purpose of research the laws of influence on strength and soils shear wave velocity from water content or saturation degree, the paper takes expansive soils as subjects, then experimental phenomena are emphasized, and experimental factors are controlled easily. Based on the test and existing achievements [3,4] , the article suggests following results: ① Compression curves of expansive soils with different water content can be normalized by G.E.S.. ② For unsaturated soils swelling pressure reflects change of generalized suction. In this paper, it is verified once again that third strength theory [3,4] (τ s=p s tg φ,τ s=mp s tg φ) is effective , and believed that the modified coefficient m in the equation relates to the definition and measure method of swelling pressure. The reason for requirement of m is that the soil is still under O.C. state at the end of swelling pressure constant volume test. For uncorrected swelling pressure, m ≥1, and for corrected swelling pressure, m ≤1. Besides shear and swelling pressure test, compression test succeeding swelling pressure test can determine the value of modification coefficient m . 2 Shear Wave Velocity and Generalized Effective Stress Shear wave velocity of soils relates to maximum shear modulus. There are some experimental equations for shear modulus. They are based on knowledge about sandy or normally consolidated soils. These soils are noted for weak dependence on structure and non-cohesion or less cohesion. G.E.S. theory believes that there is generalized suction to equal cohesion in result, and different generalized suction lead to different structural behavior. So structure soils with strong cohesion show no difference from sandy or normally consolidated soils in terms of the theory. In this way, equations of shear modulus or wave velocity can be developed. G.E.S. will instead of effective stress in these equations. Now, new equations are consistent to old equations for sandy soils, and have a bit difference for medium or low sensitive clay with less equivalent generalized suction which originate of less cohesion. Take experimental sense into account, the difference can be ignored. For unsaturated soils, above-mentioned idea is verified by test on Guangxi, Calcium soil and Nanjing soils with different water content. 3 Undrained Shear Strength and Generalized Effective Stress It is usually believed that ratio of undrained shear strength and OCR of O.C. soils have linear relationship in bilogarithmic coordinate [5] . The paper believed that generalized suction to originate of structure causes O.C. soil to depart from stable state, and similar suction also causes unsaturated or structural soils to depart also. Origins of suction may be different, but they play similar role in terms of strength theory. With current state and stable state analyzed, in like manner to calculate

In classical soil mechanics, many of theories are based on non-cohesive soils and normally consolidated saturated cohesive soils. Constitutive relations at present are actually developed on remolded or non-cohesive soils. In fact, soils in geotechnical engineering are often structural undisturbed and unsaturated. These soils have nothing in common with normally consolidated saturated soils, but none of theories is mature for them. Subgrade of existing railway is hard to be reinstated in a short time if its structural strength sustains losses. Thus it is necessary to study on mechanical behaviors and to protect structural strength and to develop test and appraise procedure for these soils. With equivalent suction including all factors which can increase the resistance against sliding between soils particles, the generalized effective stress(G.E.S.), a equivalent effective stress, comes out, and all kinds of soils are united in the G.E.S. theory [1,2] .In this paper for mentioned problems, the following items are researched with G.E.S.. 1 Study on Generalized Effective Stress and Mechanical Behaviors of Expansive Soils For the purpose of research the laws of influence on strength and soils shear wave velocity from water content or saturation degree, the paper takes expansive soils as subjects, then experimental phenomena are emphasized, and experimental factors are controlled easily. Based on the test and existing achievements [3,4] , the article suggests following results: ① Compression curves of expansive soils with different water content can be normalized by G.E.S.. ② For unsaturated soils swelling pressure reflects change of generalized suction. In this paper, it is verified once again that third strength theory [3,4] (τ s=p s tg φ,τ s=mp s tg φ) is effective , and believed that the modified coefficient m in the equation relates to the definition and measure method of swelling pressure. The reason for requirement of m is that the soil is still under O.C. state at the end of swelling pressure constant volume test. For uncorrected swelling pressure, m ≥1, and for corrected swelling pressure, m ≤1. Besides shear and swelling pressure test, compression test succeeding swelling pressure test can determine the value of modification coefficient m . 2 Shear Wave Velocity and Generalized Effective Stress Shear wave velocity of soils relates to maximum shear modulus. There are some experimental equations for shear modulus. They are based on knowledge about sandy or normally consolidated soils. These soils are noted for weak dependence on structure and non-cohesion or less cohesion. G.E.S. theory believes that there is generalized suction to equal cohesion in result, and different generalized suction lead to different structural behavior. So structure soils with strong cohesion show no difference from sandy or normally consolidated soils in terms of the theory. In this way, equations of shear modulus or wave velocity can be developed. G.E.S. will instead of effective stress in these equations. Now, new equations are consistent to old equations for sandy soils, and have a bit difference for medium or low sensitive clay with less equivalent generalized suction which originate of less cohesion. Take experimental sense into account, the difference can be ignored. For unsaturated soils, above-mentioned idea is verified by test on Guangxi, Calcium soil and Nanjing soils with different water content. 3 Undrained Shear Strength and Generalized Effective Stress It is usually believed that ratio of undrained shear strength and OCR of O.C. soils have linear relationship in bilogarithmic coordinate [5] . The paper believed that generalized suction to originate of structure causes O.C. soil to depart from stable state, and similar suction also causes unsaturated or structural soils to depart also. Origins of suction may be different, but they play similar role in terms of strength theory. With current state and stable state analyzed, in like manner to calculate OC