CN103074895A - Safety evaluating method for foundation pit anchor rod un-sticking - Google Patents

Abstract

The invention discloses a safety evaluating method for foundation pit anchor rod un-sticking, which comprises the following steps: (1) constructing an accident tree; (2) confirming a minimum cutset; (3) confirming an elementary event probability; (4) performing quantitative analysis; and (5) making an accident-preventing measure. According to the invention, an analytical method for combining an expert investigating method with an accident tree method is adopted; the probability of a bottom event of a foundation pit anchor rod un-sticking accident is given; the probability of a top event of the engineering accident is calculated; the sensibilities of all the elementary events are sequenced; the main potential factors causing the un-sticking, invalidity and damage of a foundation pit anchor rod project are analyzed; the safety evaluating report is performed; and a theoretical basis is supplied for the risk management of the system and the making of the accident-preventing measure.

Description

A kind of foundation pit anchor unsticking safe evaluation method

Technical field

The invention belongs to the Safety Evaluation Technology field, relate to a kind of foundation pit anchor unsticking safe evaluation method.

Background technology

Safety evaluation is to realize that engineering and security of system are as purpose, danger and the adverse factor that exists in engineering, the system carried out identification and analysis, judge possibility and the order of severity that it has an accident, proposition Security Countermeasures suggestions, thus the precautionary measures formulated and administrative decision provides scientific basis for engineering, system.The program of safety evaluation mainly comprises: the preparatory stage, and dangerous, adverse factor identification and analysis, the qualitative, quantitative evaluation proposes Safety Measures, forms safety evaluation conclusion and suggestion, the establishment safety evaluation report.

Safe evaluation method commonly used in the construction project has expert evaluation method, Monte Carlo simulation approach, mathematics method, event tree method (ETA), accident tree method (FTA), analytic hierarchy process (AHP) (AHP) etc.

Event tree analysis (Fault Tree Analysis, be called for short FTA) be the powerful of comprehensive identification and measure of risk, the method the result event of being concerned about as top event, find out all direct factors and the reason that causes this result event generation and the intermediate event that is in transition, until till the accident elementary event; And by based on the risk factor of the Sensitivity Analysis decision-making system of accident tree minimal cut set and the elementary event contribution degree for top event.

Bolt support is concealed work, the character that adds the soil body is complicated and changeable, it is of common occurrence that the phenomenon of disease even accident appears in the anchor pole engineering, brings great potential safety hazard to engineering construction, serious even cause engineering interruption, casualties and bring great economic loss.Advantage based on the FTA method, domestic more existing scholars are introduced into the foundation pit anchor engineering field, but only limit to the research of method and thinking, how to provide the probability of accident tree bottom event, calculate the probability of top event, remain FTA and be applied to the insoluble problem that the pit failure tree is analyzed.

Summary of the invention

The object of the invention is to overcome the defective that above-mentioned technology exists, a kind of foundation pit anchor unsticking safe evaluation method is provided, the analytical method that adopts expert survey and accident tree method to combine, the given probability of foundation pit anchor unsticking accident bottom event, calculate the top event probability that such engineering accident occurs, sensitiveness to each elementary event sorts, analysis causes the main latency of foundation pit anchor engineering unsticking failure damage, carry out safety evaluation report, for the risk management of system and the formulation of preventive action provide theoretical foundation.

Its concrete technical scheme is:

A kind of foundation pit anchor unsticking safe evaluation method may further comprise the steps:

(1) structure of accident tree

Extensive analysis causes the intermediate event of top event cause and the relation between elementary event, and put in order, then from top event, method according to Deductive method, layer by layer deeply, with the gradually refinement of each influence factor, until all factors are the elementary event that is difficult to again refinement, and according to each factor top event generation role is determined logical relation between them, consist of accident tree;

(2) minimal cut set determines

Minimal cut set adopts descending method to try to achieve, and the method is down to carry out step by step along accident tree from top event, if run into and door, then all incoming events below door is all come with in the delegation; If run into or door, then or the door below all incoming events all come same listing, by that analogy, step by step down, till all being bottom event, the bottom event set that obtains like this is called boolean and shows cut set, just can obtain minimal cut set through behind the absorption Merging of Boolean algebra, and the elementary event that comprises in the minimal cut set is called the basic reason event of accident;

(3) the elementary event probability determines

The elementary event probability of happening is determined by expert survey:

Geological conditions is constantly to change, geological environment around the operation of engineering also can change conversely, therefore the probability of happening of each elementary event is without statistics, also can't be drawn by design formulas, this paper is according to existing geologic information, tentatively take 10 years as a unit, adopt expert survey that the probability of happening of each elementary event within 10 years is provided the experience estimated value, carry out risk profile.

Key step is: a, 20 experts that foundation pit anchor relevant professional knowledge or engineering experience are arranged are investigated; B, the academic title according to each expert, the corresponding weight of specialty setting; C, judgement that each expert is done are weighted cumulative according to the weight of correspondence, what obtain at last is exactly the most probable value of required target;

(4) quantitative analysis

Two aspects of calculating that mainly comprise top event probability and each elementary event sensitivity coefficient:

A top event probability of happening utilizes minimal cut set to calculate;

If each other without the elementary event that repeats, the probability of happening of top event is in each minimal cut set:

R is the minimal cut set ordinal number in the formula; I is the elementary event ordinal number; q _iIt is the probability of i elementary event; N _GBe least partition assembly count in the system; G _rBe r minimal cut set;

If minimal cut set has repeated events each other, when namely minimal cut set intersects, adopt intersecting of occurring in the minimal cut set and turn to do not hand over and method---recursion method:

$T=F\left(1\right)+F\left(2\right)+\·\·\·\·\·\·+F\left(N_K\right)=\underset{i=1}{\overset{N_K}{\mathrm{\Σ}}}F\left(I\right)$

Wherein

F(I)＝C(I)K(I)，

K (I)=K _i,

Wherein, Be L _iSupplementary set,

N _KSum for the accident tree minimal cut set.

The ordering of B elementary event sensitiveness

The elementary event sensitivity coefficient:

Wherein, Q is that the probability of happening of top event is P (T), q _iBe the probability of happening of i bottom event, by the ordering of elementary event sensitivity coefficient, can disclose elementary event for the percentage contribution of top event;

(5) formulate preventive damage control

On the basis of qualitative or quantitative analysis, may cause the minimal cut set of accident generation or preventible complexity and the importance degree of minimum path sets elementary event combination according to each, in conjunction with practical capacity, draw up concrete, practicable preventive action, and be put to carry out.

Compared with prior art, beneficial effect of the present invention is:

(1) the present invention on the basis of the reason and characteristic of analyzing Foundation Pit of Bolt Support system generation unsticking accident, has built its accident tree graph according to the principle of accident tree.

(2) the present invention adopts the method that expert investigation and accident tree combine, and provides the experience estimated value of each elementary event probability of happening, and the probability of obtaining Foundation Pit of Bolt Support structure unsticking is 0.17023.With reference to underground construction risk probability classification standard as can be known, such event belongs to sporadic accident.

Description of drawings

Fig. 1 is anchor pole unsticking accident tree.

The specific embodiment

Below in conjunction with the drawings and specific embodiments technical scheme of the present invention is described in more detail.

The mathematical description of 1 accident tree

If x _iRepresent respectively the state variable of bottom event and top event with φ, all only get 0 or 1 two states.Top event state φ determined by bottom event state X in the accident tree fully, namely

φ＝φ(X) (1)

In the formula 1, X=(x ₁, x ₂..., x _n), claim that φ (X) is the structure function of FTA.I=1 wherein, 2 ..., n, n are the sum of bottom event.

When top event T occurs, namely be equivalent to φ=1, the corresponding bottom event state of state is component, subsystem fault state therewith, is equivalent to x _i=1.

Work as x _iOnly got 0,1 o'clock, and be respectively with door (condition and door) or the structure function of door (conditioned disjunction door)

$\mathrm{\φ}\left(X\right)=\underset{i=1}{\overset{n}{\mathrm{\Π}}}{x}_i---\left(2\right)$

$\mathrm{\φ}\left(X\right)=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-x_i)---\left(3\right)$

The construction of 2 foundation pit anchor unsticking accident tree

With reference to domestic and international foundation pit anchor unsticking cause of accident, and in conjunction with the mechanism of accident, determine that the accident tree top event is foundation pit anchor unsticking accident, then analyze from the body of rod and be in the milk body interface unsticking and grouting body and two aspects of soil layer interface unsticking, layer by layer deeply, with the gradually refinement of each influence factor, until all factors are the elementary event that is difficult to again refinement, and according to each factor top event generation role is determined logical relation between them.The fault tree graph of setting up is seen Fig. 1.The accident tree top event is foundation pit anchor unsticking accident, and intermediate event has two: the body of rod and grouting body interface unsticking and grouting body and soil layer interface unsticking.These two intermediate events are analyzed, layer by layer deeply, with the gradually refinement of each influence factor, until all factors are the elementary event that is difficult to again refinement, and according to each factor top event generation role is determined logical relation between them.

For with door, expression is only as all incoming event E1, E2 ..., when En occured, outgoing event just occured.

Be the conditioned disjunction door, expression incoming event E1, E2 ..., En has at least an event to occur, in the situation that the event a that satisfies condition, outgoing event just can occur.

For or the door, the expression have an incoming event E1 at least, E2 ..., when the En event occured, outgoing event occured.

Each Event Description of fault tree sees Table 1.

Symbol implication in table 1 accident tree

The analysis of 3 foundation pit anchor unsticking accident tree

3.1 determining of minimal cut set

Minimal cut set is in fact the contingent approach of accident, has represented the danger of system, and minimal cut set is more, and system is more dangerous.In the minimal cut set of accident tree, have 1 cut set to occur, top event just occurs.The cut set that elementary event is fewer more easily occurs, and the possibility that has an accident by this approach is just larger, therefore answer emphasis to take preventive measures to the few cut set of elementary event.

The present invention adopts descending method to find the solution the minimal cut set of accident tree.The method is down to carry out step by step along accident tree from top event, if run into and door, then all incoming events below door is all come with in the delegation; If run into or the door, then or the door below all incoming events all come same listing.By that analogy, step by step down, till all being bottom event.The bottom event set that obtains like this is called boolean and shows cut set, through just obtaining minimal cut set behind the absorption Merging of Boolean algebra is: { X ₄, { X ₁, { X ₂, { X ₃, { X ₁₀, X ₁₁, { X ₈, { X ₁₂, X ₁₃, X ₁₆, { X ₁₄, X ₁₅, X ₁₇, { X ₇, { X ₉, { X ₅, { X ₆.

This shows, the possible approaches of Foundation Pit of Bolt Support structural system generation unsticking accident has 12 kinds, the elementary event that each minimal cut set comprises only has 1 not wait to 3, that is to say, the unsticking accident will occur in system when only having 1 to 3 elementary event to occur simultaneously, the occurrence condition that such accident is described is easy to satisfy, and the possibility that accident occurs is larger.

3.2 expert survey is determined the elementary event probability of happening

Table 2 Weight of Expert is determined table

Because the probability of happening of each elementary event without statistics, also can't be drawn by design formulas, therefore, the present invention adopts expert survey that the probability of happening of each elementary event within 10 years is provided the experience estimated value.This is constantly to change because of geological conditions, and therefore the geological environment around the operation of engineering also can change conversely, according to existing geologic information, tentatively carries out risk profile take 10 years as a unit.By 20 experts that foundation pit anchor relevant professional knowledge or engineering experience are arranged are investigated, and set corresponding weight according to each expert's academic title, specialty etc., then the judgement of it being done is weighted cumulative according to the weight of correspondence, what obtain at last is exactly the most probable value of required target.

According to table 2, adopt following formula to calculate each Weight of Expert.

$W_k=\underset{i=1}{\overset{4}{\mathrm{\Σ}}}{U}_i{V}_{\mathrm{ij}}---\left(4\right)$

In the formula: W _kIt is k position expert's scoring weight; U _i, V _IjImplication see Table 2.As calculated, 20 experts' weight distribution sees Table 3.

Table 3 Weight of Expert distribution table

Weight of Expert is interval	0.8～1	0.7～0.8	0.6～0.7	0.4～0.6
					Expert's number	2	8	7	3

The probability of happening of elementary event adopts the operation hazard assessment method of U.S. Green strategic point nurse (K.J.Graham) and golden Buddhist nun (G.F.Kinney) proposition, and it is personnel's a kind of simple semi-quantitative assessment methods of danger during operation in having the potential danger environment.The possibility score value of the event of causing danger sees Table 4.According to anchor pole engineering concrete condition, ignore last 2 kinds of possibilities (extremely impossible and in fact impossible), front 5 kinds of possibilities only are discussed.In order not make differential probability greater than 1, its value be multiply by respectively 0.009.

The cause danger possibility score value of sexual behavior part of table 4

The possibility that accident occurs	Fractional value
		Can expect fully	10
Quite may	6
		Possible but not frequent	3
Possibility is little, and is fully unexpected	1
		Very impossible, it is contemplated that	0.5
Extremely impossible	0.2
		Actual impossible	0.1

The following formula of definite employing of final elementary event probability of happening:

$P_i=\left(\underset{k=1}{\overset{20}{\mathrm{\Σ}}}{W}_k{Q}_{\mathrm{kl}}\right)/\underset{i=1}{\overset{20}{\mathrm{\Σ}}}{W}_k---\left(5\right)$

In the formula: P _iThe final expert evaluation value that represents i elementary event probability of happening, Q _KiBe that k position expert is to the evaluation value of i elementary event probability of happening.

According to investigation result, it is as shown in table 5 that employing formula (4), (5) calculate the probability of happening of each event:

Table 5 elementary event probability tables

Elementary event	X 1	X 2	X 2	X 4	X 5	X 6	X 7	X 8	X 9
										The probability of happening	0.0165	0.0278	0.0017	0.024	0.0012	0.021	0.021	0.0348	0.0219
Elementary event	X 10	X 11	X 12	X 13	X 14	X 15	X 16	X 17
										The probability of happening	0.030	0.011	0.025	0.004	0.0022	0.0132	0.0129	0.025

3.3 the probability calculation of top event

If each other without the elementary event that repeats, the probability of happening of top event is in each minimal cut set:

R is the minimal cut set ordinal number in the formula; I is the elementary event ordinal number; q _iIt is the probability of i elementary event; N _GBe least partition assembly count in the system; G _rBe r minimal cut set.

Be the convenient top event probability of happening that calculates soil anchor system accident tree, carry out following simplification: 1. the probability with each elementary event is designated as respectively q _i2. all minimal cut sets that only contain an event (are designated as G ₁), the minimal cut set that contains 2 events (is designated as G ₂), the minimal cut set that contains 3 events (is designated as G ₃) separately consider.

G ₁, G ₂, G ₃Without any common factor, therefore the probability of happening of top event T can be reduced to

P(T)＝P(G ₁)+P(G ₂)+P(G ₃) (7)

The purpose of simplifying like this is that this three part is independent mutually, makes things convenient for probability calculation.Can find out G by formula (6) ₁Each part is independent mutually, owing to only containing an event, the probability of happening addition that they are contained gets final product P (G again ₁)=0.1699; G ₃Have 2 minimal cut sets, be respectively { X ₁₂, X ₁₃, X ₁₆, { X ₁₄, X ₁₅, X ₁₇, each minimal cut set contains 3 independent events, and with the probability multiplication of each event, acquired results is very little, can ignore the contribution of top event probability of happening; G ₂Only has a minimal cut set, G ₂={ by formula calculate (6), gets P (G for X10, X11} ₂)=0.030 * 0.011=0.00033.

P (T)=0.1699+0.00033=0.17023, namely the probability of top event is 0.17023.With reference to underground construction risk probability classification standard as can be known, such event belongs to sporadic accident.

3.4 sensitivity analysis

Calculate the probability of top event according to accident tree, can determine the probability that the unsticking accident may occur whole Bolt System on the one hand, can by sensitivity analysis, disclose elementary event for the percentage contribution of top event on the other hand.

The elementary event sensitivity coefficient:

$C{I}_g\left(i\right)=\frac{\frac{\∂Q}{\∂q_i}}{\frac{Q}{q_i}}=\frac{\∂Q}{\∂q_i}\·\frac{q_i}{Q}---\left(8\right)$

Wherein, Q is that the probability of happening of top event is P (T), q _iIt is the probability of happening of i bottom event.

Each elementary event sensitiveness ordering of table 6

Sequence number	Elementary event	Sensitivity coefficient
			1	X 8	0.194
2	X 2	0.159
			3	X 4	0.144
4	X 7	0.133
			4	X 6	0.133
5	X 9	0.124
			6	X 17	0.092
6	X 1	0.092
			7	X 3	0.010
8	X 5	0.008
			9	X 10	0.0018
9	X 11	0.0018
			10	X 12	0.0006
10	X 13	0.0006
			11	X 14	0.0002
11	X 15	0.0002
			11	X 16	0.0002

The order of magnitude of sensitivity coefficient is nonsensical, and its ordering is more meaningful, and the most influential bottom event occurs the accident that is conducive to seek in the accident tree top event, and table 6 is the sequencing tables that calculate with sensitivity coefficient.This ranking results is determining that each elementary event is the influence degree of foundation pit anchor unsticking accident to top event, and the establishment of safety evaluation report is had important directive significance.

Analysis according to elementary event sensitiveness can find out, the soil bolt unsticking lost efficacy the most responsive to anchoring section length; In the reason that causes the soil bolt unsticking to lose efficacy, several factors such as " the anchoring section Design of length is not enough ", " prestress application is excessive too early ", " cement mortar ratio is unreasonable ", " grouting way is unreasonable ", " the slurry compactness is not enough ", " the anchoring body surface area is too small ", " load is excessive " account for first six digits, and the sensitivity coefficient of these six events is obviously much bigger than other events, in the design and construction process of soil bolt, must draw attention.

And discovery relates to the elementary event x of water damage ₁₂Ordering the 10th in 17 events, analyze reason, owing to the event that relates to water damage all only is on " with door " structure, can not appear at separately in the minimal cut set and be in " with door " structural event, when sensitivity analysis, can be subject to being in the impact of same minimal cut set event.The forward event of safety evaluation report reply sensitivity coefficient ordering is estimated, and should consider simultaneously to relate to the most front several events of sensitivity coefficient ordering in " with door " structural event that are in, and point out corresponding Safety Measures and suggestion.

Contrast table 5,6 can find out that the sensitivity coefficient ordering is relevant with the probability size of bottom event, and the bottom event probability is larger, and its sensitivity coefficient ordering is more forward, and the probability of bottom event depends on that then the people is to the degree of awareness and the investigation result of each event.Therefore, determining of bottom event probability is of crucial importance and complicated, and bottom event method of determining probability in this paper is to be based upon on the basis of expert investigation analysis.For the Foundation Pit of Bolt Support engineering, still need a large amount of investigation statisticses to improve this work, with the bottom event probability of given accident tree more accurately.

The above; only be the better specific embodiment of the present invention; protection scope of the present invention is not limited to this; anyly be familiar with those skilled in the art in the technical scope that the present invention discloses, the simple change of the technical scheme that can obtain apparently or equivalence are replaced and are all fallen within the scope of protection of the present invention.

Claims (1)

1. a foundation pit anchor unsticking safe evaluation method is characterized in that, may further comprise the steps:

(1) structure of accident tree

Extensive analysis causes the intermediate event of top event cause and the relation between elementary event, and put in order, then from top event, method according to Deductive method, layer by layer deeply, with the gradually refinement of each influence factor, until all factors are the elementary event that is difficult to again refinement, and according to each factor top event generation role is determined logical relation between them, consist of accident tree;

(2) minimal cut set determines

Minimal cut set adopts descending method to try to achieve, and the method is down to carry out step by step along accident tree from top event, if run into and door, then all incoming events below door is all come with in the delegation; If run into or door, then or the door below all incoming events all come same listing, by that analogy, step by step down, till all being bottom event, the bottom event set that obtains like this is called boolean and shows cut set, just can obtain minimal cut set through behind the absorption Merging of Boolean algebra, and the elementary event that comprises in the minimal cut set is called the basic reason event of accident;

(3) the elementary event probability determines

The elementary event probability of happening is determined by expert survey;

(4) quantitative analysis

Two aspects of calculating that mainly comprise top event probability and each elementary event sensitivity coefficient:

A top event probability of happening utilizes minimal cut set to calculate;

If each other without the elementary event that repeats, the probability of happening of top event is in each minimal cut set:

R is the minimal cut set ordinal number in the formula; I is the elementary event ordinal number; q _iIt is the probability of i elementary event; N _GBe least partition assembly count in the system; G _rBe r minimal cut set;

If minimal cut set has repeated events each other, when namely minimal cut set intersects, adopt intersecting of occurring in the minimal cut set and turn to do not hand over and method---recursion method:

$T=F\left(1\right)+F\left(2\right)+\·\·\·\·\·\·+F\left(N_K\right)=\underset{i=1}{\overset{X_K}{\mathrm{\Σ}}}F\left(I\right)$

Wherein

F(I)＝C(I)K(I)，

K (I)=K _i, Wherein, Be K _iSupplementary set,

N _KSum for the accident tree minimal cut set.

The ordering of B elementary event sensitiveness

The elementary event sensitivity coefficient:

Wherein, Q is that the probability of happening of top event is P (T), q _iBe the probability of happening of i bottom event, by the ordering of elementary event sensitivity coefficient, can disclose elementary event for the percentage contribution of top event;

(5) formulate preventive damage control

On the basis of qualitative or quantitative analysis, may cause the minimal cut set of accident generation or preventible complexity and the importance degree of minimum path sets elementary event combination according to each, in conjunction with practical capacity, draw up concrete, practicable preventive action, and be put to carry out.

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