含水率对重塑红黏土反复抗剪强度影响试验研究

doi:10.11872/j.issn.1005-2518.2021.05.210

Abstract

Abstract:

As a special soil，red clay is widely distributed in some areas of China.Due to the engineering problems such as slope cracking，subgrade subsidence and insufficient foundation bearing capacity，the strength characteristics of red clay is one of the main problems concerned by engineers，and the stability of red clay is closely related to safety production.In order to explore the influence of water content on the repeated shear strength of red clay，the repeated direct shear test was carried out on remolded red clay in Changzhi area of Shanxi Province.Because the water content of undisturbed soil in this area is between 17.0% and 23.7%，and the plastic limit water content is 20.34%，considering the law of test results and the influence of plastic limit，soil samples with five water contents of 15.0%，18.0%，19.5%，21.0% and 24.0% were prepared for test.The test results show that when no vertical pressure is applied， repeated direct shear is conducted on the sample，and the test is stopped when the sample’s strength gradually stabilizes.When there is no vertical pressure，the shear strength decreases and tends to be stable with the increase of shear times.The displacement of secondary shear to shear strength is less than that of the first shear，and the stable shear displacement is greater than that of the first shear.In the process of shearing，the shear strength has a negative linear relationship with the water content.When there is no vertical pressure，the shear strength is equal to the cohesion，and the shear strength is defined as the true cohesion.The vertical pressure of 50，100，150 and 200 kPa was applied to carry out the direct shear test.When there is vertical pressure，the shear strength decreases with the increase of water content.The internal friction angle and cohesion of shear strength index were obtained by physical expression fitting，and compared with the internal friction angle obtained by true cohesion and no vertical pressure.The internal friction angle obtained by the two kinds of analysis is basically close，and decreases with the increase of water content，and the decreasing range gradually increases.Due to the dilatancy effect in the test process，the true cohesion first increases and then decreases with the increase of water content，and the cohesion first decreases and then increases with the increase of water content.The contrast analysis shows that the difference of cohesion is obvious，so the difference index ratio of cohesion and true cohesion with vertical pressure is 0.75~9.96，and the change rule of the difference index ratio of cohesion is the same as the fitting cohesion，and the difference index ratio reaches the minimum when the water content is 19.5%.The empirical formula can provide some reference for the reasonable selection of soil parameters in the process of geotechnical investigation，design and excavation of mines in red clay area.

Key words: remolded red clay, water content, repeated shear test, shear strength, true cohesion, difference index ratio of cohesion

CLC Number:

TU411.7

Bin LIN,Zhuhua TIAN,Yuman CHEN. Experimental Study on Effect of Water Content on Repeated Shear Strength of Remolded Red Clay[J].Gold Science and Technology, 2021, 29(5): 680-689.

Figures/Tables 12

Fig.1

Table 1

Fig.2

Fig.3

Fig.4

Table 2

Fitting parameter values of the relationship bet-ween shear stress and water content at different shear times"

剪切次数/次	$a$	$b$	$R 2$
1	-10.5783	270.1575	0.9704
2	-5.5840	137.6000	0.9729
3	-2.9095	73.6614	0.9972
4	-2.9095	73.6614	0.9972

Table 2

Fig.5

Table 3

Fig.6

Table 4

Fitting values of cohesion（c）and friction angle （φ）parameters"

含水率/%	$c$ /kPa	$φ$ /（°）	$R 2$
15.0	45.35	41.14	0.999
18.0	34.71	40.48	0.974
19.5	29.15	37.80	0.958
21.0	31.91	24.20	0.998
24.0	40.54	10.40	0.911

Table 4

Table 5

Friction calculation values and fitting parameter values of internal friction angle"

含水率/%	真黏聚力（ $c'$ ）/kPa	不同竖向压力下的摩擦力（ $τ f - c'$ ）/kPa				内摩擦角（ $φ'$ ）/（°）	$R 2$
含水率/%	真黏聚力（ $c'$ ）/kPa	50 kPa	100 kPa	150 kPa	200 kPa	内摩擦角（ $φ'$ ）/（°）	$R 2$
15.0	4.63	82.37	130.49	173.07	213.79	48.87	0.9887
18.0	10.18	65.71	105.51	165.67	187.88	45.48	0.9917
19.5	16.66	42.57	98.10	138.82	158.26	40.66	0.9923
21.0	12.96	40.72	65.66	85.14	109.21	29.95	0.9903
24.0	3.70	42.58	59.23	66.64	70.71	23.23	0.9359

Table 5

Table 6

Calculated values of Δc and kc"

含水率/%	$? c$	$k c$
15.0	40.72	8.79
18.0	24.53	2.41
19.5	12.49	0.75
21.0	18.95	1.46
24.0	36.87	9.96

Table 6

References 0

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含水率/%	平行试样反复直剪次数/次
含水率/%	试样1	试样2	试样3	试样4	试样5	试样6	试样7	试样8
15.0	5	4	5	7	3	4	5	4
18.0	4	4	4	4	6	4	4	5
19.5	4	5	4	4	5	5	4	3
21.0	4	4	4	5	3	5	4	4
24.0	4	3	3	6	4	4	4	4

竖向压力/kPa	不同含水率下的抗剪强度/kPa
竖向压力/kPa	15.0%	18.0%	19.5%	21.0%	24.0%
50	87.00	75.89	59.23	53.68	46.28
100	135.12	115.69	114.76	78.62	62.93
150	177.70	175.85	155.48	98.10	70.34
200	218.42	198.06	174.92	122.17	74.41

Experimental Study on Effect of Water Content on Repeated Shear Strength of Remolded Red Clay

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