CN108228961B - Method for predicting collapse thickness of soft-lithoid sea-erosion cave top - Google Patents

Method for predicting collapse thickness of soft-lithoid sea-erosion cave top Download PDF

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CN108228961B
CN108228961B CN201711205121.XA CN201711205121A CN108228961B CN 108228961 B CN108228961 B CN 108228961B CN 201711205121 A CN201711205121 A CN 201711205121A CN 108228961 B CN108228961 B CN 108228961B
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常方强
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Abstract

The invention discloses a method for predicting collapse thickness of a weak dike sea erosion cave top, which comprises the following steps: (1) acquiring typhoon weather and sea erosion hole data: (2) the cohesive force c and the internal friction angle of the material are tested in a laboratory
Figure DDA0001483499440000011
Calculating the tensile strength sigmat(ii) a (3) Fitting the weakened tensile strength sigma according to a least square methodtThe relation with the seawater soaking time; (4) calculating the submergence time of the top of the sea erosion tunnel; (5) according to the submerging time, the tensile strength after weakening is calculated, and therefore the slumping thickness l is calculated; the method can predict or simulate the collapse thickness of the top of the weak karst sea chest under the action of waves, has reliable results, is simple and practical, and has important significance for understanding the development process of the sea chest.

Description

Method for predicting collapse thickness of soft-lithoid sea-erosion cave top
Technical Field
The invention relates to the field of geological disasters of coastal zones, in particular to a method for predicting collapse thickness of a weak lithoid sea erosion cave top.
Background
The sea erosion cave is a cave formed after the weak part of a rocky sea cliff is eroded by waves, and is different from the forming mechanism of a land cave in that the sea erosion cave is caused by mechanical erosion of waves. According to the weak characteristics of the sea cliff, the sea erosion caves are divided into three types, namely a joint fissure type sea erosion cave, a weak interlayer type sea erosion cave and a weak lithous type sea erosion cave, wherein the weak lithous type sea erosion cave has unique forming characteristics, and the width of the weak lithous type sea erosion cave in the horizontal direction is generally kept stable under the action of long-term waves; and the height in the vertical direction and the depth in the horizontal direction gradually increase as the wave continues to act. In typhoon weather, the front of the sea cliff is often watered, the wave height is increased, and the erosion capacity to the sea erosion hole is greatly enhanced. Except that the waves slowly erode, the lower part of the weak interlayer at the top of the cavern is suspended, so that when the strength is reduced to a certain degree, the weak interlayer at the top of the cavern is subjected to overall collapse, the disintegration volume is rapidly enlarged at one time, and the growth and development processes and the shape of the marine corrosion cavern are greatly influenced.
At present, the collapse thickness of the top of the weak rock vein sea erosion cave under the action of waves is predicted by no reliable method. In view of the above, a simple and practical prediction method with reliable results has important significance for determining the collapse thickness of the top of the weak karst sea erosion cave under the action of waves by human beings, understanding the development process of the sea erosion cave and further researching geological disasters in coastal zones.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a collapse thickness prediction method for the top of the weak karst sea erosion cave, and solves the problem that no reliable and simple method for predicting the collapse thickness of the top of the weak karst sea erosion cave under the action of waves exists in the background technology.
The technical scheme adopted by the invention for solving the technical problems is as follows: the method for predicting the collapse thickness of the top of the weak dike sea eroded cave comprises the following steps:
(1) acquiring typhoon weather and sea erosion hole data: including the average depth H of water in front of the sea cliff in typhoon weather, the average wave height H and the wave duration t0(ii) a Measuring the height h of the top of the weak rock vein type sea eroded cave0Width of weak dike a;
(2) taking a weak interlayer soil sample at the top of the hole, and testing the severe gamma, cohesive force c and internal friction angle of the weak interlayer soil sample in a laboratory
Figure BDA0001483499430000021
Calculating the tensile strength sigmat，
Figure BDA0001483499430000022
(3) Testing the cohesive force and the internal friction angle of the soil sample when the weak sandwich soil sample at the top of the tunnel is immersed in seawater for different time, then calculating the tensile strength of the soil sample, establishing a fitting relation of the cohesive force, the internal friction angle and the immersion time after the immersion strength of the soil sample is weakened according to a least square method,
Figure BDA0001483499430000023
then, a relation between the tensile strength and the time is fitted by combining the formula (1),
σt＝f(t) ③
(4) calculating the submergence time of the top of the sea erosion cave,
t＝0，h0＞h+H/2 ④
t＝-t0z/H+(1/2+h/H)t0when H-H/2 < H0H + H/2 ≤fifth
Figure BDA0001483499430000024
Wherein z is the height from the beach surface at any point.
(5) Calculating the tensile strength after weakening according to the formula III and the submerging time of the formula IV, then calculating the slumping thickness l according to the following formula,
Figure BDA0001483499430000025
wherein a is the width of the weak dike measured in the step (1), and gamma is the weight of the weak dike measured in the step (2).
In a preferred embodiment of the present invention, the typhoon weather data in the step (1) is acquired by a marine observation station.
In a preferred embodiment of the present invention, the step (2) is performed to test the cohesion c and the internal friction angle
Figure BDA0001483499430000026
The method is to take the soil sample at the soft interlayer to carry out direct shear test in a laboratory.
In a preferred embodiment of the present invention, in the step (3), the top surface and the half-side cylindrical surface of the weak sandwich soil sample are waxed to prevent water from being immersed from the top surface and the half-side surface, the soil sample is completely immersed in seawater, and the cohesion and the internal friction angle of the soil sample are tested when the soil sample is immersed for different times.
Compared with the background technology, the technical scheme has the following advantages:
the prediction method comprehensively reflects wave conditions, sea erosion cavern top weak interlayer parameters and wave erosion processes, provides a soft lithoid vein type sea erosion cavern top collapse thickness prediction method, can predict the accurate collapse thickness of the soft lithoid vein type sea erosion cavern top according to wave actual measurement parameters, and is reliable in result and strong in operability; the method has important significance for determining the collapse thickness of the top of the weak rocky sea erosion cave under the action of waves, understanding the development process of the sea erosion cave and further researching geological disasters of coastal zones by human beings.
Detailed Description
The present invention will be described in detail with reference to the following examples:
example 1
The coast of a building city is a granite cliff, a soft rock vein exists, and rock pulp at the lower part is formed by erupting along a crack of the granite at the upper part again. The dike is changed into mud by strong weathering, has low strength, and is eroded and collapsed under the action of waves, so as to develop a weak dike sea chest.
The method for predicting the collapse thickness of the top of the weak dike sea erosion cavern comprises the following steps:
(1) obtaining the average water-increasing depth H, the average wave height H, the period T and the wave duration T in front of a sea cliff under typhoon weather through a marine observation station0The typhoon weather data are shown in the following table 2 in detail;
measuring the height h of the top of the weak rock vein type sea chest0Width of weak dike a; in this embodiment, the soil body at the top of the sea erosion cave is in a suspended state and gradually collapses under the action of waves, the current height of the cave top is 2.6m, and the width of the dike is 0.51 m.
(2) Taking a weak interlayer soil sample at the top of the hole, testing the gravity gamma of the weak interlayer soil sample in a laboratory, and measuring that the gravity of the soil sample is 21.0kN/m3(ii) a And the direct shear test is carried out to test the cohesive force c and the internal friction angle
Figure BDA0001483499430000031
Calculating the tensile strength sigmat，
Figure BDA0001483499430000041
The shear strength index of the soil sample of this example under the non-submerged and submerged conditions is summarized in table 1.
TABLE 1 Strength index of weak dikes under non-immersed and immersed conditions
Immersion time (h) 0 1 2 3 4 5
Cohesion (kPa) 57 52 21 9 8 6
Internal friction angle (°) 20 15 14 10 8 7
Tensile Strength (kPa) 20.7 13.9 5.2 1.6 1.1 0.7
(3) Waxing the top surface and the semi-side cylindrical surface of a weak interlayer soil sample to prevent water from being immersed from the top surface and the semi-side surface, completely immersing the soil sample into seawater, testing the cohesive force and the internal friction angle of the soil sample when immersed for different time, then calculating the tensile strength of the soil sample, and establishing a fitting relation expression of the cohesive force, the internal friction angle and the immersion time of the soil sample after the immersion strength is weakened according to a least square method
c ═ m (t) and
Figure BDA0001483499430000042
the specific relation of the embodiment is
Figure BDA0001483499430000043
Then, a relation sigma of tensile strength and time is fitted by combining the formula (1)tF (t), the specific relationship in this embodiment is
σt＝21.81exp(-0.73t) ③
Wherein c is expressed in kPa,
Figure BDA0001483499430000044
in degrees, t is h.
(4) Calculating the submergence time of the top of the sea erosion cave,
t＝0，h0＞h+H/2 ④
t＝-t0z/H+(1/2+h/H)t0when H-H/2 < H0H + H/2 ≤fifth
Figure BDA0001483499430000045
In the formula, z is a variable and represents the height of any point from the beach surface.
(5) Calculating the tensile strength after weakening according to the formula III and the submerging time of the formula IV, then calculating the slumping thickness l according to the following formula,
Figure BDA0001483499430000051
wherein a is the width of the weak dike measured in the step (1), and gamma is the weight of the weak dike measured in the step (2).
The collapse thickness of the hole top of the weak dike sea erosion hole in the embodiment under typhoon waves in 25 years, 50 years and 100 years is respectively calculated, and the calculation result is detailed in the following table:
TABLE 2 sea-eroded cave foreground wind wave data and cave roof collapse thickness
Figure BDA0001483499430000052
As shown in the table, the height of the tunnel top is greater than the invasion height of the waves in the case of the waves in 25 years, so that the collapse cannot be caused; under the condition of 50 years of waves, the submerging time of the waves is only 1.8h at the height of 2.8m, the intensity attenuation is small, and therefore the slipping and collapsing can not be caused; when the typhoon waves occur in 100 years, the cohesive force is attenuated to 8kPa when the waves act for 4 hours, the tensile strength is attenuated to 1.1kPa, and the collapse of the hole top with the thickness of 0.47m is caused.
The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims and their equivalents.

Claims (4)

1. A collapse thickness prediction method for the top of a weak dike sea erosion cave is characterized by comprising the following steps:
(1) acquiring typhoon weather and sea erosion hole data: including the average water increasing depth h and level in front of the sea cliff in typhoon weatherMean wave height H and wave duration t0(ii) a Measuring the height h of the top of the weak rock vein type sea eroded cave0Width of weak dike a;
(2) taking a weak interlayer soil sample at the top of the hole, and testing the severe gamma, cohesive force c and internal friction angle of the weak interlayer soil sample in a laboratory
Figure FDA0002907746930000011
Calculating the tensile strength sigmat，
Figure FDA0002907746930000012
(3) Testing the cohesive force and the internal friction angle of the soil sample when the weak sandwich soil sample at the top of the tunnel is immersed in seawater for different time, then calculating the tensile strength of the soil sample, establishing a fitting relation of the cohesive force, the internal friction angle and the immersion time after the immersion strength of the soil sample is weakened according to a least square method,
Figure FDA0002907746930000013
then a formula is combined to fit a relational expression of the tensile strength and the time,
σt＝f(t) ③
(4) calculating the submergence time of the top of the sea erosion cave,
t is 0, when h0When H + H/2 is greater than
t＝-t0z/H+(1/2+h/H)t0When H-H/2 < H0H + H/2 ≤fifth
Figure FDA0002907746930000014
In the formula, z is the height from any point to the beach surface;
(5) calculating the tensile strength after weakening according to the formula III according to the submerging time in the step (4), then calculating the slumping thickness l according to the following formula,
Figure FDA0002907746930000015
wherein a is the width of the weak dike measured in the step (1), and gamma is the weight of the weak dike measured in the step (2).
2. The method for predicting the collapse thickness of the top of the weak dike sea chest as claimed in claim 1, wherein: and (2) acquiring typhoon weather data through a marine observation station in the step (1).
3. The method for predicting the collapse thickness of the top of the weak dike sea chest as claimed in claim 1, wherein: the cohesive force c and the internal friction angle of the steel are tested in the step (2)
Figure FDA0002907746930000021
The method is to take the soil sample at the soft interlayer to carry out direct shear test in a laboratory.
4. The method for predicting the collapse thickness of the top of the weak dike sea chest as claimed in claim 1, wherein: and (3) waxing the top surface and the semi-side cylindrical surface of the weak interlayer soil sample to prevent water from being immersed from the top surface and the semi-side surface, completely immersing the soil sample in seawater, and testing the cohesive force and the internal friction angle of the soil sample when immersed in different time.
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CN109631727B (en) * 2018-12-14 2020-08-07 华侨大学 Method for predicting settlement depth of breakwater stone under wave action
CN110188966B (en) * 2019-06-13 2022-12-02 自然资源部第一海洋研究所 Method for predicting size of collapsed block of surface landslide caused by liquefaction of lower soil mass
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CN114169052A (en) * 2021-12-01 2022-03-11 福建工程学院 Method for judging collapse of sea erosion arch bridge into sea erosion column under wave action

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